rfc8656xml2.original.xml   rfc8656.xml 
<?xml version="1.0" encoding="US-ASCII"?> <?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd"> <!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<?rfc toc="yes"?>
<?rfc compact='yes'?> <rfc number="8656" docName="draft-ietf-tram-turnbis-29"
<?rfc subcompact='no'?> xmlns:xi="http://www.w3.org/2001/XInclude" submissionType="IETF"
<?rfc symrefs="yes"?> category="std" consensus="true" ipr="trust200902" obsoletes="5766, 6156"
<rfc category="std" docName="draft-ietf-tram-turnbis-29" ipr="trust200902" updates="" tocInclude="true" symRefs="true" sortRefs="true" xml:lang="en"
obsoletes="5766, 6156"> version="3">
<front> <front>
<title abbrev="TURN">Traversal Using Relays around NAT (TURN): Relay <title abbrev="TURN">Traversal Using Relays around NAT (TURN): Relay
Extensions to Session Traversal Utilities for NAT (STUN)</title> Extensions to Session Traversal Utilities for NAT (STUN)</title>
<author fullname="Tirumaleswar Reddy" initials="T." role="editor" <seriesInfo name="RFC" value="8656"/>
surname="Reddy">
<organization abbrev="McAfee">McAfee, Inc.</organization>
<author fullname="Tirumaleswar Reddy" initials="T." role="editor" surname="R
eddy">
<organization abbrev="McAfee">McAfee, Inc.</organization>
<address> <address>
<postal> <postal>
<street>Embassy Golf Link Business Park</street> <street>Embassy Golf Link Business Park</street>
<city>Bangalore</city> <city>Bangalore</city>
<region>Karnataka</region> <region>Karnataka</region>
<code>560071</code> <code>560071</code>
<country>India</country> <country>India</country>
</postal> </postal>
<email>kondtir@gmail.com</email> <email>kondtir@gmail.com</email>
</address> </address>
</author> </author>
<author fullname="Alan Johnston" initials="A." role="editor" surname="Johnst
<author fullname="Alan Johnston" initials="A." role="editor" on">
surname="Johnston">
<organization>Villanova University</organization> <organization>Villanova University</organization>
<address> <address>
<postal> <postal>
<street></street> <street/>
<city>Villanova</city> <city>Villanova</city>
<region>PA</region> <region>PA</region>
<code/>
<code></code> <country>United States of America</country>
<country>USA</country>
</postal> </postal>
<email>alan.b.johnston@gmail.com</email> <email>alan.b.johnston@gmail.com</email>
</address> </address>
</author> </author>
<author fullname="Philip Matthews" initials="P." surname="Matthews"> <author fullname="Philip Matthews" initials="P." surname="Matthews">
<organization>Alcatel-Lucent</organization> <organization>Alcatel-Lucent</organization>
<address> <address>
<postal> <postal>
<street>600 March Road</street> <street>600 March Road</street>
<city>Ottawa</city> <city>Ottawa</city>
<region>Ontario</region> <region>Ontario</region>
<code/>
<code></code>
<country>Canada</country> <country>Canada</country>
</postal> </postal>
<email>philip_matthews@magma.ca</email> <email>philip_matthews@magma.ca</email>
</address> </address>
</author> </author>
<author fullname="Jonathan Rosenberg" initials="J." surname="Rosenberg"> <author fullname="Jonathan Rosenberg" initials="J." surname="Rosenberg">
<organization>jdrosen.net</organization> <organization>jdrosen.net</organization>
<address> <address>
<postal> <postal>
<street></street> <street/>
<city>Edison</city> <city>Edison</city>
<region>NJ</region> <region>NJ</region>
<country>United States of America</country>
<country>USA</country>
</postal> </postal>
<email>jdrosen@jdrosen.net</email> <email>jdrosen@jdrosen.net</email>
<uri>http://www.jdrosen.net</uri> <uri>http://www.jdrosen.net</uri>
</address> </address>
</author> </author>
<date month="December" year="2019"/>
<date day="27" month="July" year="2019" />
<area>Transport</area> <area>Transport</area>
<workgroup>TRAM WG</workgroup> <workgroup>TRAM WG</workgroup>
<keyword>NAT</keyword> <keyword>NAT</keyword>
<keyword>TURN</keyword> <keyword>TURN</keyword>
<keyword>STUN</keyword> <keyword>STUN</keyword>
<keyword>ICE</keyword>
<keyword>ICEf</keyword>
<abstract> <abstract>
<t>If a host is located behind a NAT, then in certain situations it can <t>If a host is located behind a NAT, it can be impossible for that host
be impossible for that host to communicate directly with other hosts to communicate directly with other hosts (peers) in certain
(peers). In these situations, it is necessary for the host to use the situations. In these situations, it is necessary for the host to use the
services of an intermediate node that acts as a communication relay. services of an intermediate node that acts as a communication relay.
This specification defines a protocol, called TURN (Traversal Using This specification defines a protocol, called "Traversal Using Relays
Relays around NAT), that allows the host to control the operation of the around NAT" (TURN), that allows the host to control the operation of the
relay and to exchange packets with its peers using the relay. TURN relay and to exchange packets with its peers using the relay. TURN
differs from other relay control protocols in that it allows a client to differs from other relay control protocols in that it allows a client to
communicate with multiple peers using a single relay address.</t> communicate with multiple peers using a single relay address.</t>
<t>The TURN protocol was designed to be used as part of the Interactive
<t>The TURN protocol was designed to be used as part of the ICE Connectivity Establishment (ICE) approach to NAT traversal,
(Interactive Connectivity Establishment) approach to NAT traversal, though it can also be used without ICE.</t>
though it also can be used without ICE.</t> <t>This document obsoletes RFCs 5766 and 6156.</t>
<t>This document obsoletes RFC 5766 and RFC 6156.</t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section title="Introduction"> <section numbered="true" toc="default">
<name>Introduction</name>
<t>A host behind a NAT may wish to exchange packets with other hosts, <t>A host behind a NAT may wish to exchange packets with other hosts,
some of which may also be behind NATs. To do this, the hosts involved some of which may also be behind NATs. To do this, the hosts involved
can use "hole punching" techniques (see <xref target="RFC5128"></xref>) can use "hole punching" techniques (see <xref target="RFC5128" format="def
in an attempt discover a direct communication path; that is, a ault"/>)
in an attempt to discover a direct communication path; that is, a
communication path that goes from one host to another through communication path that goes from one host to another through
intervening NATs and routers, but does not traverse any relays.</t> intervening NATs and routers but does not traverse any relays.</t>
<t>As described in <xref target="RFC5128" format="default"/> and <xref
<t>As described in <xref target="RFC5128"></xref> and <xref target="RFC4787" format="default"/>, hole punching techniques will fail
target="RFC4787"></xref>, hole punching techniques will fail if both if both hosts are behind NATs that are not well behaved. For example, if
hosts are behind NATs that are not well behaved. For example, if both both hosts are behind NATs that have a mapping behavior of
hosts are behind NATs that have a mapping behavior of "address-dependent "address-dependent mapping" or "address- and port-dependent mapping"
mapping" or "address- and port- dependent mapping" (Section 4.1 in <xref (see <xref target="RFC4787" sectionFormat="of" section="4.1"/>), then
target="RFC4787"></xref>), then hole punching techniques generally hole punching techniques generally fail.</t>
fail.</t>
<t>When a direct communication path cannot be found, it is necessary to <t>When a direct communication path cannot be found, it is necessary to
use the services of an intermediate host that acts as a relay for the use the services of an intermediate host that acts as a relay for the
packets. This relay typically sits in the public Internet and relays packets. This relay typically sits in the public Internet and relays
packets between two hosts that both sit behind NATs.</t> packets between two hosts that both sit behind NATs.</t>
<t>In many enterprise networks, direct UDP transmissions are not <t>In many enterprise networks, direct UDP transmissions are not
permitted between clients on the internal networks and external IP permitted between clients on the internal networks and external IP
addresses. To permit media sessions in such a situation to use UDP and addresses. To permit media sessions in such a situation to use UDP and
avoid forcing them through TCP, an Enterprise Firewall can be configured avoid forcing them through TCP, an Enterprise Firewall can be configured
to allow UDP traffic relayed through an Enterprise relay server. WebRTC to allow UDP traffic relayed through an Enterprise relay server. WebRTC
requires support for this scenario (Section 2.3.5.1 in <xref requires support for this scenario (see <xref target="RFC7478"
target="RFC7478"></xref>). Some users of SIP or WebRTC want IP location sectionFormat="of" section="2.3.5.1"/>). Some users of SIP or WebRTC
privacy from the remote peer. In this scenario, the client can select a want IP location privacy from the remote peer. In this scenario, the
relay server offering IP location privacy and only convey the relayed client can select a relay server offering IP location privacy and only
candidates to the peer for ICE connectivity checks (see Section 4.2.4 in convey the relayed candidates to the peer for ICE connectivity checks
<xref target="I-D.ietf-rtcweb-security"></xref>).</t> (see <xref target="I-D.ietf-rtcweb-security"
sectionFormat="of" section="4.2.4"></xref>).</t>
<t>This specification defines a protocol, called "TURN", that allows a
host behind a NAT (called the "TURN client") to request that another host
(called the "TURN server") act as a relay.
<t>This specification defines a protocol, called TURN, that allows a The client can arrange for the server to relay packets to and from
host behind a NAT (called the TURN client) to request that another host certain other hosts (called "peers"), and the client can control aspects
(called the TURN server) act as a relay. The client can arrange for the of how the relaying is done. The client does this by obtaining an IP
server to relay packets to and from certain other hosts (called peers) address and port on the server, called the "relayed transport
and can control aspects of how the relaying is done. The client does address". When a peer sends a packet to the relayed transport address,
this by obtaining an IP address and port on the server, called the the server relays the transport protocol data from the packet to the
relayed transport address. When a peer sends a packet to the relayed client. The data encapsulated within a message header that allows the
transport address, the server relays the transport protocol data from client to know the peer from which the transport protocol data was
the packet to the client. The data encapsulated within a message header relayed by the server.
that allows the client to know the peer from which the transport
protocol data was relayed by the server. If the server receives an ICMP
error packet, the server also relays certain layer 3/4 header fields
from the ICMP header to the client. When the client sends a message to
the server, the server identifies the remote peer from the message
header and relays the message data to the intended peer.</t>
If the server receives an ICMP error packet, the server also relays
certain Layer 3 and 4 header fields from the ICMP header to the
client. When the client sends a message to the server, the server
identifies the remote peer from the message header and relays the
message data to the intended peer.</t>
<t>A client using TURN must have some way to communicate the relayed <t>A client using TURN must have some way to communicate the relayed
transport address to its peers, and to learn each peer's IP address and transport address to its peers and to learn each peer's IP address and
port (more precisely, each peer's server-reflexive transport address, port (more precisely, each peer's server-reflexive transport address;
see <xref target="sec-overview"></xref>). How this is done is out of the see <xref target="sec-overview" format="default"/>). How this is done is o
ut of the
scope of the TURN protocol. One way this might be done is for the client scope of the TURN protocol. One way this might be done is for the client
and peers to exchange email messages. Another way is for the client and and peers to exchange email messages. Another way is for the client and
its peers to use a special-purpose "introduction" or "rendezvous" its peers to use a special-purpose "introduction" or "rendezvous"
protocol (see <xref target="RFC5128"></xref> for more details).</t> protocol (see <xref target="RFC5128" format="default"/> for more details).
</t>
<t>If TURN is used with ICE <xref target="RFC8445"></xref>, then the <t>If TURN is used with ICE <xref target="RFC8445" format="default"/>,
relayed transport address and the IP addresses and ports of the peers then the relayed transport address and the IP addresses and ports of the
are included in the ICE candidate information that the rendezvous peers are included in the ICE candidate information that the rendezvous
protocol must carry. For example, if TURN and ICE are used as part of a protocol must carry. For example, if TURN and ICE are used as part of a
multimedia solution using SIP <xref target="RFC3261"></xref>, then SIP multimedia solution using SIP <xref target="RFC3261" format="default"/>,
serves the role of the rendezvous protocol, carrying the ICE candidate then SIP serves the role of the rendezvous protocol, carrying the ICE
information inside the body of SIP messages <xref candidate information inside the body of SIP messages <xref
target="I-D.ietf-mmusic-ice-sip-sdp"></xref>. If TURN and ICE are used target="I-D.ietf-mmusic-ice-sip-sdp" format="default"/>. If TURN and ICE a
with some other rendezvous protocol, then ICE provides guidance on the re used with some
services the rendezvous protocol must perform.</t> other rendezvous protocol, then ICE provides guidance on the services
the rendezvous protocol must perform.</t>
<t>Though the use of a TURN server to enable communication between two <t>Though the use of a TURN server to enable communication between two
hosts behind NATs is very likely to work, it comes at a high cost to the hosts behind NATs is very likely to work, it comes at a high cost to the
provider of the TURN server, since the server typically needs a provider of the TURN server since the server typically needs a
high-bandwidth connection to the Internet. As a consequence, it is best high-bandwidth connection to the Internet. As a consequence, it is best
to use a TURN server only when a direct communication path cannot be to use a TURN server only when a direct communication path cannot be
found. When the client and a peer use ICE to determine the communication found. When the client and a peer use ICE to determine the communication
path, ICE will use hole punching techniques to search for a direct path path, ICE will use hole punching techniques to search for a direct path
first and only use a TURN server when a direct path cannot be found.</t> first and only use a TURN server when a direct path cannot be found.</t>
<t>TURN was originally invented to support multimedia sessions signaled <t>TURN was originally invented to support multimedia sessions signaled
using SIP. Since SIP supports forking, TURN supports multiple peers per using SIP. Since SIP supports forking, TURN supports multiple peers per
relayed transport address; a feature not supported by other approaches relayed transport address; a feature not supported by other approaches
(e.g., SOCKS <xref target="RFC1928"></xref>). However, care has been (e.g., SOCKS <xref target="RFC1928" format="default"/>). However, care has been
taken to make sure that TURN is suitable for other types of taken to make sure that TURN is suitable for other types of
applications.</t> applications.</t>
<t>TURN was designed as one piece in the larger ICE approach to NAT <t>TURN was designed as one piece in the larger ICE approach to NAT
traversal. Implementors of TURN are urged to investigate ICE and traversal. Implementors of TURN are urged to investigate ICE and
seriously consider using it for their application. However, it is seriously consider using it for their application. However, it is
possible to use TURN without ICE.</t> possible to use TURN without ICE.</t>
<t>TURN is an extension to the Session Traversal Utilities for NAT
<t>TURN is an extension to the STUN (Session Traversal Utilities for (STUN) protocol <xref target="RFC8489" format="default"/>. Most, though
NAT) protocol <xref target="I-D.ietf-tram-stunbis"></xref>. Most, though
not all, TURN messages are STUN-formatted messages. A reader of this not all, TURN messages are STUN-formatted messages. A reader of this
document should be familiar with STUN.</t> document should be familiar with STUN.</t>
<t>The TURN specification was originally published as <xref target="RFC576
<t>The TURN specification was originally published as <xref 6" format="default"/>, which was updated by <xref target="RFC6156" format="defau
target="RFC5766"></xref>, which was updated by <xref lt"/> to add IPv6 support. This document supersedes
target="RFC6156"></xref> to add IPv6 support. This document supersedes and obsoletes both <xref target="RFC5766" format="default"/> and <xref tar
and obsoletes both <xref target="RFC5766"></xref> and <xref get="RFC6156" format="default"/>.</t>
target="RFC6156"></xref>.</t>
</section> </section>
<section numbered="true" toc="default">
<name>Terminology</name>
<section title="Terminology"> <t>
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
"OPTIONAL" in this document are to be interpreted as described in BCP 14 NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>
<xref target="RFC2119"></xref><xref target="RFC8174"></xref> when, and RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
only when, they appear in all capitals, as shown here.</t> "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
be interpreted as
<t>Readers are expected to be familiar with <xref described in BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
target="I-D.ietf-tram-stunbis"></xref> and the terms defined there.</t> when, and only when, they appear in all capitals, as shown here.
</t>
<t>Readers are expected to be familiar with <xref target="RFC8489" format= "default"/> and the terms defined there.</t>
<t>The following terms are used in this document:</t> <t>The following terms are used in this document:</t>
<dl newline="true" spacing="normal">
<t><list style="hanging"> <dt>TURN:</dt>
<t hangText="TURN:">The protocol spoken between a TURN client and a <dd>The protocol spoken between a TURN client and a
TURN server. It is an extension to the STUN protocol <xref TURN server. It is an extension to the STUN protocol <xref target="RFC
target="I-D.ietf-tram-stunbis"></xref>. The protocol allows a client 8489" format="default"/>. The protocol allows a client
to allocate and use a relayed transport address.</t> to allocate and use a relayed transport address.</dd>
<dt>TURN client:</dt>
<t hangText="TURN client:">A STUN client that implements this <dd>A STUN client that implements this
specification.</t> specification.</dd>
<dt>TURN server:</dt>
<t hangText="TURN server:">A STUN server that implements this <dd>A STUN server that implements this
specification. It relays data between a TURN client and its specification. It relays data between a TURN client and its
peer(s).</t> peer(s).</dd>
<dt>Peer:</dt>
<t hangText="Peer:">A host with which the TURN client wishes to <dd>A host with which the TURN client wishes to
communicate. The TURN server relays traffic between the TURN client communicate. The TURN server relays traffic between the TURN client
and its peer(s). The peer does not interact with the TURN server and its peer(s). The peer does not interact with the TURN server
using the protocol defined in this document; rather, the peer using the protocol defined in this document; rather, the peer
receives data sent by the TURN server and the peer sends data receives data sent by the TURN server, and the peer sends data
towards the TURN server.</t> towards the TURN server.</dd>
<dt>Transport Address:</dt>
<t hangText="Transport Address:">The combination of an IP address <dd>The combination of an IP address
and a port.</t> and a port.</dd>
<dt>Host Transport Address:</dt>
<t hangText="Host Transport Address:">A transport address on a <dd>A transport address on a
client or a peer.</t> client or a peer.</dd>
<dt>Server-Reflexive Transport Address:</dt>
<t hangText="Server-Reflexive Transport Address:">A transport <dd>A transport
address on the "external side" of a NAT. This address is allocated address on the "external side" of a NAT. This address is allocated
by the NAT to correspond to a specific host transport address.</t> by the NAT to correspond to a specific host transport address.</dd>
<dt>Relayed Transport Address:</dt>
<t hangText="Relayed Transport Address:">A transport address on the <dd>A transport address on the
TURN server that is used for relaying packets between the client and TURN server that is used for relaying packets between the client and
a peer. A peer sends to this address on the TURN server, and the a peer. A peer sends to this address on the TURN server, and the
packet is then relayed to the client.</t> packet is then relayed to the client.</dd>
<dt>TURN Server Transport Address:</dt>
<t hangText="TURN Server Transport Address:">A transport address on <dd>A transport address on
the TURN server that is used for sending TURN messages to the the TURN server that is used for sending TURN messages to the
server. This is the transport address that the client uses to server. This is the transport address that the client uses to
communicate with the server.</t> communicate with the server.</dd>
<dt>Peer Transport Address:</dt>
<t hangText="Peer Transport Address:">The transport address of the <dd>The transport address of the
peer as seen by the server. When the peer is behind a NAT, this is peer as seen by the server. When the peer is behind a NAT, this is
the peer's server-reflexive transport address.</t> the peer's server-reflexive transport address.</dd>
<dt>Allocation:</dt>
<t hangText="Allocation:">The relayed transport address granted to a <dd>The relayed transport address granted to a
client through an Allocate request, along with related state, such client through an Allocate request, along with related state, such
as permissions and expiration timers.</t> as permissions and expiration timers.</dd>
<dt>5-tuple:</dt>
<t hangText="5-tuple:">The combination (client IP address and port,
server IP address and port, and transport protocol (currently one of
UDP, TCP, DTLS/UDP or TLS/TCP) used to communicate between the
client and the server. The 5-tuple uniquely identifies this
communication stream. The 5-tuple also uniquely identifies the
Allocation on the server.</t>
<t hangText="Transport Protocol:">The protocol above IP that carries <dd>The combination (client IP address and port, server IP address and
TURN Requests, Responses, and Indications as well as providing port, and transport protocol (currently one of UDP, TCP, DTLS/UDP, or
identifiable flows using a 5-tuple. In this specification, UDP and TLS/TCP)) used to communicate between the client and the server. The
TCP are defined as transport protocols, as well as their combination 5-tuple uniquely identifies this communication stream. The 5-tuple
with a security layer using DTLS and TLS respectively.</t> also uniquely identifies the Allocation on the server.</dd>
<dt>Transport Protocol:</dt>
<t hangText="Channel:">A channel number and associated peer <dd>The protocol above IP that carries TURN Requests, Responses, and
Indications as well as providing identifiable flows using a
5-tuple. In this specification, UDP and TCP are defined as transport
protocols; this document also describes the use of UDP and TCP in
combination with a security layer using DTLS and TLS,
respectively.</dd>
<dt>Channel:</dt>
<dd>A channel number and associated peer
transport address. Once a channel number is bound to a peer's transport address. Once a channel number is bound to a peer's
transport address, the client and server can use the more transport address, the client and server can use the more
bandwidth-efficient ChannelData message to exchange data.</t> bandwidth-efficient ChannelData message to exchange data.</dd>
<dt>Permission:</dt>
<t hangText="Permission:">The IP address and transport protocol (but <dd>The IP address and transport protocol (but
not the port) of a peer that is permitted to send traffic to the not the port) of a peer that is permitted to send traffic to the
TURN server and have that traffic relayed to the TURN client. The TURN server and have that traffic relayed to the TURN client. The
TURN server will only forward traffic to its client from peers that TURN server will only forward traffic to its client from peers that
match an existing permission.</t> match an existing permission.</dd>
<dt>Realm:</dt>
<t hangText="Realm:">A string used to describe the server or a <dd>A string used to describe the server or a
context within the server. The realm tells the client which username context within the server. The realm tells the client which username
and password combination to use to authenticate requests.</t> and password combination to use to authenticate requests.</dd>
<dt>Nonce:</dt>
<t hangText="Nonce:">A string chosen at random by the server and <dd>A string chosen at random by the server and
included in the server response. To prevent replay attacks, the included in the server response. To prevent replay attacks, the
server should change the nonce regularly.</t> server should change the nonce regularly.</dd>
<dt>(D)TLS:</dt>
<t hangText="(D)TLS:">This term is used for statements that apply to <dd>This term is used for statements that apply to
both Transport Layer Security <xref target="RFC8446"></xref> and both Transport Layer Security <xref target="RFC8446" format="default"/
Datagram Transport Layer Security <xref > and
target="RFC6347"></xref>.</t> Datagram Transport Layer Security <xref target="RFC6347" format="defau
</list></t> lt"/>.</dd>
</dl>
</section> </section>
<section anchor="sec-overview" title="Overview of Operation"> <section anchor="sec-overview" numbered="true" toc="default">
<name>Overview of Operation</name>
<t>This section gives an overview of the operation of TURN. It is <t>This section gives an overview of the operation of TURN. It is
non-normative.</t> non-normative.</t>
<t>In a typical configuration, a TURN client is connected to a private
<t>In a typical configuration, a TURN client is connected to a <xref network <xref target="RFC1918" format="default"/> and, through one or more
target="RFC1918">private network</xref> and through one or more NATs to NATs, to the public Internet. On the public Internet is a TURN
the public Internet. On the public Internet is a TURN server. Elsewhere server. Elsewhere in the Internet are one or more peers with which the
in the Internet are one or more peers with which the TURN client wishes TURN client wishes to communicate. These peers may or may not be behind
to communicate. These peers may or may not be behind one or more NATs. one or more NATs. The client uses the server as a relay to send packets
The client uses the server as a relay to send packets to these peers and to these peers and to receive packets from these peers.</t>
to receive packets from these peers.</t>
<figure anchor="fig-turn-model"> <figure anchor="fig-turn-model">
<artwork><![CDATA[ Peer A <artwork name="" type="" align="left" alt=""><![CDATA[
Server-Reflexive +---------+ Peer A
Transport Address | | Server-Reflexive +---------+
192.0.2.150:32102 | | Transport Address | |
| /| | 192.0.2.150:32102 | |
TURN | / ^| Peer A | | /| |
Client's Server | / || | TURN | / ^| Peer A |
Host Transport Transport | // || | Client's Server | / || |
Address Address | // |+---------+ Host Transport Transport | // || |
198.51.100.2:49721 192.0.2.15:3478 |+-+ // Peer A Address Address | // |+---------+
| | ||N| / Host Transport 198.51.100.2:49721 192.0.2.15:3478 |+-+ // Peer A
| +-+ | ||A|/ Address | | ||N| / Host Transport
| | | | v|T| 203.0.113.2:49582 | +-+ | ||A|/ Address
| | | | /+-+ | | | | v|T| 203.0.113.2:49582
+---------+| | | |+---------+ / +---------+ | | | | /+-+
| || |N| || | // | | +---------+| | | |+---------+ / +---------+
| TURN |v | | v| TURN |/ | | | || |N| || | // | |
| Client |----|A|----------| Server |------------------| Peer B | | TURN |v | | v| TURN |/ | |
| | | |^ | |^ ^| | | Client |----|A|-------| Server |------------------| Peer B |
| | |T|| | || || | | | | |^ | |^ ^| |
+---------+ | || +---------+| |+---------+ | | |T|| | || || |
| || | | +---------+ | || +---------+| |+---------+
| || | | | || | |
+-+| | | | || | |
| | | +-+| | |
| | | | | |
Client's | Peer B | | |
Server-Reflexive Relayed Transport Client's | Peer B
Transport Address Transport Address Address Server-Reflexive Relayed Transport
192.0.2.1:7000 192.0.2.15:50000 192.0.2.210:49191 Transport Address Transport Address Address
]]></artwork> 192.0.2.1:7000 192.0.2.15:50000 192.0.2.210:49191]]></artwork>
</figure> </figure>
<t></t> <t><xref target="fig-turn-model" format="default"/> shows a typical deploy
ment. In
<t><xref target="fig-turn-model"></xref> shows a typical deployment. In
this figure, the TURN client and the TURN server are separated by a NAT, this figure, the TURN client and the TURN server are separated by a NAT,
with the client on the private side and the server on the public side of with the client on the private side and the server on the public side of
the NAT. This NAT is assumed to be a &ldquo;bad&rdquo; NAT; for example, the NAT. This NAT is assumed to be a "bad" NAT; for example,
it might have a mapping property of "address-and-port-dependent mapping" it might have a mapping property of "address-and-port-dependent mapping"
(see <xref target="RFC4787"></xref>).</t> (see <xref target="RFC4787" format="default"/>).</t>
<t>The client talks to the server from a (IP address, port) combination <t>The client talks to the server from a (IP address, port) combination
called the client's HOST TRANSPORT ADDRESS. (The combination of an IP called the client's "host transport address". (The combination of an IP
address and port is called a TRANSPORT ADDRESS.)</t> address and port is called a "transport address".)</t>
<t>The client sends TURN messages from its host transport address to a <t>The client sends TURN messages from its host transport address to a
transport address on the TURN server that is known as the TURN SERVER transport address on the TURN server that is known as the "TURN server
TRANSPORT ADDRESS. The client learns the TURN server transport address transport address". The client learns the TURN server transport address
through some unspecified means (e.g., configuration), and this address through some unspecified means (e.g., configuration), and this address
is typically used by many clients simultaneously.</t> is typically used by many clients simultaneously.</t>
<t>Since the client is behind a NAT, the server sees packets from the <t>Since the client is behind a NAT, the server sees packets from the
client as coming from a transport address on the NAT itself. This client as coming from a transport address on the NAT itself. This
address is known as the client&rsquo;s SERVER-REFLEXIVE transport address is known as the client's "server-reflexive transport
address; packets sent by the server to the client&rsquo;s address"; packets sent by the server to the client's
server-reflexive transport address will be forwarded by the NAT to the server-reflexive transport address will be forwarded by the NAT to the
client&rsquo;s host transport address.</t> client's host transport address.</t>
<t>The client uses TURN commands to create and manipulate an ALLOCATION <t>The client uses TURN commands to create and manipulate an ALLOCATION
on the server. An allocation is a data structure on the server. This on the server. An allocation is a data structure on the server. This
data structure contains, amongst other things, the RELAYED TRANSPORT data structure contains, amongst other things, the relayed transport
ADDRESS for the allocation. The relayed transport address is the address for the allocation. The relayed transport address is the
transport address on the server that peers can use to have the server transport address on the server that peers can use to have the server
relay data to the client. An allocation is uniquely identified by its relay data to the client. An allocation is uniquely identified by its
relayed transport address.</t> relayed transport address.</t>
<t>Once an allocation is created, the client can send application data <t>Once an allocation is created, the client can send application data
to the server along with an indication of to which peer the data is to to the server along with an indication of to which peer the data is to
be sent, and the server will relay this data to the intended peer. The be sent, and the server will relay this data to the intended peer. The
client sends the application data to the server inside a TURN message; client sends the application data to the server inside a TURN message;
at the server, the data is extracted from the TURN message and sent to at the server, the data is extracted from the TURN message and sent to
the peer in a UDP datagram. In the reverse direction, a peer can send the peer in a UDP datagram. In the reverse direction, a peer can send
application data in a UDP datagram to the relayed transport address for application data in a UDP datagram to the relayed transport address for
the allocation; the server will then encapsulate this data inside a TURN the allocation; the server will then encapsulate this data inside a TURN
message and send it to the client along with an indication of which peer message and send it to the client along with an indication of which peer
sent the data. Since the TURN message always contains an indication of sent the data. Since the TURN message always contains an indication of
skipping to change at line 422 skipping to change at line 372
be sent, and the server will relay this data to the intended peer. The be sent, and the server will relay this data to the intended peer. The
client sends the application data to the server inside a TURN message; client sends the application data to the server inside a TURN message;
at the server, the data is extracted from the TURN message and sent to at the server, the data is extracted from the TURN message and sent to
the peer in a UDP datagram. In the reverse direction, a peer can send the peer in a UDP datagram. In the reverse direction, a peer can send
application data in a UDP datagram to the relayed transport address for application data in a UDP datagram to the relayed transport address for
the allocation; the server will then encapsulate this data inside a TURN the allocation; the server will then encapsulate this data inside a TURN
message and send it to the client along with an indication of which peer message and send it to the client along with an indication of which peer
sent the data. Since the TURN message always contains an indication of sent the data. Since the TURN message always contains an indication of
which peer the client is communicating with, the client can use a single which peer the client is communicating with, the client can use a single
allocation to communicate with multiple peers.</t> allocation to communicate with multiple peers.</t>
<t>When the peer is behind a NAT, the client must identify the peer
<t>When the peer is behind a NAT, then the client must identify the peer
using its server-reflexive transport address rather than its host using its server-reflexive transport address rather than its host
transport address. For example, to send application data to Peer A in transport address. For example, to send application data to Peer A in
the example above, the client must specify 192.0.2.150:32102 (Peer A's the example above, the client must specify 192.0.2.150:32102 (Peer A's
server-reflexive transport address) rather than 203.0.113.2:49582 (Peer server-reflexive transport address) rather than 203.0.113.2:49582 (Peer
A's host transport address).</t> A's host transport address).</t>
<t>Each allocation on the server belongs to a single client and has <t>Each allocation on the server belongs to a single client and has
either one or two relayed transport addresses that are used only by that either one or two relayed transport addresses that are used only by that
allocation. Thus, when a packet arrives at a relayed transport address allocation. Thus, when a packet arrives at a relayed transport address
on the server, the server knows for which client the data is on the server, the server knows for which client the data is
intended.</t> intended.</t>
<t>The client may have multiple allocations on a server at the same <t>The client may have multiple allocations on a server at the same
time.</t> time.</t>
<section anchor="sec-transports" numbered="true" toc="default">
<section anchor="sec-transports" title="Transports"> <name>Transports</name>
<t>TURN, as defined in this specification, always uses UDP between the <t>TURN, as defined in this specification, always uses UDP between the
server and the peer. However, this specification allows the use of any server and the peer. However, this specification allows the use of any
one of UDP, TCP, Transport Layer Security (TLS) over TCP or Datagram one of UDP, TCP, Transport Layer Security (TLS) over TCP, or Datagram
Transport Layer Security (DTLS) over UDP to carry the TURN messages Transport Layer Security (DTLS) over UDP to carry the TURN messages
between the client and the server.</t> between the client and the server.</t>
<table align="center">
<texttable> <thead>
<ttcol align="center">TURN client to TURN server</ttcol> <tr>
<th align="center">TURN client to TURN server</th>
<ttcol align="center">TURN server to peer</ttcol> <th align="center">TURN server to peer</th>
</tr>
<c>UDP</c> </thead>
<tbody>
<c>UDP</c> <tr>
<td align="center">UDP</td>
<c>TCP</c> <td align="center">UDP</td>
</tr>
<c>UDP</c> <tr>
<td align="center">TCP</td>
<c>TLS-over-TCP</c> <td align="center">UDP</td>
</tr>
<c>UDP</c> <tr>
<td align="center">TLS-over-TCP</td>
<c>DTLS-over-UDP</c> <td align="center">UDP</td>
</tr>
<c>UDP</c> <tr>
</texttable> <td align="center">DTLS-over-UDP</td>
<td align="center">UDP</td>
</tr>
</tbody>
</table>
<t>If TCP or TLS-over-TCP is used between the client and the server, <t>If TCP or TLS-over-TCP is used between the client and the server,
then the server will convert between these transports and UDP then the server will convert between these transports and UDP
transport when relaying data to/from the peer.</t> transport when relaying data to/from the peer.</t>
<t>Since this version of TURN only supports UDP between the server and <t>Since this version of TURN only supports UDP between the server and
the peer, it is expected that most clients will prefer to use UDP the peer, it is expected that most clients will prefer to use UDP
between the client and the server as well. That being the case, some between the client and the server as well. That being the case, some
readers may wonder: Why also support TCP and TLS-over-TCP?</t> readers may wonder: Why also support TCP and TLS-over-TCP?</t>
<t>TURN supports TCP transport between the client and the server <t>TURN supports TCP transport between the client and the server
because some firewalls are configured to block UDP entirely. These because some firewalls are configured to block UDP entirely. These
firewalls block UDP but not TCP, in part because TCP has properties firewalls block UDP but not TCP, in part because TCP has properties
that make the intention of the nodes being protected by the firewall that make the intention of the nodes being protected by the firewall
more obvious to the firewall. For example, TCP has a three-way more obvious to the firewall. For example, TCP has a three-way
handshake that makes in clearer that the protected node really wishes handshake that makes it clearer that the protected node really wishes
to have that particular connection established, while for UDP the best to have that particular connection established, while for UDP, the best
the firewall can do is guess which flows are desired by using the firewall can do is guess which flows are desired by using
filtering rules. Also, TCP has explicit connection teardown; while for filtering rules. Also, TCP has explicit connection teardown; while for
UDP, the firewall has to use timers to guess when the flow is UDP, the firewall has to use timers to guess when the flow is
finished.</t> finished.</t>
<t>TURN supports TLS-over-TCP transport and DTLS-over-UDP transport <t>TURN supports TLS-over-TCP transport and DTLS-over-UDP transport
between the client and the server because (D)TLS provides additional between the client and the server because (D)TLS provides additional
security properties not provided by TURN's default digest security properties not provided by TURN's default digest
authentication; properties that some clients may wish to take authentication, properties that some clients may wish to take
advantage of. In particular, (D)TLS provides a way for the client to advantage of. In particular, (D)TLS provides a way for the client to
ascertain that it is talking to the correct server, and provides for ascertain that it is talking to the correct server and provides for
confidentiality of TURN control messages. If (D)TLS transport is used confidentiality of TURN control messages.
between the TURN client and the TURN server, the cipher suites, server
certificate validation and authentication of TURN server are discussed
in Section 6.2.3 of <xref
target="I-D.ietf-tram-stunbis">&nbsp;</xref>.&nbsp;The guidance given
in <xref target="RFC7525"></xref> MUST be followed to avoid attacks on
(D)TLS. TURN does not require (D)TLS because the overhead of using
(D)TLS is higher than that of digest authentication; for example,
using (D)TLS likely means that most application data will be doubly
encrypted (once by (D)TLS and once to ensure it is still encrypted in
the UDP datagram).</t>
<t>There is an extension to TURN for TCP transport between the server If (D)TLS transport is used between the TURN client and the TURN server, refer
and the peers <xref target="RFC6062"></xref>. For this reason, to <xref target="RFC8489" sectionFormat="of" section="6.2.3"/> for more
allocations that use UDP between the server and the peers are known as information about cipher suites, server certificate validation, and
UDP allocations, while allocations that use TCP between the server and authentication of TURN servers.
the peers are known as TCP allocations. This specification describes
only UDP allocations.</t>
The guidance given in <xref target="RFC7525" format="default"/>
<bcp14>MUST</bcp14> be followed to avoid attacks on (D)TLS. TURN does not
require (D)TLS because the overhead of using (D)TLS is higher than that of
digest authentication; for example, using (D)TLS likely means that most
application data will be doubly encrypted (once by (D)TLS and once to ensure
it is still encrypted in the UDP datagram).</t>
<t>There is an extension to TURN for TCP transport between the server
and the peers <xref target="RFC6062" format="default"/>. For this
reason, allocations that use UDP between the server and the peers are
known as "UDP allocations", while allocations that use TCP between the
server and the peers are known as "TCP allocations". This specification
describes only UDP allocations.</t>
<t>In some applications for TURN, the client may send and receive <t>In some applications for TURN, the client may send and receive
packets other than TURN packets on the host transport address it uses packets other than TURN packets on the host transport address it uses
to communicate with the server. This can happen, for example, when to communicate with the server. This can happen, for example, when
using TURN with ICE. In these cases, the client can distinguish TURN using TURN with ICE. In these cases, the client can distinguish TURN
packets from other packets by examining the source address of the packets from other packets by examining the source address of the
arriving packet: those arriving from the TURN server will be TURN arriving packet; those arriving from the TURN server will be TURN
packets. The algorithm of demultiplexing packets received from packets. The algorithm of demultiplexing packets received from
multiple protocols on the host transport address is discussed in <xref multiple protocols on the host transport address is discussed in <xref t
target="RFC7983"></xref>.</t> arget="RFC7983" format="default"/>.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Allocations"> <name>Allocations</name>
<t>To create an allocation on the server, the client uses an Allocate <t>To create an allocation on the server, the client uses an Allocate
transaction. The client sends an Allocate request to the server, and transaction. The client sends an Allocate request to the server, and
the server replies with an Allocate success response containing the the server replies with an Allocate success response containing the
allocated relayed transport address. The client can include attributes allocated relayed transport address. The client can include attributes
in the Allocate request that describe the type of allocation it in the Allocate request that describe the type of allocation it
desires (e.g., the lifetime of the allocation). Since relaying data desires (e.g., the lifetime of the allocation). Since relaying data
has security implications, the server requires that the client has security implications, the server requires that the client
authenticate itself, typically using STUN&rsquo;s long-term credential authenticate itself, typically using STUN's long-term credential
mechanism or the STUN Extension for Third-Party Authorization <xref mechanism or the STUN Extension for Third-Party Authorization <xref targ
target="RFC7635"></xref>, to show that it is authorized to use the et="RFC7635" format="default"/>, to show that it is authorized to use the
server.</t> server.</t>
<t>Once a relayed transport address is allocated, a client must keep <t>Once a relayed transport address is allocated, a client must keep
the allocation alive. To do this, the client periodically sends a the allocation alive. To do this, the client periodically sends a
Refresh request to the server. TURN deliberately uses a different Refresh request to the server. TURN deliberately uses a different
method (Refresh rather than Allocate) for refreshes to ensure that the method (Refresh rather than Allocate) for refreshes to ensure that the
client is informed if the allocation vanishes for some reason.</t> client is informed if the allocation vanishes for some reason.</t>
<t>The frequency of the Refresh transaction is determined by the <t>The frequency of the Refresh transaction is determined by the
lifetime of the allocation. The default lifetime of an allocation is lifetime of the allocation. The default lifetime of an allocation is
10 minutes -- this value was chosen to be long enough so that 10 minutes; this value was chosen to be long enough so that
refreshing is not typically a burden on the client, while expiring refreshing is not typically a burden on the client while expiring
allocations where the client has unexpectedly quit in a timely manner. allocations where the client has unexpectedly quit in a timely manner.
