wdiff rfc9793.alt-original rfc9793.txt

Network Working Group X.X.

Internet Engineering Task Force (IETF) X. Xu
Internet-Draft
Request for Comments: 9793 China Mobile
Intended status:
Category: Standards Track M.C. M. Chen
Expires: 22 June 2025
ISSN: 2070-1721 Huawei
K.P.
K. Patel
Arrcus, Inc.
I.W.
IJ. Wijnands
Individual
A.P.
T. Przygienda
Z. Zhang, Ed.
Juniper
19 December 2024
May 2025

BGP Extensions for BIER
draft-ietf-bier-idr-extensions-19 Bit Index Explicit Replication (BIER)

Abstract

Bit Index Explicit Replication (BIER) is a multicast forwarding
architecture that doesn't require an explicit tree-building protocol
and doesn't require intermediate routers to maintain per-tree
multicast states. Some BIER-specific information and state, states, which
are only in proportion to the number of BIER routers but not per-
tree, do need to be advertised, calculated, and maintained. This
document describes BGP extensions for advertising the BIER
information and methods for calculating BIER states based on the
advertisements.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on 22 June 2025.
https://www.rfc-editor.org/info/rfc9793.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language
3. BIER Path Attribute . . . . . . . . . . . . . . . . . . . . . 4
3.1. BIER MPLS Encapsulation sub-TLV . . . . . . . . . . . . . 5 Sub-TLV
3.2. BIER Non-MPLS Encapsulation sub-TLV . . . . . . . . . . . 7 Sub-TLV
3.3. BIER Nexthop sub-TLV . . . . . . . . . . . . . . . . . . 8 Sub-TLV
4. Originating/Propagating/Updating the BIER Attribute . . . . . . . 8
5. BIFT Calculation with BGP Signaling . . . . . . . . . . . . . 10
6. Example of BIER Nexthop Usage and Handling . . . . . . . . . 10
7. Operational Considerations . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
12.1.
10.1. Normative References . . . . . . . . . . . . . . . . . . 13
12.2.
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Acknowledgements
Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14

1. Introduction

Bit Index Explicit Replication (BIER) [RFC8279] is a multicast
forwarding architecture which that doesn't require an explicit tree-
building protocol and doesn't require intermediate routers to
maintain per-tree multicast states. It supports both direct and
tunneled BIER forwarding. This document describes BGP extensions for
advertising the BIER-specific BIER information and the methods for calculating BIER forwarding
states with this information. based on the advertisements. More specifically, in this
document, we define a new optional transitive BGP attribute, referred
to as the BIER attribute, "BIER attribute", to convey the BIER-
specific BIER-specific information
such as BIER Forwarding Bit-Forwarding Router identifier (BFR-
id), BitString Length Identifier (BFR-ID), BitStringLength
(BSL), and so on. The signaling is to be used in a single
Administrative Domain, Domain (AD), and Section 7 specifies procedures to
prevent the BIER attribute from "leaking out" of the domain.

2. Terminology

This document makes use of the terms terminology defined in [RFC4271] and
[RFC8279]. Some terminologies terms are listed below for convenience.

BIER: Bit Indexed Explicit Replication

BFR: BIER Forwarding Bit-Forwarding Router

BFR-ID: BIER Forwarding Router BFR Identifier

BSL: BitStringLength

BIFT: BIER Bit Index Forwarding Table

BIFT-id: BIER Bit Index Forwarding Table Identifier

BFER: BIER Forwarding Bit-Forwarding Egress Router

BFR-prefix: Each BFR is assigned a single "BFR-prefix" for each sub-
domain to which it belongs. It is recommended that the BFR-prefix
be a loopback address of the BFR.

