wdiff rfc9798.original rfc9798.txt

Internet Engineering Task Force (IETF) V. Govindan
Internet-Draft
Request for Comments: 9798 S. Venaas
Updates: 8059 (if approved) Cisco
Intended status:
Category: Experimental 21 February 2025
Expires: 25 August May 2025
ISSN: 2070-1721

PIM Join/Prune Attributes for LISP Locator/ID Separation Protocol (LISP)
Environments using Using Underlay Multicast
draft-ietf-pim-jp-extensions-lisp-09

Abstract

This document specifies an update to the PIM Receiver RLOC Join/Prune
attribute that supports the construction of multicast distribution
trees where the source and receivers are located in different
Locator/ID Separation Protocol (LISP) sites and are connected using
underlay IP Multicast. This attribute allows the receiver site to
signal the underlay multicast group to the control plane of the root
Ingress Tunnel Router (ITR). This document updates RFC 8059.

Status of This Memo

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provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.

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This Internet-Draft will expire on 25 August 2025.
https://www.rfc-editor.org/info/rfc9798.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. The case Case for extending Extending the Received ETR RLOC Attribute of RFC
8059 . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Flexible mapping Mapping of overlay Overlay to underlay group ranges: . . 3 Underlay Group Ranges
2.2. Multicast Address Range constraints: . . . . . . . . . . 3 Constraints
3. Updates to RFC 8059 . . . . . . . . . . . . . . . . . . . . . 4
3.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Receiver ETR RLOC Attribute . . . . . . . . . . . . . . . 4
3.3. Using the Receiver RLOC Attribute . . . . . . . . . . . . 4
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6.
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7.
6. Normative References . . . . . . . . . . . . . . . . . . . . 6
Acknowledgements
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6

1. Introduction

The construction of multicast distribution trees where the root and
receivers are located in different LISP sites [RFC9300] is defined in
[RFC6831].

[RFC6831] specifies that (root-EID, G) data packets are to be LISP-
encapsulated into (root-RLOC, G) multicast packets. [RFC8059]
defines PIM Join/Prune attribute extensions to construct multicast
distribution trees. Please refer to Section 3 of [RFC6831] for the
definition of the terms EID and RLOC. Endpoint ID (EID) and Routing Locator (RLOC).
We use the term root-EID or root-RLOC to refer to the source of the
multicast tree rooted at the EID or RLOC. This document extends the
Receiver ETR RLOC PIM Join/
Prune Join/Prune attribute [RFC8059] to facilitate
the construction of underlay multicast trees for (root-RLOC, G).

Specifically, the assignment of the underlay multicast group needs to
be done in consonance with the downstream xTR Tunnel Router (xTR) nodes
needed to avoid unnecessary replication or traffic hairpinning.

Since the Receiver RLOC Attribute defined in [RFC8059] only addresses
the Ingress Replication case, an extension of this document extends the scope of that
PIM Join/Prune attribute is defined by this draft to include scenarios where the underlay uses
Multicast transport. The scope extension
proposed here complies with the base
specification [RFC5384].

This document uses terminology defined in [RFC9300], such as EID,
RLOC, ITR, and ETR.

1.1. 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.

2. The case Case for extending Extending the Received ETR RLOC Attribute of RFC 8059

When LISP based LISP-based Multicast trees are constructed using IP Multicast in
the underlay, the mapping between the overlay group address and the
underlay group address becomes a crucial engineering decision: decision.

2.1. Flexible mapping Mapping of overlay Overlay to underlay group ranges: Underlay Group Ranges

Three distinct types of overlay to underlay group mappings are
possible: Many to one

* Many-to-one mapping: Many (root-EID, G) flows originating from an
RLOC can be mapped to a single underlay multicast (root-RLOC, G-u)
flow. One to many

* One-to-many mapping: Conversely a single same overlay flow can be
mapped to two or more flows, flows -- e.g., (root-RLOC, G-u1) and
(root-RLOC, (root-
RLOC, G-u2) -- to cater to the requirements of downstream xTR
nodes. One to one

* One-to-one mapping: Every (root-EID, G) flow is mapped to a unique
(root-RLOC, G-u) flow.

2.2. Multicast Address Range constraints: Constraints

Under certain conditions, different subsets of xTRs subscribing to
the same overlay multicast stream may be constrained to use distinct
underlay multicast mapping ranges.

This introduces a trade-off between replication overhead and the
flexibility of address range assignment, which may be necessary in
specific use-cases use cases like Proxy Tunnel Routers or when using nodes with
limited hardware resources as explained below: below.

Inter-site Proxy Tunnel Routers (PxTR):
When multiple LISP sites are interconnected through a LISP-based
transit, the site border node (PxTR) connects the site-facing
interfaces with the external LISP core. In such cases, different
ranges of multicast group addresses may be used for constructing
(S-RLOC, G) trees within the LISP site and in the external LISP
core. This distinction is desirable for various operational
reasons
reasons.