However, the client can request a longer lifetime in the Allocate However, the client can request a longer lifetime in the Allocate
request and may modify its request in a Refresh request, and the request and may modify its request in a Refresh request, and the
server always indicates the actual lifetime in the response. The server always indicates the actual lifetime in the response. The
client must issue a new Refresh transaction within "lifetime" seconds client must issue a new Refresh transaction within "lifetime" seconds
of the previous Allocate or Refresh transaction. Once a client no of the previous Allocate or Refresh transaction. Once a client no
longer wishes to use an allocation, it should delete the allocation longer wishes to use an allocation, it should delete the allocation
using a Refresh request with a requested lifetime of 0.</t> using a Refresh request with a requested lifetime of zero.</t>
<t>Both the server and client keep track of a value known as the <t>Both the server and client keep track of a value known as the
5-TUPLE. At the client, the 5-tuple consists of the client's host "5-tuple". At the client, the 5-tuple consists of the client's host
transport address, the server transport address, and the transport transport address, the server transport address, and the transport
protocol used by the client to communicate with the server. At the protocol used by the client to communicate with the server. At the
server, the 5-tuple value is the same except that the client's host server, the 5-tuple value is the same except that the client's host
transport address is replaced by the client's server-reflexive transport address is replaced by the client's server-reflexive
address, since that is the client's address as seen by the server.</t> address since that is the client's address as seen by the server.</t>
<t>Both the client and the server remember the 5-tuple used in the <t>Both the client and the server remember the 5-tuple used in the
Allocate request. Subsequent messages between the client and the Allocate request. Subsequent messages between the client and the
server use the same 5-tuple. In this way, the client and server know server use the same 5-tuple. In this way, the client and server know
which allocation is being referred to. If the client wishes to which allocation is being referred to. If the client wishes to
allocate a second relayed transport address, it must create a second allocate a second relayed transport address, it must create a second
allocation using a different 5-tuple (e.g., by using a different allocation using a different 5-tuple (e.g., by using a different
client host address or port).</t> client host address or port).</t>
<aside>
<t><list> <t>NOTE: While the terminology used in this document refers to
<t>NOTE: While the terminology used in this document refers to
5-tuples, the TURN server can store whatever identifier it likes 5-tuples, the TURN server can store whatever identifier it likes
that yields identical results. Specifically, an implementation may that yields identical results. Specifically, an implementation may
use a file-descriptor in place of a 5-tuple to represent a TCP use a file descriptor in place of a 5-tuple to represent a TCP
connection.</t> connection.</t>
</list></t> </aside>
<figure anchor="fig-allocate"> <figure anchor="fig-allocate">
<artwork><![CDATA[TURN TURN <artwork name="" type="" align="left" alt=""><![CDATA[
Peer Peer TURN TURN Peer Peer
client server A B client server A B
|-- Allocate request --------------->| | | |-- Allocate request --------------->| | |
| (invalid or missing credentials) | | | | (invalid or missing credentials) | | |
| | | | | | | |
|<--------------- Allocate failure --| | | |<--------------- Allocate failure --| | |
| (401 Unauthenticated) | | | | (401 Unauthenticated) | | |
| | | | | | | |
|-- Allocate request --------------->| | | |-- Allocate request --------------->| | |
| (valid credentials) | | | | (valid credentials) | | |
| | | | | | | |
|<---------- Allocate success resp --| | | |<---------- Allocate success resp --| | |
| (192.0.2.15:50000) | | | | (192.0.2.15:50000) | | |
// // // // // // // //
| | | | | | | |
|-- Refresh request ---------------->| | | |-- Refresh request ---------------->| | |
| | | | | | | |
|<----------- Refresh success resp --| | | |<----------- Refresh success resp --| | |
| | | | | | | |
]]></artwork> ]]></artwork>
<postamble></postamble>
</figure> </figure>
<t>In <xref target="fig-allocate"></xref>, the client sends an <t>In <xref target="fig-allocate" format="default"/>, the client sends a n
Allocate request to the server with invalid or missing credentials. Allocate request to the server with invalid or missing credentials.
Since the server requires that all requests be authenticated using Since the server requires that all requests be authenticated using
STUN's long-term credential mechanism, the server rejects the request STUN's long-term credential mechanism, the server rejects the request
with a 401 (Unauthorized) error code. The client then tries again, with a 401 (Unauthorized) error code. The client then tries again,
this time including credentials. This time, the server accepts the this time including credentials. This time, the server accepts the
Allocate request and returns an Allocate success response containing Allocate request and returns an Allocate success response containing
(amongst other things) the relayed transport address assigned to the (amongst other things) the relayed transport address assigned to the
allocation. Sometime later, the client decides to refresh the allocation. Sometime later, the client decides to refresh the
allocation and thus sends a Refresh request to the server. The refresh allocation; thus, it sends a Refresh request to the server. The refresh
is accepted and the server replies with a Refresh success is accepted and the server replies with a Refresh success
response.</t> response.</t>
</section> </section>
<section anchor="sec-permission-overview" title="Permissions"> <section anchor="sec-permission-overview" numbered="true" toc="default">
<name>Permissions</name>
<t>To ease concerns amongst enterprise IT administrators that TURN <t>To ease concerns amongst enterprise IT administrators that TURN
could be used to bypass corporate firewall security, TURN includes the could be used to bypass corporate firewall security, TURN includes the
notion of permissions. TURN permissions mimic the address-restricted notion of permissions. TURN permissions mimic the address-restricted
filtering mechanism of NATs that comply with <xref filtering mechanism of NATs that comply with <xref target="RFC4787" form
target="RFC4787"></xref>.</t> at="default"/>.</t>
<t>An allocation can have zero or more permissions. Each permission <t>An allocation can have zero or more permissions. Each permission
consists of an IP address and a lifetime. When the server receives a consists of an IP address and a lifetime. When the server receives a
UDP datagram on the allocation's relayed transport address, it first UDP datagram on the allocation's relayed transport address, it first
checks the list of permissions. If the source IP address of the checks the list of permissions. If the source IP address of the
datagram matches a permission, the application data is relayed to the datagram matches a permission, the application data is relayed to the
client, otherwise the UDP datagram is silently discarded.</t> client; otherwise, the UDP datagram is silently discarded.</t>
<t>A permission expires after 5 minutes if it is not refreshed, and <t>A permission expires after 5 minutes if it is not refreshed, and
there is no way to explicitly delete a permission. This behavior was there is no way to explicitly delete a permission. This behavior was
selected to match the behavior of a NAT that complies with <xref selected to match the behavior of a NAT that complies with <xref target=
target="RFC4787"></xref>.</t> "RFC4787" format="default"/>.</t>
<t>The client can install or refresh a permission using either a <t>The client can install or refresh a permission using either a
CreatePermission request or a ChannelBind request. Using the CreatePermission request or a ChannelBind request. Using the
CreatePermission request, multiple permissions can be installed or CreatePermission request, multiple permissions can be installed or
refreshed with a single request -- this is important for applications refreshed with a single request; this is important for applications
that use ICE. For security reasons, permissions can only be installed that use ICE. For security reasons, permissions can only be installed
or refreshed by transactions that can be authenticated; thus, Send or refreshed by transactions that can be authenticated; thus, Send
indications and ChannelData messages (which are used to send data to indications and ChannelData messages (which are used to send data to
peers) do not install or refresh any permissions.</t> peers) do not install or refresh any permissions.</t>
<t>Note that permissions are within the context of an allocation, so <t>Note that permissions are within the context of an allocation, so
adding or expiring a permission in one allocation does not affect adding or expiring a permission in one allocation does not affect
other allocations.</t> other allocations.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Send Mechanism"> <name>Send Mechanism</name>
<t>There are two mechanisms for the client and peers to exchange <t>There are two mechanisms for the client and peers to exchange
application data using the TURN server. The first mechanism uses the application data using the TURN server. The first mechanism uses the
Send and Data methods, the second mechanism uses channels. Common to Send and Data methods, the second mechanism uses channels. Common to
both mechanisms is the ability of the client to communicate with both mechanisms is the ability of the client to communicate with
multiple peers using a single allocated relayed transport address; multiple peers using a single allocated relayed transport address;
thus, both mechanisms include a means for the client to indicate to thus, both mechanisms include a means for the client to indicate to
the server which peer should receive the data, and for the server to the server which peer should receive the data and for the server to
indicate to the client which peer sent the data.</t> indicate to the client which peer sent the data.</t>
<t>The Send mechanism uses Send and Data indications. Send indications <t>The Send mechanism uses Send and Data indications. Send indications
are used to send application data from the client to the server, while are used to send application data from the client to the server, while
Data indications are used to send application data from the server to Data indications are used to send application data from the server to
the client.</t> the client.</t>
<t>When using the Send mechanism, the client sends a Send indication <t>When using the Send mechanism, the client sends a Send indication
to the TURN server containing (a) an XOR-PEER-ADDRESS attribute to the TURN server containing (a) an XOR-PEER-ADDRESS attribute
specifying the (server-reflexive) transport address of the peer and specifying the (server-reflexive) transport address of the peer and
(b) a DATA attribute holding the application data. When the TURN (b) a DATA attribute holding the application data. When the TURN
server receives the Send indication, it extracts the application data server receives the Send indication, it extracts the application data
from the DATA attribute and sends it in a UDP datagram to the peer, from the DATA attribute and sends it in a UDP datagram to the peer,
using the allocated relay address as the source address. Note that using the allocated relay address as the source address. Note that
there is no need to specify the relayed transport address, since it is there is no need to specify the relayed transport address since it is
implied by the 5-tuple used for the Send indication.</t> implied by the 5-tuple used for the Send indication.</t>
<t>In the reverse direction, UDP datagrams arriving at the relayed <t>In the reverse direction, UDP datagrams arriving at the relayed
transport address on the TURN server are converted into Data transport address on the TURN server are converted into Data
indications and sent to the client, with the server-reflexive indications and sent to the client, with the server-reflexive
transport address of the peer included in an XOR-PEER-ADDRESS transport address of the peer included in an XOR-PEER-ADDRESS
attribute and the data itself in a DATA attribute. Since the relayed attribute and the data itself in a DATA attribute. Since the relayed
transport address uniquely identified the allocation, the server knows transport address uniquely identified the allocation, the server knows
which client should receive the data.</t> which client should receive the data.</t>
<t>Some ICMP (Internet Control Message Protocol) packets arriving at <t>Some ICMP (Internet Control Message Protocol) packets arriving at
the relayed transport address on the TURN server may be converted into the relayed transport address on the TURN server may be converted into
Data indications and sent to the client, with the transport address of Data indications and sent to the client, with the transport address of
the peer included in an XOR-PEER-ADDRESS attribute and the ICMP type the peer included in an XOR-PEER-ADDRESS attribute and the ICMP type
and code in a ICMP attribute. ICMP attribute forwarding always uses and code in an ICMP attribute. ICMP attribute forwarding always uses
Data indications containing the XOR-PEER-ADDRESS and ICMP attributes, Data indications containing the XOR-PEER-ADDRESS and ICMP attributes,
even when using the channel mechanism to forward UDP data.</t> even when using the channel mechanism to forward UDP data.</t>
<t>Send and Data indications cannot be authenticated since the
<t>Send and Data indications cannot be authenticated, since the
long-term credential mechanism of STUN does not support authenticating long-term credential mechanism of STUN does not support authenticating
indications. This is not as big an issue as it might first appear, indications. This is not as big an issue as it might first appear
since the client-to-server leg is only half of the total path to the since the client-to-server leg is only half of the total path to the
peer. Applications that want end-to-end security should encrypt the peer. Applications that want end-to-end security should encrypt the
data sent between the client and a peer.</t> data sent between the client and a peer.</t>
<t>Because Send indications are not authenticated, it is possible for <t>Because Send indications are not authenticated, it is possible for
an attacker to send bogus Send indications to the server, which will an attacker to send bogus Send indications to the server, which will
then relay these to a peer. To partly mitigate this attack, TURN then relay these to a peer. To partly mitigate this attack, TURN
requires that the client install a permission towards a peer before requires that the client install a permission towards a peer before
sending data to it using a Send indication. The technique to fully sending data to it using a Send indication. The technique to fully
mitigate the attack is discussed in <xref mitigate the attack is discussed in <xref target="fate-data" format="def
target="fate-data"></xref>.</t> ault"/>.</t>
<figure anchor="fig-send-data"> <figure anchor="fig-send-data">
<artwork><![CDATA[TURN TURN <artwork name="" type="" align="left" alt=""><![CDATA[
Peer Peer TURN TURN Peer Peer
client server A B client server A B
| | | | | | | |
|-- CreatePermission req (Peer A) -->| | | |-- CreatePermission req (Peer A) ->| | |
|<-- CreatePermission success resp --| | | |<- CreatePermission success resp --| | |
| | | | | | | |
|--- Send ind (Peer A)-------------->| | | |--- Send ind (Peer A)------------->| | |
| |=== data ===>| | | |=== data ===>| |
| | | | | | | |
| |<== data ====| | | |<== data ====| |
|<-------------- Data ind (Peer A) --| | | |<------------- Data ind (Peer A) --| | |
| | | | | | | |
| | | | | | | |
|--- Send ind (Peer B)-------------->| | | |--- Send ind (Peer B)------------->| | |
| | dropped | | | | dropped | |
| | | | | | | |
| |<== data ==================| | |<== data ==================|
| dropped | | | | dropped | | |
| | | | | | | |
]]></artwork> ]]></artwork></figure>
<t>In <xref target="fig-send-data" format="default"/>, the client has al
<postamble></postamble> ready
</figure>
<t>In <xref target="fig-send-data"></xref>, the client has already
created an allocation and now wishes to send data to its peers. The created an allocation and now wishes to send data to its peers. The
client first creates a permission by sending the server a client first creates a permission by sending the server a
CreatePermission request specifying Peer A's (server-reflexive) IP CreatePermission request specifying Peer A's (server-reflexive) IP
address in the XOR-PEER-ADDRESS attribute; if this was not done, the address in the XOR-PEER-ADDRESS attribute; if this was not done, the
server would not relay data between the client and the server. The server would not relay data between the client and the server. The
client then sends data to Peer A using a Send indication; at the client then sends data to Peer A using a Send indication; at the
server, the application data is extracted and forwarded in a UDP server, the application data is extracted and forwarded in a UDP
datagram to Peer A, using the relayed transport address as the source datagram to Peer A, using the relayed transport address as the source
transport address. When a UDP datagram from Peer A is received at the transport address. When a UDP datagram from Peer A is received at the
relayed transport address, the contents are placed into a Data relayed transport address, the contents are placed into a Data
indication and forwarded to the client. Later, the client attempts to indication and forwarded to the client. Later, the client attempts to
exchange data with Peer B; however, no permission has been installed exchange data with Peer B; however, no permission has been installed
for Peer B, so the Send indication from the client and the UDP for Peer B, so the Send indication from the client and the UDP
datagram from the peer are both dropped by the server.</t> datagram from the peer are both dropped by the server.</t>
</section> </section>
<section title="Channels"> <section numbered="true" toc="default">
<t>For some applications (e.g., Voice over IP), the 36 bytes of <name>Channels</name>
<t>For some applications (e.g., Voice over IP (VoIP)), the 36 bytes of
overhead that a Send indication or Data indication adds to the overhead that a Send indication or Data indication adds to the
application data can substantially increase the bandwidth required application data can substantially increase the bandwidth required
between the client and the server. To remedy this, TURN offers a between the client and the server. To remedy this, TURN offers a
second way for the client and server to associate data with a specific second way for the client and server to associate data with a specific
peer.</t> peer.</t>
<t>This second way uses an alternate packet format known as the <t>This second way uses an alternate packet format known as the
ChannelData message. The ChannelData message does not use the STUN "ChannelData message". The ChannelData message does not use the STUN
header used by other TURN messages, but instead has a 4-byte header header used by other TURN messages, but instead has a 4-byte header
that includes a number known as a channel number. Each channel number that includes a number known as a "channel number". Each channel number
in use is bound to a specific peer and thus serves as a shorthand for in use is bound to a specific peer; thus, it serves as a shorthand for
the peer's host transport address.</t> the peer's host transport address.</t>
<t>To bind a channel to a peer, the client sends a ChannelBind request <t>To bind a channel to a peer, the client sends a ChannelBind request
to the server, and includes an unbound channel number and the to the server and includes an unbound channel number and the
transport address of the peer. Once the channel is bound, the client transport address of the peer. Once the channel is bound, the client
can use a ChannelData message to send the server data destined for the can use a ChannelData message to send the server data destined for the
peer. Similarly, the server can relay data from that peer towards the peer. Similarly, the server can relay data from that peer towards the
client using a ChannelData message.</t> client using a ChannelData message.</t>
<t>Channel bindings last for 10 minutes unless refreshed; this
<t>Channel bindings last for 10 minutes unless refreshed -- this
lifetime was chosen to be longer than the permission lifetime. Channel lifetime was chosen to be longer than the permission lifetime. Channel
bindings are refreshed by sending another ChannelBind request bindings are refreshed by sending another ChannelBind request
rebinding the channel to the peer. Like permissions (but unlike rebinding the channel to the peer. Like permissions (but unlike
allocations), there is no way to explicitly delete a channel binding; allocations), there is no way to explicitly delete a channel binding;
the client must simply wait for it to time out.</t> the client must simply wait for it to time out.</t>
<figure anchor="fig-channels"> <figure anchor="fig-channels">
<artwork><![CDATA[TURN TURN <artwork name="" type="" align="left" alt=""><![CDATA[
Peer Peer TURN TURN Peer Peer
client server A B client server A B
| | | | | | | |
|-- ChannelBind req ---------------->| | | |-- ChannelBind req --------------->| | |
| (Peer A to 0x4001) | | | | (Peer A to 0x4001) | | |
| | | | | | | |
|<---------- ChannelBind succ resp --| | | |<---------- ChannelBind succ resp -| | |
| | | | | | | |
|-- (0x4001) data ------------------>| | | |-- (0x4001) data ----------------->| | |
| |=== data ===>| | | |=== data ===>| |
| | | | | | | |
| |<== data ====| | | |<== data ====| |
|<------------------ (0x4001) data --| | | |<------------------ (0x4001) data -| | |
| | | | | | | |
|--- Send ind (Peer A)-------------->| | | |--- Send ind (Peer A)------------->| | |
| |=== data ===>| | | |=== data ===>| |
| | | | | | | |
| |<== data ====| | | |<== data ====| |
|<------------------ (0x4001) data --| | | |<------------------ (0x4001) data -| | |
| | | | | | | |
]]></artwork> ]]></artwork>
</figure> </figure>
<t><xref target="fig-channels" format="default"/> shows the channel mech
<t><xref target="fig-channels"></xref> shows the channel mechanism in anism in
use. The client has already created an allocation and now wishes to use. The client has already created an allocation and now wishes to
bind a channel to Peer A. To do this, the client sends a ChannelBind bind a channel to Peer A. To do this, the client sends a ChannelBind
request to the server, specifying the transport address of Peer A and request to the server, specifying the transport address of Peer A and
a channel number (0x4001). After that, the client can send application a channel number (0x4001). After that, the client can send application
data encapsulated inside ChannelData messages to Peer A: this is shown data encapsulated inside ChannelData messages to Peer A: this is shown
as "(0x4001) data" where 0x4001 is the channel number. When the as "(0x4001) data" where 0x4001 is the channel number. When the
ChannelData message arrives at the server, the server transfers the ChannelData message arrives at the server, the server transfers the
data to a UDP datagram and sends it to Peer A (which is the peer bound data to a UDP datagram and sends it to Peer A (which is the peer bound
to channel number 0x4001).</t> to channel number 0x4001).</t>
<t>In the reverse direction, when Peer A sends a UDP datagram to the <t>In the reverse direction, when Peer A sends a UDP datagram to the
relayed transport address, this UDP datagram arrives at the server on relayed transport address, this UDP datagram arrives at the server on
the relayed transport address assigned to the allocation. Since the the relayed transport address assigned to the allocation. Since the
UDP datagram was received from Peer A, which has a channel number UDP datagram was received from Peer A, which has a channel number
assigned to it, the server encapsulates the data into a ChannelData assigned to it, the server encapsulates the data into a ChannelData
message when sending the data to the client.</t> message when sending the data to the client.</t>
<t>Once a channel has been bound, the client is free to intermix <t>Once a channel has been bound, the client is free to intermix
ChannelData messages and Send indications. In the figure, the client ChannelData messages and Send indications. In the figure, the client
later decides to use a Send indication rather than a ChannelData later decides to use a Send indication rather than a ChannelData
message to send additional data to Peer A. The client might decide to message to send additional data to Peer A. The client might decide to
do this, for example, so it can use the DONT-FRAGMENT attribute (see do this, for example, so it can use the DONT-FRAGMENT attribute (see
the next section). However, once a channel is bound, the server will the next section). However, once a channel is bound, the server will
always use a ChannelData message, as shown in the call flow.</t> always use a ChannelData message, as shown in the call flow.</t>
<t>Note that ChannelData messages can only be used for peers to which <t>Note that ChannelData messages can only be used for peers to which
the client has bound a channel. In the example above, Peer A has been the client has bound a channel. In the example above, Peer A has been
bound to a channel, but Peer B has not, so application data to and bound to a channel, but Peer B has not, so application data to and
from Peer B would use the Send mechanism.</t> from Peer B would use the Send mechanism.</t>
</section> </section>
<section anchor="unpriv" numbered="true" toc="default">
<section anchor="unpriv" title="Unprivileged TURN Servers"> <name>Unprivileged TURN Servers</name>
<t>This version of TURN is designed so that the server can be <t>This version of TURN is designed so that the server can be
implemented as an application that runs in user space under commonly implemented as an application that runs in user space under commonly
available operating systems without requiring special privileges. This available operating systems without requiring special privileges. This
design decision was made to make it easy to deploy a TURN server: for design decision was made to make it easy to deploy a TURN server: for
example, to allow a TURN server to be integrated into a peer-to-peer example, to allow a TURN server to be integrated into a peer-to-peer
application so that one peer can offer NAT traversal services to application so that one peer can offer NAT traversal services to
another peer and to use (D)TLS to secure the TURN connection.</t> another peer and to use (D)TLS to secure the TURN connection.</t>
<t>This design decision has the following implications for data <t>This design decision has the following implications for data
relayed by a TURN server:<list style="symbols"> relayed by a TURN server:</t>
<t>The value of the Diffserv field may not be preserved across the <ul spacing="normal">
server;</t> <li>The value of the Diffserv field may not be preserved across the
server;</li>
<t>The Time to Live (TTL) field may be reset, rather than <li>The Time to Live (TTL) field may be reset, rather than
decremented, across the server;</t> decremented, across the server;</li>
<li>The Explicit Congestion Notification (ECN) field may be reset
<t>The Explicit Congestion Notification (ECN) field may be reset by the server;</li>
by the server;</t> <li>There is no end-to-end fragmentation since the packet is
reassembled at the server.</li>
<t>There is no end-to-end fragmentation, since the packet is </ul>
re-assembled at the server.</t> <t>Future work may specify alternate TURN semantics that address
</list>Future work may specify alternate TURN semantics that address
these limitations.</t> these limitations.</t>
</section> </section>
<section title="Avoiding IP Fragmentation"> <section numbered="true" toc="default">
<t>For reasons described in <xref target="Frag-Harmful"></xref>, <name>Avoiding IP Fragmentation</name>
applications, especially those sending large volumes of data, should <t>For reasons described in <xref target="FRAG-HARMFUL"
avoid having their packets fragmented. <xref format="default"/>, applications, especially those sending large
target="I-D.ietf-intarea-frag-fragile"></xref> discusses issues volumes of data, should avoid having their packets fragmented. <xref
associated with IP fragmentation and proposes alternatives to IP target="I-D.ietf-intarea-frag-fragile" format="default"/> discusses issu
fragmentation. Applications using TCP can more or less ignore this es associated
with IP fragmentation and proposes alternatives to IP
fragmentation.
Applications using TCP can, more or less, ignore this
issue because fragmentation avoidance is now a standard part of TCP, issue because fragmentation avoidance is now a standard part of TCP,
but applications using UDP (and thus any application using this but applications using UDP (and, thus, any application using this
version of TURN) need to avoid IP fragmentation by sending version of TURN) need to avoid IP fragmentation by sending
sufficiently small messages or use UDP fragmentation <xref sufficiently small messages or by using UDP fragmentation <xref
target="I-D.ietf-tsvwg-udp-options"></xref>. Note that the UDP target="I-D.ietf-tsvwg-udp-options" format="default"/>. Note that the UD
P
fragmentation option needs to be supported by both endpoints, and at fragmentation option needs to be supported by both endpoints, and at
the time of writing of this document, UDP fragmentation support is the time of writing of this document, UDP fragmentation support is
under discussion and is not deployed.</t> under discussion and is not deployed.</t>
<t>The application running on the client and the peer can take one of <t>The application running on the client and the peer can take one of
two approaches to avoid IP fragmentation until UDP fragmentation two approaches to avoid IP fragmentation until UDP fragmentation
support is available. The first uses messages that are limited to a support is available. The first uses messages that are limited to a
predetermined fixed maximum and the second relies on network feedback predetermined fixed maximum, and the second relies on network feedback
to adapt that maximum.</t> to adapt that maximum.</t>
<t>The first approach is to avoid sending large amounts of application <t>The first approach is to avoid sending large amounts of application
data in the TURN messages/UDP datagrams exchanged between the client data in the TURN messages/UDP datagrams exchanged between the client
and the peer. This is the approach taken by most VoIP (Voice-over-IP) and the peer. This is the approach taken by most VoIP
applications. In this approach, the application MUST assume a PMTU of applications. In this approach, the application <bcp14>MUST</bcp14>
1280 bytes, as IPv6 requires that every link in the Internet have an assume a Path MTU (PMTU) of 1280 bytes because IPv6 requires that every
MTU of 1280 octets or greater as specified in <xref link in the Internet has an MTU of 1280 octets or greater as
target="RFC8200"></xref>. If IPv4 support on legacy or otherwise specified in <xref target="RFC8200" format="default"/>. If IPv4
unusual networks is a consideration, the application MAY assume an support on legacy or otherwise unusual networks is a consideration,
effective MTU of 576 bytes for IPv4 datagrams, as every IPv4 host must the application <bcp14>MAY</bcp14> assume an effective MTU of 576
be capable of receiving a packet whose length is equal to 576 bytes as bytes for IPv4 datagrams, as every IPv4 host must be capable of
discussed in <xref target="RFC0791"></xref> and <xref receiving a packet with a length equal to 576 bytes as discussed in
target="RFC1122"></xref>.</t> <xref target="RFC0791" format="default"/> and <xref target="RFC1122"
format="default"/>.</t>
<t>The exact amount of application data that can be included while <t>The exact amount of application data that can be included while
avoiding fragmentation depends on the details of the TURN session avoiding fragmentation depends on the details of the TURN session
between the client and the server: whether UDP, TCP, or (D)TLS between the client and the server: whether UDP, TCP, or (D)TLS
transport is used, whether ChannelData messages or Send/Data transport is used; whether ChannelData messages or Send/Data
indications are used, and whether any additional attributes (such as indications are used; and whether any additional attributes (such as
the DONT-FRAGMENT attribute) are included. Another factor, which is the DONT-FRAGMENT attribute) are included. Another factor, which is
hard to determine, is whether the MTU is reduced somewhere along the hard to determine, is whether the MTU is reduced somewhere along the
path for other reasons, such as the use of IP-in-IP tunneling.</t> path for other reasons, such as the use of IP-in-IP tunneling.</t>
<t>As a guideline, sending a maximum of 500 bytes of application data <t>As a guideline, sending a maximum of 500 bytes of application data
in a single TURN message (by the client on the client-to-server leg) in a single TURN message (by the client on the client-to-server leg)
or a UDP datagram (by the peer on the peer-to-server leg) will or a UDP datagram (by the peer on the peer-to-server leg) will
generally avoid IP fragmentation. To further reduce the chance of generally avoid IP fragmentation. To further reduce the chance of
fragmentation, it is recommended that the client use ChannelData fragmentation, it is recommended that the client use ChannelData
messages when transferring significant volumes of data, since the messages when transferring significant volumes of data since the
overhead of the ChannelData message is less than Send and Data overhead of the ChannelData message is less than Send and Data
indications.</t> indications.</t>
<t>The second approach the client and peer can take to avoid <t>The second approach the client and peer can take to avoid
fragmentation is to use a path MTU discovery algorithm to determine fragmentation is to use a path MTU discovery algorithm to determine
the maximum amount of application data that can be sent without the maximum amount of application data that can be sent without
fragmentation. The classic path MTU discovery algorithm defined in fragmentation. The classic path MTU discovery algorithm defined in
<xref target="RFC1191"></xref> may not be able to discover the MTU of <xref target="RFC1191" format="default"/> may not be able to discover th e MTU of
the transmission path between the client and the peer since:</t> the transmission path between the client and the peer since:</t>
<ul empty="false" spacing="normal">
<t><list> <li>A probe packet with a Don't Fragment (DF) bit in the IPv4 header s
<t>- a probe packet with DF bit in the IPv4 header set to test a et to test a
path for a larger MTU can be dropped by routers, or</t> path for a larger MTU can be dropped by routers, or</li>
<li>ICMP error messages can be dropped by middleboxes.</li>
<t>- ICMP error messages can be dropped by middle boxes.</t> </ul>
</list></t>
<t>As a result, the client and server need to use a path MTU discovery <t>As a result, the client and server need to use a path MTU discovery
algorithm that does not require ICMP messages. The Packetized Path MTU algorithm that does not require ICMP messages. The Packetized Path MTU
Discovery algorithm defined in <xref target="RFC4821"></xref> is one Discovery algorithm defined in <xref target="RFC4821" format="default"/>
such algorithm.</t> is one
such algorithm, and a set of algorithms is defined in <xref target="I-D.
