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PIM Join/ Prune Attributes for LISP Environments using Underlay Multicast
draft-ietf-pim-jp-extensions-lisp-05

Document Type Active Internet-Draft (pim WG)
Authors Vengada Prasad Govindan , Stig Venaas
Last updated 2024-02-26
Replaces draft-vgovindan-pim-jp-extensions-lisp
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draft-ietf-pim-jp-extensions-lisp-05
Internet Engineering Task Force                              V. Govindan
Internet-Draft                                                 S. Venaas
Updates: 8059 (if approved)                                        Cisco
Intended status: Experimental                           26 February 2024
Expires: 29 August 2024

    PIM Join/ Prune Attributes for LISP Environments using Underlay
                               Multicast
                  draft-ietf-pim-jp-extensions-lisp-05

Abstract

   This document specifies an update to the PIM Receiver RLOC Join/
   Prune attribute that supports the construction of multicast
   distribution trees where the root 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).

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 of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 29 August 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components

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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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
   3.  Updates to RFC 8059 . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     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  . . . . . . . . . . . . . . . . . . . .   5
   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 J/P attribute extensions to construct multicast
   distribution trees.  This document extends the Receiver ETR RLOC PIM
   J/P 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 and avoid
   unnecessary replication or traffic hairpinning.

   Since the Receiver RLOC Attribute defined in [RFC8059] only addresses
   the Ingress Replication case, an extension of the scope of that PIM
   J/P 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.

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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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

   When LISP based Multicast trees can be built using IP Multicast in
   the underlay, the mapping between the overlay group address and the
   underlay group address becomes a very crucial engineering decision:

   Flexible mapping of overlay to underlay group ranges:
    Three different types of overlay to underlay group mappings are
    possible: Many to one mapping: Many (root-EID, G) flows originating
    from a RLOC can be mapped to the same underlay (root-RLOC, G-u)
    flow.  One to many mapping: Conversely the 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 different
    (root-RLOC, G-u) flow.

   Multicast Address Range constraints:
    It is possible that under certain circumstances, differnt subsets of
    xTRs subscribing to the same overlay multicast stream would be
    constrained to use different underlay multicast mapping ranges.
    This definitely involves a trade-off between replication and the
    flexibility in assigning address ranges and could be required in
    certain situations further below.

   Inter-site PxTR:
    When multiple LISP sites are connected through a LISP based transit,
    the site border node interconnects the site-facing interfaces and
    the external LISP based core.  Under such circumstances, there could
    be different ranges of multicast group addresses used for building
    the (S-RLOC, G) trees inside the LISP site and the external LISP
    based core.  This is desired for various reasons:

   Hardware resource restrictions:
    Platform limitations could force engineering decisions to be made on
    restricting multicast address ranges in the underlay.

3.  Updates to RFC 8059

3.1.  Scope

   There are no changes proposed to the syntax and semantics of the
   Transport attributed defined in RFC8059 [RFC8059].

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   The scope of the updates proposed to RFC 8059 [RFC8059] are 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 Receiver RLOC field of the Receiver RLOC Attribute MAY contain a
    multicast IP address.  This 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.  The source IP 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, beyond the scope of this document.

   *  It identifies the upstream LISP site where the underlay multicast
      tree 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 oif-list 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.

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4.  Acknowledgements

   The authors would like to thank Dino Farinacci, Victor Moreno, Alvaro
   Retana and Aswin Kuppusami for their valuable comments.  The authors
   also thank Sankaralingam T and Amit Kumar for their contributions to
   the document.

5.  IANA Considerations

   No new requests to IANA.

6.  Security Considerations

   There is perhaps a new attack vector where an attacker can send a
   bunch of joins with different group addresses.  It may interfere with
   other multicast traffic if those group addresses overlap.  Also, it
   may take up a lot of resources if replication for thousands of groups
   are requested.  However PIM authentication could be used here.  Since
   explicit tracking could be done, an implementation may consider knobs
   to ensure that for each ETR RLOC (the RLOC used as the source of the
   overlay join), there could be a configurable number of maximum
   permissible group(s).

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>.

   [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>.

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   [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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