PIM Join/Prune Attributes for LISP Environments using Underlay Multicast
draft-ietf-pim-jp-extensions-lisp-09

Internet Engineering Task Force                              V. Govindan
Internet-Draft                                                 S. Venaas
Updates: 8059 (if approved)                                        Cisco
Intended status: Experimental                           21 February 2025
Expires: 25 August 2025

PIM Join/Prune Attributes for LISP Environments 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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Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  The case for extending the Received ETR RLOC Attribute of RFC
           8059  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Flexible mapping of overlay to underlay group ranges: . .   3
     2.2.  Multicast Address Range constraints:  . . . . . . . . . .   3
   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.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   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.  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 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 nodes needed to avoid
   unnecessary replication or traffic hairpinning.

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   Since the Receiver RLOC Attribute defined in [RFC8059] only addresses
   the Ingress Replication case, an extension of 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 for extending the Received ETR RLOC Attribute of RFC 8059

   When 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:

2.1.  Flexible mapping of overlay to underlay group ranges:

   Three distinct types of overlay to underlay group mappings are
   possible: 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 mapping: Conversely a single same overlay
   flow can be mapped to two or more flows, e.g., (root-RLOC, G-u1) and
   (root-RLOC, G-u2) to cater to the requirements of downstream xTR
   nodes.  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:

   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 like Proxy Tunnel Routers or when using nodes with
   limited hardware resources as explained 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

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     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

   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:

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   *  It chooses an underlay multicast group that it can join.  This is
      a matter of local decision, 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.

6.  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.

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7.  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>.

Authors' Addresses

   Vengada Prasad Govindan
   Cisco
   Email: venggovi@cisco.com

   Stig Venaas
   Cisco
   Email: svenaas@cisco.com

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