<t><xref target="I-D.ietf-tram-stun-pmtud"></xref> is an ietf-tsvwg-datagram-plpmtud" format="default"/>. </t>
implementation of <xref target="RFC4821"></xref> that uses STUN to <t><xref target="I-D.ietf-tram-stun-pmtud" format="default"/> is an
discover the path MTU, and so might be a suitable approach to be used implementation of <xref target="RFC4821" format="default"/> that uses ST
UN to
discover the path MTU; so it might be a suitable approach to be used
in conjunction with a TURN server that supports the DONT-FRAGMENT in conjunction with a TURN server that supports the DONT-FRAGMENT
attribute. When the client includes the DONT-FRAGMENT attribute in a attribute. When the client includes the DONT-FRAGMENT attribute in a
Send indication, this tells the server to set the DF bit in the Send indication, this tells the server to set the DF bit in the
resulting UDP datagram that it sends to the peer. Since some servers resulting UDP datagram that it sends to the peer. Since some servers
may be unable to set the DF bit, the client should also include this may be unable to set the DF bit, the client should also include this
attribute in the Allocate request -- any server that does not support attribute in the Allocate request; any server that does not support
the DONT-FRAGMENT attribute will indicate this by rejecting the the DONT-FRAGMENT attribute will indicate this by rejecting the
Allocate request. If the TURN server carrying out packet translation Allocate request. If the TURN server carrying out packet translation
from IPv4-to-IPv6 is unable to access the state of Don't Fragment (DF) from IPv4-to-IPv6 is unable to access the state of the Don't Fragment (D
bit in the IPv4 header, it MUST reject the Allocate request with F)
DONT-FRAGMENT attribute.</t> bit in the IPv4 header, it <bcp14>MUST</bcp14> reject the Allocate reque
st with
the DONT-FRAGMENT attribute.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="RTP Support"> <name>RTP Support</name>
<t>One of the envisioned uses of TURN is as a relay for clients and <t>One of the envisioned uses of TURN is as a relay for clients and
peers wishing to exchange real-time data (e.g., voice or video) using peers wishing to exchange real-time data (e.g., voice or video) using
RTP. To facilitate the use of TURN for this purpose, TURN includes RTP. To facilitate the use of TURN for this purpose, TURN includes
some special support for older versions of RTP.</t> some special support for older versions of RTP.</t>
<t>Old versions of RTP <xref target="RFC3550" format="default"/> require
<t>Old versions of RTP <xref target="RFC3550"></xref> required that d that
the RTP stream be on an even port number and the associated RTP the RTP stream be on an even port number and the associated RTP
Control Protocol (RTCP) stream, if present, be on the next highest Control Protocol (RTCP) stream, if present, be on the next highest
port. To allow clients to work with peers that still require this, port. To allow clients to work with peers that still require this,
TURN allows the client to request that the server allocate a relayed TURN allows the client to request that the server allocate a relayed
transport address with an even port number, and to optionally request transport address with an even port number and optionally request
the server reserve the next-highest port number for a subsequent the server reserve the next-highest port number for a subsequent
allocation.</t> allocation.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Happy Eyeballs for TURN"> <name>Happy Eyeballs for TURN</name>
<t>If an IPv4 path to reach a TURN server is found, but the TURN <t>If an IPv4 path to reach a TURN server is found, but the TURN
server's IPv6 path is not working, a dual-stack TURN client can server's IPv6 path is not working, a dual-stack TURN client can
experience a significant connection delay compared to an IPv4-only experience a significant connection delay compared to an IPv4-only
TURN client. To overcome these connection setup problems, the TURN TURN client. To overcome these connection setup problems, the TURN
client needs to query both A and AAAA records for the TURN server client needs to query both A and AAAA records for the TURN server
specified using a domain name and try connecting to the TURN server specified using a domain name and try connecting to the TURN server
using both IPv6 and IPv4 addresses in a fashion similar to the Happy using both IPv6 and IPv4 addresses in a fashion similar to the Happy
Eyeballs mechanism defined in <xref target="RFC8305"></xref>. The TURN Eyeballs mechanism defined in <xref target="RFC8305" format="default"/>. The TURN
client performs the following steps based on the transport protocol client performs the following steps based on the transport protocol
being used to connect to the TURN server.</t> being used to connect to the TURN server.</t>
<ul spacing="normal">
<li>For TCP or TLS-over-TCP, the results of the Happy Eyeballs
procedure <xref target="RFC8305" format="default"/> are used by the
TURN
client for sending its TURN messages to the server.</li>
<li>For clear text UDP, send TURN Allocate requests to both IP
address families as discussed in <xref target="RFC8305" format="defa
ult"/>
without authentication information.
<t><list style="symbols"> If the TURN server requires
<t>For TCP or TLS-over-TCP, the results of the Happy Eyeballs authentication, it will send back a 401 unauthenticated response;
procedure <xref target="RFC8305"></xref> are used by the TURN the TURN client will use the first UDP connection on which a 401
client for sending its TURN messages to the server.</t>
<t>For clear text UDP, send TURN Allocate requests to both IP
address families as discussed in <xref target="RFC8305"></xref>,
without authentication information. If the TURN server requires
authentication, it will send back a 401 unauthenticated response
and the TURN client uses the first UDP connection on which a 401
error response is received. If a 401 error response is received error response is received. If a 401 error response is received
from both IP address families then the TURN client can silently from both IP address families, then the TURN client can silently
abandon the UDP connection on the IP address family with lower abandon the UDP connection on the IP address family with lower
precedence. If the TURN server does not require authentication (as precedence. If the TURN server does not require authentication (as
described in Section 9 of <xref target="RFC8155"></xref>), it is described in <xref target="RFC8155"
sectionFormat="of" section="9"/>), it is
possible for both Allocate requests to succeed. In this case, the possible for both Allocate requests to succeed. In this case, the
TURN client sends a Refresh with LIFETIME value of 0 on the TURN client sends a Refresh with a LIFETIME value of zero on the
allocation using the IP address family with lower precedence to allocation using the IP address family with lower precedence to
delete the allocation.</t> delete the allocation.</li>
<li>For DTLS over UDP, initiate a DTLS handshake to both IP address
<t>For DTLS over UDP, initiate DTLS handshake to both IP address families as discussed in <xref target="RFC8305" format="default"/>,
families as discussed in <xref target="RFC8305"></xref> and use and use the first DTLS session that is established. If the DTLS
the first DTLS session that is established. If the DTLS session is session is established on both IP address families, then the client
established on both IP address families then the client sends DTLS sends a DTLS close_notify alert to terminate the DTLS session using
close_notify alert to terminate the DTLS session using the IP the IP address family with lower precedence. If the TURN over DTLS
address family with lower precedence. If TURN over DTLS server has server has been configured to require a cookie exchange (<xref
been configured to require a cookie exchange (Section 4.2 in <xref target="RFC6347" sectionFormat="of" section="4.2"/>) and
target="RFC6347"></xref>) and HelloVerifyRequest is received from a HelloVerifyRequest is received from the TURN servers on both IP
the TURN servers on both IP address families then the client can address families, then the client can silently abandon the
silently abandon the connection on the IP address family with connection on the IP address family with lower precedence.</li>
lower precedence.</t> </ul>
</list></t>
</section> </section>
</section> </section>
<section title="Discovery of TURN server"> <section numbered="true" toc="default">
<name>Discovery of TURN Server</name>
<t>Methods of TURN server discovery, including using anycast, are <t>Methods of TURN server discovery, including using anycast, are
described in <xref target="RFC8155"></xref>. If a host with multiple described in <xref target="RFC8155" format="default"/>. If a host with
interfaces discovers a TURN server in each interface, the mechanism multiple interfaces discovers a TURN server in each interface, the
described in <xref target="RFC7982"></xref> can be used by the TURN mechanism described in <xref target="RFC7982" format="default"/> can be
client to influence the TURN server selection. The syntax of the "turn" used by the TURN client to influence the TURN server selection. The
and "turns" URIs are defined in Section 3.1 of <xref syntax of the "turn" and "turns" URIs are defined in <xref
target="RFC7065"></xref>. DTLS as a transport protocol for TURN is target="RFC7065" sectionFormat="of" section="3.1"/>. DTLS as a transport
defined in <xref target="RFC7350"></xref>.</t> protocol for TURN is defined in <xref target="RFC7350"
format="default"/>.</t>
<section title="TURN URI Scheme Semantics"> <section numbered="true" toc="default">
<name>TURN URI Scheme Semantics</name>
<t>The "turn" and "turns" URI schemes are used to designate a TURN <t>The "turn" and "turns" URI schemes are used to designate a TURN
server (also known as a relay) on Internet hosts accessible using the server (also known as a "relay") on Internet hosts accessible using the
TURN protocol. The TURN protocol supports sending messages over UDP, TURN protocol. The TURN protocol supports sending messages over UDP,
TCP, TLS-over-TCP or DTLS-over-UDP. The "turns" URI scheme MUST be TCP, TLS-over-TCP, or DTLS-over-UDP. The "turns" URI scheme <bcp14>MUST< /bcp14> be
used when TURN is run over TLS-over-TCP or in DTLS-over-UDP, and the used when TURN is run over TLS-over-TCP or in DTLS-over-UDP, and the
"turn" scheme MUST be used otherwise. The required &lt;host&gt; part "turn" scheme <bcp14>MUST</bcp14> be used otherwise. The required &lt;ho st&gt; part
of the "turn" URI denotes the TURN server host. The &lt;port&gt; part, of the "turn" URI denotes the TURN server host. The &lt;port&gt; part,
if present, denotes the port on which the TURN server is awaiting if present, denotes the port on which the TURN server is awaiting
connection requests. If it is absent, the default port is 3478 for connection requests. If it is absent, the default port is 3478 for
both UDP and TCP. The default port for TURN over TLS and TURN over both UDP and TCP. The default port for TURN over TLS and TURN over
DTLS is 5349.</t> DTLS is 5349.</t>
</section> </section>
</section> </section>
<!-- Overview --> <section anchor="sec-general-behavior" numbered="true" toc="default">
<name>General Behavior</name>
<section anchor="sec-general-behavior" title="General Behavior">
<t>This section contains general TURN processing rules that apply to all <t>This section contains general TURN processing rules that apply to all
TURN messages.</t> TURN messages.</t>
<t>TURN is an extension to STUN. All TURN messages, with the exception <t>TURN is an extension to STUN. All TURN messages, with the exception
of the ChannelData message, are STUN-formatted messages. All the base of the ChannelData message, are STUN-formatted messages. All the base
processing rules described in <xref processing rules described in <xref target="RFC8489" format="default"/> ap
target="I-D.ietf-tram-stunbis"></xref> apply to STUN-formatted messages. ply to STUN-formatted messages.
This means that all the message-forming and message-processing This means that all the message-forming and message-processing
descriptions in this document are implicitly prefixed with the rules of descriptions in this document are implicitly prefixed with the rules of
<xref target="I-D.ietf-tram-stunbis"></xref>.</t> <xref target="RFC8489" format="default"/>.</t>
<t><xref target="RFC8489" format="default"/> specifies an
<t><xref target="I-D.ietf-tram-stunbis"></xref> specifies an authentication mechanism called the "long-term credential mechanism". TURN
authentication mechanism called the long-term credential mechanism. TURN servers and clients <bcp14>MUST</bcp14> implement this mechanism, and the
servers and clients MUST implement this mechanism, and the authentication options are discussed in <xref target="sec-rcv-allocate" fo
authentication options are discussed in <xref rmat="default"/>.</t>
target="sec-rcv-allocate"></xref>.</t>
<t>Note that the long-term credential mechanism applies only to requests <t>Note that the long-term credential mechanism applies only to requests
and cannot be used to authenticate indications; thus, indications in and cannot be used to authenticate indications; thus, indications in
TURN are never authenticated. If the server requires requests to be TURN are never authenticated. If the server requires requests to be
authenticated, then the server's administrator MUST choose a realm value authenticated, then the server's administrator <bcp14>MUST</bcp14> choose a realm value
that will uniquely identify the username and password combination that that will uniquely identify the username and password combination that
the client must use, even if the client uses multiple servers under the client must use, even if the client uses multiple servers under
different administrations. The server's administrator MAY choose to different administrations. The server's administrator <bcp14>MAY</bcp14> c
allocate a unique username to each client, or MAY choose to allocate the hoose to
allocate a unique username to each client, or it <bcp14>MAY</bcp14> choose
to allocate the
same username to more than one client (for example, to all clients from same username to more than one client (for example, to all clients from
the same department or company). For each Allocate request, the server the same department or company). For each Allocate request, the server
SHOULD generate a new random nonce when the allocation is first <bcp14>SHOULD</bcp14> generate a new random nonce when the allocation is f
attempted following the randomness recommendations in <xref irst
target="RFC4086"></xref> and SHOULD expire the nonce at least once every attempted following the randomness recommendations in <xref target="RFC408
6" format="default"/> and <bcp14>SHOULD</bcp14> expire the nonce at least once e
very
hour during the lifetime of the allocation. The server uses the hour during the lifetime of the allocation. The server uses the
mechanism described in section 9.2 of <xref mechanism described in <xref target="RFC8489"
target="I-D.ietf-tram-stunbis"></xref> to indicate that it supports sectionFormat="of" section="9.2"/> to indicate that it supports
<xref target="I-D.ietf-tram-stunbis"></xref>.</t> <xref target="RFC8489" format="default"/>.</t>
<t>All requests after the initial Allocate must use the same username as <t>All requests after the initial Allocate must use the same username as
that used to create the allocation, to prevent attackers from hijacking that used to create the allocation to prevent attackers from hijacking
the client's allocation. Specifically, if the server requires the use of the client's allocation.</t>
the long-term credential mechanism, and if a non-Allocate request passes <t>Specifically, if:
authentication under this mechanism, and if the 5-tuple identifies an </t>
existing allocation, but the request does not use the same username as <ul>
used to create the allocation, then the request MUST be rejected with a <li>the server requires the use of the long-term credential mechanism, and;
441 (Wrong Credentials) error.</t> </li>
<li>a non-Allocate request passes authentication under this mechanism, and;
</li>
<li>the 5-tuple identifies an existing allocation, but;
</li>
<li>the request does not use the same username as used to create the allocation,
</li>
</ul>
<t> then the request <bcp14>MUST</bcp14> be rejected with a 441 (Wrong
Credentials) error.</t>
<t>When a TURN message arrives at the server from the client, the server <t>When a TURN message arrives at the server from the client, the server
uses the 5-tuple in the message to identify the associated allocation. uses the 5-tuple in the message to identify the associated allocation.
For all TURN messages (including ChannelData) EXCEPT an Allocate For all TURN messages (including ChannelData) EXCEPT an Allocate
request, if the 5-tuple does not identify an existing allocation, then request, if the 5-tuple does not identify an existing allocation, then
the message MUST either be rejected with a 437 Allocation Mismatch error the message <bcp14>MUST</bcp14> either be rejected with a 437 Allocation M
(if it is a request) or silently ignored (if it is an indication or a ismatch error
(if it is a request) or be silently ignored (if it is an indication or a
ChannelData message). A client receiving a 437 error response to a ChannelData message). A client receiving a 437 error response to a
request other than Allocate MUST assume the allocation no longer request other than Allocate <bcp14>MUST</bcp14> assume the allocation no l onger
exists.</t> exists.</t>
<t><xref target="RFC8489" format="default"/> defines a number of
<t><xref target="I-D.ietf-tram-stunbis"></xref> defines a number of
attributes, including the SOFTWARE and FINGERPRINT attributes. The attributes, including the SOFTWARE and FINGERPRINT attributes. The
client SHOULD include the SOFTWARE attribute in all Allocate and Refresh client <bcp14>SHOULD</bcp14> include the SOFTWARE attribute in all Allocat
requests and MAY include it in any other requests or indications. The e and Refresh
server SHOULD include the SOFTWARE attribute in all Allocate and Refresh requests and <bcp14>MAY</bcp14> include it in any other requests or indica
responses (either success or failure) and MAY include it in other tions. The
responses or indications. The client and the server MAY include the server <bcp14>SHOULD</bcp14> include the SOFTWARE attribute in all Allocat
e and Refresh
responses (either success or failure) and <bcp14>MAY</bcp14> include it in
other
responses or indications. The client and the server <bcp14>MAY</bcp14> inc
lude the
FINGERPRINT attribute in any STUN-formatted messages defined in this FINGERPRINT attribute in any STUN-formatted messages defined in this
document.</t> document.</t>
<t>TURN does not use the backwards-compatibility mechanism described in <t>TURN does not use the backwards-compatibility mechanism described in
<xref target="I-D.ietf-tram-stunbis"></xref>.</t> <xref target="RFC8489" format="default"/>.</t>
<t>TURN, as defined in this specification, supports both IPv4 and IPv6. <t>TURN, as defined in this specification, supports both IPv4 and IPv6.
IPv6 support in TURN includes IPv4-to-IPv6, IPv6-to-IPv6, and IPv6 support in TURN includes IPv4-to-IPv6, IPv6-to-IPv6, and
IPv6-to-IPv4 relaying. When only a single address type is desired, the IPv6-to-IPv4 relaying. When only a single address type is desired, the
REQUESTED-ADDRESS-FAMILY attribute is used to explicitly request the REQUESTED-ADDRESS-FAMILY attribute is used to explicitly request the
address type the TURN server will allocate (e.g., an IPv4-only node may address type the TURN server will allocate (e.g., an IPv4-only node may
request the TURN server to allocate an IPv6 address). If both IPv4 and request the TURN server to allocate an IPv6 address). If both IPv4 and
IPv6 are desired, the single ADDITIONAL-ADDRESS-FAMILY attribute IPv6 are desired, the single ADDITIONAL-ADDRESS-FAMILY attribute
indicates a request to the server to allocate one IPv4 and one IPv6 indicates a request to the server to allocate one IPv4 and one IPv6
relay address in a single Allocate request. This saves local ports on relay address in a single Allocate request. This saves local ports on
the client and reduces the number of messages sent between the client the client and reduces the number of messages sent between the client
skipping to change at line 1119 skipping to change at line 1029
IPv6 support in TURN includes IPv4-to-IPv6, IPv6-to-IPv6, and IPv6 support in TURN includes IPv4-to-IPv6, IPv6-to-IPv6, and
IPv6-to-IPv4 relaying. When only a single address type is desired, the IPv6-to-IPv4 relaying. When only a single address type is desired, the
REQUESTED-ADDRESS-FAMILY attribute is used to explicitly request the REQUESTED-ADDRESS-FAMILY attribute is used to explicitly request the
address type the TURN server will allocate (e.g., an IPv4-only node may address type the TURN server will allocate (e.g., an IPv4-only node may
request the TURN server to allocate an IPv6 address). If both IPv4 and request the TURN server to allocate an IPv6 address). If both IPv4 and
IPv6 are desired, the single ADDITIONAL-ADDRESS-FAMILY attribute IPv6 are desired, the single ADDITIONAL-ADDRESS-FAMILY attribute
indicates a request to the server to allocate one IPv4 and one IPv6 indicates a request to the server to allocate one IPv4 and one IPv6
relay address in a single Allocate request. This saves local ports on relay address in a single Allocate request. This saves local ports on
the client and reduces the number of messages sent between the client the client and reduces the number of messages sent between the client
and the TURN server.</t> and the TURN server.</t>
<t>By default, TURN runs on the same ports as STUN: 3478 for TURN over <t>By default, TURN runs on the same ports as STUN: 3478 for TURN over
UDP and TCP, and 5349 for TURN over (D)TLS. However, TURN has its own UDP and TCP, and 5349 for TURN over (D)TLS. However, TURN has its own
set of Service Record (SRV) names: "turn" for UDP and TCP, and "turns" set of Service Record (SRV) names: "turn" for UDP and TCP, and "turns"
for (D)TLS. Either the DNS resolution procedures or the ALTERNATE-SERVER for (D)TLS. Either the DNS resolution procedures or the ALTERNATE-SERVER
procedures, both described in <xref procedures, both described in <xref target="sec-create-allocation" format=
target="sec-create-allocation"></xref>, can be used to run TURN on a "default"/>, can be used to run TURN on a
different port.</t> different port.</t>
<t>To ensure interoperability, a TURN server <bcp14>MUST</bcp14> support t
<t>To ensure interoperability, a TURN server MUST support the use of UDP he use of UDP
transport between the client and the server, and SHOULD support the use transport between the client and the server, and it <bcp14>SHOULD</bcp14>
of TCP, TLS-over-TCP and DTLS-over-UDP transports.</t> support the use
of TCP, TLS-over-TCP, and DTLS-over-UDP transports.</t>
<t>When UDP or DTLS-over-UDP transport is used between the client and <t>When UDP or DTLS-over-UDP transport is used between the client and
the server, the client will retransmit a request if it does not receive the server, the client will retransmit a request if it does not receive
a response within a certain timeout period. Because of this, the server a response within a certain timeout period. Because of this, the server
may receive two (or more) requests with the same 5-tuple and same may receive two (or more) requests with the same 5-tuple and same
transaction id. STUN requires that the server recognize this case and transaction id. STUN requires that the server recognize this case and
treat the request as idempotent (see <xref treat the request as idempotent (see <xref target="RFC8489" format="defaul
target="I-D.ietf-tram-stunbis"></xref>). Some implementations may choose t"/>). Some implementations may choose
to meet this requirement by remembering all received requests and the to meet this requirement by remembering all received requests and the
corresponding responses for 40 seconds (Section 6.3.1 in <xref corresponding responses for 40 seconds (<xref
target="I-D.ietf-tram-stunbis"></xref>). Other implementations may target="RFC8489" sectionFormat="of" section="6.3.1"/>). Other implementati
ons may
choose to reprocess the request and arrange that such reprocessing choose to reprocess the request and arrange that such reprocessing
returns essentially the same response. To aid implementors who choose returns essentially the same response. To aid implementors who choose
the latter approach (the so-called "stateless stack approach"), this the latter approach (the so-called "stateless stack approach"), this
specification includes some implementation notes on how this might be specification includes some implementation notes on how this might be
done. Implementations are free to choose either approach or choose some done. Implementations are free to choose either approach or some
other approach that gives the same results.</t> other approach that gives the same results.</t>
<t>To mitigate either intentional or unintentional denial-of-service <t>To mitigate either intentional or unintentional denial-of-service
attacks against the server by clients with valid usernames and attacks against the server by clients with valid usernames and
passwords, it is RECOMMENDED that the server impose limits on both the passwords, it is <bcp14>RECOMMENDED</bcp14> that the server impose limits on both the
number of allocations active at one time for a given username and on the number of allocations active at one time for a given username and on the
amount of bandwidth those allocations can use. The server should reject amount of bandwidth those allocations can use. The server should reject
new allocations that would exceed the limit on the allowed number of new allocations that would exceed the limit on the allowed number of
allocations active at one time with a 486 (Allocation Quota Exceeded) allocations active at one time with a 486 (Allocation Quota Exceeded)
(see <xref target="sec-rcv-allocate"></xref>), and since UDP does not (see <xref target="sec-rcv-allocate" format="default"/>), and since UDP do es not
include a congestion control mechanism, it should discard application include a congestion control mechanism, it should discard application
data traffic that exceeds the bandwidth quota.</t> data traffic that exceeds the bandwidth quota.</t>
</section> </section>
<section anchor="sec-allocations" numbered="true" toc="default">
<section anchor="sec-allocations" title="Allocations"> <name>Allocations</name>
<t>All TURN operations revolve around allocations, and all TURN messages <t>All TURN operations revolve around allocations, and all TURN messages
are associated with either a single or dual allocation. An allocation are associated with either a single or dual allocation. An allocation
conceptually consists of the following state data:<list style="symbols"> conceptually consists of the following state data:</t>
<t>the relayed transport address or addresses;</t> <ul spacing="normal">
<li>the relayed transport address or addresses;</li>
<t>the 5-tuple: (client's IP address, client's port, server IP <li>the 5-tuple: (client's IP address, client's port, server IP
address, server port, transport protocol);</t> address, server port, and transport protocol);</li>
<li>the authentication information;</li>
<t>the authentication information;</t> <li>the time-to-expiry for each relayed transport address;</li>
<li>a list of permissions for each relayed transport address;</li>
<t>the time-to-expiry for each relayed transport address;</t> <li>a list of channel-to-peer bindings for each relayed transport
address.</li>
<t>a list of permissions for each relayed transport address;</t> </ul>
<t>The relayed transport address is the transport address
<t>a list of channel to peer bindings for each relayed transport
address.</t>
</list>The relayed transport address is the transport address
allocated by the server for communicating with peers, while the 5-tuple allocated by the server for communicating with peers, while the 5-tuple
describes the communication path between the client and the server. On describes the communication path between the client and the server. On
the client, the 5-tuple uses the client's host transport address; on the the client, the 5-tuple uses the client's host transport address; on the
server, the 5-tuple uses the client's server-reflexive transport server, the 5-tuple uses the client's server-reflexive transport
address. The relayed transport address MUST be unique across all address. The relayed transport address <bcp14>MUST</bcp14> be unique acros s all
allocations so it can be used to uniquely identify the allocation, and allocations so it can be used to uniquely identify the allocation, and
an allocation in this context can be either a single or dual an allocation in this context can be either a single or dual
allocation.</t> allocation.</t>
<t>The authentication information (e.g., username, password, realm, and <t>The authentication information (e.g., username, password, realm, and
nonce) is used to both verify subsequent requests and to compute the nonce) is used to both verify subsequent requests and to compute the
message integrity of responses. The username, realm, and nonce values message integrity of responses. The username, realm, and nonce values
are initially those used in the authenticated Allocate request that are initially those used in the authenticated Allocate request that
creates the allocation, though the server can change the nonce value creates the allocation, though the server can change the nonce value
during the lifetime of the allocation using a 438 (Stale Nonce) reply. during the lifetime of the allocation using a 438 (Stale Nonce) reply.
For security reasons, the server MUST NOT store the password explicitly For security reasons, the server <bcp14>MUST NOT</bcp14> store the
and MUST store the key value, which is a cryptographic hash over the password explicitly and <bcp14>MUST</bcp14> store the key value, which
username, realm, and password (see Section 16.1.3 in <xref is a cryptographic hash over the username, realm, and password (see
target="I-D.ietf-tram-stunbis"></xref>).</t> <xref target="RFC8489" sectionFormat="of" section="16.1.3"/>).</t>
<t>Note that if the response contains a PASSWORD-ALGORITHMS attribute <t>Note that if the response contains a PASSWORD-ALGORITHMS attribute
and this attribute contains both MD5 and SHA-256 algorithms, and the and this attribute contains both MD5 and SHA-256 algorithms, and the
client also supports both the algorithms, the request MUST contain a client also supports both the algorithms, the request <bcp14>MUST</bcp14> contain a
PASSWORD-ALGORITHM attribute with the SHA-256 algorithm.</t> PASSWORD-ALGORITHM attribute with the SHA-256 algorithm.</t>
<t>The time-to-expiry is the time in seconds left until the allocation <t>The time-to-expiry is the time in seconds left until the allocation
expires. Each Allocate or Refresh transaction sets this timer, which expires. Each Allocate or Refresh transaction sets this timer, which
then ticks down towards 0. By default, each Allocate or Refresh then ticks down towards zero. By default, each Allocate or Refresh
transaction resets this timer to the default lifetime value of 600 transaction resets this timer to the default lifetime value of 600
seconds (10 minutes), but the client can request a different value in seconds (10 minutes), but the client can request a different value in
the Allocate and Refresh request. Allocations can only be refreshed the Allocate and Refresh request. Allocations can only be refreshed
using the Refresh request; sending data to a peer does not refresh an using the Refresh request; sending data to a peer does not refresh an
allocation. When an allocation expires, the state data associated with allocation. When an allocation expires, the state data associated with
the allocation can be freed.</t> the allocation can be freed.</t>
<t>The list of permissions is described in <xref target="sec-permissions"
<t>The list of permissions is described in <xref format="default"/> and the list of channels is described
target="sec-permissions"></xref> and the list of channels is described in <xref target="sec-channels" format="default"/>.</t>
in <xref target="sec-channels"></xref>.</t>
</section> </section>
<section anchor="sec-create-allocation" numbered="true" toc="default">
<section anchor="sec-create-allocation" title="Creating an Allocation"> <name>Creating an Allocation</name>
<t>An allocation on the server is created using an Allocate <t>An allocation on the server is created using an Allocate
transaction.</t> transaction.</t>
<section anchor="sec-send-allocate" numbered="true" toc="default">
<section anchor="sec-send-allocate" title="Sending an Allocate Request"> <name>Sending an Allocate Request</name>
<t>The client forms an Allocate request as follows.</t> <t>The client forms an Allocate request as follows.</t>
<t>The client first picks a host transport address. It is <bcp14>RECOMME
<t>The client first picks a host transport address. It is RECOMMENDED NDED</bcp14>
that the client picks a currently unused transport address, typically that the client pick a currently unused transport address, typically
by allowing the underlying OS to pick a currently unused port.</t> by allowing the underlying OS to pick a currently unused port.</t>
<t>The client then picks a transport protocol that the client supports <t>The client then picks a transport protocol that the client supports
to use between the client and the server based on the transport to use between the client and the server based on the transport
protocols supported by the server. Since this specification only protocols supported by the server. Since this specification only
allows UDP between the server and the peers, it is RECOMMENDED that allows UDP between the server and the peers, it is <bcp14>RECOMMENDED</b cp14> that
the client pick UDP unless it has a reason to use a different the client pick UDP unless it has a reason to use a different
transport. One reason to pick a different transport would be that the transport. One reason to pick a different transport would be that the
client believes, either through configuration or discovery or by client believes, either through configuration or discovery or by
experiment, that it is unable to contact any TURN server using UDP. experiment, that it is unable to contact any TURN server using UDP.
See <xref target="sec-transports"></xref> for more discussion.</t> See <xref target="sec-transports" format="default"/> for more discussion
.</t>
<t>The client also picks a server transport address, which SHOULD be <t>The client also picks a server transport address, which <bcp14>SHOULD
</bcp14> be
done as follows. The client uses one or more procedures described in done as follows. The client uses one or more procedures described in
<xref target="RFC8155"></xref> to discover a TURN server and uses the <xref target="RFC8155" format="default"/> to discover a TURN server and
TURN server resolution mechanism defined in <xref uses the
target="RFC5928"></xref> and <xref target="RFC7350"></xref> to get a TURN server resolution mechanism defined in <xref target="RFC5928" forma
t="default"/> and <xref target="RFC7350" format="default"/> to get a
list of server transport addresses that can be tried to create a TURN list of server transport addresses that can be tried to create a TURN
allocation.</t> allocation.</t>
<t>The client <bcp14>MUST</bcp14> include a REQUESTED-TRANSPORT attribut
e in the
request.
<t>The client MUST include a REQUESTED-TRANSPORT attribute in the This attribute specifies the transport protocol between the
request. This attribute specifies the transport protocol between the server and the peers (note that this is *not* the transport protocol
server and the peers (note that this is NOT the transport protocol
that appears in the 5-tuple). In this specification, the that appears in the 5-tuple). In this specification, the
REQUESTED-TRANSPORT type is always UDP. This attribute is included to REQUESTED-TRANSPORT type is always UDP. This attribute is included to
allow future extensions to specify other protocols.</t> allow future extensions to specify other protocols.</t>
<t>If the client wishes to obtain a relayed transport address of a <t>If the client wishes to obtain a relayed transport address of a
specific address type then it includes a REQUESTED-ADDRESS-FAMILY specific address type, then it includes a REQUESTED-ADDRESS-FAMILY
attribute in the request. This attribute indicates the specific attribute in the request. This attribute indicates the specific
address type the client wishes the TURN server to allocate. Clients address type the client wishes the TURN server to allocate. Clients
MUST NOT include more than one REQUESTED-ADDRESS-FAMILY attribute in <bcp14>MUST NOT</bcp14> include more than one REQUESTED-ADDRESS-FAMILY a
an Allocate request. Clients MUST NOT include a ttribute in
an Allocate request. Clients <bcp14>MUST NOT</bcp14> include a
REQUESTED-ADDRESS-FAMILY attribute in an Allocate request that REQUESTED-ADDRESS-FAMILY attribute in an Allocate request that
contains a RESERVATION-TOKEN attribute, for the reason that the server contains a RESERVATION-TOKEN attribute, for the reason that the server
uses the previously reserved transport address corresponding to the uses the previously reserved transport address corresponding to the
included token and the client cannot obtain a relayed transport included token and the client cannot obtain a relayed transport
address of a specific address type.</t> address of a specific address type.</t>
<t>If the client wishes to obtain one IPv6 and one IPv4 relayed <t>If the client wishes to obtain one IPv6 and one IPv4 relayed
transport address then it includes an ADDITIONAL-ADDRESS-FAMILY transport address, then it includes an ADDITIONAL-ADDRESS-FAMILY
attribute in the request. This attribute specifies that the server attribute in the request. This attribute specifies that the server
must allocate both address types. The attribute value in the must allocate both address types. The attribute value in the
ADDITIONAL-ADDRESS-FAMILY MUST be set to 0x02 (IPv6 address family). ADDITIONAL-ADDRESS-FAMILY <bcp14>MUST</bcp14> be set to 0x02 (IPv6 addre
Clients MUST NOT include REQUESTED-ADDRESS-FAMILY and ss family).
ADDITIONAL-ADDRESS-FAMILY attributes in the same request. Clients MUST Clients <bcp14>MUST NOT</bcp14> include REQUESTED-ADDRESS-FAMILY and
NOT include ADDITIONAL-ADDRESS-FAMILY attribute in a Allocate request ADDITIONAL-ADDRESS-FAMILY attributes in the same request. Clients <bcp14
that contains a RESERVATION-TOKEN attribute. Clients MUST NOT include >MUST
ADDITIONAL-ADDRESS-FAMILY attribute in a Allocate request that NOT</bcp14> include the ADDITIONAL-ADDRESS-FAMILY attribute in an Alloca
contains an EVEN-PORT attribute with the R bit set to 1. The reason te request
behind the restriction is if EVEN-PORT with R bit set to 1 is allowed that contains a RESERVATION-TOKEN attribute.
Clients <bcp14>MUST NOT</bcp14> include
the ADDITIONAL-ADDRESS-FAMILY attribute in an Allocate request that
contains an EVEN-PORT attribute with the R (Reserved) bit set to 1.
The reason behind the restriction is that if the EVEN-PORT attribute wit
h the R bit set to 1 is allowed
with the ADDITIONAL-ADDRESS-FAMILY attribute, two tokens will have to with the ADDITIONAL-ADDRESS-FAMILY attribute, two tokens will have to
be returned in success response and requires changes to the way be returned in the success response and changes will be required to the
RESERVATION-TOKEN is handled.</t> way
the RESERVATION-TOKEN attribute is handled.</t>
<t>If the client wishes the server to initialize the time-to-expiry <t>If the client wishes the server to initialize the time-to-expiry
field of the allocation to some value other than the default lifetime, field of the allocation to some value other than the default lifetime,
then it MAY include a LIFETIME attribute specifying its desired value. then it <bcp14>MAY</bcp14> include a LIFETIME attribute specifying its d esired value.
This is just a hint, and the server may elect to use a different This is just a hint, and the server may elect to use a different
value. Note that the server will ignore requests to initialize the value. Note that the server will ignore requests to initialize the
field to less than the default value.</t> field to less than the default value.</t>
<t>If the client wishes to later use the DONT-FRAGMENT attribute in <t>If the client wishes to later use the DONT-FRAGMENT attribute in
one or more Send indications on this allocation, then the client one or more Send indications on this allocation, then the client
SHOULD include the DONT-FRAGMENT attribute in the Allocate request. <bcp14>SHOULD</bcp14> include the DONT-FRAGMENT attribute in the Allocat e request.