NLRI: Network Layer Reachability Information [RFC4271]

AFI: Address Family Identifier [RFC4760]

SAFI: Subsequent Address Family Identifier [RFC4760]

2.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

3. BIER Path Attribute

This specification defines an optional, transitive BGP path
attribute, referred to as the BIER attribute. "BIER attribute". This attribute can
be attached to a BGP UPDATE message by the originator for NLRIs of
AFI 1 or 2 and SAFI 1,2, 1, 2, or 4 to indicate the BIER-specific
information of a particular BFR identified by the /32 (for IPv4) or
/128 (for IPv6) host address prefix contained in the NLRI. The
attachment of the BIER attribute to non-host address prefixes is not
defined by this document. It may be specified in the future, for example
example, by
[I-D.ietf-bier-prefix-redistribute]. [BIER-Prefix-Redistribute].

If the BIER path attribute is present, the NLRI is referred to as a
"BFR-prefix". Use of the attribute with other AFIs/SAFIs is outside
the scope of this document.

The BIER path attribute is an optional, transitive BGP path attribute
with type code TBD 41 and of variable length. The attribute value
portion carries BIER TLVs, which are encoded as follows:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Value (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Length field defines the length of the value portion in octets
(thus, a TLV with no value portion would have a length of zero). The
TLV is not padded to 4-octet alignment. Unknown and unsupported
types MUST be preserved and propagated within the BIER Attribute. attribute.
The presence of unknown or unexpected TLVs MUST NOT result in the
NLRI or the BIER Attribute attribute being considered malformed.

When creating a BIER attribute, a BFR MUST include one BIER TLV for
every Sub-domain sub-domain that the prefix belongs to. The attribute type code
for the BIER Attribute attribute is TBD. 41. The value field of the BIER Attribute attribute
contains one or more BIER TLV shown TLVs as follows: shown below:

Type: 1. 1

Length: Two 2 octets encoding the length in octets of the Value part.

Sub-domain [RFC8279]: a one-octet

Sub-domain: A 1-octet field encoding the sub-domain ID corresponding
to the BFR-ID. BFR-ID [RFC8279]: a two-octet (see [RFC8279]).

BFR-ID: A 2-octet field encoding the BFR-ID. BFR-ID (see [RFC8279]).

Reserved: SHOULD be set to 0 on transmission and MUST be ignored on
reception.

Sub-TLVs: contains Contains one or more sub-TLV. sub-TLVs.

The BIER TLV MAY appear multiple times in the BIER Path Attribute, path attribute,
one for each sub-domain. There MUST be no more than one BIER TLV
with the same Sub-domain value; if there is, the entire BIER Path
Attribute path
attribute MUST be ignored.

A BIER TLV may have sub-TLVs, which may have their own sub-TLVs. All
those are referred to as sub-TLVs and share the same Type space,
regardless of the level.

3.1. BIER MPLS Encapsulation sub-TLV Sub-TLV

The BIER MPLS Encapsulation sub-TLV has the following format. It MAY
appear multiple times in the BIER TLV.

The BIER MPLS Encapsulation Sub-TLV sub-TLV has the following format:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS Len | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ sub-TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: 2

Length: Two 2 octets encoding the length in octets of the Value part.
The value is 4 or other (depending on sub-TLVs) sub-TLVs).

Max SI: A 1-octet field encoding the maximum Maximum Set Identifier (SI) (see
Section 1 of [RFC8279]) used in the encapsulation for this BIER
sub-domain for this BitString length.

BS Len (BitString Length): Len: BitString Length. A 4-bit field encoding the supported
BitString length associated with this BFR-prefix. The values
allowed in this field are specified in Section 2 of [RFC8296].

Label: A 20-bit value representing the first label in the label
range.

The "label range" is the set of labels beginning with the Label and
ending with (Label + (Max SI)). A unique label range is allocated
for each BitString length and sub-domain-id. These labels are used
for BIER forwarding forwarding, as described in [RFC8279] and [RFC8296].

The size of the label range is determined by the number of SIs
(Section 1 of [RFC8279]) that are used in the network. Each SI maps
to a single label in the label range: the first label is for SI=0,
the second label is for SI=1, etc.

If the label associated with the Maximum Set Identifier SI exceeds the 20-bit range,
the BIER MPLS Encapsulation Sub-TLV sub-TLV containing the error MUST be
ignored.