Hardware resource restrictions:
Platform limitations may necessitate engineering decisions to
restrict multicast address ranges in the underlay due to hardware
resource constraints.

3. Updates to RFC 8059

3.1. Scope

No changes are proposed to the syntax or semantics of the Transport
Attribute defined in RFC 8059 [RFC8059].

The scope of the updates to RFC 8059 [RFC8059] is limited to the case where
the "Transport" field of the Transport Attribute is set to zero
(Multicast) only.

3.2. Receiver ETR RLOC Attribute

The definition of the "Receiver RLOC" field of the Receiver ETR RLOC
attribute RFC 8059 [RFC8059] is updated as follows:

| Receiver RLOC:
| The RLOC address on which the receiver ETR wishes to receive
| the encapsulated flow. A unicast IP Receiver RLOC address is
| used for unicast-encapsulated flows. Alternately, a multicast
| IP Receiver RLOC address is used for for multicast-encapsulated
| flows. A multicast IP address MUST be used only when the
| underlay network of the LISP core supports IP Multicast
| transport.

The definitions of the other fields of the Receiver ETR RLOC
Attribute remain unchanged.

When the ITR needs to track the list of ETRs from which the PIM joins
are received, the ITR MUST use the source IP address field of the
incoming PIM Join/Prune message. The source IP address of the PIM
Join/Prune MUST be an ETR RLOC IP address.

3.3. Using the Receiver RLOC Attribute

When the ETR determines to use the multicast underlay:

* It chooses an underlay multicast group that it can join. This is
a matter of local decision, which is beyond the scope of this
document.

* It identifies the upstream LISP site where the underlay multicast
tree needs to be rooted.

* It constructs the PIM Join/Prune message as specified in RFC 8059
[RFC8059]. Only the Receiver RLOC attribute is encoded as above.

When the ITR receives a PIM Join/Prune message:

* It allocates a new entry in the OutgoingInterfaceList RFC 6831 [RFC6831]
for every unique underlay multicast mapping.

* The ITR MAY apply local policy to perform any kind of rate-
limiting on the number of copies it needs to make in the underlay.
Such actions are beyond the scope of this document.

4. Acknowledgements

The authors would like to thank Dino Farinacci, Victor Moreno, Alvaro
Retana, Aswin Kuppusami, Joe Clarke and Peter Yee for their valuable
comments. The authors also thank Sankaralingam T and Amit Kumar for
their contributions to the document. The authors thank Gunter van de
Velde for his valuable comments.

5. IANA Considerations

No new requests to IANA.

This document has no IANA actions.

5. Security Considerations

An attack vector arises where an attacker sends numerous PIM Join
messages with different group addresses. This could interfere with
legitimate multicast traffic if the group addresses overlap.
Additionally, resource exhaustion may occur if replication is
requested for a large number of groups, potentially resulting in
significant resource consumption. To mitigate these risks, PIM
authentication mechanisms RFC 5796 [RFC5796] could be employed to validate
join requests. Furthermore, implementations may consider explicit
tracking mechanisms to manage joins more effectively. Configurable
controls could be introduced, allowing for a maximum permissible
number of groups for each ETR RLOC used as the source of overlay
joins. These controls would limit the impact of such attacks and
ensure that resource allocation is managed appropriately.

6. 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>.

[RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol
Independent Multicast (PIM) Join Attribute Format",
RFC 5384, DOI 10.17487/RFC5384, November 2008,
<https://www.rfc-editor.org/info/rfc5384>.

[RFC5796] Atwood, W., Islam, S., and M. Siami, "Authentication and
Confidentiality in Protocol Independent Multicast Sparse
Mode (PIM-SM) Link-Local Messages", RFC 5796,
DOI 10.17487/RFC5796, March 2010,
<https://www.rfc-editor.org/info/rfc5796>.

[RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The
Locator/ID Separation Protocol (LISP) for Multicast
Environments", RFC 6831, DOI 10.17487/RFC6831, January
2013, <https://www.rfc-editor.org/info/rfc6831>.

[RFC8059] Arango, J., Venaas, S., Kouvelas, I., and D. Farinacci,
"PIM Join Attributes for Locator/ID Separation Protocol
(LISP) Environments", RFC 8059, DOI 10.17487/RFC8059,
January 2017, <https://www.rfc-editor.org/info/rfc8059>.

[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>.

[RFC9300] Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, Ed., "The Locator/ID Separation Protocol
(LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
<https://www.rfc-editor.org/info/rfc9300>.

Acknowledgements

The authors would like to thank Dino Farinacci, Victor Moreno, Alvaro
Retana, Aswin Kuppusami, Joe Clarke, and Peter Yee for their valuable
comments. The authors also thank Sankaralingam T and Amit Kumar for
their contributions to the document. The authors thank Gunter Van de
Velde for his valuable comments.

Authors' Addresses

Vengada Prasad Govindan
Cisco
Email: venggovi@cisco.com

Stig Venaas
Cisco
Email: svenaas@cisco.com