This allows the client to test whether this attribute is supported by This allows the client to test whether this attribute is supported by
the server.</t> the server.</t>
<t>If the client requires the port number of the relayed transport <t>If the client requires the port number of the relayed transport
address be even, the client includes the EVEN-PORT attribute. If this address to be even, the client includes the EVEN-PORT attribute. If this
attribute is not included, then the port can be even or odd. By attribute is not included, then the port can be even or odd. By
setting the R bit in the EVEN-PORT attribute to 1, the client can setting the R bit in the EVEN-PORT attribute to 1, the client can
request that the server reserve the next highest port number (on the request that the server reserve the next highest port number (on the
same IP address) for a subsequent allocation. If the R bit is 0, no same IP address) for a subsequent allocation. If the R bit is 0, no
such request is made.</t> such request is made.</t>
<t>The client <bcp14>MAY</bcp14> also include a RESERVATION-TOKEN attrib
<t>The client MAY also include a RESERVATION-TOKEN attribute in the ute in the
request to ask the server to use a previously reserved port for the request to ask the server to use a previously reserved port for the
allocation. If the RESERVATION-TOKEN attribute is included, then the allocation. If the RESERVATION-TOKEN attribute is included, then the
client MUST omit the EVEN-PORT attribute.</t> client <bcp14>MUST</bcp14> omit the EVEN-PORT attribute.</t>
<t>Once constructed, the client sends the Allocate request on the <t>Once constructed, the client sends the Allocate request on the
5-tuple.</t> 5-tuple.</t>
</section>
<section anchor="sec-rcv-allocate" title="Receiving an Allocate Request"> </section>
<section anchor="sec-rcv-allocate" numbered="true" toc="default">
<name>Receiving an Allocate Request</name>
<t>When the server receives an Allocate request, it performs the <t>When the server receives an Allocate request, it performs the
following checks:<list style="numbers"> following checks:</t>
<t>The TURN server provided by the local or access network MAY <ol spacing="normal" type="1">
allow unauthenticated request in order to accept Allocation <li>The TURN server provided by the local or access network
requests from new and/or guest users in the network who do not <bcp14>MAY</bcp14> allow an unauthenticated request in order to
necessarily possess long term credentials for STUN authentication. accept Allocation requests from new and/or guest users in the
Making STUN authentication optional and its security implications network who do not necessarily possess long-term credentials for
are discussed in <xref target="RFC8155"></xref>. Otherwise, the STUN authentication. The security implications of STUN and making
server MUST require that the request be authenticated. If the STUN authentication optional are discussed in <xref target="RFC8155"
request is authenticated, the authentication MUST be done either format="default"/>. Otherwise, the server <bcp14>MUST</bcp14>
using the long-term credential mechanism of <xref require that the request be authenticated. If the request is
target="I-D.ietf-tram-stunbis"></xref> or the STUN Extension for authenticated, the authentication <bcp14>MUST</bcp14> be done either
Third-Party Authorization <xref target="RFC7635"></xref> unless using the long-term credential mechanism of <xref target="RFC8489"
the client and server agree to use another mechanism through some format="default"/> or using the STUN Extension for Third-Party
procedure outside the scope of this document.</t> Authorization <xref target="RFC7635" format="default"/> unless the
client and server agree to use another mechanism through some
<t>The server checks if the 5-tuple is currently in use by an procedure outside the scope of this document.</li>
<li>The server checks if the 5-tuple is currently in use by an
existing allocation. If yes, the server rejects the request with a existing allocation. If yes, the server rejects the request with a
437 (Allocation Mismatch) error.</t> 437 (Allocation Mismatch) error.</li>
<li>The server checks if the request contains a REQUESTED-TRANSPORT
<t>The server checks if the request contains a REQUESTED-TRANSPORT
attribute. If the REQUESTED-TRANSPORT attribute is not included or attribute. If the REQUESTED-TRANSPORT attribute is not included or
is malformed, the server rejects the request with a 400 (Bad is malformed, the server rejects the request with a 400 (Bad
Request) error. Otherwise, if the attribute is included but Request) error. Otherwise, if the attribute is included but
specifies a protocol that is not supported by the server, the specifies a protocol that is not supported by the server, the
server rejects the request with a 442 (Unsupported Transport server rejects the request with a 442 (Unsupported Transport
Protocol) error.</t> Protocol) error.</li>
<li>The request may contain a DONT-FRAGMENT attribute. If it does,
<t>The request may contain a DONT-FRAGMENT attribute. If it does,
but the server does not support sending UDP datagrams with the DF but the server does not support sending UDP datagrams with the DF
bit set to 1 (see <xref target="sec-ip-header-fields"></xref> and bit set to 1 (see Sections <xref target="sec-ip-header-fields" forma
<xref target="sec-ip-header-fields-tcp-udp"></xref>), then the t="counter"/> and
<xref target="sec-ip-header-fields-tcp-udp" format="counter"/>), the
n the
server treats the DONT-FRAGMENT attribute in the Allocate request server treats the DONT-FRAGMENT attribute in the Allocate request
as an unknown comprehension-required attribute.</t> as an unknown comprehension-required attribute.</li>
<li>The server checks if the request contains a RESERVATION-TOKEN
<t>The server checks if the request contains a RESERVATION-TOKEN
attribute. If yes, and the request also contains an EVEN-PORT or attribute. If yes, and the request also contains an EVEN-PORT or
REQUESTED-ADDRESS-FAMILY or ADDITIONAL-ADDRESS-FAMILY attribute, REQUESTED-ADDRESS-FAMILY or ADDITIONAL-ADDRESS-FAMILY attribute,
the server rejects the request with a 400 (Bad Request) error. the server rejects the request with a 400 (Bad Request) error.
Otherwise, it checks to see if the token is valid (i.e., the token Otherwise, it checks to see if the token is valid (i.e., the token
is in range and has not expired and the corresponding relayed is in range and has not expired, and the corresponding relayed
transport address is still available). If the token is not valid transport address is still available). If the token is not valid
for some reason, the server rejects the request with a 508 for some reason, the server rejects the request with a 508
(Insufficient Capacity) error.</t> (Insufficient Capacity) error.</li>
<t>The server checks if the request contains both <li>The server checks if the request contains both
REQUESTED-ADDRESS-FAMILY and ADDITIONAL-ADDRESS-FAMILY attributes. REQUESTED-ADDRESS-FAMILY and ADDITIONAL-ADDRESS-FAMILY attributes.
If yes, then the server rejects the request with a 400 (Bad If yes, then the server rejects the request with a 400 (Bad
Request) error.</t> Request) error.</li>
<li>If the server does not support the address family requested by
<t>If the server does not support the address family requested by the client in REQUESTED-ADDRESS-FAMILY, or if the allocation of the
the client in REQUESTED-ADDRESS-FAMILY or if the allocation of the requested address family is disabled by local policy, it <bcp14>MUST
requested address family is disabled by local policy, it MUST </bcp14>
generate an Allocate error response, and it MUST include an generate an Allocate error response, and it <bcp14>MUST</bcp14> incl
ude an
ERROR-CODE attribute with the 440 (Address Family not Supported) ERROR-CODE attribute with the 440 (Address Family not Supported)
response code. If the REQUESTED-ADDRESS-FAMILY attribute is absent response code. If the REQUESTED-ADDRESS-FAMILY attribute is absent
and the server does not support IPv4 address family, the server and the server does not support the IPv4 address family, the server
MUST include an ERROR-CODE attribute with the 440 (Address Family <bcp14>MUST</bcp14> include an ERROR-CODE attribute with the 440 (Ad
dress Family
not Supported) response code. If the REQUESTED-ADDRESS-FAMILY not Supported) response code. If the REQUESTED-ADDRESS-FAMILY
attribute is absent and the server supports IPv4 address family, attribute is absent and the server supports the IPv4 address family,
the server MUST allocate an IPv4 relayed transport address for the the server <bcp14>MUST</bcp14> allocate an IPv4 relayed transport ad
TURN client.</t> dress for the
TURN client.</li>
<t>The server checks if the request contains an EVEN-PORT <li>The server checks if the request contains an EVEN-PORT
attribute with the R bit set to 1. If yes, and the request also attribute with the R bit set to 1. If yes, and the request also
contains an ADDITIONAL-ADDRESS-FAMILY attribute, the server contains an ADDITIONAL-ADDRESS-FAMILY attribute, the server
rejects the request with a 400 (Bad Request) error. Otherwise, the rejects the request with a 400 (Bad Request) error. Otherwise, the
server checks if it can satisfy the request (i.e., can allocate a server checks if it can satisfy the request (i.e., can allocate a
relayed transport address as described below). If the server relayed transport address as described below). If the server
cannot satisfy the request, then the server rejects the request cannot satisfy the request, then the server rejects the request
with a 508 (Insufficient Capacity) error.</t> with a 508 (Insufficient Capacity) error.</li>
<li>The server checks if the request contains an
<t>The server checks if the request contains an
ADDITIONAL-ADDRESS-FAMILY attribute. If yes, and the attribute ADDITIONAL-ADDRESS-FAMILY attribute. If yes, and the attribute
value is 0x01 (IPv4 address family), then the server rejects the value is 0x01 (IPv4 address family), then the server rejects the
request with a 400 (Bad Request) error. Otherwise, the server request with a 400 (Bad Request) error. Otherwise, the server
checks if it can allocate relayed transport addresses of both checks if it can allocate relayed transport addresses of both
address types. If the server cannot satisfy the request, then the address types. If the server cannot satisfy the request, then the
server rejects the request with a 508 (Insufficient Capacity) server rejects the request with a 508 (Insufficient Capacity)
error. If the server can partially meet the request, i.e. if it error. If the server can partially meet the request, i.e., if it
can only allocate one relayed transport address of a specific can only allocate one relayed transport address of a specific
address type, then it includes ADDRESS-ERROR-CODE attribute in the address type, then it includes ADDRESS-ERROR-CODE attribute in the
success response to inform the client the reason for partial success response to inform the client the reason for partial
failure of the request. The error code value signaled in the failure of the request. The error code value signaled in the
ADDRESS-ERROR-CODE attribute could be 440 (Address Family not ADDRESS-ERROR-CODE attribute could be 440 (Address Family not
Supported) or 508 (Insufficient Capacity). If the server can fully Supported) or 508 (Insufficient Capacity). If the server can fully
meet the request, then the server allocates one IPv4 and one IPv6 meet the request, then the server allocates one IPv4 and one IPv6
relay address, and returns an Allocate success response containing relay address and returns an Allocate success response containing
the relayed transport addresses assigned to the dual allocation in the relayed transport addresses assigned to the dual allocation in
two XOR-RELAYED-ADDRESS attributes.</t> two XOR-RELAYED-ADDRESS attributes.</li>
<li>At any point, the server <bcp14>MAY</bcp14> choose to reject the
<t>At any point, the server MAY choose to reject the request with request with a 486 (Allocation Quota Reached) error if it feels the
a 486 (Allocation Quota Reached) error if it feels the client is client is trying to exceed some locally defined allocation
trying to exceed some locally defined allocation quota. The server quota. The server is free to define this allocation quota any way it
is free to define this allocation quota any way it wishes, but wishes, but it <bcp14>SHOULD</bcp14> define it based on the username
SHOULD define it based on the username used to authenticate the used to authenticate the request and not on the client's transport
request, and not on the client's transport address.</t> address.</li>
<li>Also, at any point, the server <bcp14>MAY</bcp14> choose to reject
<t>Also at any point, the server MAY choose to reject the request the request
with a 300 (Try Alternate) error if it wishes to redirect the with a 300 (Try Alternate) error if it wishes to redirect the
client to a different server. The use of this error code and client to a different server. The use of this error code and
attribute follow the specification in <xref attribute follows the specification in <xref target="RFC8489" format
target="I-D.ietf-tram-stunbis"></xref>.</t> ="default"/>.</li>
</list></t> </ol>
<t>If all the checks pass, the server creates the allocation. The <t>If all the checks pass, the server creates the allocation. The
5-tuple is set to the 5-tuple from the Allocate request, while the 5-tuple is set to the 5-tuple from the Allocate request, while the
list of permissions and the list of channels are initially empty.</t> list of permissions and the list of channels are initially empty.</t>
<t>The server chooses a relayed transport address for the allocation <t>The server chooses a relayed transport address for the allocation
as follows:<list style="symbols"> as follows:</t>
<t>If the request contains a RESERVATION-TOKEN attribute, the
<ul spacing="normal">
<li>If the request contains a RESERVATION-TOKEN attribute, the
server uses the previously reserved transport address server uses the previously reserved transport address
corresponding to the included token (if it is still available). corresponding to the included token (if it is still available).
Note that the reservation is a server-wide reservation and is not Note that the reservation is a server-wide reservation and is not
specific to a particular allocation, since the Allocate request specific to a particular allocation since the Allocate request
containing the RESERVATION-TOKEN uses a different 5-tuple than the containing the RESERVATION-TOKEN uses a different 5-tuple than the
Allocate request that made the reservation. The 5-tuple for the Allocate request that made the reservation. The 5-tuple for the
Allocate request containing the RESERVATION-TOKEN attribute can be Allocate request containing the RESERVATION-TOKEN attribute can be
any allowed 5-tuple; it can use a different client IP address and any allowed 5-tuple; it can use a different client IP address and
port, a different transport protocol, and even different server IP port, a different transport protocol, and even a different server IP
address and port (provided, of course, that the server IP address address and port (provided, of course, that the server IP address
and port are ones on which the server is listening for TURN and port are ones on which the server is listening for TURN
requests).</t> requests).</li>
<li>If the request contains an EVEN-PORT attribute with the R bit
<t>If the request contains an EVEN-PORT attribute with the R bit
set to 0, then the server allocates a relayed transport address set to 0, then the server allocates a relayed transport address
with an even port number.</t> with an even port number.</li>
<li>If the request contains an EVEN-PORT attribute with the R bit
<t>If the request contains an EVEN-PORT attribute with the R bit
set to 1, then the server looks for a pair of port numbers N and set to 1, then the server looks for a pair of port numbers N and
N+1 on the same IP address, where N is even. Port N is used in the N+1 on the same IP address, where N is even. Port N is used in the
current allocation, while the relayed transport address with port current allocation, while the relayed transport address with port
N+1 is assigned a token and reserved for a future allocation. The N+1 is assigned a token and reserved for a future allocation. The
server MUST hold this reservation for at least 30 seconds, and MAY server <bcp14>MUST</bcp14> hold this reservation for at least 30 sec onds and <bcp14>MAY</bcp14>
choose to hold longer (e.g., until the allocation with port N choose to hold longer (e.g., until the allocation with port N
expires). The server then includes the token in a expires). The server then includes the token in a
RESERVATION-TOKEN attribute in the success response.</t> RESERVATION-TOKEN attribute in the success response.</li>
<li>Otherwise, the server allocates any available relayed transport
<t>Otherwise, the server allocates any available relayed transport address.</li>
address.</t> </ul>
</list></t> <t>In all cases, the server <bcp14>SHOULD</bcp14> only allocate ports fr
om the range
<t>In all cases, the server SHOULD only allocate ports from the range 49152 - 65535 (the Dynamic and/or Private Port range <xref target="PORT-
49152 &ndash; 65535 (the Dynamic and/or Private Port range <xref NUMBERS" format="default"/>), unless the TURN server application
target="Port-Numbers"></xref>), unless the TURN server application
knows, through some means not specified here, that other applications knows, through some means not specified here, that other applications
running on the same host as the TURN server application will not be running on the same host as the TURN server application will not be
impacted by allocating ports outside this range. This condition can impacted by allocating ports outside this range. This condition can
often be satisfied by running the TURN server application on a often be satisfied by running the TURN server application on a
dedicated machine and/or by arranging that any other applications on dedicated machine and/or by arranging that any other applications on
the machine allocate ports before the TURN server application starts. the machine allocate ports before the TURN server application starts.
In any case, the TURN server SHOULD NOT allocate ports in the range 0 In any case, the TURN server <bcp14>SHOULD NOT</bcp14> allocate ports in the range 0
- 1023 (the Well-Known Port range) to discourage clients from using - 1023 (the Well-Known Port range) to discourage clients from using
TURN to run standard services.</t> TURN to run standard services.</t>
<aside>
<t><list> <t>NOTE: The use of randomized port assignments to avoid certain
<t>NOTE: The use of randomized port assignments to avoid certain types of attacks is described in <xref target="RFC6056" format="defa
types of attacks is described in <xref target="RFC6056"></xref>. ult"/>.
It is RECOMMENDED that a TURN server implement a randomized port It is <bcp14>RECOMMENDED</bcp14> that a TURN server implement a rand
assignment algorithm from <xref target="RFC6056"></xref>. This is omized port
assignment algorithm from <xref target="RFC6056" format="default"/>.
This is
especially applicable to servers that choose to pre-allocate a especially applicable to servers that choose to pre-allocate a
number of ports from the underlying OS and then later assign them number of ports from the underlying OS and then later assign them
to allocations; for example, a server may choose this technique to to allocations; for example, a server may choose this technique to
implement the EVEN-PORT attribute.</t> implement the EVEN-PORT attribute.</t></aside>
</list></t>
<t>The server determines the initial value of the time-to-expiry field <t>The server determines the initial value of the time-to-expiry field
as follows. If the request contains a LIFETIME attribute, then the as follows. If the request contains a LIFETIME attribute, then the
server computes the minimum of the client's proposed lifetime and the server computes the minimum of the client's proposed lifetime and the
server's maximum allowed lifetime. If this computed value is greater server's maximum allowed lifetime. If this computed value is greater
than the default lifetime, then the server uses the computed lifetime than the default lifetime, then the server uses the computed lifetime
as the initial value of the time-to-expiry field. Otherwise, the as the initial value of the time-to-expiry field. Otherwise, the
server uses the default lifetime. It is RECOMMENDED that the server server uses the default lifetime. It is <bcp14>RECOMMENDED</bcp14> that the server
use a maximum allowed lifetime value of no more than 3600 seconds (1 use a maximum allowed lifetime value of no more than 3600 seconds (1
hour). Servers that implement allocation quotas or charge users for hour). Servers that implement allocation quotas or charge users for
allocations in some way may wish to use a smaller maximum allowed allocations in some way may wish to use a smaller maximum allowed
lifetime (perhaps as small as the default lifetime) to more quickly lifetime (perhaps as small as the default lifetime) to more quickly
remove orphaned allocations (that is, allocations where the remove orphaned allocations (that is, allocations where the
corresponding client has crashed or terminated or the client corresponding client has crashed or terminated, or the client
connection has been lost for some reason). Also, note that the time- connection has been lost for some reason). Also, note that the time-
to-expiry is recomputed with each successful Refresh request, and thus to-expiry is recomputed with each successful Refresh request, and thus,
the value computed here applies only until the first refresh.</t> the value computed here applies only until the first refresh.</t>
<t>Once the allocation is created, the server replies with a success <t>Once the allocation is created, the server replies with a success
response. The success response contains:<list style="symbols"> response. The success response contains:</t>
<t>An XOR-RELAYED-ADDRESS attribute containing the relayed <ul spacing="normal">
<li>An XOR-RELAYED-ADDRESS attribute containing the relayed
transport address or two XOR-RELAYED-ADDRESS attributes containing transport address or two XOR-RELAYED-ADDRESS attributes containing
the relayed transport addresses.</t> the relayed transport addresses.</li>
<li>A LIFETIME attribute containing the current value of the
<t>A LIFETIME attribute containing the current value of the time-to-expiry timer.</li>
time-to-expiry timer.</t> <li>A RESERVATION-TOKEN attribute (if a second relayed transport
address was reserved).</li>
<t>A RESERVATION-TOKEN attribute (if a second relayed transport <li>An XOR-MAPPED-ADDRESS attribute containing the client's IP
address was reserved).</t> address and port (from the 5-tuple).</li>
</ul>
<t>An XOR-MAPPED-ADDRESS attribute containing the client's IP <aside>
address and port (from the 5-tuple).</t> <t>NOTE: The XOR-MAPPED-ADDRESS attribute is included in the
</list></t>
<t><list>
<t>NOTE: The XOR-MAPPED-ADDRESS attribute is included in the
response as a convenience to the client. TURN itself does not make response as a convenience to the client. TURN itself does not make
use of this value, but clients running ICE can often need this use of this value, but clients running ICE can often need this
value and can thus avoid having to do an extra Binding transaction value and can thus avoid having to do an extra Binding transaction
with some STUN server to learn it.</t> with some STUN server to learn it.</t>
</list></t> </aside>
<t>The response (either success or error) is sent back to the client <t>The response (either success or error) is sent back to the client
on the 5-tuple.</t> on the 5-tuple.</t>
<aside>
<t><list> <t>NOTE: When the Allocate request is sent over UDP, <xref target="RFC
<t>NOTE: When the Allocate request is sent over UDP, <xref 8489" format="default"/> requires that the server
target="I-D.ietf-tram-stunbis"></xref> requires that the server
handle the possible retransmissions of the request so that handle the possible retransmissions of the request so that
retransmissions do not cause multiple allocations to be created. retransmissions do not cause multiple allocations to be created.
Implementations may achieve this using the so-called "stateless Implementations may achieve this using the so-called "stateless
stack approach" as follows. To detect retransmissions when the stack approach" as follows. To detect retransmissions when the
original request was successful in creating an allocation, the original request was successful in creating an allocation, the
server can store the transaction id that created the request with server can store the transaction id that created the request with
the allocation data and compare it with incoming Allocate requests the allocation data and compare it with incoming Allocate requests
on the same 5-tuple. Once such a request is detected, the server on the same 5-tuple. Once such a request is detected, the server
can stop parsing the request and immediately generate a success can stop parsing the request and immediately generate a success
response. When building this response, the value of the LIFETIME response. When building this response, the value of the LIFETIME
attribute can be taken from the time-to-expiry field in the attribute can be taken from the time-to-expiry field in the
allocate state data, even though this value may differ slightly allocate state data, even though this value may differ slightly
from the LIFETIME value originally returned. In addition, the from the LIFETIME value originally returned. In addition, the
server may need to store an indication of any reservation token server may need to store an indication of any reservation token
returned in the original response, so that this may be returned in returned in the original response so that this may be returned in
any retransmitted responses.</t> any retransmitted responses.</t>
<t>For the case where the original request was unsuccessful in
<t>For the case where the original request was unsuccessful in
creating an allocation, the server may choose to do nothing creating an allocation, the server may choose to do nothing
special. Note, however, that there is a rare case where the server special. Note, however, that there is a rare case where the server
rejects the original request but accepts the retransmitted request rejects the original request but accepts the retransmitted request
(because conditions have changed in the brief intervening time (because conditions have changed in the brief intervening time
period). If the client receives the first failure response, it period). If the client receives the first failure response, it
will ignore the second (success) response and believe that an will ignore the second (success) response and believe that an
allocation was not created. An allocation created in this matter allocation was not created.
will eventually timeout, since the client will not refresh it.
An allocation created in this manner
will eventually time out since the client will not refresh it.
Furthermore, if the client later retries with the same 5-tuple but Furthermore, if the client later retries with the same 5-tuple but
different transaction id, it will receive a 437 (Allocation a different transaction id, it will receive a 437 (Allocation
Mismatch), which will cause it to retry with a different 5-tuple. Mismatch) error response, which will cause it to retry with a differ
ent 5-tuple.
The server may use a smaller maximum lifetime value to minimize The server may use a smaller maximum lifetime value to minimize
the lifetime of allocations "orphaned" in this manner.</t> the lifetime of allocations "orphaned" in this manner.</t>
</list></t> </aside>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving an Allocate Success Response"> <name>Receiving an Allocate Success Response</name>
<t>If the client receives an Allocate success response, then it MUST <t>If the client receives an Allocate success response, then it <bcp14>M
UST</bcp14>
check that the mapped address and the relayed transport address or check that the mapped address and the relayed transport address or
addresses are part of an address family or families that the client addresses are part of an address family or families that the client
understands and is prepared to handle. If these addresses are not part understands and is prepared to handle. If these addresses are not part
of an address family or families which the client is prepared to of an address family or families that the client is prepared to
handle, then the client MUST delete the allocation (<xref handle, then the client <bcp14>MUST</bcp14> delete the allocation (<xref
target="sec-refreshing-allocation"></xref>) and MUST NOT attempt to target="sec-refreshing-allocation" format="default"/>) and <bcp14>MUST NOT</bcp
14> attempt to
create another allocation on that server until it believes the create another allocation on that server until it believes the
mismatch has been fixed.</t> mismatch has been fixed.</t>
<t>Otherwise, the client creates its own copy of the allocation data <t>Otherwise, the client creates its own copy of the allocation data
structure to track what is happening on the server. In particular, the structure to track what is happening on the server. In particular, the
client needs to remember the actual lifetime received back from the client needs to remember the actual lifetime received back from the
server, rather than the value sent to the server in the request. The server, rather than the value sent to the server in the request. The
client must also remember the 5-tuple used for the request and the client must also remember the 5-tuple used for the request and the
username and password it used to authenticate the request to ensure username and password it used to authenticate the request to ensure
that it reuses them for subsequent messages. The client also needs to that it reuses them for subsequent messages. The client also needs to
track the channels and permissions it establishes on the server.</t> track the channels and permissions it establishes on the server.</t>
<t>If the client receives an Allocate success response but with an
<t>If the client receives an Allocate success response but with
ADDRESS-ERROR-CODE attribute in the response and the error code value ADDRESS-ERROR-CODE attribute in the response and the error code value
signaled in the ADDRESS-ERROR-CODE attribute is 440 (Address Family signaled in the ADDRESS-ERROR-CODE attribute is 440 (Address Family
not Supported), the client MUST NOT retry its request for the rejected not Supported), the client <bcp14>MUST NOT</bcp14> retry its request
address type. If the client receives an ADDRESS-ERROR-CODE attribute for the rejected address type. If the client receives an
in the response and the error code value signaled in the ADDRESS-ERROR-CODE attribute in the response and the error code value
ADDRESS-ERROR-CODE attribute is 508 (Insufficient Capacity), the signaled in the ADDRESS-ERROR-CODE attribute is 508 (Insufficient
client SHOULD wait at least 1 minute before trying to request any more Capacity), the client <bcp14>SHOULD</bcp14> wait at least 1 minute
allocations on this server for the rejected address type.</t> before trying to request any more allocations on this server for the
rejected address type.</t>
<t>The client will probably wish to send the relayed transport address <t>The client will probably wish to send the relayed transport address
to peers (using some method not specified here) so the peers can to peers (using some method not specified here) so the peers can
communicate with it. The client may also wish to use the communicate with it. The client may also wish to use the
server-reflexive address it receives in the XOR-MAPPED-ADDRESS server-reflexive address it receives in the XOR-MAPPED-ADDRESS
attribute in its ICE processing.</t> attribute in its ICE processing.</t>
</section> </section>
<section anchor="sec-allocate-error-response" <section anchor="sec-allocate-error-response" numbered="true" toc="default
title="Receiving an Allocate Error Response"> ">
<name>Receiving an Allocate Error Response</name>
<t>If the client receives an Allocate error response, then the <t>If the client receives an Allocate error response, then the
processing depends on the actual error code returned:<list processing depends on the actual error code returned:</t>
style="symbols">
<t>(Request timed out): There is either a problem with the server,
or a problem reaching the server with the chosen transport. The
client considers the current transaction as having failed but MAY
choose to retry the Allocate request using a different transport
(e.g., TCP instead of UDP).</t>
<t>300 (Try Alternate): The server would like the client to use <dl newline="true" spacing="normal">
<dt>408 (Request timed out):</dt> <dd>There is either a problem with t
he
server or a problem reaching the server with the chosen
transport. The client considers the current transaction as having
failed but <bcp14>MAY</bcp14> choose to retry the Allocate request
using a different transport (e.g., TCP instead of UDP).</dd>
<dt>300 (Try Alternate):</dt> <dd>The server would like the client to
use
the server specified in the ALTERNATE-SERVER attribute instead. the server specified in the ALTERNATE-SERVER attribute instead.
The client considers the current transaction as having failed, but The client considers the current transaction as having failed, but i
SHOULD try the Allocate request with the alternate server before t
<bcp14>SHOULD</bcp14> try the Allocate request with the alternate se
rver before
trying any other servers (e.g., other servers discovered using the trying any other servers (e.g., other servers discovered using the
DNS resolution procedures). When trying the Allocate request with DNS resolution procedures). When trying the Allocate request with
the alternate server, the client follows the ALTERNATE-SERVER the alternate server, the client follows the ALTERNATE-SERVER
procedures specified in <xref procedures specified in <xref target="RFC8489" format="default"/>.</
target="I-D.ietf-tram-stunbis"></xref>.</t> dd>
<dt>400 (Bad Request):</dt> <dd>The server believes the client's reque
<t>400 (Bad Request): The server believes the client's request is st is
malformed for some reason. The client considers the current malformed for some reason. The client considers the current
transaction as having failed. The client MAY notify the user or transaction as having failed. The client <bcp14>MAY</bcp14> notify t
operator and SHOULD NOT retry the request with this server until he user or
it believes the problem has been fixed.</t> operator and <bcp14>SHOULD NOT</bcp14> retry the request with this s
erver until
<t>401 (Unauthorized): If the client has followed the procedures it believes the problem has been fixed.</dd>
<dt>401 (Unauthorized):</dt><dd> If the client has followed the proced
ures
of the long-term credential mechanism and still gets this error, of the long-term credential mechanism and still gets this error,
then the server is not accepting the client's credentials. In this then the server is not accepting the client's credentials. In this
case, the client considers the current transaction as having case, the client considers the current transaction as having
failed and SHOULD notify the user or operator. The client SHOULD failed and <bcp14>SHOULD</bcp14> notify the user or operator. The cl
NOT send any further requests to this server until it believes the ient <bcp14>SHOULD
problem has been fixed.</t> NOT</bcp14> send any further requests to this server until it believ
es the
<t>403 (Forbidden): The request is valid, but the server is problem has been fixed.</dd>
<dt>403 (Forbidden):</dt> <dd>The request is valid, but the server is
refusing to perform it, likely due to administrative restrictions. refusing to perform it, likely due to administrative restrictions.
The client considers the current transaction as having failed. The The client considers the current transaction as having failed. The
client MAY notify the user or operator and SHOULD NOT retry the client <bcp14>MAY</bcp14> notify the user or operator and <bcp14>SHO ULD NOT</bcp14> retry the
same request with this server until it believes the problem has same request with this server until it believes the problem has
been fixed.</t> been fixed.</dd>
<dt>420 (Unknown Attribute):</dt> <dd>If the client included a DONT-FR
<t>420 (Unknown Attribute): If the client included a DONT-FRAGMENT AGMENT
attribute in the request and the server rejected the request with attribute in the request and the server rejected the request with
a 420 error code and listed the DONT-FRAGMENT attribute in the a 420 error code and listed the DONT-FRAGMENT attribute in the
UNKNOWN-ATTRIBUTES attribute in the error response, then the UNKNOWN-ATTRIBUTES attribute in the error response, then the
client now knows that the server does not support the client now knows that the server does not support the
DONT-FRAGMENT attribute. The client considers the current DONT-FRAGMENT attribute. The client considers the current
transaction as having failed but MAY choose to retry the Allocate transaction as having failed but <bcp14>MAY</bcp14> choose to retry
request without the DONT-FRAGMENT attribute.</t> the Allocate
request without the DONT-FRAGMENT attribute.</dd>
<t>437 (Allocation Mismatch): This indicates that the client has <dt>437 (Allocation Mismatch):</dt> <dd>This indicates that the client
has
picked a 5-tuple that the server sees as already in use. One way picked a 5-tuple that the server sees as already in use. One way
this could happen is if an intervening NAT assigned a mapped this could happen is if an intervening NAT assigned a mapped
transport address that was used by another client that recently transport address that was used by another client that recently
crashed. The client considers the current transaction as having crashed. The client considers the current transaction as having
failed. The client SHOULD pick another client transport address failed. The client <bcp14>SHOULD</bcp14> pick another client transpo rt address
and retry the Allocate request (using a different transaction id). and retry the Allocate request (using a different transaction id).
The client SHOULD try three different client transport addresses The client <bcp14>SHOULD</bcp14> try three different client transpor t addresses
before giving up on this server. Once the client gives up on the before giving up on this server. Once the client gives up on the
server, it SHOULD NOT try to create another allocation on the server, it <bcp14>SHOULD NOT</bcp14> try to create another allocatio
server for 2 minutes.</t> n on the
server for 2 minutes.</dd>
<t>438 (Stale Nonce): See the procedures for the long-term <dt>438 (Stale Nonce):</dt> <dd>See the procedures for the long-term
credential mechanism <xref credential mechanism <xref target="RFC8489" format="default"/>.</dd>
target="I-D.ietf-tram-stunbis"></xref>.</t> <dt>440 (Address Family not Supported):</dt> <dd>The server does not s
upport
<t>440 (Address Family not Supported): The server does not support
the address family requested by the client. If the client receives the address family requested by the client. If the client receives
an Allocate error response with the 440 (Unsupported Address an Allocate error response with the 440 (Address Family not
Family) error code, the client MUST NOT retry the request.</t> Supported) error code, the client <bcp14>MUST NOT</bcp14> retry the r
equest.</dd>
<t>441 (Wrong Credentials): The client should not receive this <dt>441 (Wrong Credentials):</dt> <dd>The client should not receive th
error in response to a Allocate request. The client MAY notify the is
user or operator and SHOULD NOT retry the same request with this error in response to an Allocate request. The client <bcp14>MAY</bcp
server until it believes the problem has been fixed.</t> 14> notify the
user or operator and <bcp14>SHOULD NOT</bcp14> retry the same reques
<t>442 (Unsupported Transport Address): The client should not t with this
server until it believes the problem has been fixed.</dd>
<dt>442 (Unsupported Transport Address):</dt> <dd>The client should no
t
receive this error in response to a request for a UDP allocation. receive this error in response to a request for a UDP allocation.
The client MAY notify the user or operator and SHOULD NOT The client <bcp14>MAY</bcp14> notify the user or operator and <bcp14 >SHOULD NOT</bcp14>
reattempt the request with this server until it believes the reattempt the request with this server until it believes the
problem has been fixed.</t> problem has been fixed.</dd>
<dt>486 (Allocation Quota Reached):</dt> <dd>The server is currently u
<t>486 (Allocation Quota Reached): The server is currently unable nable
to create any more allocations with this username. The client to create any more allocations with this username. The client
considers the current transaction as having failed. The client considers the current transaction as having failed. The client
SHOULD wait at least 1 minute before trying to create any more <bcp14>SHOULD</bcp14> wait at least 1 minute before trying to create
allocations on the server.</t> any more
allocations on the server.</dd>
<t>508 (Insufficient Capacity): The server has no more relayed <dt>508 (Insufficient Capacity):</dt> <dd>
transport addresses available, or has none with the requested
properties, or the one that was reserved is no longer available.
