BESS                                                            Z. Zhang
Internet-Draft                                               L. Giuliano
Updates: 6514 (if approved)                             Juniper Networks
Intended status: Standards Track                        January 18, 2018
Expires: July 22, 2018

                    MVPN and MSDP SA Interoperation


   This document specifies the procedures for interoperation between
   MVPN Source Active routes and customer MSDP Source Active routes,
   which is useful for MVPN provider networks offering services to
   customers with an existing MSDP infrastructure.  Without the
   procedures described in this document, VPN-specific MSDP sessions are
   required among the PEs that are customer MSDP peers.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC2119.

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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   This Internet-Draft will expire on July 22, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  MVPN RPT-SPT Mode . . . . . . . . . . . . . . . . . . . .   4
   3.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Terminologies

   Familiarity with MVPN and MSDP protocols and procedures is assumed.
   Some terminologies are listed below for convenience.

   o  ASM: Any source multicast.

   o  SPT: Source-specific Shortest-path Tree.

   o  C-S: A multicast source address, identifying a multicast source
      located at a VPN customer site.

   o  C-G: A multicast group address used by a VPN customer.

   o  C-RP: A multicast Rendezvous Point for a VPN customer.

   o  EC: Extended Community.

2.  Introduction

   Section "14.  Supporting PIM-SM without Inter-Site Shared C-Trees" of
   [RFC6514] specifies the procedures for MVPN PEs to discover (C-S,C-G)
   via MVPN Source Active A-D routes and then send (C-S,C-G) C-multicast
   routes towards the ingress PEs, to establish SPTs for customer ASM
   flows for which they have downstream receivers.  (C-*,C-G)

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   C-multicast routes are not sent among the PEs so inter-site shared
   C-Trees are not used and the method is generally referred to as "spt-
   only" mode.

   With this mode, the MVPN Source Active routes are functionally
   similar to MSDP Source-Active messages [RFC3618].  One or more of the
   PEs, say PE1, either act as a C-RP and learn of (C-S,C-G) via PIM
   Register messages, or have MSDP sessions with some MSDP peers and
   learn (C-S,C-G) via MSDP SA messages.  In either case, PE1 will then
   originate MVPN SA routes for other PEs to learn the (C-S,C-G).

   [RFC6514] only specifies that a PE receiving the MVPN SA routes, say
   PE2, will advertise (C-S,C-G) C-multicast routes if it has
   corresponding (C-*,C-G) state learnt from its CE.  PE2 may also have
   MSDP sessions with other C-RPs at its site, but [RFC6514] does not
   specify that it advertise MSDP SA messages to those MSDP peers for
   the (C-S,C-G) that it learns via MVPN SA routes.  PE2 would need to
   have an MSDP session with PE1 (that advertised the MVPN SA messages)
   to learn the sources via MSDP SA messages, for it to advertise the
   MSDP SA to its local peers.  To make things worse, unless blocked by
   policy control, PE2 would in turn advertise MVPN SA routes because of
   those MSDP SA messages that it receives from PE1, which are redundant
   and unnecessary.  Also notice that the PE1-PE2 MSDP session is VPN-
   specific, while the BGP sessions over which the MVPN routes are
   advertised are not.

   If a PE does advertise MSDP SA messages based on received MVPN SA
   routes, the VPN-specific MSDP sessions are no longer needed.
   Additionally, this MVPN/MSDP SA interoperation has the following
   inherent benefits for a BGP based solution.

   o  MSDP SA refreshes are replaced with BGP hard state.

   o  Route Reflectors can be used instead of having peer-to-peer

   o  VPN extranet mechanisms can be used to propagate (C-S,C-G)
      information across VPNs with flexible policy control.

   While MSDP Source Active routes contain the source, group and RP
   address of a given multicast flow, MVPN Source Active routes only
   contain the source and group.  MSDP requires the RP address
   information in order to perform peer-RPF.  Therefore, this document
   describes how to convey the RP address information into the MVPN
   Source Active route using an Extended Community so this information
   can be shared with an existing MSDP infrastructure.

