Internet Engineering Task Force                              V. Govindan
Internet-Draft                                                 S. Venaas
Intended status: Experimental                                      Cisco
Expires: 21 October 2022                                   19 April 2022

    PIM Join/ Prune Attributes for LISP Environments using Underlay


   This document specifies an extension to 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 ITR
   (Ingress Tunnel Router).

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   Copyright (c) 2022 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
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The construction of multicast distribution trees where the root and
   receivers are located in different LISP sites [RFC6830] is defined in

   [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 [RFC6830], 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",
   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.  The overlay can use ASM while the underlay
    can use SSM ranges.

   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.

   Other Use-cases:

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   Editorial Note: Comments from Stig: There should be some text
   indicating that the group address used should ideally only be used
   for LISP encapsulation (if ASM), and perhaps that it is preferrable
   to use an SSM group.  Also, that the group obviously must be a group
   that the underlay supports/allows.  I think it is also worth noting
   that ideally, different ETRs should request the same group.

3.  Acknowledgements

   The authors would like to thank Dino Farinacci and Victor Moreno for
   their valuable comments.

4.  Contributors


   Amit Kumar

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 (?) should come to the
   rescue here.  TBD Since explicit tracking would be done, perhaps it
   is worth enforcing 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).  TBD

   Ed Note: To be addressed - Comments from Stig: Regarding security
   considerations and PIM authentication.  The only solution we have
   here is to use IP-Sec to sign the J/P messages.  I don't know if
   anyone has tried to us IPSec between LISP RLOCs.  Are there any LISP
   security mechanisms that would help here for authenticating LISP
   encapsulated messages between xTRs?

7.  Normative References

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5384]  Boers, A., Wijnands, I., and E. Rosen, "The Protocol
              Independent Multicast (PIM) Join Attribute Format",
              RFC 5384, DOI 10.17487/RFC5384, November 2008,

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,

   [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, <>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <>.

   [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, <>.

Authors' Addresses

   Vengada Prasad Govindan

   Stig Venaas

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