MVPN and MSDP SA Interoperation

Versions: 00                                                            
BESS                                                            Z. Zhang
Internet-Draft                                               L. Giuliano
Intended status: Standards Track                        Juniper Networks
Expires: March 31, 2018                               September 27, 2017

                    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 March 31, 2018.

Copyright Notice

   Copyright (c) 2017 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

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   ( in effect on the date of
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Table of Contents

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

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)
   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.

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   With this mode, the MVPN Source Active routes are functionally
   similar 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  BGP route propagation/selection rules remove the need for RPF
      checking required by MSDP.

   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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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

   When an MVPN PE advertises an MVPN SA route, 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 in the VRF 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.

   If an MVPN PE has one or more MSDP sessions and receives an MVPN SA
   route that is selected as the best MVPN SA route for a given
   (C-S,C-G), the PE generates an MSDP SA and transmits it to those MSDP
   peers.  The Global Administrative field in the MVPN SA RP-address EC
   of the MVPN SA route is used to populate the RP address of the MSDP
   SA.  If the MVPN SA route does not have the EC, the local RP address
   of the VRF is be used to populate the RP address field of the MSDP

   If an MVPN PE receives the withdraw of an MVPN SA route, a new best
   MVPN SA route for the (C-S,C-G) may be selected.  A new MSDP SA
   message is advertised if the RP address determined according to the
   newly selected best MVPN SA route is different from before.  If there
   is no MVPN SA route left for the (C-S,C-G), the previously advertised
   MSDP SA message will not be refreshed and will eventually time out.

4.  IANA Considerations

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

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5.  Acknowledgements

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

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,

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

   [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,

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks


   Lenny Giuliano
   Juniper Networks


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