If the same BitString length is repeated in multiple BIER MPLS
Encapsulation Sub-TLVs sub-TLVs inside the same BIER TLV, all BIER MPLS
Encapsulation Sub-TLVs sub-TLVs in the BIER TLV MUST be ignored.

Label ranges within all BIER MPLS Encapsulation Sub-TLVs sub-TLVs advertised
by the same BFR MUST NOT overlap. If an overlap is detected, all
BIER MPLS Encapsulation Sub-TLVs sub-TLVs advertised by the BFR MUST be
ignored.

3.2. BIER Non-MPLS Encapsulation sub-TLV Sub-TLV

The BIER non-MPLS Encapsulation sub-TLV is used for non-MPLS
encapsulation and has the following format. It MAY appear multiple
times within a single BIER TLV. If the same BitString length is
repeated in multiple BIER non-MPLS encapsulation Sub-TLVs Encapsulation sub-TLVs inside the
same BIER TLV, the BIER TLV MUST be ignored.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS LEN Len | BIFT-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ sub-TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: 3. 3

Length: Two 2 octets encoding the length in octets of the Value part.
The value is 4 or other (depending on sub-TLVs).

Max SI: A 1-octet field encoding the Maximum Set Identifier
(Section 1 of [RFC8279]) used in the encapsulation for this BIER
subdomain
sub-domain for this BitString length. The first BIFT-id is for
SI=0, the second BIFT-id is for SI=1, etc. If the BIFT-id
associated with the Maximum Set Identifier SI exceeds the 20-bit range, the sub-TLV sub-
TLV MUST be ignored.

BIFT-id: A 20-bit field representing the first BIFT-id in the
BIFT-id range.

BS Len: BitString Length (BS Len): Length. A 4-bit field encoding the bitstring BitString
length (as per [RFC8296]) supported for the encapsulation.

BIFT-id: A 20-bit field representing the first BIFT-id in the BIFT-
id range.

The "BIFT-id range" is the set of 20-bit values beginning with the
BIFT-id and ending with (BIFT-id + (Max SI)). These BIFT-id's BIFT-ids are
used for BIER forwarding forwarding, as described in [RFC8279] and [RFC8296].

The size of the BIFT-id range is determined by the number of SI's SIs
(Section 1 of [RFC8279]) that are used in the network. Each SI maps
to a single BIFT-id in the BIFT-id range: the first BIFT-id is for
SI=0, the second BIFT-id is for SI=1, etc.

If the BIFT-id associated with the Maximum Set Identifier SI exceeds the 20-bit
range, the BIER non-MPLS Encapsulation sub-TLV containing the error
MUST be ignored.

BIFT-id ranges within all the BIER non-MPLS Encapsulation sub-TLVs
advertised by the same BFR MUST NOT overlap. If an overlap is
detected, all the BIER non-MPLS Encapsulation sub-TLV sub-TLVs advertised by
the BFR MUST be ignored. However, the BIFT-id ranges may overlap
across different encapsulation types and that is allowed. As an
example, the BIFT-id value in the non-MPLS encapsulation Encapsulation sub-TLV may
overlap with the Label value in the Label range in the BIER MPLS
encapsulation
Encapsulation sub-TLV.

3.3. BIER Nexthop sub-TLV Sub-TLV

The BIER Nexthop sub-TLV MAY be included, and it MUST NOT be included
more than once in each of the MPLS or non-MPLS Encapsulation sub-TLV
as well as sub-TLVs
or in the top-level BIER TLV. It is used when calculating BIFT
entries, as described in Section 5 and illustrated in Section 6.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nexthop |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: 4

Length: 2 octets. The value is 4 if the Nexthop is an IPv4 address
and 16 if the Nexthop is an IPv6 address address.

Nexthop: 4 or 16 octets of an IPv4/IPv6 address address.