The client considers the current operation as having failed. If
the client is using either the EVEN-PORT or the RESERVATION-TOKEN
attribute, then the client MAY choose to remove or modify this
attribute and try again immediately. Otherwise, the client SHOULD
wait at least 1 minute before trying to create any more
allocations on this server.</t>
</list></t>
The server has no more relayed transport addresses available or has
none with the requested properties, or the one that was reserved
is no longer available. The client considers the current
operation as having failed. If the client is using either the
EVEN-PORT or the RESERVATION-TOKEN attribute, then the client
<bcp14>MAY</bcp14> choose to remove or modify this attribute and
try again immediately. Otherwise, the client <bcp14>SHOULD</bcp14>
wait at least 1 minute before trying to create any more
allocations on this server.</dd>
</dl>
<t>Note that the error code values 486 and 508 indicate to a <t>Note that the error code values 486 and 508 indicate to a
eavesdropper that several other users are using the server at this eavesdropper that several other users are using the server at this
time, similar to that of the HTTP error response code 503, but does time, similar to that of the HTTP error response code 503, but
it does
not reveal any information about the users using the TURN server.</t> not reveal any information about the users using the TURN server.</t>
<t>An unknown error response <bcp14>MUST</bcp14> be handled as described
<t>An unknown error response MUST be handled as described in <xref in <xref target="RFC8489" format="default"/>.</t>
target="I-D.ietf-tram-stunbis"></xref>.</t>
</section> </section>
</section> </section>
<section anchor="sec-refreshing-allocation" numbered="true" toc="default">
<section anchor="sec-refreshing-allocation" <name>Refreshing an Allocation</name>
title="Refreshing an Allocation">
<t>A Refresh transaction can be used to either (a) refresh an existing <t>A Refresh transaction can be used to either (a) refresh an existing
allocation and update its time-to-expiry or (b) delete an existing allocation and update its time-to-expiry or (b) delete an existing
allocation.</t> allocation.</t>
<t>If a client wishes to continue using an allocation, then the client <t>If a client wishes to continue using an allocation, then the client
MUST refresh it before it expires. It is suggested that the client <bcp14>MUST</bcp14> refresh it before it expires. It is suggested that the client
refresh the allocation roughly 1 minute before it expires. If a client refresh the allocation roughly 1 minute before it expires. If a client
no longer wishes to use an allocation, then it SHOULD explicitly delete no longer wishes to use an allocation, then it <bcp14>SHOULD</bcp14> expli
the allocation. A client MAY refresh an allocation at any time for other citly delete
the allocation. A client <bcp14>MAY</bcp14> refresh an allocation at any t
ime for other
reasons.</t> reasons.</t>
<section title="Sending a Refresh Request"> <section numbered="true" toc="default">
<name>Sending a Refresh Request</name>
<t>If the client wishes to immediately delete an existing allocation, <t>If the client wishes to immediately delete an existing allocation,
it includes a LIFETIME attribute with a value of 0. All other forms of it includes a LIFETIME attribute with a value of zero. All other forms o f
the request refresh the allocation.</t> the request refresh the allocation.</t>
<t>When refreshing a dual allocation, the client includes <t>When refreshing a dual allocation, the client includes
REQUESTED-ADDRESS-FAMILY attribute indicating the address family type a REQUESTED-ADDRESS-FAMILY attribute indicating the address family type
that should be refreshed. If no REQUESTED-ADDRESS-FAMILY is included that should be refreshed. If no REQUESTED-ADDRESS-FAMILY attribute is in
cluded,
then the request should be treated as applying to all current then the request should be treated as applying to all current
allocations. The client MUST only include a family type it previously allocations. The client <bcp14>MUST</bcp14> only include a family type i t previously
allocated and has not yet deleted. This process can also be used to allocated and has not yet deleted. This process can also be used to
delete an allocation of a specific address type, by setting the delete an allocation of a specific address type by setting the
lifetime of that refresh request to 0. Deleting a single allocation lifetime of that Refresh request to zero. Deleting a single allocation
destroys any permissions or channels associated with that particular destroys any permissions or channels associated with that particular
allocation; it MUST NOT affect any permissions or channels associated allocation; it <bcp14>MUST NOT</bcp14> affect any permissions or channel s associated
with allocations for the other address family.</t> with allocations for the other address family.</t>
<t>The Refresh transaction updates the time-to-expiry timer of an <t>The Refresh transaction updates the time-to-expiry timer of an
allocation. If the client wishes the server to set the time-to-expiry allocation. If the client wishes the server to set the time-to-expiry
timer to something other than the default lifetime, it includes a timer to something other than the default lifetime, it includes a
LIFETIME attribute with the requested value. The server then computes LIFETIME attribute with the requested value. The server then computes
a new time-to-expiry value in the same way as it does for an Allocate a new time-to-expiry value in the same way as it does for an Allocate
transaction, with the exception that a requested lifetime of 0 causes transaction, with the exception that a requested lifetime of zero causes
the server to immediately delete the allocation.</t> the server to immediately delete the allocation.</t>
</section> </section>
<section anchor="sec-rcv-refresh" numbered="true" toc="default">
<section anchor="sec-rcv-refresh" title="Receiving a Refresh Request"> <name>Receiving a Refresh Request</name>
<t>When the server receives a Refresh request, it processes the <t>When the server receives a Refresh request, it processes the
request as per <xref target="sec-general-behavior"></xref> plus the request as per <xref target="sec-general-behavior" format="default"/> pl us the
specific rules mentioned here.</t> specific rules mentioned here.</t>
<t>If the server receives a Refresh Request with a <t>If the server receives a Refresh Request with a
REQUESTED-ADDRESS-FAMILY attribute and the attribute value does not REQUESTED-ADDRESS-FAMILY attribute and the attribute value does not
match the address family of the allocation, the server MUST reply with match the address family of the allocation, the server <bcp14>MUST</bcp1 4> reply with
a 443 (Peer Address Family Mismatch) Refresh error response.</t> a 443 (Peer Address Family Mismatch) Refresh error response.</t>
<t>The server computes a value called the "desired lifetime" as <t>The server computes a value called the "desired lifetime" as
follows: if the request contains a LIFETIME attribute and the follows: if the request contains a LIFETIME attribute and the
attribute value is 0, then the "desired lifetime" is 0. Otherwise, if attribute value is zero, then the "desired lifetime" is zero. Otherwise, if
the request contains a LIFETIME attribute, then the server computes the request contains a LIFETIME attribute, then the server computes
the minimum of the client's requested lifetime and the server's the minimum of the client's requested lifetime and the server's
maximum allowed lifetime. If this computed value is greater than the maximum allowed lifetime. If this computed value is greater than the
default lifetime, then the "desired lifetime" is the computed value. default lifetime, then the "desired lifetime" is the computed value.
Otherwise, the "desired lifetime" is the default lifetime.</t> Otherwise, the "desired lifetime" is the default lifetime.</t>
<t>Subsequent processing depends on the "desired lifetime" value:</t>
<t>Subsequent processing depends on the "desired lifetime" value:<list <ul spacing="normal">
style="symbols"> <li>If the "desired lifetime" is zero, then the request succeeds and
<t>If the "desired lifetime" is 0, then the request succeeds and the allocation is deleted.</li>
the allocation is deleted.</t> <li>If the "desired lifetime" is non-zero, then the request
<t>If the "desired lifetime" is non-zero, then the request
succeeds and the allocation's time-to-expiry is set to the succeeds and the allocation's time-to-expiry is set to the
"desired lifetime".</t> "desired lifetime".</li>
</list>If the request succeeds, then the server sends a success </ul>
response containing:<list style="symbols"> <t>If the request succeeds, then the server sends a success
<t>A LIFETIME attribute containing the current value of the response containing:</t>
time-to-expiry timer.</t> <ul spacing="normal">
</list></t> <li>A LIFETIME attribute containing the current value of the
time-to-expiry timer.</li>
<t></t> </ul>
<t><list> <aside>
<t>NOTE: A server need not do anything special to implement <t>NOTE: A server need not do anything special to implement
idempotency of Refresh requests over UDP using the "stateless idempotency of Refresh requests over UDP using the "stateless
stack approach". Retransmitted Refresh requests with a non-zero stack approach". Retransmitted Refresh requests with a non-zero
"desired lifetime" will simply refresh the allocation. A "desired lifetime" will simply refresh the allocation. A
retransmitted Refresh request with a zero "desired lifetime" will retransmitted Refresh request with a zero "desired lifetime" will
cause a 437 (Allocation Mismatch) response if the allocation has cause a 437 (Allocation Mismatch) response if the allocation has
already been deleted, but the client will treat this as equivalent already been deleted, but the client will treat this as equivalent
to a success response (see below).</t> to a success response (see below).</t>
</list></t> </aside>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving a Refresh Response"> <name>Receiving a Refresh Response</name>
<t>If the client receives a success response to its Refresh request <t>If the client receives a success response to its Refresh request
with a non-zero lifetime, it updates its copy of the allocation data with a non-zero lifetime, it updates its copy of the allocation data
structure with the time-to-expiry value contained in the response. If structure with the time-to-expiry value contained in the response. If
the client receives a 437 (Allocation Mismatch) error response to its the client receives a 437 (Allocation Mismatch) error response to its
request to refresh the allocation, it should consider the allocation request to refresh the allocation, it should consider the allocation
no longer exists. If the client receives a 438 (Stale Nonce) error to no longer exists. If the client receives a 438 (Stale Nonce) error to
its request to refresh the allocation, it should reattempt the request its request to refresh the allocation, it should reattempt the request
with the new nonce value.</t> with the new nonce value.</t>
<t>If the client receives a 437 (Allocation Mismatch) error response <t>If the client receives a 437 (Allocation Mismatch) error response
to a request to delete the allocation, then the allocation no longer to a request to delete the allocation, then the allocation no longer
exists and it should consider its request as having effectively exists and it should consider its request as having effectively
succeeded.</t> succeeded.</t>
</section> </section>
</section> </section>
<section anchor="sec-permissions" numbered="true" toc="default">
<section anchor="sec-permissions" title="Permissions"> <name>Permissions</name>
<t>For each allocation, the server keeps a list of zero or more <t>For each allocation, the server keeps a list of zero or more
permissions. Each permission consists of an IP address and an associated permissions. Each permission consists of an IP address and an associated
time-to-expiry. While a permission exists, all peers using the IP time-to-expiry. While a permission exists, all peers using the IP
address in the permission are allowed to send data to the client. The address in the permission are allowed to send data to the client. The
time-to-expiry is the number of seconds until the permission expires. time-to-expiry is the number of seconds until the permission expires.
Within the context of an allocation, a permission is uniquely identified Within the context of an allocation, a permission is uniquely identified
by its associated IP address.</t> by its associated IP address.</t>
<t>By sending either CreatePermission requests or ChannelBind requests, <t>By sending either CreatePermission requests or ChannelBind requests,
the client can cause the server to install or refresh a permission for a the client can cause the server to install or refresh a permission for a
given IP address. This causes one of two things to happen:<list given IP address. This causes one of two things to happen:</t>
style="symbols"> <ul spacing="normal">
<t>If no permission for that IP address exists, then a permission is <li>If no permission for that IP address exists, then a permission is
created with the given IP address and a time-to-expiry equal to created with the given IP address and a time-to-expiry equal to
Permission Lifetime.</t> Permission Lifetime.</li>
<li>If a permission for that IP address already exists, then the
<t>If a permission for that IP address already exists, then the
time-to-expiry for that permission is reset to Permission time-to-expiry for that permission is reset to Permission
Lifetime.</t> Lifetime.</li>
</list>The Permission Lifetime MUST be 300 seconds (= 5 minutes).</t> </ul>
<t>The Permission Lifetime <bcp14>MUST</bcp14> be 300 seconds (= 5 minutes
<t>Each permission&rsquo;s time-to-expiry decreases down once per second ).</t>
until it reaches 0; at which point, the permission expires and is <t>Each permission's time-to-expiry decreases down once per second
until it reaches zero, at which point, the permission expires and is
deleted.</t> deleted.</t>
<t>CreatePermission and ChannelBind requests may be freely intermixed on <t>CreatePermission and ChannelBind requests may be freely intermixed on
a permission. A given permission may be initially installed and/or a permission. A given permission may be initially installed and/or
refreshed with a CreatePermission request, and then later refreshed with refreshed with a CreatePermission request and then later refreshed with
a ChannelBind request, or vice versa.</t> a ChannelBind request, or vice versa.</t>
<t>When a UDP datagram arrives at the relayed transport address for the <t>When a UDP datagram arrives at the relayed transport address for the
allocation, the server extracts the source IP address from the IP allocation, the server extracts the source IP address from the IP
header. The server then compares this address with the IP address header. The server then compares this address with the IP address
associated with each permission in the list of permissions for the associated with each permission in the list of permissions for the
allocation. Note that only addresses are compared and port numbers are allocation. Note that only addresses are compared and port numbers are
not considered. If no match is found, relaying is not permitted, and the not considered. If no match is found, relaying is not permitted and the
server silently discards the UDP datagram. If an exact match is found, server silently discards the UDP datagram. If an exact match is found,
the permission check is considered to have succeeded and the server the permission check is considered to have succeeded and the server
continues to process the UDP datagram as specified elsewhere (<xref continues to process the UDP datagram as specified elsewhere (<xref target
target="sec-sending-data-indication"></xref>).</t> ="sec-sending-data-indication" format="default"/>).</t>
<t>The permissions for one allocation are totally unrelated to the <t>The permissions for one allocation are totally unrelated to the
permissions for a different allocation. If an allocation expires, all permissions for a different allocation. If an allocation expires, all
its permissions expire with it.</t> its permissions expire with it.</t>
<aside>
<t><list> <t>NOTE: Though TURN permissions expire after 5 minutes, many NATs
<t>NOTE: Though TURN permissions expire after 5 minutes, many NATs
deployed at the time of publication expire their UDP bindings deployed at the time of publication expire their UDP bindings
considerably faster. Thus, an application using TURN will probably considerably faster. Thus, an application using TURN will probably
wish to send some sort of keep-alive traffic at a much faster rate. wish to send some sort of keep-alive traffic at a much faster rate.
Applications using ICE should follow the keep-alive guidelines of Applications using ICE should follow the keep-alive guidelines of
ICE <xref target="RFC8445"></xref>, and applications not using ICE ICE <xref target="RFC8445" format="default"/>, and applications not us ing ICE
are advised to do something similar.</t> are advised to do something similar.</t>
</list></t> </aside>
</section> </section>
<section numbered="true" toc="default">
<section title="CreatePermission"> <name>CreatePermission</name>
<t>TURN supports two ways for the client to install or refresh <t>TURN supports two ways for the client to install or refresh
permissions on the server. This section describes one way: the permissions on the server. This section describes one way: the
CreatePermission request.</t> CreatePermission request.</t>
<t>A CreatePermission request may be used in conjunction with either the <t>A CreatePermission request may be used in conjunction with either the
Send mechanism in <xref target="sec-sendanddata"></xref> or the Channel Send mechanism in <xref target="sec-sendanddata" format="default"/> or the
mechanism in <xref target="sec-channels"></xref>.</t> Channel
mechanism in <xref target="sec-channels" format="default"/>.</t>
<section title="Forming a CreatePermission Request"> <section numbered="true" toc="default">
<name>Forming a CreatePermission Request</name>
<t>The client who wishes to install or refresh one or more permissions <t>The client who wishes to install or refresh one or more permissions
can send a CreatePermission request to the server.</t> can send a CreatePermission request to the server.</t>
<t>When forming a CreatePermission request, the client <bcp14>MUST</bcp1
<t>When forming a CreatePermission request, the client MUST include at 4> include at
least one XOR-PEER-ADDRESS attribute, and MAY include more than one least one XOR-PEER-ADDRESS attribute and <bcp14>MAY</bcp14> include more
than one
such attribute. The IP address portion of each XOR-PEER-ADDRESS such attribute. The IP address portion of each XOR-PEER-ADDRESS
attribute contains the IP address for which a permission should be attribute contains the IP address for which a permission should be
installed or refreshed. The port portion of each XOR-PEER-ADDRESS installed or refreshed. The port portion of each XOR-PEER-ADDRESS
attribute will be ignored and can be any arbitrary value. The various attribute will be ignored and can be any arbitrary value. The various
XOR-PEER-ADDRESS attributes MAY appear in any order. The client MUST XOR-PEER-ADDRESS attributes <bcp14>MAY</bcp14> appear in any order. The client <bcp14>MUST</bcp14>
only include XOR-PEER-ADDRESS attributes with addresses of the same only include XOR-PEER-ADDRESS attributes with addresses of the same
address family as that of the relayed transport address for the address family as that of the relayed transport address for the
allocation. For dual allocations obtained using the allocation. For dual allocations obtained using the
ADDITIONAL-ADDRESS-FAMILY attribute, the client MAY include ADDITIONAL-ADDRESS-FAMILY attribute, the client <bcp14>MAY</bcp14> inclu de
XOR-PEER-ADDRESS attributes with addresses of IPv4 and IPv6 address XOR-PEER-ADDRESS attributes with addresses of IPv4 and IPv6 address
families.</t> families.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving a CreatePermission Request"> <name>Receiving a CreatePermission Request</name>
<t>When the server receives the CreatePermission request, it processes <t>When the server receives the CreatePermission request, it processes
as per <xref target="sec-general-behavior"></xref> plus the specific as per <xref target="sec-general-behavior" format="default"/> plus the s pecific
rules mentioned here.</t> rules mentioned here.</t>
<t>The message is checked for validity. The CreatePermission request <t>The message is checked for validity. The CreatePermission request
MUST contain at least one XOR-PEER-ADDRESS attribute and MAY contain <bcp14>MUST</bcp14> contain at least one XOR-PEER-ADDRESS attribute and <bcp14>MAY</bcp14> contain
multiple such attributes. If no such attribute exists, or if any of multiple such attributes. If no such attribute exists, or if any of
these attributes are invalid, then a 400 (Bad Request) error is these attributes are invalid, then a 400 (Bad Request) error is
returned. If the request is valid, but the server is unable to satisfy returned. If the request is valid, but the server is unable to satisfy
the request due to some capacity limit or similar, then a 508 the request due to some capacity limit or similar, then a 508
(Insufficient Capacity) error is returned.</t> (Insufficient Capacity) error is returned.</t>
<t>If an XOR-PEER-ADDRESS attribute contains an address of an address <t>If an XOR-PEER-ADDRESS attribute contains an address of an address
family that is not the same as that of a relayed transport address for family that is not the same as that of a relayed transport address for
the allocation, the server MUST generate an error response with the the allocation, the server <bcp14>MUST</bcp14> generate an error respons e with the
443 (Peer Address Family Mismatch) response code.</t> 443 (Peer Address Family Mismatch) response code.</t>
<t>The server <bcp14>MAY</bcp14> impose restrictions on the IP address a
<t>The server MAY impose restrictions on the IP address allowed in the llowed in the
XOR-PEER-ADDRESS attribute -- if a value is not allowed, the server XOR-PEER-ADDRESS attribute; if a value is not allowed, the server
rejects the request with a 403 (Forbidden) error.</t> rejects the request with a 403 (Forbidden) error.</t>
<t>If the message is valid and the server is capable of carrying out <t>If the message is valid and the server is capable of carrying out
the request, then the server installs or refreshes a permission for the request, then the server installs or refreshes a permission for
the IP address contained in each XOR-PEER-ADDRESS attribute as the IP address contained in each XOR-PEER-ADDRESS attribute as
described in <xref target="sec-permissions"></xref>. The port portion described in <xref target="sec-permissions" format="default"/>. The port portion
of each attribute is ignored and may be any arbitrary value.</t> of each attribute is ignored and may be any arbitrary value.</t>
<t>The server then responds with a CreatePermission success response. <t>The server then responds with a CreatePermission success response.
There are no mandatory attributes in the success response.</t> There are no mandatory attributes in the success response.</t>
<aside>
<t><list> <t>NOTE: A server need not do anything special to implement
<t>NOTE: A server need not do anything special to implement
idempotency of CreatePermission requests over UDP using the idempotency of CreatePermission requests over UDP using the
"stateless stack approach". Retransmitted CreatePermission "stateless stack approach". Retransmitted CreatePermission
requests will simply refresh the permissions.</t> requests will simply refresh the permissions.</t>
</list></t> </aside>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving a CreatePermission Response"> <name>Receiving a CreatePermission Response</name>
<t>If the client receives a valid CreatePermission success response, <t>If the client receives a valid CreatePermission success response,
then the client updates its data structures to indicate that the then the client updates its data structures to indicate that the
permissions have been installed or refreshed.</t> permissions have been installed or refreshed.</t>
</section> </section>
</section> </section>
<section anchor="sec-sendanddata" numbered="true" toc="default">
<section anchor="sec-sendanddata" title="Send and Data Methods"> <name>Send and Data Methods</name>
<t>TURN supports two mechanisms for sending and receiving data from <t>TURN supports two mechanisms for sending and receiving data from
peers. This section describes the use of the Send and Data mechanisms, peers. This section describes the use of the Send and Data mechanisms,
while <xref target="sec-channels"></xref> describes the use of the while <xref target="sec-channels" format="default"/> describes the use of the
Channel mechanism.</t> Channel mechanism.</t>
<section anchor="sec-forming-indication" numbered="true" toc="default">
<section anchor="sec-forming-indication" <name>Forming a Send Indication</name>
title="Forming a Send Indication">
<t>The client can use a Send indication to pass data to the server for <t>The client can use a Send indication to pass data to the server for
relaying to a peer. A client may use a Send indication even if a relaying to a peer. A client may use a Send indication even if a
channel is bound to that peer. However, the client MUST ensure that channel is bound to that peer. However, the client <bcp14>MUST</bcp14> e nsure that
there is a permission installed for the IP address of the peer to there is a permission installed for the IP address of the peer to
which the Send indication is being sent; this prevents a third party which the Send indication is being sent; this prevents a third party
from using a TURN server to send data to arbitrary destinations.</t> from using a TURN server to send data to arbitrary destinations.</t>
<t>When forming a Send indication, the client <bcp14>MUST</bcp14> includ
<t>When forming a Send indication, the client MUST include an e an
XOR-PEER-ADDRESS attribute and a DATA attribute. The XOR-PEER-ADDRESS XOR-PEER-ADDRESS attribute and a DATA attribute. The XOR-PEER-ADDRESS
attribute contains the transport address of the peer to which the data attribute contains the transport address of the peer to which the data
is to be sent, and the DATA attribute contains the actual application is to be sent, and the DATA attribute contains the actual application
data to be sent to the peer.</t> data to be sent to the peer.</t>
<t>The client <bcp14>MAY</bcp14> include a DONT-FRAGMENT attribute in th
<t>The client MAY include a DONT-FRAGMENT attribute in the Send e Send
indication if it wishes the server to set the DF bit on the UDP indication if it wishes the server to set the DF bit on the UDP
datagram sent to the peer.</t> datagram sent to the peer.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving a Send Indication"> <name>Receiving a Send Indication</name>
<t>When the server receives a Send indication, it processes as per <t>When the server receives a Send indication, it processes as per
<xref target="sec-general-behavior"></xref> plus the specific rules <xref target="sec-general-behavior" format="default"/> plus the specific rules
mentioned here.</t> mentioned here.</t>
<t>The message is first checked for validity. The Send indication <bcp14
<t>The message is first checked for validity. The Send indication MUST >MUST</bcp14>
contain both an XOR-PEER-ADDRESS attribute and a DATA attribute. If contain both an XOR-PEER-ADDRESS attribute and a DATA attribute. If
one of these attributes is missing or invalid, then the message is one of these attributes is missing or invalid, then the message is
discarded. Note that the DATA attribute is allowed to contain zero discarded. Note that the DATA attribute is allowed to contain zero
bytes of data.</t> bytes of data.</t>
<t>The Send indication may also contain the DONT-FRAGMENT attribute. <t>The Send indication may also contain the DONT-FRAGMENT attribute.
If the server is unable to set the DF bit on outgoing UDP datagrams If the server is unable to set the DF bit on outgoing UDP datagrams
when this attribute is present, then the server acts as if the when this attribute is present, then the server acts as if the
DONT-FRAGMENT attribute is an unknown comprehension-required attribute DONT-FRAGMENT attribute is an unknown comprehension-required attribute
(and thus the Send indication is discarded).</t> (and thus the Send indication is discarded).</t>
<t>The server also checks that there is a permission installed for the <t>The server also checks that there is a permission installed for the
IP address contained in the XOR-PEER-ADDRESS attribute. If no such IP address contained in the XOR-PEER-ADDRESS attribute. If no such
permission exists, the message is discarded. Note that a Send permission exists, the message is discarded. Note that a Send
indication never causes the server to refresh the permission.</t> indication never causes the server to refresh the permission.</t>
<t>The server <bcp14>MAY</bcp14> impose restrictions on the IP address a
<t>The server MAY impose restrictions on the IP address and port nd port
values allowed in the XOR-PEER-ADDRESS attribute -- if a value is not values allowed in the XOR-PEER-ADDRESS attribute; if a value is not
allowed, the server silently discards the Send indication.</t> allowed, the server silently discards the Send indication.</t>
<t>If everything is OK, then the server forms a UDP datagram as <t>If everything is OK, then the server forms a UDP datagram as
follows:<list style="symbols"> follows:</t>
<t>the source transport address is the relayed transport address <ul spacing="normal">
<li>the source transport address is the relayed transport address
of the allocation, where the allocation is determined by the of the allocation, where the allocation is determined by the
5-tuple on which the Send indication arrived;</t> 5-tuple on which the Send indication arrived;</li>
<li>the destination transport address is taken from the
<t>the destination transport address is taken from the XOR-PEER-ADDRESS attribute;</li>
XOR-PEER-ADDRESS attribute;</t> <li>the data following the UDP header is the contents of the value
field of the DATA attribute.</li>
<t>the data following the UDP header is the contents of the value </ul>
field of the DATA attribute.</t>
</list></t>
<t>The handling of the DONT-FRAGMENT attribute (if present), is <t>The handling of the DONT-FRAGMENT attribute (if present), is
described in <xref target="sec-ip-header-fields"></xref> and <xref described in Sections <xref target="sec-ip-header-fields" format="counte
target="sec-ip-header-fields-tcp-udp"></xref>.</t> r"/> and <xref target="sec-ip-header-fields-tcp-udp" format="counter"/>.</t>
<t>The resulting UDP datagram is then sent to the peer.</t> <t>The resulting UDP datagram is then sent to the peer.</t>
</section> </section>
<section anchor="sec-sending-data-indication" numbered="true" toc="default
<section anchor="sec-sending-data-indication" ">
title="Receiving a UDP Datagram"> <name>Receiving a UDP Datagram</name>
<t>When the server receives a UDP datagram at a currently allocated <t>When the server receives a UDP datagram at a currently allocated
relayed transport address, the server looks up the allocation relayed transport address, the server looks up the allocation
associated with the relayed transport address. The server then checks associated with the relayed transport address. The server then checks
to see whether the set of permissions for the allocation allow the to see whether the set of permissions for the allocation allow the
relaying of the UDP datagram as described in <xref relaying of the UDP datagram as described in <xref target="sec-permissio
target="sec-permissions"></xref>.</t> ns" format="default"/>.</t>
<t>If relaying is permitted, then the server checks if there is a <t>If relaying is permitted, then the server checks if there is a
channel bound to the peer that sent the UDP datagram (see <xref channel bound to the peer that sent the UDP datagram (see <xref target="
target="sec-channels"></xref>). If a channel is bound, then processing sec-channels" format="default"/>). If a channel is bound, then processing
proceeds as described in <xref proceeds as described in <xref target="sec-channel-relaying" format="def
target="sec-channel-relaying"></xref>.</t> ault"/>.</t>
<t>If relaying is permitted but no channel is bound to the peer, then <t>If relaying is permitted but no channel is bound to the peer, then
the server forms and sends a Data indication. The Data indication MUST the server forms and sends a Data indication. The Data indication <bcp14 >MUST</bcp14>
contain both an XOR-PEER-ADDRESS and a DATA attribute. The DATA contain both an XOR-PEER-ADDRESS and a DATA attribute. The DATA
attribute is set to the value of the &lsquo;data octets&rsquo; field attribute is set to the value of the "data octets" field
from the datagram, and the XOR-PEER-ADDRESS attribute is set to the from the datagram, and the XOR-PEER-ADDRESS attribute is set to the
source transport address of the received UDP datagram. The Data source transport address of the received UDP datagram. The Data
indication is then sent on the 5-tuple associated with the indication is then sent on the 5-tuple associated with the
allocation.</t> allocation.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving a Data Indication"> <name>Receiving a Data Indication</name>
<t>When the client receives a Data indication, it checks that the Data <t>When the client receives a Data indication, it checks that the Data
indication contains an XOR-PEER-ADDRESS attribute, and discards the indication contains an XOR-PEER-ADDRESS attribute and discards the
indication if it does not. The client SHOULD also check that the indication if it does not. The client <bcp14>SHOULD</bcp14> also check t
hat the
XOR-PEER-ADDRESS attribute value contains an IP address with which the XOR-PEER-ADDRESS attribute value contains an IP address with which the
client believes there is an active permission, and discard the Data client believes there is an active permission and discard the Data
indication otherwise.</t> indication otherwise.</t>
<aside>
<t><list> <t>NOTE: The latter check protects the client against an attacker
<t>NOTE: The latter check protects the client against an attacker
who somehow manages to trick the server into installing who somehow manages to trick the server into installing
permissions not desired by the client.</t> permissions not desired by the client.</t>
</list></t> </aside>
<t>If the XOR-PEER-ADDRESS is present and valid, the client checks <t>If the XOR-PEER-ADDRESS is present and valid, the client checks
that the Data indication contains either a DATA attribute or an ICMP that the Data indication contains either a DATA attribute or an ICMP
attribute and discards the indication if it does not. Note that a DATA attribute and discards the indication if it does not. Note that a DATA
attribute is allowed to contain zero bytes of data. Processing of Data attribute is allowed to contain zero bytes of data. Processing of Data
indications with an ICMP attribute is described in <xref indications with an ICMP attribute is described in <xref target="receive
target="receive-senderror"></xref>.</t> -senderror" format="default"/>.</t>
<t>If the Data indication passes the above checks, the client delivers <t>If the Data indication passes the above checks, the client delivers
the data octets inside the DATA attribute to the application, along the data octets inside the DATA attribute to the application, along
with an indication that they were received from the peer whose with an indication that they were received from the peer whose
transport address is given by the XOR-PEER-ADDRESS attribute.</t> transport address is given by the XOR-PEER-ADDRESS attribute.</t>
</section> </section>
<section anchor="sec-sending-senderror-indication" numbered="true" toc="de
<section anchor="sec-sending-senderror-indication" fault">
title="Receiving an ICMP Packet"> <name>Receiving an ICMP Packet</name>
<t>When the server receives an ICMP packet, the server verifies that <t>When the server receives an ICMP packet, the server verifies that
the type is either 3 or 11 for an ICMPv4 <xref the type is either 3 or 11 for an ICMPv4 <xref target="RFC0792" format="
target="RFC0792"></xref> packet or either 1, 2, or 3 for an ICMPv6 default"/> packet or either 1, 2, or 3 for an ICMPv6
<xref target="RFC4443"></xref> packet. It also verifies that the IP <xref target="RFC4443" format="default"/> packet. It also verifies that
the IP
packet in the ICMP packet payload contains a UDP header. If either of packet in the ICMP packet payload contains a UDP header. If either of
these conditions fail, then the ICMP packet is silently dropped. If a these conditions fail, then the ICMP packet is silently dropped. If a
UDP header is present, the server extracts the source and destination UDP header is present, the server extracts the source and destination
IP address and UDP port information.</t> IP address and UDP port information.</t>
<t>The server looks up the allocation whose relayed transport address <t>The server looks up the allocation whose relayed transport address
corresponds to the encapsulated packet's source IP address and UDP corresponds to the encapsulated packet's source IP address and UDP
port. If no such allocation exists, the packet is silently dropped. port. If no such allocation exists, the packet is silently dropped.
The server then checks to see whether the set of permissions for the The server then checks to see whether the set of permissions for the
allocation allows the relaying of the ICMP packet. For ICMP packets, allocation allows the relaying of the ICMP packet. For ICMP packets,
the source IP address MUST NOT be checked against the permissions list the source IP address <bcp14>MUST NOT</bcp14> be checked against the per missions list
as it would be for UDP packets. Instead, the server extracts the as it would be for UDP packets. Instead, the server extracts the
destination IP address from the encapsulated IP header. The server destination IP address from the encapsulated IP header. The server
then compares this address with the IP address associated with each then compares this address with the IP address associated with each
permission in the list of permissions for the allocation. If no match permission in the list of permissions for the allocation. If no match
is found, relaying is not permitted, and the server silently discards is found, relaying is not permitted and the server silently discards
the ICMP packet. Note that only addresses are compared and port the ICMP packet. Note that only addresses are compared and port
numbers are not considered.</t> numbers are not considered.</t>
<t>If relaying is permitted, then the server forms and sends a Data
<t>If relaying is permitted then the server forms and sends a Data indication. The Data indication <bcp14>MUST</bcp14> contain both an XOR-
indication. The Data indication MUST contain both an XOR-PEER-ADDRESS PEER-ADDRESS
and an ICMP attribute. The ICMP attribute is set to the value of the and an ICMP attribute. The ICMP attribute is set to the value of the
type and code fields from the ICMP packet. The IP address portion of type and code fields from the ICMP packet. The IP address portion of
XOR-PEER-ADDRESS attribute is set to the destination IP address in the XOR-PEER-ADDRESS attribute is set to the destination IP address in the
encapsulated IP header. At the time of writing of this specification, encapsulated IP header. At the time of writing of this specification,
Socket APIs on some operating systems do not deliver the destination Socket APIs on some operating systems do not deliver the destination
port in the encapsulated UDP header to applications without superuser port in the encapsulated UDP header to applications without superuser
privileges. If destination port in the encapsulated UDP header is privileges. If destination port in the encapsulated UDP header is
available to the server then the port portion of XOR-PEER-ADDRESS available to the server, then the port portion of the XOR-PEER-ADDRESS
attribute is set to the destination port otherwise the port portion is attribute is set to the destination port; otherwise, the port portion is
set to 0. The Data indication is then sent on the 5-tuple associated set to zero. The Data indication is then sent on the 5-tuple associated
with the allocation.</t> with the allocation.</t>
<aside>
<t>Implementation Note: New ICMP types or codes can be defined in <t>Implementation Note: New ICMP types or codes can be defined in
future specifications. If the server receives an ICMP error packet, future specifications. If the server receives an ICMP error packet,
and the new type or code field can help the client to make use of the and the new type or code field can help the client to make use of the
ICMP error notification and generate feedback to the application ICMP error notification and generate feedback to the application
layer, the server sends the Data indication with an ICMP attribute layer, the server sends the Data indication with an ICMP attribute
conveying the new ICMP type or code.</t> conveying the new ICMP type or code.</t></aside>
</section> </section>
<section anchor="receive-senderror" numbered="true" toc="default">
<section anchor="receive-senderror" <name>Receiving a Data Indication with an ICMP Attribute</name>
title="Receiving a Data Indication with an ICMP attribute">
<t>When the client receives a Data indication with an ICMP attribute, <t>When the client receives a Data indication with an ICMP attribute,
it checks that the Data indication contains an XOR-PEER-ADDRESS it checks that the Data indication contains an XOR-PEER-ADDRESS
attribute, and discards the indication if it does not. The client attribute and discards the indication if it does not. The client
SHOULD also check that the XOR-PEER-ADDRESS attribute value contains <bcp14>SHOULD</bcp14> also check that the XOR-PEER-ADDRESS attribute val
an IP address with an active permission, and discard the Data ue contains
an IP address with an active permission and discard the Data
indication otherwise.</t> indication otherwise.</t>
<t>If the Data indication passes the above checks, the client signals <t>If the Data indication passes the above checks, the client signals
the application of the error condition, along with an indication that the application of the error condition along with an indication that
it was received from the peer whose transport address is given by the it was received from the peer whose transport address is given by the
XOR-PEER-ADDRESS attribute. The application can make sense of the XOR-PEER-ADDRESS attribute. The application can make sense of the
meaning of the type and code values in the ICMP attribute by using the meaning of the type and code values in the ICMP attribute by using the
family field in the XOR-PEER-ADDRESS attribute.</t> family field in the XOR-PEER-ADDRESS attribute.</t>
</section> </section>
</section> </section>
<!-- Sending and Receiving Data --> <section anchor="sec-channels" numbered="true" toc="default">
<name>Channels</name>
<section anchor="sec-channels" title="Channels">
<t>Channels provide a way for the client and server to send application <t>Channels provide a way for the client and server to send application
data using ChannelData messages, which have less overhead than Send and data using ChannelData messages, which have less overhead than Send and
Data indications.</t> Data indications.</t>
<t>The ChannelData message (see <xref target="sec-channeldata-msg" format=
<t>The ChannelData message (see <xref "default"/>) starts with a two-byte field that
target="sec-channeldata-msg"></xref>) starts with a two-byte field that
carries the channel number. The values of this field are allocated as carries the channel number. The values of this field are allocated as
follows:<list style="empty"> follows:</t>
<t>0x0000 through 0x3FFF: These values can never be used for channel
numbers.</t>
<t>0x4000 through 0x4FFF: These values are the allowed channel <table anchor="channels">
numbers (4096 possible values).</t>
<t>0x5000-0xFFFF: Reserved (For DTLS-SRTP multiplexing collision <tbody>
avoidance, see <xref target="RFC7983"></xref>.</t> <tr>
</list></t> <td>0x0000 through 0x3FFF:</td>
<td>These values can never be used for channel numbers.</td>
</tr>
<tr>
<td>0x4000 through 0x4FFF:</td>
<td>These values are the allowed channel numbers (4096 possible values).</
td>
</tr>
<tr>
<td>0x5000 through 0xFFFF:</td>
<td>Reserved (For DTLS-SRTP multiplexing collision avoidance, see <xref
target="RFC7983" format="default"/>).</td>
</tr>
</tbody>
</table>
<t>Note that the channel number range is not backwards compatible with <t>Note that the channel number range is not backwards compatible with
<xref target="RFC5766"></xref>, which could prevent an RFC5766-compliant <xref target="RFC5766" format="default"/>, which could prevent a client
client from establishing channel bindings with a TURN server that compliant with RFC 5766 from establishing channel bindings with a
complies with this specification. .</t> TURN server that complies with this specification.</t>
<t>According to <xref target="RFC7983" format="default"/>, ChannelData mes
<t>According to <xref target="RFC7983"></xref>, ChannelData messages can sages can
be distinguished from other multiplexed protocols by examining the first be distinguished from other multiplexed protocols by examining the first
byte of the message:</t> byte of the message:</t>
<t><figure anchor="fig-demultiplexing"> <table anchor="fig-demultiplexing">
<artwork><![CDATA[+------------+------------------------------+
| [0..3] | STUN | <tbody>
| | | <tr>
+-------------------------------------------+ <td align="left">[0..3]</td>
| [16..19] | ZRTP | <td align="center">STUN</td>
| | |
+-------------------------------------------+ </tr>
| [20..63] | DTLS | <tr>
| | | <td align="left">[16..19]</td>
+-------------------------------------------+ <td align="center">ZRTP</td>
| [64..79] | TURN Channel |
| | | </tr>
+-------------------------------------------+ <tr>
| [128..191] | RTP/RTCP | <td align="left">[20..63]</td>
| | | <td align="center">DTLS</td>
+-------------------------------------------+
| Others | Reserved, MUST be dropped | </tr>
| | and an alert MAY be logged | <tr>
+-------------------------------------------+ <td align="left">[64..79]</td>
]]></artwork> <td align="center">TURN Channel</td>
</figure></t>
</tr>
<tr>
<td align="left">[128..191]</td>
<td align="center">RTP/RTCP</td>
</tr>
<tr>
<td align="left">Others</td>
<td align="center">Reserved; <bcp14>MUST</bcp14> be dropped and an alert
<bcp14>MAY</bcp14> be logged</td>
</tr>
</tbody>
</table>
<t>Reserved values may be used in the future by other protocols. When <t>Reserved values may be used in the future by other protocols. When
the client uses channel binding, it MUST comply with the demultiplexing the client uses channel binding, it <bcp14>MUST</bcp14> comply with the de multiplexing
scheme discussed above.</t> scheme discussed above.</t>
<t>Channel bindings are always initiated by the client. The client can <t>Channel bindings are always initiated by the client. The client can
bind a channel to a peer at any time during the lifetime of the bind a channel to a peer at any time during the lifetime of the
allocation. The client may bind a channel to a peer before exchanging allocation. The client may bind a channel to a peer before exchanging
data with it, or after exchanging data with it (using Send and Data data with it or after exchanging data with it (using Send and Data
indications) for some time, or may choose never to bind a channel to it. indications) for some time, or may choose never to bind a channel to it.