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   The procedures apply to Global Table Multicast (GTM) [RFC7716] as

2.1.  MVPN RPT-SPT Mode

   For comparison, another method of supporting customer ASM is
   generally referred to "rpt-spt" mode.  Section "13.  Switching from a
   Shared C-Tree to a Source C-Tree" of [RFC6514] specifies the MVPN SA
   procedures for that mode, but those SA routes are replacement for
   PIM-ASM assert and (s,g,rpt) prune mechanisms, not for source
   discovery purpose.  MVPN/MSDP SA interoperation for the "rpt-spt"
   mode is outside of the scope of this document.  In the rest of the
   document, the "spt-only" mode is assumed.

3.  Specification

   The MVPN PEs that act as customer RPs or have one or more MSDP
   sessions in a VPN (or the global table in case of GTM) are treated as
   an MSDP mesh group for that VPN (or the global table).  In the rest
   of the document, it is referred to as the PE mesh group.  It MUST not
   include other MSDP speakers, and is integrated into the rest of MSDP
   infrastructure for the VPN (or the global table) following normal
   MSDP rules and practices.

   When an MVPN PE advertises an MVPN SA route following procedures in
   [RFC6514] for the "spt-only" mode, it SHOULD attach an "MVPN SA RP-
   address Extended Community".  This is a Transitive IPv4-Address-
   Specific Extended Community.  The Local Administrative field is set
   to zero and the Global Administrative field is set to an RP address
   determined as the following:

   o  If the (C-S,C-G) is learnt as result of PIM Register mechanism,
      the local RP address for the C-G is used.

   o  If the (C-S,C-G) is learnt as result of incoming MSDP SA messages,
      the RP address in the selected MSDP SA message is used.

   In addition to procedures in [RFC6514], an MVPN PE may be provisioned
   to generate MSDP SA messages from received MVPN SA routes, with or
   without fine policy control.  If a received MVPN SA route is to
   trigger MSDP SA message, it is treated as if a corresponding MSDP SA
   message was received from within the PE mesh group and normal MSDP
   procedure is followed (e.g. an MSDP SA message is advertised to other
   MSDP peers outside the PE mesh group).  The (S,G) information comes
   from the (C-S,C-G) encoding in the MVPN SA NLRI and the RP address
   comes from the "MVPN SA RP-address EC" mentioned above.  If the
   received MVPN SA route does not have the EC (this could be from a
   legacy PE that does not have the capability to attach the EC), the

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   local RP address for the C-G is used.  In that case, it is possible
   that receiving PE's RP for the C-G is actually the MSDP peer to which
   the generated MSDP message is advertised, causing the peer to discard
   it due to RPF failure.  To get around that problem the peer SHOULD
   use local policy to accept the MSDP SA message.

   An MVPN PE MAY treat only the best MVPN SA route selected by BGP
   route selection process (instead of all MVPN SA routes) for a given
   (C-S,C-G) as a received MSDP SA message (and advertise corresponding
   MSDP message).  In that case, if the selected best MVPN SA route does
   not have the "MVPN SA RP-address EC" but another route for the same
   (C-S, C-G) does, then the best route with the EC SHOULD be chosen.
   As a result, when/if the best MVPN SA route with the EC changes, a
   new MSDP SA message is advertised if the RP address determined
   according to the newly selected MVPN SA route is different from
   before.  The previously advertised MSDP SA message with the older RP
   address will be timed out.

4.  IANA Considerations

   This document introduces a new Transitive IPv4 Address Specific
   Extended Community "MVPN SA RP-address Extended Community".  An IANA
   request will be submitted for a subcode of 0x20 (pending approval and
   subject to change) in the Transitive IPv4-Address-Specific Extended
   Community Sub-Types registry.

5.  Acknowledgements

   The authors thank Eric Rosen and Vinod Kumar for their review,
   comments, questions and suggestions for this document.  The authors
   also thank Yajun Liu for her review and comments.

6.  References

6.1.  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,

   [RFC3618]  Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
              Discovery Protocol (MSDP)", RFC 3618,
              DOI 10.17487/RFC3618, October 2003,

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   [RFC6514]  Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
              Encodings and Procedures for Multicast in MPLS/BGP IP
              VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,

6.2.  Informative References

   [RFC7716]  Zhang, J., Giuliano, L., Rosen, E., Ed., Subramanian, K.,
              and D. Pacella, "Global Table Multicast with BGP Multicast
              VPN (BGP-MVPN) Procedures", RFC 7716,
              DOI 10.17487/RFC7716, December 2015,

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks


   Lenny Giuliano
   Juniper Networks


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