4. Originating/Propagating/Updating the BIER Attribute

A BIER Forwarding Bit-Forwarding Egress Router (BFER) MUST attach a BIER attribute to
its own /32 (for IPv4) or /128 (for IPv6) host BFR-prefix NLRI. The
BIER attribute MUST include one BIER TLV for each BIER sub-domain
that it supports. Each BIER TLV MUST include an MPLS and/or non-MPLS
Encapsulation sub-TLV, sub-TLV and MAY include a BIER Nexthop sub-TLV with the
Nexthop set to the BIER prefix. If the BIER Nexthop sub-TLV is not
included, the BIER prefix will be used by receiving BFRs as the BIER nexthop
next hop when calculating BIFT.

When a BFR receives an update with the BIER path attribute, the
attribute is parsed with the following validations:

* Syntactic checking based on the length Length field of TLVs and sub-TLVs:

- The total length of BIER TLVs (including the type Type and length Length
fields) MUST be equal to the BIER path attribute length.

- The total length of sub-TLVs (including the type Type and length Length
fields) of a TLV MUST be equal to the length of the TLV.

* Semantic checking as per Section 3.

If the syntactic checking fails, the attribute is considered
malformed and the "attribute discard" action [RFC7606] about for the BIER
attribute MUST be taken. If the semantic checking passes, BIFT
entries are calculated as described in Section 5. Otherwise
(semantic (i.e.,
if semantic checking fails), some or all BIER TLVs are ignored, per
the rules given in Section 3, and if the remaining data permits, BIFT
entries are calculated per Section 5.

When a BFR re-advertises a BGP NLRI with a BIER attribute, for the
sub-domains that this BFR supports, in the corresponding BIER TLV TLV, it
SHOULD set/update the BIER Nexthop sub-TLV to use its own BIER
prefix,
prefix; in which case case, it MUST replace the MPLS or non-MPLS
Encapsulation sub-TLV with its own, i.e., as if the BFR is attaching
the encapsulation sub-TLV for its own BIER prefix. If it does not
update the BIER Nexthop sub-TLVs, it MUST NOT update the MPLS or non-MPLS non-
MPLS Encapsulation sub-TLV. If it does not support a sub-domain, it
MUST NOT update the corresponding BIER TLV.

It's possible that the BFR supports some but not all BitStringLengths
(BSLs) in the received MPLS or non-MPLS Encapsulation sub-TLVs.
After setting/updating the BIER Nexthop sub-TLV in the top BIER TLV
to itself, for the BSLs that it does support, the BFR MUST remove the
BIER Nexthop sub-TLV (if present) in the corresponding MPLS
Encapsulation sub-TLVs. For the BSLs that it does not support:

* If a BIER Nexthop sub-TLV is included in the MPLS Encapsulation sub-
TLV,
sub-TLV, it MUST NOT be updated.

* Otherwise, if a BIER Nexthop sub-TLV was is included in the received
BIER TLV, its original value (before changed for supported BSLs by
this BFR) MUST be copied into the MPLS Encapsulation sub-TLV.

* Otherwise, a BIER Nexthop sub-TLV MUST be added to the MPLS
Encapsulation sub-TLV with its value set to the BFR-prefix.

All impacted length Length fields (e.g., the MPLS Encapsulation sub-TLV Length,
Length and the top-level BIER TLV Length) MUST be updated
accordingly.

Since the BIER attribute is an optional, transitive BGP path
attribute, a non-BFR BGP speaker could still re-advertise the
received route with a BIER attribute.

Two different BFR-prefixes MUST NOT have the same non-zero BFR-ID in
the same sub-domain. If a duplication is detected, the receiving BFR
MUST NOT use the BFR-prefixes with the same BFR-ID for BIFT
calculation for the sub-domain and an error SHOULD be logged.

5. BIFT Calculation with BGP Signaling

As pointed out in [RFC8279], BIFTs are derived from the unicast FIB
by adding BIER-specific information.