The client can also bind channels to some peers while not binding The client can also bind channels to some peers while not binding
channels to other peers.</t> channels to other peers.</t>
<t>Channel bindings are specific to an allocation so that the use of a
<t>Channel bindings are specific to an allocation, so that the use of a
channel number or peer transport address in a channel binding in one channel number or peer transport address in a channel binding in one
allocation has no impact on their use in a different allocation. If an allocation has no impact on their use in a different allocation. If an
allocation expires, all its channel bindings expire with it.</t> allocation expires, all its channel bindings expire with it.</t>
<t>A channel binding consists of:</t>
<t>A channel binding consists of:<list style="symbols"> <ul spacing="normal">
<t>a channel number;</t> <li>a channel number;</li>
<li>a transport address (of the peer); and</li>
<t>a transport address (of the peer); and</t> <li>A time-to-expiry timer.</li>
</ul>
<t>A time-to-expiry timer.</t> <t>Within the context of an allocation, a channel binding is
</list>Within the context of an allocation, a channel binding is
uniquely identified either by the channel number or by the peer's uniquely identified either by the channel number or by the peer's
transport address. Thus, the same channel cannot be bound to two transport address. Thus, the same channel cannot be bound to two
different transport addresses, nor can the same transport address be different transport addresses, nor can the same transport address be
bound to two different channels.</t> bound to two different channels.</t>
<t>A channel binding lasts for 10 minutes unless refreshed. Refreshing <t>A channel binding lasts for 10 minutes unless refreshed. Refreshing
the binding (by the server receiving a ChannelBind request rebinding the the binding (by the server receiving a ChannelBind request rebinding the
channel to the same peer) resets the time-to-expiry timer back to 10 channel to the same peer) resets the time-to-expiry timer back to 10
minutes.</t> minutes.</t>
<t>When the channel binding expires, the channel becomes unbound. Once <t>When the channel binding expires, the channel becomes unbound. Once
unbound, the channel number can be bound to a different transport unbound, the channel number can be bound to a different transport
address, and the transport address can be bound to a different channel address, and the transport address can be bound to a different channel
number. To prevent race conditions, the client MUST wait 5 minutes after number. To prevent race conditions, the client <bcp14>MUST</bcp14> wait 5 minutes after
the channel binding expires before attempting to bind the channel number the channel binding expires before attempting to bind the channel number
to a different transport address or the transport address to a different to a different transport address or the transport address to a different
channel number.</t> channel number.</t>
<t>When binding a channel to a peer, the client <bcp14>SHOULD</bcp14> be p
<t>When binding a channel to a peer, the client SHOULD be prepared to repared to
receive ChannelData messages on the channel from the server as soon as receive ChannelData messages on the channel from the server as soon as
it has sent the ChannelBind request. Over UDP, it is possible for the it has sent the ChannelBind request. Over UDP, it is possible for the
client to receive ChannelData messages from the server before it client to receive ChannelData messages from the server before it
receives a ChannelBind success response.</t> receives a ChannelBind success response.</t>
<t>In the other direction, the client <bcp14>MAY</bcp14> elect to send Cha
<t>In the other direction, the client MAY elect to send ChannelData nnelData
messages before receiving the ChannelBind success response. Doing so, messages before receiving the ChannelBind success response. Doing so,
however, runs the risk of having the ChannelData messages dropped by the however, runs the risk of having the ChannelData messages dropped by the
server if the ChannelBind request does not succeed for some reason server if the ChannelBind request does not succeed for some reason
(e.g., packet lost if the request is sent over UDP, or the server being (e.g., packet lost if the request is sent over UDP or the server being
unable to fulfill the request). A client that wishes to be safe should unable to fulfill the request). A client that wishes to be safe should
either queue the data or use Send indications until the channel binding either queue the data or use Send indications until the channel binding
is confirmed.</t> is confirmed.</t>
<section title="Sending a ChannelBind Request"> <section numbered="true" toc="default">
<name>Sending a ChannelBind Request</name>
<t>A channel binding is created or refreshed using a ChannelBind <t>A channel binding is created or refreshed using a ChannelBind
transaction. A ChannelBind transaction also creates or refreshes a transaction. A ChannelBind transaction also creates or refreshes a
permission towards the peer (see <xref permission towards the peer (see <xref target="sec-permissions" format="
target="sec-permissions"></xref>).</t> default"/>).</t>
<t>To initiate the ChannelBind transaction, the client forms a <t>To initiate the ChannelBind transaction, the client forms a
ChannelBind request. The channel to be bound is specified in a ChannelBind request. The channel to be bound is specified in a
CHANNEL-NUMBER attribute, and the peer's transport address is CHANNEL-NUMBER attribute, and the peer's transport address is
specified in an XOR-PEER-ADDRESS attribute. <xref specified in an XOR-PEER-ADDRESS attribute. <xref target="sec-receiving-
target="sec-receiving-ChannelBind"></xref> describes the restrictions ChannelBind" format="default"/> describes the restrictions
on these attributes. The client MUST only include an XOR-PEER-ADDRESS on these attributes. The client <bcp14>MUST</bcp14> only include an XOR-
PEER-ADDRESS
attribute with an address of the same address family as that of a attribute with an address of the same address family as that of a
relayed transport address for the allocation.</t> relayed transport address for the allocation.</t>
<t>Rebinding a channel to the same transport address that it is <t>Rebinding a channel to the same transport address that it is
already bound to provides a way to refresh a channel binding and the already bound to provides a way to refresh a channel binding and the
corresponding permission without sending data to the peer. Note corresponding permission without sending data to the peer. Note,
however, that permissions need to be refreshed more frequently than however, that permissions need to be refreshed more frequently than
channels.</t> channels.</t>
</section> </section>
<section anchor="sec-receiving-ChannelBind" numbered="true" toc="default">
<section anchor="sec-receiving-ChannelBind" <name>Receiving a ChannelBind Request</name>
title="Receiving a ChannelBind Request">
<t>When the server receives a ChannelBind request, it processes as per <t>When the server receives a ChannelBind request, it processes as per
<xref target="sec-general-behavior"></xref> plus the specific rules <xref target="sec-general-behavior" format="default"/> plus the specific rules
mentioned here.</t> mentioned here.</t>
<t>The server checks the following:</t>
<t>The server checks the following:<list style="symbols"> <ul spacing="normal">
<t>The request contains both a CHANNEL-NUMBER and an <li>The request contains both a CHANNEL-NUMBER and an
XOR-PEER-ADDRESS attribute;</t> XOR-PEER-ADDRESS attribute;</li>
<li>The channel number is in the range 0x4000 through 0x4FFF
<t>The channel number is in the range 0x4000 through 0x4FFF (inclusive);</li>
(inclusive);</t> <li>The channel number is not currently bound to a different
transport address (same transport address is OK);</li>
<t>The channel number is not currently bound to a different <li>The transport address is not currently bound to a different
transport address (same transport address is OK);</t> channel number.</li>
</ul>
<t>The transport address is not currently bound to a different
channel number.</t>
</list></t>
<t>If any of these tests fail, the server replies with a 400 (Bad <t>If any of these tests fail, the server replies with a 400 (Bad
Request) error. If the XOR-PEER-ADDRESS attribute contains an address Request) error. If the XOR-PEER-ADDRESS attribute contains an address
of an address family that is not the same as that of a relayed of an address family that is not the same as that of a relayed
transport address for the allocation, the server MUST generate an transport address for the allocation, the server <bcp14>MUST</bcp14> gen erate an
error response with the 443 (Peer Address Family Mismatch) response error response with the 443 (Peer Address Family Mismatch) response
code.</t> code.</t>
<t>The server <bcp14>MAY</bcp14> impose restrictions on the IP address a
<t>The server MAY impose restrictions on the IP address and port nd port
values allowed in the XOR-PEER-ADDRESS attribute -- if a value is not values allowed in the XOR-PEER-ADDRESS attribute; if a value is not
allowed, the server rejects the request with a 403 (Forbidden) allowed, the server rejects the request with a 403 (Forbidden)
error.</t> error.</t>
<t>If the request is valid, but the server is unable to fulfill the <t>If the request is valid, but the server is unable to fulfill the
request due to some capacity limit or similar, the server replies with request due to some capacity limit or similar, the server replies with
a 508 (Insufficient Capacity) error.</t> a 508 (Insufficient Capacity) error.</t>
<t>Otherwise, the server replies with a ChannelBind success response. <t>Otherwise, the server replies with a ChannelBind success response.
There are no required attributes in a successful ChannelBind There are no required attributes in a successful ChannelBind
response.</t> response.</t>
<t>If the server can satisfy the request, then the server creates or <t>If the server can satisfy the request, then the server creates or
refreshes the channel binding using the channel number in the refreshes the channel binding using the channel number in the
CHANNEL-NUMBER attribute and the transport address in the CHANNEL-NUMBER attribute and the transport address in the
XOR-PEER-ADDRESS attribute. The server also installs or refreshes a XOR-PEER-ADDRESS attribute. The server also installs or refreshes a
permission for the IP address in the XOR-PEER-ADDRESS attribute as permission for the IP address in the XOR-PEER-ADDRESS attribute as
described in <xref target="sec-permissions"></xref>.</t> described in <xref target="sec-permissions" format="default"/>.</t>
<aside>
<t><list> <t>NOTE: A server need not do anything special to implement
<t>NOTE: A server need not do anything special to implement
idempotency of ChannelBind requests over UDP using the "stateless idempotency of ChannelBind requests over UDP using the "stateless
stack approach". Retransmitted ChannelBind requests will simply stack approach". Retransmitted ChannelBind requests will simply
refresh the channel binding and the corresponding permission. refresh the channel binding and the corresponding permission.
Furthermore, the client must wait 5 minutes before binding a Furthermore, the client must wait 5 minutes before binding a
previously bound channel number or peer address to a different previously bound channel number or peer address to a different
channel, eliminating the possibility that the transaction would channel, eliminating the possibility that the transaction would
initially fail but succeed on a retransmission.</t> initially fail but succeed on a retransmission.</t>
</list></t> </aside>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving a ChannelBind Response"> <name>Receiving a ChannelBind Response</name>
<t>When the client receives a ChannelBind success response, it updates <t>When the client receives a ChannelBind success response, it updates
its data structures to record that the channel binding is now active. its data structures to record that the channel binding is now active.
It also updates its data structures to record that the corresponding It also updates its data structures to record that the corresponding
permission has been installed or refreshed.</t> permission has been installed or refreshed.</t>
<t>If the client receives a ChannelBind failure response that <t>If the client receives a ChannelBind failure response that
indicates that the channel information is out-of-sync between the indicates that the channel information is out of sync between the
client and the server (e.g., an unexpected 400 "Bad Request" client and the server (e.g., an unexpected 400 "Bad Request"
response), then it is RECOMMENDED that the client immediately delete response), then it is <bcp14>RECOMMENDED</bcp14> that the client immedia tely delete
the allocation and start afresh with a new allocation.</t> the allocation and start afresh with a new allocation.</t>
</section> </section>
<section anchor="sec-channeldata-msg" numbered="true" toc="default">
<section anchor="sec-channeldata-msg" title="The ChannelData Message"> <name>The ChannelData Message</name>
<t>The ChannelData message is used to carry application data between <t>The ChannelData message is used to carry application data between
the client and the server. It has the following format:</t> the client and the server. It has the following format:</t>
<figure>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork><![CDATA[
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Channel Number | Length | | Channel Number | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
/ Application Data / / Application Data /
/ / / /
| | | |
| +-------------------------------+ | +-------------------------------+
| | | |
+-------------------------------+]]></artwork> +-------------------------------+]]></artwork>
</figure> </figure>
<t>The Channel Number field specifies the number of the channel on <t>The Channel Number field specifies the number of the channel on
which the data is traveling, and thus the address of the peer that is which the data is traveling, and thus, the address of the peer that is
sending or is to receive the data.</t> sending or is to receive the data.</t>
<t>The Length field specifies the length in bytes of the application <t>The Length field specifies the length in bytes of the application
data field (i.e., it does not include the size of the ChannelData data field (i.e., it does not include the size of the ChannelData
header). Note that 0 is a valid length.</t> header). Note that 0 is a valid length.</t>
<t>The Application Data field carries the data the client is trying to <t>The Application Data field carries the data the client is trying to
send to the peer, or that the peer is sending to the client.</t> send to the peer, or that the peer is sending to the client.</t>
</section> </section>
<section anchor="sec-sending-channeldata-msg" numbered="true" toc="default
<section anchor="sec-sending-channeldata-msg" ">
title="Sending a ChannelData Message"> <name>Sending a ChannelData Message</name>
<t>Once a client has bound a channel to a peer, then when the client <t>Once a client has bound a channel to a peer, then when the client
has data to send to that peer it may use either a ChannelData message has data to send to that peer, it may use either a ChannelData message
or a Send indication; that is, the client is not obligated to use the or a Send indication; that is, the client is not obligated to use the
channel when it exists and may freely intermix the two message types channel when it exists and may freely intermix the two message types
when sending data to the peer. The server, on the other hand, MUST use when sending data to the peer. The server, on the other hand, <bcp14>MUS T</bcp14> use
the ChannelData message if a channel has been bound to the peer. The the ChannelData message if a channel has been bound to the peer. The
server uses a Data indication to signal the XOR-PEER-ADDRESS and ICMP server uses a Data indication to signal the XOR-PEER-ADDRESS and ICMP
attributes to the client even if a channel has been bound to the attributes to the client even if a channel has been bound to the
peer.</t> peer.</t>
<t>The fields of the ChannelData message are filled in as described in <t>The fields of the ChannelData message are filled in as described in
<xref target="sec-channeldata-msg"></xref>.</t> <xref target="sec-channeldata-msg" format="default"/>.</t>
<t>Over TCP and TLS-over-TCP, the ChannelData message <bcp14>MUST</bcp14
<t>Over TCP and TLS-over-TCP, the ChannelData message MUST be padded > be padded
to a multiple of four bytes in order to ensure the alignment of to a multiple of four bytes in order to ensure the alignment of
subsequent messages. The padding is not reflected in the length field subsequent messages. The padding is not reflected in the length field
of the ChannelData message, so the actual size of a ChannelData of the ChannelData message, so the actual size of a ChannelData
message (including padding) is (4 + Length) rounded up to the nearest message (including padding) is (4 + Length) rounded up to the nearest
multiple of 4 (See section 14 in <xref multiple of 4 (see <xref target="RFC8489" section="14" sectionFormat="of
target="I-D.ietf-tram-stunbis"></xref>). Over UDP, the padding is not "/>). Over UDP, the padding is not
required but MAY be included.</t> required but <bcp14>MAY</bcp14> be included.</t>
<t>The ChannelData message is then sent on the 5-tuple associated with <t>The ChannelData message is then sent on the 5-tuple associated with
the allocation.</t> the allocation.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="Receiving a ChannelData Message"> <name>Receiving a ChannelData Message</name>
<t>The receiver of the ChannelData message uses the first byte to <t>The receiver of the ChannelData message uses the first byte to
distinguish it from other multiplexed protocols, as described in <xref distinguish it from other multiplexed protocols as described in <xref
target="fig-demultiplexing"></xref>. If the message uses a value in target="fig-demultiplexing" format="default"/>. If the message uses a
the reserved range (0x5000 through 0xFFFF), then the message is value in the reserved range (0x5000 through 0xFFFF), then the message
silently discarded.</t> is silently discarded.</t>
<t>If the ChannelData message is received in a UDP datagram, and if <t>If the ChannelData message is received in a UDP datagram, and if
the UDP datagram is too short to contain the claimed length of the the UDP datagram is too short to contain the claimed length of the
ChannelData message (i.e., the UDP header length field value is less ChannelData message (i.e., the UDP header length field value is less
than the ChannelData header length field value + 4 + 8), then the than the ChannelData header length field value + 4 + 8), then the
message is silently discarded.</t> message is silently discarded.</t>
<t>If the ChannelData message is received over TCP or over <t>If the ChannelData message is received over TCP or over
TLS-over-TCP, then the actual length of the ChannelData message is as TLS-over-TCP, then the actual length of the ChannelData message is as
described in <xref target="sec-sending-channeldata-msg"></xref>.</t> described in <xref target="sec-sending-channeldata-msg" format="default"
/>.</t>
<t>If the ChannelData message is received on a channel that is not <t>If the ChannelData message is received on a channel that is not
bound to any peer, then the message is silently discarded.</t> bound to any peer, then the message is silently discarded.</t>
<t>On the client, it is <bcp14>RECOMMENDED</bcp14> that the client disca
<t>On the client, it is RECOMMENDED that the client discard the rd the
ChannelData message if the client believes there is no active ChannelData message if the client believes there is no active
permission towards the peer. On the server, the receipt of a permission towards the peer. On the server, the receipt of a
ChannelData message MUST NOT refresh either the channel binding or the ChannelData message <bcp14>MUST NOT</bcp14> refresh either the channel b inding or the
permission towards the peer.</t> permission towards the peer.</t>
<t>On the server, if no errors are detected, the server relays the <t>On the server, if no errors are detected, the server relays the
application data to the peer by forming a UDP datagram as application data to the peer by forming a UDP datagram as
follows:<list style="symbols"> follows:</t>
<t>the source transport address is the relayed transport address <ul spacing="normal">
<li>the source transport address is the relayed transport address
of the allocation, where the allocation is determined by the of the allocation, where the allocation is determined by the
5-tuple on which the ChannelData message arrived;</t> 5-tuple on which the ChannelData message arrived;</li>
<li>the destination transport address is the transport address to
<t>the destination transport address is the transport address to which the channel is bound;</li>
which the channel is bound;</t> <li>the data following the UDP header is the contents of the data
field of the ChannelData message.</li>
<t>the data following the UDP header is the contents of the data </ul>
field of the ChannelData message.</t> <t>The resulting UDP datagram is then sent to the peer. Note
</list>The resulting UDP datagram is then sent to the peer. Note
that if the Length field in the ChannelData message is 0, then there that if the Length field in the ChannelData message is 0, then there
will be no data in the UDP datagram, but the UDP datagram is still will be no data in the UDP datagram, but the UDP datagram is still
formed and sent (Section 4.1 in <xref target="RFC6263"></xref>).</t> formed and sent (<xref target="RFC6263"
sectionFormat="of" section="4.1"/>).</t>
</section> </section>
<section anchor="sec-channel-relaying" numbered="true" toc="default">
<section anchor="sec-channel-relaying" <name>Relaying Data from the Peer</name>
title="Relaying Data from the Peer">
<t>When the server receives a UDP datagram on the relayed transport <t>When the server receives a UDP datagram on the relayed transport
address associated with an allocation, the server processes it as address associated with an allocation, the server processes it as
described in <xref target="sec-sending-data-indication"></xref>. If described in <xref target="sec-sending-data-indication" format="default" />. If
that section indicates that a ChannelData message should be sent that section indicates that a ChannelData message should be sent
(because there is a channel bound to the peer that sent to the UDP (because there is a channel bound to the peer that sent to the UDP
datagram), then the server forms and sends a ChannelData message as datagram), then the server forms and sends a ChannelData message as
described in <xref target="sec-sending-channeldata-msg"></xref>.</t> described in <xref target="sec-sending-channeldata-msg" format="default"
/>.</t>
<t>When the server receives an ICMP packet, the server processes it as <t>When the server receives an ICMP packet, the server processes it as
described in <xref described in <xref target="sec-sending-senderror-indication" format="def
target="sec-sending-senderror-indication"></xref>.</t> ault"/>.</t>
</section> </section>
</section> </section>
<section title="Packet Translations"> <section numbered="true" toc="default">
<name>Packet Translations</name>
<t>This section addresses IPv4-to-IPv6, IPv6-to-IPv4, and IPv6-to-IPv6 <t>This section addresses IPv4-to-IPv6, IPv6-to-IPv4, and IPv6-to-IPv6
translations. Requirements for translation of the IP addresses and port translations. Requirements for translation of the IP addresses and port
numbers of the packets are described above. The following sections numbers of the packets are described above. The following sections
specify how to translate other header fields.</t> specify how to translate other header fields.</t>
<t>As discussed in <xref target="unpriv" format="default"/>, translations
<t>As discussed in <xref target="unpriv"></xref>, translations in TURN in TURN
are designed so that a TURN server can be implemented as an application are designed so that a TURN server can be implemented as an application
that runs in user space under commonly available operating systems and that runs in user space under commonly available operating systems and
that does not require special privileges. The translations specified in that does not require special privileges. The translations specified in
the following sections follow this principle.</t> the following sections follow this principle.</t>
<t>The descriptions below have two parts: a preferred behavior and an <t>The descriptions below have two parts: a preferred behavior and an
alternate behavior. The server SHOULD implement the preferred behavior, alternate behavior. The server <bcp14>SHOULD</bcp14> implement the preferr
but if that is not possible for a particular field, the server MUST ed behavior,
implement the alternate behavior and MUST NOT do anything else for the but if that is not possible for a particular field, the server <bcp14>MUST
reasons detailed in <xref target="RFC7915"></xref>. The TURN server </bcp14>
solely relies on the DF bit in the IPv4 header and Fragmentation header implement the alternate behavior and <bcp14>MUST NOT</bcp14> do anything e
in IPv6 header to handle fragmentation using the approach described in lse for the
<xref target="RFC7915"></xref> and does not rely on the DONT-FRAGMENT reasons detailed in <xref target="RFC7915" format="default"/>. The TURN se
attribute, ignoring the DONT-FRAGMENT is only applicable for UDP-to-UDP rver
relay, and not for TCP-to-UDP relay.</t> solely relies on the DF bit in the IPv4 header and the Fragment header
in the IPv6 header to handle fragmentation using the approach described in
<section title="IPv4-to-IPv6 Translations"> <xref target="RFC7915" format="default"/> and does not rely on the DONT-FR
<t>Time to Live (TTL) field<list style="empty"> AGMENT
<t>Preferred Behavior: As specified in Section 4 of <xref attribute; ignoring the DONT-FRAGMENT attribute is only applicable for UDP
target="RFC7915"></xref>.</t> -to-UDP
relay and not for TCP-to-UDP relay.</t>
<t>Alternate Behavior: Set the outgoing value to the default for <section numbered="true" toc="default">
outgoing packets.</t> <name>IPv4-to-IPv6 Translations</name>
</list></t>
<t>Time to Live (TTL) field</t>
<ul empty="true" spacing="normal">
<li>Preferred Behavior: As specified in <xref
target="RFC7915" sectionFormat="of" section="4"/>.</li>
<li>Alternate Behavior: Set the outgoing value to the default for
outgoing packets.</li>
</ul>
<t>Traffic Class</t> <t>Traffic Class</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: As specified in <xref
<t>Preferred behavior: As specified in Section 4 of <xref target="RFC7915" sectionFormat="of" section="4"/>.</li>
target="RFC7915"></xref>.</t> <li>Alternate behavior: The TURN server sets the Traffic Class to
the default value for outgoing packets.</li>
<t>Alternate behavior: The TURN server sets the Traffic Class to </ul>
the default value for outgoing packets.</t>
</list></t>
<t>Flow Label</t> <t>Flow Label</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: The TURN server can use the 5-tuple of
<t>Preferred behavior: The TURN server can use the 5-tuple of relayed transport address, peer transport address, and UDP protocol
relayed transport address, peer transport address and UDP protocol number to identify each flow and to generate and set the flow
number to identify each flow, and to generate and set the flow label value in the IPv6 packet as discussed in <xref
label value in the IPv6 packet as discussed in Section 3 of <xref target="RFC6437" sectionFormat="of" section="3" format="default"/>. I
target="RFC6437"></xref>. If the TURN server is incapable of f the TURN server is incapable of
generating the flow label value from the IPv6 packet's 5-tuple, it generating the flow label value from the IPv6 packet's 5-tuple, it
sets the Flow label to 0.</t> sets the Flow label to zero.</li>
<li>Alternate behavior: The alternate behavior is the same as the
<t>Alternate behavior: The alternate behavior is the same as the
preferred behavior for a TURN server that does not support flow preferred behavior for a TURN server that does not support flow
labels.</t> labels.</li>
</list></t> </ul>
<t>Hop Limit</t> <t>Hop Limit</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: As specified in <xref
<t>Preferred behavior: As specified in Section 4 of <xref target="RFC7915" sectionFormat="of" section="4" />.</li>
target="RFC7915"></xref>.</t> <li>Alternate behavior: The TURN server sets the Hop Limit to the
default value for outgoing packets.</li>
<t>Alternate behavior: The TURN server sets the Hop Limit to the </ul>
default value for outgoing packets.</t>
</list></t>
<t>Fragmentation</t> <t>Fragmentation</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: As specified in <xref
<t>Preferred behavior: As specified in Section 4 of <xref target="RFC7915" sectionFormat="of" section="4"/>.</li>
target="RFC7915"></xref>.</t> <li>Alternate behavior: The TURN server assembles incoming
<t>Alternate behavior: The TURN server assembles incoming
fragments. The TURN server follows its default behavior to send fragments. The TURN server follows its default behavior to send
outgoing packets.</t> outgoing packets.</li>
<li>For both preferred and alternate behavior, the DONT-FRAGMENT
<t>For both preferred and alternate behavior, the DONT-FRAGMENT attribute <bcp14>MUST</bcp14> be ignored by the server.</li>
attribute MUST be ignored by the server.</t> </ul>
</list></t>
<t>Extension Headers</t> <t>Extension Headers</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: The outgoing packet uses the system
<t>Preferred behavior: The outgoing packet uses the system
defaults for IPv6 extension headers, with the exception of the defaults for IPv6 extension headers, with the exception of the
Fragmentation header as described above.</t> Fragment header as described above.</li>
<li>Alternate behavior: Same as preferred.</li>
<t>Alternate behavior: Same as preferred.</t> </ul>
</list></t>
</section> </section>
<section numbered="true" toc="default">
<section title="IPv6-to-IPv6 Translations"> <name>IPv6-to-IPv6 Translations</name>
<t>Flow Label</t> <t>Flow Label</t>
<t>The TURN server should consider that it is handling two different <t>NOTE: The TURN server should consider that it is handling two different
IPv6 flows. Therefore, the Flow label <xref target="RFC6437"></xref> IPv6 flows. Therefore, the Flow label <xref target="RFC6437" format="def
SHOULD NOT be copied as part of the translation.</t> ault"/>
<bcp14>SHOULD NOT</bcp14> be copied as part of the translation.
<t><list> </t>
<t>Preferred behavior: The TURN server can use the 5-tuple of <ul empty="true" spacing="normal">
relayed transport address, peer transport address and UDP protocol
number to identify each flow, and to generate and set the flow
label value in the IPv6 packet as discussed in Section 3 of <xref
target="RFC6437"></xref>. If the TURN server is incapable of
generating the flow label value from the IPv6 packet's 5-tuple, it
sets the Flow label to 0.</t>
<t>Alternate behavior: The alternate behavior is the same as the <li>Preferred behavior: The TURN server can use the 5-tuple of relayed
transport address, peer transport address, and UDP protocol number to
identify each flow and to generate and set the flow label value in the IPv6
packet as discussed in <xref target="RFC6437" sectionFormat="of"
section="3"/>. If the TURN server is incapable of generating the flow
label value from the IPv6 packet's 5-tuple, it sets the Flow label to
zero.</li>
<li>Alternate behavior: The alternate behavior is the same as the
preferred behavior for a TURN server that does not support flow preferred behavior for a TURN server that does not support flow
labels.</t> labels.</li>
</list></t> </ul>
<t>Hop Limit</t> <t>Hop Limit</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: The TURN server acts as a regular router
<t>Preferred behavior: The TURN server acts as a regular router
with respect to decrementing the Hop Limit and generating an with respect to decrementing the Hop Limit and generating an
ICMPv6 error if it reaches zero.</t> ICMPv6 error if it reaches zero.</li>
<li>Alternate behavior: The TURN server sets the Hop Limit to the
<t>Alternate behavior: The TURN server sets the Hop Limit to the default value for outgoing packets.</li>
default value for outgoing packets.</t> </ul>
</list></t>
<t>Fragmentation</t> <t>Fragmentation</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: If the incoming packet did not include a
<t>Preferred behavior: If the incoming packet did not include a
Fragment header and the outgoing packet size does not exceed the Fragment header and the outgoing packet size does not exceed the
outgoing link's MTU, the TURN server sends the outgoing packet outgoing link's MTU, the TURN server sends the outgoing packet
without a Fragment header.</t> without a Fragment header.</li>
<li>If the incoming packet did not include a Fragment header and
<t>If the incoming packet did not include a Fragment header and
the outgoing packet size exceeds the outgoing link's MTU, the TURN the outgoing packet size exceeds the outgoing link's MTU, the TURN
server drops the outgoing packet and send an ICMP message of type server drops the outgoing packet and sends an ICMP message of type
2 code 0 ("Packet too big") to the sender of the incoming packet. 2 code 0 ("Packet too big") to the sender of the incoming packet.
If the ICMPv6 packet ("Packet too big") is being sent to the peer, If the ICMPv6 packet ("Packet too big") is being sent to the peer,
the TURN server SHOULD reduce the MTU reported in the ICMP message the TURN server <bcp14>SHOULD</bcp14> reduce the MTU reported in the ICMP message
by 48 bytes to allow room for the overhead of a Data by 48 bytes to allow room for the overhead of a Data
indication.</t> indication.</li>
<li>If the incoming packet included a Fragment header and the
<t>If the incoming packet included a Fragment header and the
outgoing packet size (with a Fragment header included) does not outgoing packet size (with a Fragment header included) does not
exceed the outgoing link's MTU, the TURN server sends the outgoing exceed the outgoing link's MTU, the TURN server sends the outgoing
packet with a Fragment header. The TURN server sets the fields of packet with a Fragment header. The TURN server sets the fields of
the Fragment header as appropriate for a packet originating from the Fragment header as appropriate for a packet originating from
the server.</t> the server.</li>
<li>If the incoming packet included a Fragment header and the
<t>If the incoming packet included a Fragment header and the
outgoing packet size exceeds the outgoing link's MTU, the TURN outgoing packet size exceeds the outgoing link's MTU, the TURN
server MUST fragment the outgoing packet into fragments of no more server <bcp14>MUST</bcp14> fragment the outgoing packet into fragmen ts of no more
than 1280 bytes. The TURN server sets the fields of the Fragment than 1280 bytes. The TURN server sets the fields of the Fragment
header as appropriate for a packet originating from the header as appropriate for a packet originating from the
server.</t> server.</li>
<li>Alternate behavior: The TURN server assembles incoming
<t>Alternate behavior: The TURN server assembles incoming
fragments. The TURN server follows its default behavior to send fragments. The TURN server follows its default behavior to send
outgoing packets.</t> outgoing packets.</li>
<li>For both preferred and alternate behavior, the DONT-FRAGMENT
<t>For both preferred and alternate behavior, the DONT-FRAGMENT attribute <bcp14>MUST</bcp14> be ignored by the server.</li>
attribute MUST be ignored by the server.</t> </ul>
</list></t>
<t>Extension Headers</t> <t>Extension Headers</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: The outgoing packet uses the system
<t>Preferred behavior: The outgoing packet uses the system
defaults for IPv6 extension headers, with the exception of the defaults for IPv6 extension headers, with the exception of the
Fragmentation header as described above.</t> Fragment header as described above.</li>
<li>Alternate behavior: Same as preferred.</li>
<t>Alternate behavior: Same as preferred.</t> </ul>
</list></t>
</section> </section>
<section numbered="true" toc="default">
<section title="IPv6-to-IPv4 Translations"> <name>IPv6-to-IPv4 Translations</name>
<t>Type of Service and Precedence</t> <t>Type of Service and Precedence</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: As specified in <xref
<t>Preferred behavior: As specified in Section 5 of <xref target="RFC7915" sectionFormat="of" section="5"/>.</li>
target="RFC7915"></xref>.</t> <li>Alternate behavior: The TURN server sets the Type of Service
and Precedence to the default value for outgoing packets.</li>
<t>Alternate behavior: The TURN server sets the Type of Service </ul>
and Precedence to the default value for outgoing packets.</t>
</list></t>
<t>Time to Live</t> <t>Time to Live</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: As specified in <xref
<t>Preferred behavior: As specified in Section 5 of <xref target="RFC7915" sectionFormat="of" section="5"/>.</li>
target="RFC7915"></xref>.</t> <li>Alternate behavior: The TURN server sets the Time to Live to
the default value for outgoing packets.</li>
<t>Alternate behavior: The TURN server sets the Time to Live to </ul>
the default value for outgoing packets.</t>
</list></t>
<t>Fragmentation</t> <t>Fragmentation</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: As specified in <xref
<t>Preferred behavior: As specified in Section 5 of <xref target="RFC7915" sectionFormat="of" section="5"/>. Additionally, when t
target="RFC7915"></xref>. Additionally, when the outgoing packet's he outgoing packet's
size exceeds the outgoing link's MTU, the TURN server needs to size exceeds the outgoing link's MTU, the TURN server needs to
generate an ICMP error (ICMPv6 Packet Too Big) reporting the MTU generate an ICMP error (ICMPv6 "Packet too big") reporting the MTU
size. If the ICMPv4 packet (Destination Unreachable (Type 3) with size. If the ICMPv4 packet (Destination Unreachable (Type 3) with
Code 4) is being sent to the peer, the TURN server SHOULD reduce Code 4) is being sent to the peer, the TURN server <bcp14>SHOULD</bc p14> reduce
the MTU reported in the ICMP message by 48 bytes to allow room for the MTU reported in the ICMP message by 48 bytes to allow room for
the overhead of a Data indication.</t> the overhead of a Data indication.</li>
<li>Alternate behavior: The TURN server assembles incoming
<t>Alternate behavior: The TURN server assembles incoming
fragments. The TURN server follows its default behavior to send fragments. The TURN server follows its default behavior to send
outgoing packets.</t> outgoing packets.</li>
<li>For both preferred and alternate behavior, the DONT-FRAGMENT
<t>For both preferred and alternate behavior, the DONT-FRAGMENT attribute <bcp14>MUST</bcp14> be ignored by the server.</li>
attribute MUST be ignored by the server.</t> </ul>
</list></t>
</section> </section>
</section> </section>
<section anchor="sec-ip-header-fields" numbered="true" toc="default">
<section anchor="sec-ip-header-fields" title="UDP-to-UDP relay"> <name>UDP-to-UDP Relay</name>
<t>This section describes how the server sets various fields in the IP <t>This section describes how the server sets various fields in the IP
header for UDP-to-UDP relay from the client to the peer or vice versa. header for UDP-to-UDP relay from the client to the peer or vice versa.
The descriptions in this section apply: (a) when the server sends a UDP The descriptions in this section apply (a) when the server sends a UDP
datagram to the peer, or (b) when the server sends a Data indication or datagram to the peer or (b) when the server sends a Data indication or
ChannelData message to the client over UDP transport. The descriptions ChannelData message to the client over UDP transport. The descriptions
in this section do not apply to TURN messages sent over TCP or TLS in this section do not apply to TURN messages sent over TCP or TLS
transport from the server to the client.</t> transport from the server to the client.</t>
<t>The descriptions below have two parts: a preferred behavior and an <t>The descriptions below have two parts: a preferred behavior and an
alternate behavior. The server SHOULD implement the preferred behavior, alternate behavior. The server <bcp14>SHOULD</bcp14> implement the preferr
but if that is not possible for a particular field, then it SHOULD ed behavior,
but if that is not possible for a particular field, then it <bcp14>SHOULD<
/bcp14>
implement the alternative behavior.</t> implement the alternative behavior.</t>
<t>Differentiated Services Code Point (DSCP) field <xref target="RFC2474"
<t>Differentiated Services Code Point (DSCP) field <xref format="default"/></t>
target="RFC2474"></xref><list style="empty"> <ul empty="true" spacing="normal">
<t>Preferred Behavior: Set the outgoing value to the incoming value, <li>Preferred Behavior: Set the outgoing value to the incoming value
unless the server includes a differentiated services classifier and unless the server includes a differentiated services classifier and
marker <xref target="RFC2474"></xref>.</t> marker <xref target="RFC2474" format="default"/>.</li>
<li>Alternate Behavior: Set the outgoing value to a fixed value,
<t>Alternate Behavior: Set the outgoing value to a fixed value, which by default is Best Effort unless configured otherwise.</li>
which by default is Best Effort unless configured otherwise.</t> <li>In both cases, if the server is immediately adjacent to a
differentiated services classifier and marker, then DSCP <bcp14>MAY</b
<t>In both cases, if the server is immediately adjacent to a cp14> be set
differentiated services classifier and marker, then DSCP MAY be set to any arbitrary value in the direction towards the classifier.</li>
to any arbitrary value in the direction towards the classifier.</t> </ul>
</list></t>
<t><vspace blankLines="1" /></t>
<t>Explicit Congestion Notification (ECN) field <xref <t>Explicit Congestion Notification (ECN) field <xref target="RFC3168" for
target="RFC3168"></xref><list style="empty"> mat="default"/></t>
<t>Preferred Behavior: Set the outgoing value to the incoming value. <ul empty="true" spacing="normal">
<li>Preferred Behavior: Set the outgoing value to the incoming value.
The server may perform Active Queue Management, in which case it The server may perform Active Queue Management, in which case it
SHOULD behave as a ECN aware router <xref target="RFC3168"></xref> <bcp14>SHOULD</bcp14> behave as an ECN-aware router <xref target="RFC3 168" format="default"/>
and can mark traffic with Congestion Experienced (CE) instead of and can mark traffic with Congestion Experienced (CE) instead of
dropping the packet. The use of ECT(1) is subject to experimental dropping the packet. The use of ECT(1) is subject to experimental
usage <xref target="RFC8311"></xref>.</t> usage <xref target="RFC8311" format="default"/>.</li>
<li>Alternate Behavior: Set the outgoing value to Not-ECT
<t>Alternate Behavior: Set the outgoing value to Not-ECT (=0b00).</li>
(=0b00).</t> </ul>
</list></t>
<t><vspace blankLines="1" /></t>
<t>IPv4 Fragmentation fields (applicable only for IPv4-to-IPv4 <t>IPv4 Fragmentation fields (applicable only for IPv4-to-IPv4
relay)<list> relay)</t>
<t>Preferred Behavior: When the server sends a packet to a peer in <ul empty="true" spacing="normal">
<li>Preferred Behavior: When the server sends a packet to a peer in
response to a Send indication containing the DONT-FRAGMENT response to a Send indication containing the DONT-FRAGMENT
attribute, then set the outgoing UDP packet to not fragment. In all attribute, then set the outgoing UDP packet to not fragment. In all
other cases when sending an outgoing packet containing application other cases, when sending an outgoing packet containing application
data (e.g., Data indication, ChannelData message, or DONT-FRAGMENT data (e.g., Data indication, a ChannelData message, or the DONT-FRAGME
NT
attribute not included in the Send indication), copy the DF bit from attribute not included in the Send indication), copy the DF bit from
the DF bit of the incoming packet that contained the application the DF bit of the incoming packet that contained the application
data.</t> data.</li>
<li>Set the other fragmentation fields (Identification, More
<t>Set the other fragmentation fields (Identification, More
Fragments, Fragment Offset) as appropriate for a packet originating Fragments, Fragment Offset) as appropriate for a packet originating
from the server.</t> from the server.</li>
<li>Alternate Behavior: As described in the Preferred Behavior,
<t>Alternate Behavior: As described in the Preferred Behavior, except always assume the incoming DF bit is 0.</li>
except always assume the incoming DF bit is 0.</t> <li>In both the Preferred and Alternate Behaviors, the resulting
<t>In both the Preferred and Alternate Behaviors, the resulting
packet may be too large for the outgoing link. If this is the case, packet may be too large for the outgoing link. If this is the case,
then the normal fragmentation rules apply <xref then the normal fragmentation rules apply <xref target="RFC1122" forma
target="RFC1122"></xref>.</t> t="default"/>.</li>
</list></t> </ul>
<t><vspace blankLines="1" /></t>
<t>IPv4 Options<list>
<t>Preferred Behavior: The outgoing packet uses the system defaults
for IPv4 options.</t>
<t>Alternate Behavior: Same as preferred.</t> <t>IPv4 Options</t>
</list></t> <ul empty="true" spacing="normal">
<li>Preferred Behavior: The outgoing packet uses the system defaults
for IPv4 options.</li>
<li>Alternate Behavior: Same as preferred.</li>
</ul>
</section> </section>
<section anchor="sec-ip-header-fields-tcp-udp" title="TCP-to-UDP relay"> <section anchor="sec-ip-header-fields-tcp-udp" numbered="true" toc="default"
>
<name>TCP-to-UDP Relay</name>
<t>This section describes how the server sets various fields in the IP <t>This section describes how the server sets various fields in the IP
header for TCP-to-UDP relay from the client to the peer. The header for TCP-to-UDP relay from the client to the peer. The
descriptions in this section apply when the server sends a UDP datagram descriptions in this section apply when the server sends a UDP datagram
to the peer. Note that the server does not perform per-packet to the peer. Note that the server does not perform per-packet
translation for TCP-to-UDP relaying.</t> translation for TCP-to-UDP relaying.</t>
<t>Multipath TCP <xref target="I-D.ietf-mptcp-rfc6824bis"
<t>Multipath TCP <xref target="I-D.ietf-mptcp-rfc6824bis"></xref> is not format="default"/> is not supported by this version of TURN because TCP
supported by this version of TURN because TCP multi-path is not used by multipath is not used by either SIP or WebRTC protocols <xref
either SIP or WebRTC protocols <xref target="RFC7478"></xref> for media target="RFC7478" format="default"/> for media and non-media data. TCP
and non-media data. TCP connection between the TURN client and server connection between the TURN client and server can use the TCP
can use TCP-AO <xref target="RFC5925"></xref> but UDP does not provide a Authentication Option (TCP-AO) <xref target="RFC5925"
similar type of authentication though it might be added in the future format="default"/>, but UDP does not provide a similar type of
<xref target="I-D.ietf-tsvwg-udp-options"></xref>. Even if both TCP-AO authentication, though it might be added in the future <xref
and UDP authentication would be used between TURN client and server, it target="I-D.ietf-tsvwg-udp-options" format="default"/>. Even if both
would not change the end-to-end security properties of the application TCP-AO and UDP authentication would be used between TURN client and
payload being relayed. Therefore applications using TURN will need to server, it would not change the end-to-end security properties of the
secure their application data end-to-end appropriately, e.g., SRTP for application payload being relayed. Therefore, applications using TURN
RTP applications. Note that TCP-AO option obsoletes TCP MD5 option.</t> will need to secure their application data end to end appropriately,
e.g., Secure Real-time Transport Protocol (SRTP) for RTP
applications. Note that the TCP-AO option obsoletes the TCP MD5
option.</t>
<t>Unlike UDP, TCP without the TCP Fast Open extension <xref <t>Unlike UDP, TCP without the TCP Fast Open extension <xref
target="RFC7413"></xref> does not support 0-RTT session resumption. The target="RFC7413" format="default"/> does not support 0-RTT session
TCP user timeout <xref target="RFC5482"></xref> equivalent for resumption. The TCP user timeout <xref target="RFC5482"
application data relayed by the TURN is the use of RTP control protocol format="default"/> equivalent for application data relayed by the TURN
(RTCP). As a reminder, RTCP is a fundamental and integral part of is the use of RTP control protocol (RTCP). As a reminder, RTCP is a
RTP.</t> fundamental and integral part of RTP.</t>
<t>The descriptions below have two parts: a preferred behavior and an <t>The descriptions below have two parts: a preferred behavior and an
alternate behavior. The server SHOULD implement the preferred behavior, alternate behavior. The server <bcp14>SHOULD</bcp14> implement the preferr
but if that is not possible for a particular field, then it SHOULD ed behavior,
but if that is not possible for a particular field, then it <bcp14>SHOULD<
/bcp14>
implement the alternative behavior.</t> implement the alternative behavior.</t>
<t>For the UDP datagram sent to the peer based on a Send Indication or
<t>For the UDP datagram sent to the peer based on Send Indication or
ChannelData message arriving at the TURN server over a TCP Transport, ChannelData message arriving at the TURN server over a TCP Transport,
the server sets various fields in the IP header as follows:</t> the server sets various fields in the IP header as follows:</t>
<t>Differentiated Services Code Point (DSCP) field <xref <t>Differentiated Services Code Point (DSCP) field <xref target="RFC2474"
target="RFC2474"></xref><list style="empty"> format="default"/></t>
<t>Preferred Behavior: The TCP connection can only use a single DSCP <ul empty="true" spacing="normal">
code point so inter flow differentiation is not possible, see <li>Preferred Behavior: The TCP connection can only use a single DSCP,
Section 5.1 of <xref target="RFC7657"></xref>. The server sets the so inter-flow differentiation is not possible; see
outgoing value to the DSCP code point used by the TCP connection, <xref target="RFC7657" sectionFormat="of" section="5.1"/>. The server
sets the
outgoing value to the DSCP used by the TCP connection,
unless the server includes a differentiated services classifier and unless the server includes a differentiated services classifier and
marker <xref target="RFC2474"></xref>.</t> marker <xref target="RFC2474" format="default"/>.</li>
<li>Alternate Behavior: Set the outgoing value to a fixed value,
<t>Alternate Behavior: Set the outgoing value to a fixed value, which by default is Best Effort unless configured otherwise.</li>
which by default is Best Effort unless configured otherwise.</t> <li>In both cases, if the server is immediately adjacent to a
differentiated services classifier and marker, then DSCP <bcp14>MAY</b
<t>In both cases, if the server is immediately adjacent to a cp14> be set
differentiated services classifier and marker, then DSCP MAY be set to any arbitrary value in the direction towards the classifier.</li>
to any arbitrary value in the direction towards the classifier.</t> </ul>
</list></t>
<t><vspace blankLines="1" /></t>
<t>Explicit Congestion Notification (ECN) field <xref <t>Explicit Congestion Notification (ECN) field <xref target="RFC3168" for
target="RFC3168"></xref><list style="empty"> mat="default"/></t>
<t>Preferred Behavior: No mechanism is defined to indicate what ECN <ul empty="true" spacing="normal">
<li>Preferred Behavior: No mechanism is defined to indicate what ECN
value should be used for the outgoing UDP datagrams of an value should be used for the outgoing UDP datagrams of an
allocation, therefore set the outgoing value to Not-ECT (=0b00).</t> allocation; therefore, set the outgoing value to Not-ECT (=0b00).</li>
<li>Alternate Behavior: Same as preferred.</li>
<t>Alternate Behavior: Same as preferred.</t> </ul>
</list></t>
<t><vspace blankLines="1" /></t>
<t>IPv4 Fragmentation fields (applicable only for IPv4-to-IPv4 <t>IPv4 Fragmentation fields (applicable only for IPv4-to-IPv4
relay)<list> relay)</t>
<t>Preferred Behavior: When the server sends a packet to a peer in <ul empty="true" spacing="normal">
<li>Preferred Behavior: When the server sends a packet to a peer in
response to a Send indication containing the DONT-FRAGMENT response to a Send indication containing the DONT-FRAGMENT
attribute, then set the outgoing UDP packet to not fragment. In all attribute, set the outgoing UDP packet to not fragment. In all
other cases when sending an outgoing UDP packet containing other cases, when sending an outgoing UDP packet containing
application data (e.g., Data indication, ChannelData message, or application data (e.g., Data indication, ChannelData message, or
DONT-FRAGMENT attribute not included in the Send indication), set DONT-FRAGMENT attribute not included in the Send indication), set
the DF bit in the outgoing IP header to 0.</t> the DF bit in the outgoing IP header to 0.</li>
<li>Alternate Behavior: Same as preferred.</li>
<t>Alternate Behavior: Same as preferred.</t> </ul>
</list></t> <t>IPv6 Fragmentation fields</t>
<ul empty="true" spacing="normal">
<t>IPv6 Fragmentation fields<list> <li>Preferred Behavior: If the TCP traffic arrives over IPv6, the
<t>Preferred Behavior: If the TCP traffic arrives over IPv6, the server relies on the presence of the DONT-FRAGMENT attribute in the se
server relies on the presence of DONT-FRAGMENT attribute in the send nd
indication to set the outgoing UDP packet to not fragment.</t> indication to set the outgoing UDP packet to not fragment.</li>
<li>Alternate Behavior: Same as preferred.</li>
<t>Alternate Behavior: Same as preferred.</t> </ul>
</list></t>
<t><vspace blankLines="1" /></t>
<t>IPv4 Options<list>
<t>Preferred Behavior: The outgoing packet uses the system defaults
for IPv4 options.</t>
<t>Alternate Behavior: Same as preferred.</t> <t>IPv4 Options</t>
</list></t> <ul empty="true" spacing="normal">
<li>Preferred Behavior: The outgoing packet uses the system defaults
for IPv4 options.</li>
<li>Alternate Behavior: Same as preferred.</li>
</ul>
</section> </section>
<section anchor="UDP-to-TCP" numbered="true" toc="default">
<section anchor="UDP-to-TCP" title="UDP-to-TCP relay"> <name>UDP-to-TCP Relay</name>
<t>This section describes how the server sets various fields in the IP <t>This section describes how the server sets various fields in the IP
header for UDP-to-TCP relay from the peer to the client. The header for UDP-to-TCP relay from the peer to the client. The
descriptions in this section apply when the server sends a Data descriptions in this section apply when the server sends a Data
indication or ChannelData message to the client over TCP or TLS indication or ChannelData message to the client over TCP or TLS
transport. Note that the server does not perform per-packet translation transport. Note that the server does not perform per-packet translation
for UDP-to-TCP relaying.</t> for UDP-to-TCP relaying.</t>
<t>The descriptions below have two parts: a preferred behavior and an <t>The descriptions below have two parts: a preferred behavior and an
alternate behavior. The server SHOULD implement the preferred behavior, alternate behavior. The server <bcp14>SHOULD</bcp14> implement the preferr
but if that is not possible for a particular field, then it SHOULD ed behavior,
but if that is not possible for a particular field, then it <bcp14>SHOULD<
/bcp14>
implement the alternative behavior.</t> implement the alternative behavior.</t>
<t>The TURN server sets IP header fields in the TCP packets on a <t>The TURN server sets IP header fields in the TCP packets on a
per-connection basis for the TCP connection as follows:</t> per-connection basis for the TCP connection as follows:</t>
<t>Differentiated Services Code Point (DSCP) field <xref target="RFC2474"
<t>Differentiated Services Code Point (DSCP) field <xref format="default"/></t>
target="RFC2474"></xref><list style="empty"> <ul empty="true" spacing="normal">
<t>Preferred Behavior: Ignore the incoming DSCP value. When TCP is <li>Preferred Behavior: Ignore the incoming DSCP value. When TCP is
used between the client and the server, a single DSCP should be used used between the client and the server, a single DSCP should be used
for all traffic on that TCP connection. Note, TURN/ICE occurs before for all traffic on that TCP connection. Note, TURN/ICE occurs before
application data is exchanged.</t> application data is exchanged.</li>
<li>Alternate Behavior: Same as preferred.</li>
<t>Alternate Behavior: Same as preferred.</t> </ul>
</list></t>
<t><vspace blankLines="1" /></t>
<t>Explicit Congestion Notification (ECN) field <xref
target="RFC3168"></xref><list style="empty">
<t>Preferred Behavior: Ignore, ECN signals are dropped in the TURN
server for the incoming UDP datagrams from the peer.</t>
<t>Alternate Behavior: Same as preferred.</t>
</list></t>
<t><vspace blankLines="1" /></t> <t>Explicit Congestion Notification (ECN) field <xref target="RFC3168" for
mat="default"/></t>
<ul empty="true" spacing="normal">
<li>Preferred Behavior: Ignore; ECN signals are dropped in the TURN
server for the incoming UDP datagrams from the peer.</li>
<li>Alternate Behavior: Same as preferred.</li>
</ul>
<t>Fragmentation <list> <t>Fragmentation </t>
<t>Preferred Behavior: Any fragmented packets are reassembled in the <ul empty="true" spacing="normal">
<li>Preferred Behavior: Any fragmented packets are reassembled in the
server and then forwarded to the client over the TCP connection. server and then forwarded to the client over the TCP connection.
ICMP messages resulting from the UDP datagrams sent to the peer are ICMP messages resulting from the UDP datagrams sent to the peer are
processed by the server as described in <xref processed by the server as described in <xref target="sec-sending-send
target="sec-sending-senderror-indication"></xref> and forwarded to error-indication" format="default"/> and forwarded to
the client using TURN's mechanism for relevant ICMP types and the client using TURN's mechanism for relevant ICMP types and
codes.</t> codes.</li>
<li>Alternate Behavior: Same as preferred.</li>
<t>Alternate Behavior: Same as preferred.</t> </ul>
</list></t>
<t><vspace blankLines="1" /></t>
<t>Extension Headers</t> <t>Extension Headers</t>
<ul empty="true" spacing="normal">
<t><list> <li>Preferred behavior: The outgoing packet uses the system defaults
<t>Preferred behavior: The outgoing packet uses the system defaults for IPv6 extension headers.</li>
for IPv6 extension headers.</t> <li>Alternate behavior: Same as preferred.</li>
</ul>
<t>Alternate behavior: Same as preferred.</t> <t>IPv4 Options</t>
</list></t> <ul empty="true" spacing="normal">
<li>Preferred Behavior: The outgoing packet uses the system defaults
<t>IPv4 Options<list> for IPv4 options.</li>
<t>Preferred Behavior: The outgoing packet uses the system defaults <li>Alternate Behavior: Same as preferred.</li>
for IPv4 options.</t> </ul>
<t>Alternate Behavior: Same as preferred.</t>
</list></t>
</section> </section>
<section anchor="sec-stun-methods" numbered="true" toc="default">
<section anchor="sec-stun-methods" title="STUN Methods"> <name>STUN Methods</name>
<t>This section lists the codepoints for the STUN methods defined in <t>This section lists the code points for the STUN methods defined in
this specification. See elsewhere in this document for the semantics of this specification. See elsewhere in this document for the semantics of
these methods.</t> these methods.</t>
<figure> <table anchor="stun-methods">
<preamble></preamble> <tbody>
<tr>
<artwork><![CDATA[ 0x003 : Allocate (only request/response s <td>0x003</td>
emantics defined) <td>Allocate</td>
0x004 : Refresh (only request/response semantics defined) <td>(only request/response semantics defined)</td>
0x006 : Send (only indication semantics defined) </tr>
0x007 : Data (only indication semantics defined) <tr>
0x008 : CreatePermission (only request/response semantics defined <td>0x004</td>
0x009 : ChannelBind (only request/response semantics defined) <td>Refresh</td>
<td>(only request/response semantics defined)</td>
</tr>
<tr>
<td>0x006</td>
<td>Send</td>
<td>(only indication semantics defined)</td>
</tr>
<tr>
<td>0x007</td>
<td>Data</td>
<td>(only indication semantics defined)</td>
</tr>
<tr>
<td>0x008</td>
<td>CreatePermission</td>
<td>(only request/response semantics defined)</td>
</tr>
<tr>
<td>0x009</td>
<td>ChannelBind</td>
<td>(only request/response semantics defined)</td>
</tr>
</tbody>
</table>
]]></artwork>
</figure>
</section> </section>
<section anchor="sec-stun-attributes" numbered="true" toc="default">
<name>STUN Attributes</name>
<t>This STUN extension defines the following
attributes:</t>
<section anchor="sec-stun-attributes" title="STUN Attributes"> <table anchor="stun-attributes">
<figure>
<preamble>This STUN extension defines the following
attributes:</preamble>
<artwork><![CDATA[
0x000C: CHANNEL-NUMBER
0x000D: LIFETIME
0x0010: Reserved (was BANDWIDTH)
0x0012: XOR-PEER-ADDRESS
0x0013: DATA
0x0016: XOR-RELAYED-ADDRESS
0x0017: REQUESTED-ADDRESS-FAMILY
0x0018: EVEN-PORT
0x0019: REQUESTED-TRANSPORT
0x001A: DONT-FRAGMENT
0x0021: Reserved (was TIMER-VAL)
0x0022: RESERVATION-TOKEN
TBD-CA: ADDITIONAL-ADDRESS-FAMILY
TBD-CA: ADDRESS-ERROR-CODE
TBD-CA: ICMP
]]></artwork>
<postamble></postamble> <tbody>
</figure> <tr>
<td>0x000C</td>
<td>CHANNEL-NUMBER</td>
</tr>
<tr>
<td>0x000D</td>
<td>LIFETIME</td>
</tr>
<tr>
<td>0x0010</td>
<td>Reserved (was BANDWIDTH)</td>
</tr>
<tr>
<td>0x0012</td>
<td>XOR-PEER-ADDRESS</td>
</tr>
<tr>
<td>0x0013</td>
<td>DATA</td>
</tr>
<tr>
<td>0x0016</td>
<td>XOR-RELAYED-ADDRESS</td>
</tr>
<tr>
<td>0x0017</td>
<td>REQUESTED-ADDRESS-FAMILY</td>
</tr>
<tr>
<td>0x0018</td>
<td>EVEN-PORT</td>
</tr>
<tr>
<td>0x0019</td>
<td>REQUESTED-TRANSPORT</td>
</tr>
<tr>
<td>0x001A</td>
<td>DONT-FRAGMENT</td>
</tr>
<tr>
<td>0x0021</td>
<td>Reserved (was TIMER-VAL)</td>
</tr>
<tr>
<td>0x0022</td>
<td>RESERVATION-TOKEN</td>
</tr>
<tr>
<td>0x8000</td>
<td>ADDITIONAL-ADDRESS-FAMILY</td>
</tr>
<tr>
<td>0x8001</td>
<td>ADDRESS-ERROR-CODE</td>
</tr>
<tr>
<td>0x8004</td>
<td>ICMP</td>
</tr>
</tbody>
</table>
<t>Some of these attributes have lengths that are not multiples of 4. By <t>Some of these attributes have lengths that are not multiples of 4. By
the rules of STUN, any attribute whose length is not a multiple of 4 the rules of STUN, any attribute whose length is not a multiple of 4
bytes MUST be immediately followed by 1 to 3 padding bytes to ensure the bytes <bcp14>MUST</bcp14> be immediately followed by 1 to 3 padding bytes
next attribute (if any) would start on a 4-byte boundary (see <xref to ensure the
target="I-D.ietf-tram-stunbis"></xref>).</t> next attribute (if any) would start on a 4-byte boundary (see <xref target
="RFC8489" format="default"/>).</t>
<section anchor="channelnums" title="CHANNEL-NUMBER"> <section anchor="channelnums" numbered="true" toc="default">
<name>CHANNEL-NUMBER</name>
<t>The CHANNEL-NUMBER attribute contains the number of the channel. <t>The CHANNEL-NUMBER attribute contains the number of the channel.
The value portion of this attribute is 4 bytes long and consists of a The value portion of this attribute is 4 bytes long and consists of a
16-bit unsigned integer, followed by a two-octet RFFU (Reserved For 16-bit unsigned integer followed by a two-octet RFFU (Reserved For
Future Use) field, which MUST be set to 0 on transmission and MUST be Future Use) field, which <bcp14>MUST</bcp14> be set to 0 on transmission
and <bcp14>MUST</bcp14> be
ignored on reception.</t> ignored on reception.</t>
<figure>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork><![CDATA[ 0 1 2 3
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Channel Number | RFFU = 0 |
| Channel Number | RFFU = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> ]]></artwork>
</figure> -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</figure>
</section> </section>
<section numbered="true" toc="default">
<section title="LIFETIME"> <name>LIFETIME</name>
<t>The LIFETIME attribute represents the duration for which the server <t>The LIFETIME attribute represents the duration for which the server
will maintain an allocation in the absence of a refresh. The TURN will maintain an allocation in the absence of a refresh. The TURN
client can include the LIFETIME attribute with the desired lifetime in client can include the LIFETIME attribute with the desired lifetime in
Allocate and Refresh requests. The value portion of this attribute is Allocate and Refresh requests. The value portion of this attribute is
4-bytes long and consists of a 32-bit unsigned integral value 4 bytes long and consists of a 32-bit unsigned integral value
representing the number of seconds remaining until expiration.</t> representing the number of seconds remaining until expiration.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="XOR-PEER-ADDRESS"> <name>XOR-PEER-ADDRESS</name>
<t>The XOR-PEER-ADDRESS specifies the address and port of the peer as <t>The XOR-PEER-ADDRESS attribute specifies the address and port of the
peer as
seen from the TURN server. (For example, the peer's server-reflexive seen from the TURN server. (For example, the peer's server-reflexive
transport address if the peer is behind a NAT.) It is encoded in the transport address if the peer is behind a NAT.) It is encoded in the
same way as XOR-MAPPED-ADDRESS <xref same way as the XOR-MAPPED-ADDRESS attribute <xref target="RFC8489" form
target="I-D.ietf-tram-stunbis"></xref>.</t> at="default"/>.</t>
</section> </section>
<section title="DATA"> <section numbered="true" toc="default">
<name>DATA</name>
<t>The DATA attribute is present in all Send indications. If the ICMP <t>The DATA attribute is present in all Send indications. If the ICMP
attribute is not present in a Data indication, it contains a DATA attribute is not present in a Data indication, it contains a DATA
attribute. The value portion of this attribute is variable length and attribute. The value portion of this attribute is variable length and
consists of the application data (that is, the data that would consists of the application data (that is, the data that would
immediately follow the UDP header if the data was been sent directly immediately follow the UDP header if the data was sent directly
between the client and the peer). The application data is equivalent between the client and the peer). The application data is equivalent
to the "UDP user data" and does not include the "surplus area" defined to the "UDP user data" and does not include the "surplus area" defined
in Section 4 of <xref target="I-D.ietf-tsvwg-udp-options"></xref>. If in <xref target="I-D.ietf-tsvwg-udp-options"
sectionFormat="of" section="4" />. If
the length of this attribute is not a multiple of 4, then padding must the length of this attribute is not a multiple of 4, then padding must
be added after this attribute.</t> be added after this attribute.</t>
</section> </section>
<section title="XOR-RELAYED-ADDRESS"> <section numbered="true" toc="default">
<t>The XOR-RELAYED-ADDRESS is present in Allocate responses. It <name>XOR-RELAYED-ADDRESS</name>
<t>The XOR-RELAYED-ADDRESS attribute is present in Allocate responses. I
t
specifies the address and port that the server allocated to the specifies the address and port that the server allocated to the
client. It is encoded in the same way as XOR-MAPPED-ADDRESS <xref client. It is encoded in the same way as the XOR-MAPPED-ADDRESS
target="I-D.ietf-tram-stunbis"></xref>.</t> attribute <xref target="RFC8489" format="default"/>.</t>
</section> </section>
<section anchor="sec-requested-address-family" numbered="true" toc="defaul
<section anchor="sec-requested-address-family" t">
title="REQUESTED-ADDRESS-FAMILY"> <name>REQUESTED-ADDRESS-FAMILY</name>
<t>This attribute is used in Allocate and Refresh requests to specify <t>This attribute is used in Allocate and Refresh requests to specify
the address type requested by the client. The value of this attribute the address type requested by the client. The value of this attribute
is 4 bytes with the following format:</t> is 4 bytes with the following format:</t>
<figure>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork><![CDATA[ 0 1 2 3
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Family | Reserved |
| Family | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> ]]></artwork>
</figure> -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</figure>
<t></t> <dl newline="false" spacing="normal">
<dt>Family:</dt>
<t><list style="hanging"> <dd>There are two values defined for this field and specified in
<t hangText="Family:">there are two values defined for this field <xref target="RFC8489" section="14.1" sectionFormat="of"/>: 0x01 for
and specified in <xref target="I-D.ietf-tram-stunbis"></xref>, IPv4 addresses and 0x02 for IPv6 addresses.</dd>
Section 14.1: 0x01 for IPv4 addresses and 0x02 for IPv6 <dt>Reserved:</dt>
addresses.</t> <dd>At this point, the 24 bits in the Reserved
field <bcp14>MUST</bcp14> be set to zero by the client and <bcp14>MU
<t hangText="Reserved:">at this point, the 24 bits in the Reserved ST</bcp14> be ignored by the
field MUST be set to zero by the client and MUST be ignored by the server.</dd>
server.</t> </dl>
</list></t>
</section> </section>
<section numbered="true" toc="default">
<section title="EVEN-PORT"> <name>EVEN-PORT</name>
<t>This attribute allows the client to request that the port in the <t>This attribute allows the client to request that the port in the
relayed transport address be even, and (optionally) that the server relayed transport address be even and (optionally) that the server
reserve the next-higher port number. The value portion of this reserve the next-higher port number. The value portion of this
attribute is 1 byte long. Its format is:</t> attribute is 1 byte long. Its format is:</t>
<figure>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<preamble></preamble> 0
<artwork><![CDATA[ 0
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|R| RFFU | |R| RFFU |
+-+-+-+-+-+-+-+-+]]></artwork> +-+-+-+-+-+-+-+-+]]></artwork>
</figure> </figure>
<t>The value contains a single 1-bit flag:</t>
<t></t> <dl newline="false" spacing="normal">
<dt>R:</dt>
<t>The value contains a single 1-bit flag:<list style="hanging"> <dd>If 1, the server is requested to reserve the
<t hangText="R:">If 1, the server is requested to reserve the
next-higher port number (on the same IP address) for a subsequent next-higher port number (on the same IP address) for a subsequent
allocation. If 0, no such reservation is requested.</t> allocation. If 0, no such reservation is requested.</dd>
<dt>RFFU:</dt>
<t hangText="RFFU:">Reserved For Future Use.</t> <dd>Reserved For Future Use.</dd>
</list>The RFFU field must be set to zero on transmission and </dl>
<t>The RFFU field must be set to zero on transmission and
ignored on reception.</t> ignored on reception.</t>
<t>Since the length of this attribute is not a multiple of 4, padding <t>Since the length of this attribute is not a multiple of 4, padding
must immediately follow this attribute.</t> must immediately follow this attribute.</t>
</section> </section>
<section anchor="sec-requested-transport" numbered="true" toc="default">
<section anchor="sec-requested-transport" title="REQUESTED-TRANSPORT"> <name>REQUESTED-TRANSPORT</name>
<t>This attribute is used by the client to request a specific <t>This attribute is used by the client to request a specific
transport protocol for the allocated transport address. The value of transport protocol for the allocated transport address. The value of
this attribute is 4 bytes with the following format:</t> this attribute is 4 bytes with the following format:</t>
<figure>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork><![CDATA[ 0 1 2 0 1 2 3
3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol | RFFU |
| Protocol | RFFU | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> ]]></artwork>
</figure> -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</figure>
<t>The Protocol field specifies the desired protocol. The codepoints <t>The Protocol field specifies the desired protocol. The code points
used in this field are taken from those allowed in the Protocol field used in this field are taken from those allowed in the Protocol field
in the IPv4 header and the NextHeader field in the IPv6 header <xref in the IPv4 header and the NextHeader field in the IPv6 header <xref
target="Protocol-Numbers"></xref>. This specification only allows the target="PROTOCOL-NUMBERS" format="default"/>. This specification only
use of codepoint 17 (User Datagram Protocol).</t> allows the use of code point 17 (User Datagram Protocol).</t>
<t>The RFFU field <bcp14>MUST</bcp14> be set to zero on transmission and
<t>The RFFU field MUST be set to zero on transmission and MUST be <bcp14>MUST</bcp14> be
ignored on reception. It is reserved for future uses.</t> ignored on reception. It is reserved for future uses.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="DONT-FRAGMENT"> <name>DONT-FRAGMENT</name>
<t>This attribute is used by the client to request that the server set <t>This attribute is used by the client to request that the server set
the DF (Don't Fragment) bit in the IP header when relaying the the DF (Don't Fragment) bit in the IP header when relaying the
application data onward to the peer, and for determining the server application data onward to the peer and for determining the server
capability in Allocate requests. This attribute has no value part and capability in Allocate requests. This attribute has no value part, and
thus the attribute length field is 0.</t> thus, the attribute length field is 0.</t>
</section> </section>
<section numbered="true" toc="default">
<section title="RESERVATION-TOKEN"> <name>RESERVATION-TOKEN</name>
<t>The RESERVATION-TOKEN attribute contains a token that uniquely <t>The RESERVATION-TOKEN attribute contains a token that uniquely
identifies a relayed transport address being held in reserve by the identifies a relayed transport address being held in reserve by the
server. The server includes this attribute in a success response to server. The server includes this attribute in a success response to
tell the client about the token, and the client includes this tell the client about the token, and the client includes this
attribute in a subsequent Allocate request to request the server use attribute in a subsequent Allocate request to request the server use
that relayed transport address for the allocation.</t> that relayed transport address for the allocation.</t>
<t>The attribute value is 8 bytes and contains the token value.</t> <t>The attribute value is 8 bytes and contains the token value.</t>
</section> </section>
<section anchor="sec-additional-address-family" numbered="true" toc="defau
<section anchor="sec-additional-address-family" lt">
title="ADDITIONAL-ADDRESS-FAMILY"> <name>ADDITIONAL-ADDRESS-FAMILY</name>
<t>This attribute is used by clients to request the allocation of a <t>This attribute is used by clients to request the allocation of an
IPv4 and IPv6 address type from a server. It is encoded in the same IPv4 and IPv6 address type from a server. It is encoded in the same
way as REQUESTED-ADDRESS-FAMILY <xref way as the REQUESTED-ADDRESS-FAMILY attribute; see <xref
target="sec-requested-address-family"></xref>. The target="sec-requested-address-family" format="default"/>. The
ADDITIONAL-ADDRESS-FAMILY attribute MAY be present in Allocate ADDITIONAL-ADDRESS-FAMILY attribute <bcp14>MAY</bcp14> be present in
request. The attribute value of 0x02 (IPv6 address) is the only valid the Allocate request. The attribute value of 0x02 (IPv6 address) is
value in Allocate request.</t> the only valid value in Allocate request.</t>
</section> </section>
<section anchor="sec-address-error-code" numbered="true" toc="default">
<section anchor="sec-address-error-code" title="ADDRESS-ERROR-CODE "> <name>ADDRESS-ERROR-CODE</name>
<t>This attribute is used by servers to signal the reason for not <t>This attribute is used by servers to signal the reason for not
allocating the requested address family. The value portion of this allocating the requested address family. The value portion of this
attribute is variable length with the following format:</t> attribute is variable length with the following format:</t>
<figure>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork><![CDATA[ 0 1 2 0 1 2 3
3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Family | Reserved |Class| Number |
| Family | Reserved |Class| Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reason Phrase (variable) ..