For each sub-domain, a BFR calculates the corresponding BIFTs by
going through the BIER prefixes whose BIER attribute includes a BIER
TLV for the sub-domain. For a non-zero BFR-id in the BIER TLV, a
BIFT entry is created or updated. The entry's BFR Neighbor (BFR-NBR)
[RFC8279] is the Nexthop in the BIER Nexthop sub-TLV in the
corresponding MPLS Encapsulation sub-TLV, sub-TLV or in the top-level BIER TLV
if the MPLS Encapsulation sub-TLV does not have a BIER Nexthop sub-TLV. sub-
TLV. If there is no BIER Nexthop sub-TLV at all, The the entry's BFR Neighbor BFR-NBR
is the BIER prefix itself. The BIER label or BIFT-id for the entry
is derived from the Label Range label range in the MPLS Encapsulation sub-TLV or
from the BIFT-id Range range in the non-MPLS Encapsulation sub-TLV.

BIER traffic is sent to the BFR-NBR either directly (BIER header
directly follows a layer Layer 2 header) if the BFR-NBR is directly
connected,
connected or via a tunnel otherwise. tunnel. Notice that, if a non-BFR BGP speaker re-advertises re-
advertises a BIER prefix (in this case case, it can not cannot update the BIER
attribute since it is not capable), or if a BFR BGP speaker
re-advertises re-
advertises a BIER prefix without updating the BIER Nexthop sub-
TLV, sub-TLV,
the BFR receiving the prefix will tunnel BIER traffic - -- the BGP
speaker re-advertising the BIER prefix will not see the BIER traffic
for the BIER prefix.

How the tunnel is set up and chosen is outside the scope of this
document. It can be any kind of tunnel, e.g., MPLS Label Switched
Path or IP/GRE, as long as the tunnel header can indicate that the
payload is BIER.

6. Example of BIER Nexthop Usage and Handling

Consider a simple topology as follows:

----- BFER1
/
BFR1 --- non-BFR --- BFR2 ------ BFER2
\
----- BFER3

The BFER1/2/3 each advertises a route for its loopback address with a
BIER path attribute, listing one BIER TLV for each subdomain sub-domain that it
is in, with a non-zero BFR-ID and an MPLS Encapsulation sub-TLV. A
BIER Nexthop sub-TLV is not included in the one from BFER1 but is
included in the ones from BFER2/3. The BIER Nexthop sub-TLV encodes
the BFR-prefix of BFER2 and BFER3 BFER3, respectively.

When BFR2 receives the route, it calculates its BIFT entries.
Because the route from BFER1 does not include a BIER Nexthop, BFR2
uses BFRer1's BFR1's BFR-prefix as the nexthop. next hop.

When BFR2 re-advertises the routes to the non-BFR, it adds a BIER
Nexthop sub-TLV to the BFER1 route, route and updates the BIER Nexthop sub-
TLV in the BFER2/3 routes, all encoding BFR2's own address. It also
updates the MPLS Encapsulation sub-TLV to encode its own labels.

When the non-BFR receives the routes, since it does not support BIER,
no BIER-specific action is taken and the routes are re-advertised to
BFR1 with the BIER path attribute unchanged.

When BFR1 receives the routes, it calculates the BIFT entries, using
BFR2's address encoded in the BIER Nexthop sub-TLV as the nexthop. next hop.
Because BFR2 is not directly connected, a tunnel must be used.

7. Operational Considerations

It's assumed by

In this document document, it is assumed that the BIER domain [RFC8279] is
aligned with an Administrative Domain (AD) (AD), which may be composed of
multiple Autonomous Systems. Use of the BIER attribute in other
scenarios is outside the scope of this document.

BFR-prefixes are typically loopback addresses on the BFRs. They are
distributed throughout the AD AD, but they do not need to be distributed
outside the AD for the BIER BIER's purposes. This is analogous to that the
Provider Edge router's loopback addresses that are distributed inside
the
AD AD, but they do not need to be distributed outside the AD.

If prefixes are distributed outside of the AD with the BIER attribute
attached and the neighboring AD also deploys deploying BIER, then the two
BIER domains, which should be independent of each other, may be
incorrectly joined together and most likely have conflicting
configurations, causing security risks and operational troubles.