| Reason Phrase (variable) .. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> ]]></artwork>
</figure> </figure>
<dl newline="false" spacing="normal">
<t><list style="hanging"> <dt>Family:</dt>
<t hangText="Family:">there are two values defined for this field <dd>There are two values defined for this field and specified in
and specified in <xref target="I-D.ietf-tram-stunbis"></xref>, <xref target="RFC8489" sectionFormat="of" section="14.1"/>: 0x01 for
Section 14.1: 0x01 for IPv4 addresses and 0x02 for IPv6 IPv4 addresses and 0x02 for IPv6 addresses.</dd>
addresses.</t> <dt>Reserved:</dt>
<dd>At this point, the 13 bits in the Reserved
<t hangText="Reserved:">at this point, the 13 bits in the Reserved field <bcp14>MUST</bcp14> be set to zero by the server and <bcp14>MU
field MUST be set to zero by the server and MUST be ignored by the ST</bcp14> be ignored by the
client.</t> client.</dd>
<dt>Class:</dt>
<t hangText="Class:">The Class represents the hundreds digit of <dd>The Class represents the hundreds digit of
the error code and is defined in section 14.8 of <xref the error code and is defined in <xref
target="I-D.ietf-tram-stunbis"></xref>.</t> target="RFC8489" sectionFormat="of" section="14.8"/>.</dd>
<dt>Number:</dt>
<t hangText="Number:">this 8-bit field contains the reason server <dd>This 8-bit field contains the reason the server
cannot allocate one of the requested address types. The error code cannot allocate one of the requested address types. The error code
values could be either 440 (unsupported address family) or 508 values could be either 440 (Address Family not Supported) or 508
(insufficient capacity). The number representation is defined in (Insufficient Capacity). The number representation is defined in
section 14.8 of <xref target="I-D.ietf-tram-stunbis"></xref>.</t> <xref target="RFC8489" sectionFormat="of" section="14.8"/>.</dd>
<dt>Reason Phrase:</dt>
<t hangText="Reason Phrase:">The recommended reason phrases for <dd>The recommended reason phrases for
error codes 440 and 508 are explained in <xref error codes 440 and 508 are explained in <xref target="sec-stun-erro
target="sec-stun-errors"></xref>. The reason phrase MUST be a rs" format="default"/>. The reason phrase <bcp14>MUST</bcp14> be a
UTF-8 <xref target="RFC3629"></xref> encoded sequence of less than UTF-8 <xref target="RFC3629" format="default"/> encoded sequence of
less than
128 characters (which can be as long as 509 bytes when encoding 128 characters (which can be as long as 509 bytes when encoding
them or 763 bytes when decoding them).</t> them or 763 bytes when decoding them).</dd>
</list></t> </dl>
</section> </section>
<section anchor="icmp" numbered="true" toc="default">
<section anchor="icmp" title="ICMP "> <name>ICMP</name>
<t>This attribute is used by servers to signal the reason an UDP <t>This attribute is used by servers to signal the reason a UDP
packet was dropped. The following is the format of the ICMP packet was dropped. The following is the format of the ICMP
attribute.</t> attribute.</t>
<figure>
<figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork><![CDATA[ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | ICMP Type | ICMP Code |
| Reserved | ICMP Type | ICMP Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Data |
| Error Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> ]]></artwork>
</figure> </figure>
<t><list style="hanging">
<t hangText="Reserved:">This field MUST be set to 0 when sent, and
MUST be ignored when received.</t>
<t hangText="ICMP Type:">The field contains the value in the ICMP
type. Its interpretation depends whether the ICMP was received
over IPv4 or IPv6.</t>
<t hangText="ICMP Code:">The field contains the value in the ICMP
code. Its interpretation depends whether the ICMP was received
over IPv4 or IPv6.</t>
<t hangText="Error Data:">This field size is 4 bytes long. If the <dl newline="false" spacing="normal">
ICMPv6 type is 2 (Packet Too Big Message) or ICMPv4 type is 3 ( <dt>Reserved:</dt>
Destination Unreachable) and Code is 4 (fragmentation needed and <dd>This field <bcp14>MUST</bcp14> be set to 0 when sent and
DF set), the Error Data field will be set to the Maximum <bcp14>MUST</bcp14> be ignored when received.</dd>
Transmission Unit of the next-hop link (Section 3.2 of <xref <dt>ICMP Type:</dt>
target="RFC4443"></xref>) and Section 4 of <xref <dd>The field contains the value of the ICMP
target="RFC1191"></xref>). For other ICMPv6 types and ICMPv4 types type. Its interpretation depends on whether the ICMP was received
and codes, Error Data field MUST be set to zero.</t> over IPv4 or IPv6.</dd>
</list></t> <dt>ICMP Code:</dt>
<dd>The field contains the value of the ICMP
code. Its interpretation depends on whether the ICMP was received
over IPv4 or IPv6.</dd>
<dt>Error Data:</dt>
<dd>This field size is 4 bytes long. If the ICMPv6 type is 2
("Packet too big" message) or ICMPv4 type is 3 (Destination
Unreachable) and Code is 4 (fragmentation needed and DF set), the
Error Data field will be set to the Maximum Transmission Unit of the
next-hop link (<xref target="RFC4443" sectionFormat="of"
section="3.2"/> and <xref target="RFC1191"
sectionFormat="of" section="4"/>). For other ICMPv6 types and ICMPv4 t
ypes and
codes, the Error Data field <bcp14>MUST</bcp14> be set to zero.</dd>
</dl>
</section> </section>
</section> </section>
<section anchor="sec-stun-errors" numbered="true" toc="default">
<section anchor="sec-stun-errors" title="STUN Error Response Codes"> <name>STUN Error Response Codes</name>
<t>This document defines the following error response codes:<list <t>This document defines the following error response codes:</t>
style="hanging"> <dl newline="true" spacing="normal">
<t hangText="403">(Forbidden): The request was valid but cannot be <dt>403 (Forbidden):</dt>
performed due to administrative or similar restrictions.</t> <dd>The request was valid but cannot be
performed due to administrative or similar restrictions.</dd>
<t hangText="437">(Allocation Mismatch): A request was received by <dt>437 (Allocation Mismatch):</dt>
<dd>A request was received by
the server that requires an allocation to be in place, but no the server that requires an allocation to be in place, but no
allocation exists, or a request was received that requires no allocation exists, or a request was received that requires no
allocation, but an allocation exists.</t> allocation, but an allocation exists.</dd>
<dt>440 (Address Family not Supported):</dt>
<t hangText="440">(Address Family not Supported): The server does <dd>The server does
not support the address family requested by the client.</t> not support the address family requested by the client.</dd>
<dt>441 (Wrong Credentials):</dt>
<t hangText="441">(Wrong Credentials): The credentials in the <dd>(Wrong Credentials): The credentials in the
(non-Allocate) request do not match those used to create the (non-Allocate) request do not match those used to create the
allocation.</t> allocation.</dd>
<dt>442 (Unsupported Transport Protocol):</dt>
<t hangText="442">(Unsupported Transport Protocol): The Allocate <dd>The Allocate
request asked the server to use a transport protocol between the request asked the server to use a transport protocol between the
server and the peer that the server does not support. NOTE: This server and the peer that the server does not support. NOTE: This
does NOT refer to the transport protocol used in the 5-tuple.</t> does NOT refer to the transport protocol used in the 5-tuple.</dd>
<dt>443 (Peer Address Family Mismatch):</dt>
<t hangText="443">(Peer Address Family Mismatch). A peer address is <dd>A peer address is
part of a different address family than that of the relayed part of a different address family than that of the relayed
transport address of the allocation.</t> transport address of the allocation.</dd>
<dt>486 (Allocation Quota Reached):</dt>
<t hangText="486">(Allocation Quota Reached): No more allocations <dd>No more allocations
using this username can be created at the present time.</t> using this username can be created at the present time.</dd>
<dt>508 (Insufficient Capacity):</dt>
<t hangText="508">(Insufficient Capacity): The server is unable to <dd>The server is unable to
carry out the request due to some capacity limit being reached. In carry out the request due to some capacity limit being reached. In
an Allocate response, this could be due to the server having no more an Allocate response, this could be due to the server having no more
relayed transport addresses available at that time, having none with relayed transport addresses available at that time, having none with
the requested properties, or the one that corresponds to the the requested properties, or the one that corresponds to the
specified reservation token is not available.</t> specified reservation token is not available.</dd>
</list></t> </dl>
</section> </section>
<section numbered="true" toc="default">
<section title="Detailed Example"> <name>Detailed Example</name>
<t>This section gives an example of the use of TURN, showing in detail <t>This section gives an example of the use of TURN, showing in detail
the contents of the messages exchanged. The example uses the network the contents of the messages exchanged. The example uses the network
diagram shown in the Overview (<xref diagram shown in the Overview (<xref target="fig-turn-model" format="defau
target="fig-turn-model"></xref>).</t> lt"/>).</t>
<t>For each message, the attributes included in the message and their <t>For each message, the attributes included in the message and their
values are shown. For convenience, values are shown in a human-readable values are shown. For convenience, values are shown in a human-readable
format rather than showing the actual octets; for example, format rather than showing the actual octets; for example,
"XOR-RELAYED-ADDRESS=192.0.2.15:9000" shows that the XOR-RELAYED-ADDRESS "XOR-RELAYED-ADDRESS=192.0.2.15:9000" shows that the XOR-RELAYED-ADDRESS
attribute is included with an address of 192.0.2.15 and a port of 9000, attribute is included with an address of 192.0.2.15 and a port of 9000;
here the address and port are shown before the xor-ing is done. For here, the address and port are shown before the xor-ing is done. For
attributes with string-like values (e.g., SOFTWARE="Example client, attributes with string-like values (e.g., SOFTWARE="Example client,
version 1.03" and NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda"), the value version 1.03" and NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda"), the value
of the attribute is shown in quotes for readability, but these quotes do of the attribute is shown in quotes for readability, but these quotes do
not appear in the actual value.</t> not appear in the actual value.</t>
<figure>
<t></t> <artwork name="" type="" align="left" alt=""><![CDATA[
TURN TURN Peer Peer
<figure> client server A B
<artwork><![CDATA[TURN TURN Pe | | | |
er Peer |--- Allocate request -------------->| | |
client server A B | Transaction-Id=0xA56250D3F17ABE679422DE85 | |
| | | | | SOFTWARE="Example client, version 1.03" | |
|--- Allocate request -------------->| | | | LIFETIME=3600 (1 hour) | | |
| Transaction-Id=0xA56250D3F17ABE679422DE85 | | | REQUESTED-TRANSPORT=17 (UDP) | | |
| SOFTWARE="Example client, version 1.03" | | | DONT-FRAGMENT | | |
| LIFETIME=3600 (1 hour) | | | | | | |
| REQUESTED-TRANSPORT=17 (UDP) | | | |<-- Allocate error response --------| | |
| DONT-FRAGMENT | | | | Transaction-Id=0xA56250D3F17ABE679422DE85 | |
| | | | | SOFTWARE="Example server, version 1.17" | |
|<-- Allocate error response --------| | | | ERROR-CODE=401 (Unauthorized) | | |
| Transaction-Id=0xA56250D3F17ABE679422DE85 | | | REALM="example.com" | | |
| SOFTWARE="Example server, version 1.17" | | | NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | |
| ERROR-CODE=401 (Unauthorized) | | | | PASSWORD-ALGORITHMS=MD5 and SHA256 | |
| REALM="example.com" | | | | | | |
| NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | | |--- Allocate request -------------->| | |
| PASSWORD-ALGORITHMS=MD5 and SHA256 | | | Transaction-Id=0xC271E932AD7446A32C234492 | |
| | | | | SOFTWARE="Example client 1.03" | | |
|--- Allocate request -------------->| | | | LIFETIME=3600 (1 hour) | | |
| Transaction-Id=0xC271E932AD7446A32C234492 | | | REQUESTED-TRANSPORT=17 (UDP) | | |
| SOFTWARE="Example client 1.03" | | | | DONT-FRAGMENT | | |
| LIFETIME=3600 (1 hour) | | | | USERNAME="George" | | |
| REQUESTED-TRANSPORT=17 (UDP) | | | | REALM="example.com" | | |
| DONT-FRAGMENT | | | | NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | |
| USERNAME="George" | | | | PASSWORD-ALGORITHMS=MD5 and SHA256 | |
| REALM="example.com" | | | | PASSWORD-ALGORITHM=SHA256 | | |
| NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | | | MESSAGE-INTEGRITY=... | | |
| PASSWORD-ALGORITHMS=MD5 and SHA256 | | | MESSAGE-INTEGRITY-SHA256=... | | |
| PASSWORD-ALGORITHM=SHA256 | | | | | | |
| MESSAGE-INTEGRITY=... | | | |<-- Allocate success response ------| | |
| MESSAGE-INTEGRITY-SHA256=... | | | | Transaction-Id=0xC271E932AD7446A32C234492 | |
| | | | | SOFTWARE="Example server, version 1.17" | |
|<-- Allocate success response ------| | | | LIFETIME=1200 (20 minutes) | | |
| Transaction-Id=0xC271E932AD7446A32C234492 | | | XOR-RELAYED-ADDRESS=192.0.2.15:50000 | |
| SOFTWARE="Example server, version 1.17" | | | XOR-MAPPED-ADDRESS=192.0.2.1:7000 | |
| LIFETIME=1200 (20 minutes) | | | | MESSAGE-INTEGRITY-SHA256=... | | |
| XOR-RELAYED-ADDRESS=192.0.2.15:50000 | |
| XOR-MAPPED-ADDRESS=192.0.2.1:7000 | |
| MESSAGE-INTEGRITY-SHA256=... | | |
]]></artwork> ]]></artwork>
</figure>
<postamble></postamble>
</figure>
<t>The client begins by selecting a host transport address to use for <t>The client begins by selecting a host transport address to use for
the TURN session; in this example, the client has selected the TURN session; in this example, the client has selected
198.51.100.2:49721 as shown in <xref target="fig-turn-model"></xref>. 198.51.100.2:49721 as shown in <xref target="fig-turn-model" format="defau lt"/>.
The client then sends an Allocate request to the server at the server The client then sends an Allocate request to the server at the server
transport address. The client randomly selects a 96-bit transaction id transport address. The client randomly selects a 96-bit transaction id
of 0xA56250D3F17ABE679422DE85 for this transaction; this is encoded in of 0xA56250D3F17ABE679422DE85 for this transaction; this is encoded in
the transaction id field in the fixed header. The client includes a the transaction id field in the fixed header. The client includes a
SOFTWARE attribute that gives information about the client's software; SOFTWARE attribute that gives information about the client's software;
here the value is "Example client, version 1.03" to indicate that this here, the value is "Example client, version 1.03" to indicate that this
is version 1.03 of something called the Example client. The client is version 1.03 of something called the "Example client". The client
includes the LIFETIME attribute because it wishes the allocation to have includes the LIFETIME attribute because it wishes the allocation to have
a longer lifetime than the default of 10 minutes; the value of this a longer lifetime than the default of 10 minutes; the value of this
attribute is 3600 seconds, which corresponds to 1 hour. The client must attribute is 3600 seconds, which corresponds to 1 hour. The client must
always include a REQUESTED-TRANSPORT attribute in an Allocate request always include a REQUESTED-TRANSPORT attribute in an Allocate request,
and the only value allowed by this specification is 17, which indicates and the only value allowed by this specification is 17, which indicates
UDP transport between the server and the peers. The client also includes UDP transport between the server and the peers. The client also includes
the DONT-FRAGMENT attribute because it wishes to use the DONT-FRAGMENT the DONT-FRAGMENT attribute because it wishes to use the DONT-FRAGMENT
attribute later in Send indications; this attribute consists of only an attribute later in Send indications; this attribute consists of only an
attribute header, there is no value part. We assume the client has not attribute header; there is no value part. We assume the client has not
recently interacted with the server, thus the client does not include recently interacted with the server; thus, the client does not include
USERNAME, USERHASH, REALM, NONCE, PASSWORD-ALGORITHMS, the USERNAME, USERHASH, REALM, NONCE, PASSWORD-ALGORITHMS,
PASSWORD-ALGORITHM, MESSAGE-INTEGRITY or MESSAGE-INTEGRITY-SHA256 PASSWORD-ALGORITHM, MESSAGE-INTEGRITY, or MESSAGE-INTEGRITY-SHA256
attribute. Finally, note that the order of attributes in a message is attribute. Finally, note that the order of attributes in a message is
arbitrary (except for the MESSAGE-INTEGRITY, MESSAGE-INTEGRITY-SHA256 arbitrary (except for the MESSAGE-INTEGRITY, MESSAGE-INTEGRITY-SHA256
and FINGERPRINT attributes) and the client could have used a different and FINGERPRINT attributes), and the client could have used a different
order.</t> order.</t>
<t>Servers require any request to be authenticated. Thus, when the <t>Servers require any request to be authenticated. Thus, when the
server receives the initial Allocate request, it rejects the request server receives the initial Allocate request, it rejects the request
because the request does not contain the authentication attributes. because the request does not contain the authentication attributes.
Following the procedures of the long-term credential mechanism of STUN Following the procedures of the long-term credential mechanism of STUN
<xref target="I-D.ietf-tram-stunbis"></xref>, the server includes an <xref target="RFC8489" format="default"/>, the server includes an
ERROR-CODE attribute with a value of 401 (Unauthorized), a REALM ERROR-CODE attribute with a value of 401 (Unauthorized), a REALM
attribute that specifies the authentication realm used by the server (in attribute that specifies the authentication realm used by the server (in
this case, the server's domain "example.com"), and a nonce value in a this case, the server's domain "example.com"), and a nonce value in a
NONCE attribute. The NONCE attribute starts with the "nonce cookie" with NONCE attribute. The NONCE attribute starts with the "nonce cookie" with
the STUN Security Feature "Password algorithm" bit set to 1. The server the STUN Security Feature "Password algorithm" bit set to 1. The server
includes a PASSWORD-ALGORITHMS attribute that specifies the list of includes a PASSWORD-ALGORITHMS attribute that specifies the list of
algorithms that the server can use to derive the long-term password. If algorithms that the server can use to derive the long-term password. If
the server sets the STUN Security Feature "Username anonymity" bit to 1 the server sets the STUN Security Feature "Username anonymity" bit to 1,
then the client uses the USERHASH attribute instead of the USERNAME then the client uses the USERHASH attribute instead of the USERNAME
attribute in the Allocate request to anonymise the username. The server attribute in the Allocate request to anonymize the username. The server
also includes a SOFTWARE attribute that gives information about the also includes a SOFTWARE attribute that gives information about the
server's software.</t> server's software.</t>
<t>The client, upon receipt of the 401 error, reattempts the Allocate
<t>The client, upon receipt of the 401 error, re-attempts the Allocate
request, this time including the authentication attributes. The client request, this time including the authentication attributes. The client
selects a new transaction id, and then populates the new Allocate selects a new transaction id and then populates the new Allocate
request with the same attributes as before. The client includes a request with the same attributes as before. The client includes a
USERNAME attribute and uses the realm value received from the server to USERNAME attribute and uses the realm value received from the server to
help it determine which value to use; here the client is configured to help it determine which value to use; here, the client is configured to
use the username "George" for the realm "example.com". The client use the username "George" for the realm "example.com". The client
includes the PASSWORD-ALGORITHM attribute indicating the algorithm that includes the PASSWORD-ALGORITHM attribute indicating the algorithm that
the server must use to derive the long- term password. The client also the server must use to derive the long-term password. The client also
includes the REALM, PASSWORD-ALGORITHMS and NONCE attributes, which are includes the REALM, PASSWORD-ALGORITHMS, and NONCE attributes, which are
just copied from the 401 error response. Finally, the client includes just copied from the 401 error response. Finally, the client includes
MESSAGE-INTEGRITY-SHA256 attribute as the last attributes in the MESSAGE-INTEGRITY-SHA256 attribute as the last attributes in the
message, whose value is Hashed Message Authentication Code - Secure Hash message whose value is Hashed Message Authentication Code - Secure Hash
Algorithm 2 (HMAC-SHA2) hash over the contents of the message (shown as Algorithm 2 (HMAC-SHA2) hash over the contents of the message (shown as
just "..." above); this HMAC-SHA2 computation includes a password value. just "..." above); this HMAC-SHA2 computation includes a password value.
Thus, an attacker cannot compute the message integrity value without Thus, an attacker cannot compute the message integrity value without
somehow knowing the secret password.</t> somehow knowing the secret password.</t>
<t>The server, upon receipt of the authenticated Allocate request, <t>The server, upon receipt of the authenticated Allocate request,
checks that everything is OK, then creates an allocation. The server checks that everything is OK, then creates an allocation. The server
replies with an Allocate success response. The server includes a replies with an Allocate success response. The server includes a
LIFETIME attribute giving the lifetime of the allocation; here, the LIFETIME attribute giving the lifetime of the allocation; here, the
server has reduced the client's requested 1-hour lifetime to just 20 server has reduced the client's requested 1-hour lifetime to just 20
minutes, because this particular server doesn't allow lifetimes longer minutes because this particular server doesn't allow lifetimes longer
than 20 minutes. The server includes an XOR-RELAYED-ADDRESS attribute than 20 minutes. The server includes an XOR-RELAYED-ADDRESS attribute
whose value is the relayed transport address of the allocation. The whose value is the relayed transport address of the allocation. The
server includes an XOR-MAPPED-ADDRESS attribute whose value is the server includes an XOR-MAPPED-ADDRESS attribute whose value is the
server-reflexive address of the client; this value is not used otherwise server-reflexive address of the client; this value is not used otherwise
in TURN but is returned as a convenience to the client. The server in TURN but is returned as a convenience to the client. The server
includes a MESSAGE-INTEGRITY-SHA256 attribute to authenticate the includes a MESSAGE-INTEGRITY-SHA256 attribute to authenticate the
response and to ensure its integrity; note that the response does not response and to ensure its integrity; note that the response does not
contain the USERNAME, REALM, and NONCE attributes. The server also contain the USERNAME, REALM, and NONCE attributes. The server also
includes a SOFTWARE attribute.</t> includes a SOFTWARE attribute.</t>
<figure>
<t></t> <artwork name="" type="" align="left" alt=""><![CDATA[
TURN TURN Peer Peer
<figure> client server A B
<artwork><![CDATA[TURN TURN Pe |--- CreatePermission request ------>| | |
er Peer | Transaction-Id=0xE5913A8F460956CA277D3319 | |
client server A B | XOR-PEER-ADDRESS=192.0.2.150:0 | | |
|--- CreatePermission request ------>| | | | USERNAME="George" | | |
| Transaction-Id=0xE5913A8F460956CA277D3319 | | | REALM="example.com" | | |
| XOR-PEER-ADDRESS=192.0.2.150:0 | | | | NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | |
| USERNAME="George" | | | | PASSWORD-ALGORITHMS=MD5 and SHA256 | |
| REALM="example.com" | | | | PASSWORD-ALGORITHM=SHA256 | | |
| NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | | | MESSAGE-INTEGRITY-SHA256=... | | |
| PASSWORD-ALGORITHMS=MD5 and SHA256 | | | | | |
| PASSWORD-ALGORITHM=SHA256 | | | |<-- CreatePermission success resp.--| | |
| MESSAGE-INTEGRITY-SHA256=... | | | | Transaction-Id=0xE5913A8F460956CA277D3319 | |
| | | | | MESSAGE-INTEGRITY-SHA256=... | | |
|<-- CreatePermission success resp.--| | |
| Transaction-Id=0xE5913A8F460956CA277D3319 | |
| MESSAGE-INTEGRITY-SHA256=... | | |
]]></artwork> ]]></artwork>
</figure>
<postamble></postamble>
</figure>
<t>The client then creates a permission towards Peer A in preparation <t>The client then creates a permission towards Peer A in preparation
for sending it some application data. This is done through a for sending it some application data. This is done through a
CreatePermission request. The XOR-PEER-ADDRESS attribute contains the IP CreatePermission request. The XOR-PEER-ADDRESS attribute contains the IP
address for which a permission is established (the IP address of peer address for which a permission is established (the IP address of peer
A); note that the port number in the attribute is ignored when used in a A); note that the port number in the attribute is ignored when used in a
CreatePermission request, and here it has been set to 0; also, note how CreatePermission request, and here it has been set to 0; also, note how
the client uses Peer A's server-reflexive IP address and not its the client uses Peer A's server-reflexive IP address and not its
(private) host address. The client uses the same username, realm, and (private) host address. The client uses the same username, realm, and
nonce values as in the previous request on the allocation. Though it is nonce values as in the previous request on the allocation. Though it is
allowed to do so, the client has chosen not to include a SOFTWARE allowed to do so, the client has chosen not to include a SOFTWARE
skipping to change at line 3442 skipping to change at line 3196
for sending it some application data. This is done through a for sending it some application data. This is done through a
CreatePermission request. The XOR-PEER-ADDRESS attribute contains the IP CreatePermission request. The XOR-PEER-ADDRESS attribute contains the IP
address for which a permission is established (the IP address of peer address for which a permission is established (the IP address of peer
A); note that the port number in the attribute is ignored when used in a A); note that the port number in the attribute is ignored when used in a
CreatePermission request, and here it has been set to 0; also, note how CreatePermission request, and here it has been set to 0; also, note how
the client uses Peer A's server-reflexive IP address and not its the client uses Peer A's server-reflexive IP address and not its
(private) host address. The client uses the same username, realm, and (private) host address. The client uses the same username, realm, and
nonce values as in the previous request on the allocation. Though it is nonce values as in the previous request on the allocation. Though it is
allowed to do so, the client has chosen not to include a SOFTWARE allowed to do so, the client has chosen not to include a SOFTWARE
attribute in this request.</t> attribute in this request.</t>
<t>The server receives the CreatePermission request, creates the <t>The server receives the CreatePermission request, creates the
corresponding permission, and then replies with a CreatePermission corresponding permission, and then replies with a CreatePermission
success response. Like the client, the server chooses not to include the success response. Like the client, the server chooses not to include the
SOFTWARE attribute in its reply. Again, note how success responses SOFTWARE attribute in its reply. Again, note how success responses
contains a MESSAGE-INTEGRITY-SHA256 attribute (assuming the server uses contain a MESSAGE-INTEGRITY-SHA256 attribute (assuming the server uses
the long-term credential mechanism), but no USERNAME, REALM, and NONCE the long-term credential mechanism) but no USERNAME, REALM, and NONCE
attributes.</t> attributes.</t>
<figure>
<t></t> <artwork name="" type="" align="left" alt=""><![CDATA[
TURN TURN Peer Peer
<figure> client server A B
<artwork><![CDATA[TURN TURN Pe |--- Send indication --------------->| | |
er Peer | Transaction-Id=0x1278E9ACA2711637EF7D3328 | |
client server A B | XOR-PEER-ADDRESS=192.0.2.150:32102 | |
|--- Send indication --------------->| | | | DONT-FRAGMENT | | |
| Transaction-Id=0x1278E9ACA2711637EF7D3328 | | | DATA=... | | |
| XOR-PEER-ADDRESS=192.0.2.150:32102 | | | |- UDP dgm ->| |
| DONT-FRAGMENT | | | | | data=... | |
| DATA=... | | | | | | |
| |-- UDP dgm ->| | | |<- UDP dgm -| |
| | data=... | | | | data=... | |
| | | | |<-- Data indication ----------------| | |
| |<- UDP dgm --| | | Transaction-Id=0x8231AE8F9242DA9FF287FEFF | |
| | data=... | | | XOR-PEER-ADDRESS=192.0.2.150:32102 | |
|<-- Data indication ----------------| | | | DATA=... | | |
| Transaction-Id=0x8231AE8F9242DA9FF287FEFF | |
| XOR-PEER-ADDRESS=192.0.2.150:32102 | |
| DATA=... | | |
]]></artwork> ]]></artwork>
</figure>
<postamble></postamble>
</figure>
<t>The client now sends application data to Peer A using a Send <t>The client now sends application data to Peer A using a Send
indication. Peer A's server-reflexive transport address is specified in indication. Peer A's server-reflexive transport address is specified in
the XOR-PEER-ADDRESS attribute, and the application data (shown here as the XOR-PEER-ADDRESS attribute, and the application data (shown here as
just "...") is specified in the DATA attribute. The client is doing a just "...") is specified in the DATA attribute. The client is doing a
form of path MTU discovery at the application layer and thus specifies form of path MTU discovery at the application layer and, thus, specifies
(by including the DONT-FRAGMENT attribute) that the server should set (by including the DONT-FRAGMENT attribute) that the server should set
the DF bit in the UDP datagram to send to the peer. Indications cannot the DF bit in the UDP datagram to send to the peer. Indications cannot
be authenticated using the long-term credential mechanism of STUN, so no be authenticated using the long-term credential mechanism of STUN, so no
MESSAGE-INTEGRITY or MESSAGE-INTEGRITY-SHA256 attribute is included in MESSAGE-INTEGRITY or MESSAGE-INTEGRITY-SHA256 attribute is included in
the message. An application wishing to ensure that its data is not the message. An application wishing to ensure that its data is not
altered or forged must integrity-protect its data at the application altered or forged must integrity-protect its data at the application
level.</t> level.</t>
<t>Upon receipt of the Send indication, the server extracts the <t>Upon receipt of the Send indication, the server extracts the
application data and sends it in a UDP datagram to Peer A, with the application data and sends it in a UDP datagram to Peer A, with the
relayed transport address as the source transport address of the relayed transport address as the source transport address of the
datagram, and with the DF bit set as requested. Note that, had the datagram and with the DF bit set as requested. Note that had the
client not previously established a permission for Peer A's client not previously established a permission for Peer A's
server-reflexive IP address, then the server would have silently server-reflexive IP address, the server would have silently
discarded the Send indication instead.</t> discarded the Send indication instead.</t>
<t>Peer A then replies with its own UDP datagram containing application <t>Peer A then replies with its own UDP datagram containing application
data. The datagram is sent to the relayed transport address on the data. The datagram is sent to the relayed transport address on the
server. When this arrives, the server creates a Data indication server. When this arrives, the server creates a Data indication
containing the source of the UDP datagram in the XOR-PEER-ADDRESS containing the source of the UDP datagram in the XOR-PEER-ADDRESS
attribute, and the data from the UDP datagram in the DATA attribute. The attribute, and the data from the UDP datagram in the DATA attribute. The
resulting Data indication is then sent to the client.</t> resulting Data indication is then sent to the client.</t>
<figure>
<t></t> <artwork name="" type="" align="left" alt=""><![CDATA[
TURN TURN Peer Peer
<figure> client server A B
<artwork><![CDATA[TURN TURN Pe |--- ChannelBind request ----------->| | |
er Peer | Transaction-Id=0x6490D3BC175AFF3D84513212 | |
client server A B | CHANNEL-NUMBER=0x4000 | | |
|--- ChannelBind request ----------->| | | | XOR-PEER-ADDRESS=192.0.2.210:49191 | |
| Transaction-Id=0x6490D3BC175AFF3D84513212 | | | USERNAME="George" | | |
| CHANNEL-NUMBER=0x4000 | | | | REALM="example.com" | | |
| XOR-PEER-ADDRESS=192.0.2.210:49191 | | | NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | |
| USERNAME="George" | | | | PASSWORD-ALGORITHMS=MD5 and SHA256 | |
| REALM="example.com" | | | | PASSWORD-ALGORITHM=SHA256 | | |
| NONCE="obMatJos2gAAAadl7W7PeDU4hKE72jda" | | | MESSAGE-INTEGRITY-SHA256=... | | |
| PASSWORD-ALGORITHMS=MD5 and SHA256 | | | | | |
| PASSWORD-ALGORITHM=SHA256 | | | |<-- ChannelBind success response ---| | |
| MESSAGE-INTEGRITY-SHA256=... | | | | Transaction-Id=0x6490D3BC175AFF3D84513212 | |
| | | | | MESSAGE-INTEGRITY-SHA256=... | | |
|<-- ChannelBind success response ---| | |
| Transaction-Id=0x6490D3BC175AFF3D84513212 | |
| MESSAGE-INTEGRITY-SHA256=... | | |
]]></artwork> ]]></artwork>
</figure>
<postamble></postamble>
</figure>
<t>The client now binds a channel to Peer B, specifying a free channel <t>The client now binds a channel to Peer B, specifying a free channel
number (0x4000) in the CHANNEL-NUMBER attribute, and Peer B's transport number (0x4000) in the CHANNEL-NUMBER attribute, and Peer B's transport
address in the XOR-PEER-ADDRESS attribute. As before, the client re-uses address in the XOR-PEER-ADDRESS attribute. As before, the client reuses
the username, realm, and nonce from its last request in the message.</t> the username, realm, and nonce from its last request in the message.</t>
<t>Upon receipt of the request, the server binds the channel number to <t>Upon receipt of the request, the server binds the channel number to
the peer, installs a permission for Peer B's IP address, and then the peer, installs a permission for Peer B's IP address, and then
replies with ChannelBind success response.</t> replies with a ChannelBind success response.</t>
<figure>
<t></t> <artwork name="" type="" align="left" alt=""><![CDATA[
TURN TURN Peer Peer
<figure> client server A B
<artwork><![CDATA[TURN TURN Pe |--- ChannelData ------------------>| | |
er Peer | Channel-number=0x4000 |--- UDP datagram --------->|
client server A B | Data=... | Data=... |
|--- ChannelData ------------------->| | | | | | |
| Channel-number=0x4000 |--- UDP datagram --------->| | |<-- UDP datagram ----------|
| Data=... | Data=... | | | Data=... | |
| | | | |<-- ChannelData -------------------| | |
| |<-- UDP datagram ----------| | Channel-number=0x4000 | | |
| | Data=... | | | Data=... | | |
|<-- ChannelData --------------------| | |
| Channel-number=0x4000 | | |
| Data=... | | |
]]></artwork> ]]></artwork>
</figure>
<postamble></postamble>
</figure>
<t>The client now sends a ChannelData message to the server with data <t>The client now sends a ChannelData message to the server with data
destined for Peer B. The ChannelData message is not a STUN message, and destined for Peer B. The ChannelData message is not a STUN message;
thus has no transaction id. Instead, it has only three fields: a channel thus, it has no transacti