To prevent that, a boundary router of the AD that supports the BIER
attribute MUST support a per-EBGP-session/group policy, policy based on an External BGP (EBGP)
session/group that indicates whether the attribute is allowed and allowed; by default
default, it is NOT allowed. If it is not allowed, the BIER attribute
MUST NOT be sent to any EBGP peer of the session/group. If a BIER
attribute is received from the peer, it MUST be treated exactly as if
it were an unrecognized non-transitive attribute. That is, "it it MUST
be quietly ignored and not passed along to other BGP peers". peers.

8. IANA Considerations

IANA is requested to assign a has assigned codepoint TBD 41 to the BIER attribute in the "BGP Path
Attributes" registry (https://www.iana.org/assignments/bgp-
parameters/bgp-parameters.xhtml#bgp-parameters-2) to the BIER
attribute. <https://www.iana.org/assignments/bgp-
parameters> as follows:

+=======+======+===========+
| Value Name | Code | Reference
===== ==== =========
TBD |
+=======+======+===========+
| 41 | BIER This document | RFC 9793 |
+-------+------+-----------+

Table 1

IANA is requested to create a registry in has created the BGP Parameters registry
group for "BGP BIER TLV and SUB-TLV Types". Sub-TLV Types" registry within
the "Border Gateway Protocol (BGP) Parameters" registry group. The
type field for the registry consists of two 2 octets, with possible
values from 0 to
655355 65535 (the value 0 is reserved). The allocation
policy for this field is to be "First First Come First Serve" Served [RFC8126].

Five

The five initial values are to be have been allocated from the "BGP BIER TLV and
Sub-TLV Types" registry as follows:

+=========+================================+===========+
| Value | Name | Reference
===== ==== ========= |
+=========+================================+===========+
| 0 | Reserved This document | RFC 9793 |
+---------+--------------------------------+-----------+
| 1 | BIER TLV This document | RFC 9793 |
+---------+--------------------------------+-----------+
| 2 | MPLS Encapsulation sub-TLV This document | RFC 9793 |
+---------+--------------------------------+-----------+
| 3 | non-MPLS Encapsulation sub-TLV This document | RFC 9793 |
+---------+--------------------------------+-----------+
| 4 | BIER Nexthop sub-TLV This document | RFC 9793 |
+---------+--------------------------------+-----------+
| 5-65535 | Unassigned |
+---------+--------------------------------------------+

Table 2

9. Security Considerations

This document introduces no new security considerations beyond those
already discussed in [RFC4271] and [RFC8279] [RFC4271], [RFC8279], and the operational
considerations (Section 7) of this document.

12.

10. References

12.1.

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.

[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.

12.2.

10.2. Informative References

[I-D.ietf-bier-prefix-redistribute]

[BIER-Prefix-Redistribute]
Zhang, Z., Wu, B., Zhang, Z. J., Wijnands, I., Liu, Y.,
and H. Bidgoli, "BIER Prefix Redistribute", Work in
Progress, Internet-Draft, draft-ietf-bier-prefix-
redistribute-07, 28 August 2024,
redistribute-08, 23 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
prefix-redistribute-07>.
prefix-redistribute-08>.

[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.

[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

11.

Acknowledgements

Thanks a lot for to Eric Rosen and Peter Psenak for their valuable comments on
this document.

10.

Contributors

This document has the following contributors: contributor:

Zheng (Sandy) Zhang
ZTE
Email: zhang.zheng@zte.com.cn

Authors' Addresses

Xiaohu Xu
China Mobile
Email: xuxiaohu@cmss.chinamobile.com

Mach

Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com

Keyur Patel
Arrcus, Inc.
Email: keyur@arrcus.com

IJsbrand Wijnands
Individual
Email: ice@braindump.be
Antoni

Tony Przygienda
Juniper
Email: prz@juniper.net

Zhaohui Zhang (editor)
Juniper
Email: zzhang@juniper.net