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BESS                                                            Z. Zhang
Internet-Draft                                                    W. Lin
Intended status: Standards Track                        Juniper Networks
Expires: April 16, 2021                                       J. Rabadan
                                                        October 13, 2020

               Multicast in L3VPNs Signaled by EVPN SAFI


   [ietf-bess-evpn-prefix-advertisement] specifies an EVPN SAFI Type-5
   route that can be used to signal L3VPNs.  This document specifies
   procedures for multicast in such an L3VPN.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.

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
   Task Force (IETF).  Note that other groups may also distribute
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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
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   This Internet-Draft will expire on April 16, 2021.

Copyright Notice

   Copyright (c) 2020 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
   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 extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Optimized Inter-Subnet Multicast for EVPN . . . . . . . .   3
     2.2.  Using [RFC6514] Procedures  . . . . . . . . . . . . . . .   4
     2.3.  Using [RFC6037] Procedures  . . . . . . . . . . . . . . .   4
     2.4.  Adapted [RFC6514] Procedures  . . . . . . . . . . . . . .   5
   3.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Terminology

   It is expected that audience is familiar with EVPN and MVPN concepts
   and terminologies.  For convenience, the following terms are briefly

   o  PMSI: P-Multicast Service Interface - a conceptual interface for a
      PE to send customer multicast traffic to all or some PEs in the
      same VPN.

   o  I-PMSI: Inclusive PMSI - to all PEs in the same VPN.

   o  S-PMSI: Selective PMSI - to some of the PEs in the same VPN.

   o  Leaf A-D routes: For explicit leaf tracking purpose.  Triggered by
      S-PMSI A-D routes and targeted at triggering route's originator.

   o  IMET A-D route: Inclusive Multicast Ethernet Tag A-D route.  The
      EVPN equivalent of MVPN Intra-AS I-PMSI A-D route.

   o  SMET A-D route: Selective Multicast Ethernet Tag A-D route.  The
      EVPN equivalent of MVPN Leaf A-D route but unsolicited and

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2.  Introduction

   Traditionally, an L3VPN is signaled with BGP "MPLS-labeled VPN
   address" SAFI and uses MPLS as provider tunnel as specified in
   [RFC4364>].  Multicast support in such an L3VPN is specified in
   [RFC6513] and [RFC6514].

   [ietf-bess-evpn-prefix-advertisement] specifies another way of
   signaling L3VPN via EVPN SAFI Type-5 routes for two reasons:

   o  VXLAN tunnels can be used, either for deployment scenarios where
      MPLS is not desired or for the purpose of better ECMP hashing.

   o  In an environment where EVPN is already needed for L2VPN, an
      operator may prefer just using an additional EVPN route type to
      signal L3VPN routes, instead of using another SAFI.  This is
      especially the case when L3VPN is used to provide inter-DC

   [ietf-bess-evpn-prefix-advertisement] does not define procedures for
   multicast.  This document provides three options for different
   deployment scenarios.

2.1.  Optimized Inter-Subnet Multicast for EVPN

   If all multicast senders and receivers are in an EVPN domain
   (including both intra-DC and inter-DC cases), the Optimized Inter-
   Subnet Multicast (OISM) procedures defined in [ietf-bess-evpn-irb-
   mcast] is the best and preferred option.  The advantages are that no
   new procedures are needed and Any Source Multicast (ASM) does not
   need PIM Rendezvous Point (RP) procedures.

   This does require that, if not all BDs are presented on every PE,
   then a Supplemental Bridge Domain (SBD) needs to be configured on
   every PE.  Since the "Interface-less IP-VRF-to-IP-VRF Model" defined
   in Section 4.4.1 of [ietf-bess-evpn-prefix-advertisement] does not
   use SBD, for multicast purpose it is better to move away from that

   Additionally, in case of inter-DC, the SBD needs be stretched across
   DCs even if regular BDs are not stretched.  If the number of PEs in
   all DCs becomes very large, segmentation procedures defined in [ietf-
   bess-evpn-bum-procedures-update] and further enhanced in [zzhang-
   bess-mvpn-evpn-cmcast-enhancements] can be used.  Alternatively, MVPN
   procedures defined in [RFC6514] can be used/adapted for an L3VPN
   signaled by EVPN Type-5 routes, as described in the following two

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2.2.  Using [RFC6514] Procedures

   If the OISM procedure cannot be used for any of the following
   situations that use L3VPN signaled by EVPN Type-5 routes:

   o  There are senders/receivers not on a BD of an EVPN domain and OISM
      cannot extend to connect them.

   o  Stretching SBD across a DCI is not desired as described in the
      previous section.

   o  It's a pure L3VPN scenario, where EVPN does not add any value.

   MVPN procedures defined in [RFC6514] (often referred to as BGP-MVPN)
   can be used as is as long as:

   o  The MVPN procedures treat EVPN Type-5 routes the same as routes
      signaled with "MPLS-labeled VPN address" when it comes to UMH

   o  The EVPN Type-5 routes to C-RP or C-src carry the VRF Route Import
      Extended Community and Source AS Extended Extended Community.

   In other words, the only difference is that the routes used for UMH
   selection now includes those signaled via EVPN Type-5 routes, and
   they MUST carry the two ECs mentioned above.  The rest of [RFC6514]
   procedures are unchanged.

   The EVPN Type-2 signaled IP routes may be used as well, though from
   MVPN point of view, they're no different from "local" routes
   associated with IRB interfaces.

2.3.  Using [RFC6037] Procedures

   The historic RFC 6037 describes the legacy PIM-based MVPN (often
   referred to as Rosen/PIM-MVPN).  While the BGP-MVPN specified in
   [RFC6514] is widely used and deemed more scalable and more versatile,
   the legacy PIM/Rosen-MVPN is still used by some operators, and in
   case of EVPN-signaled L3VPN, it can also be used, perhaps with little
   implementation change, especially if PIM-ASM based Multicast
   Distribution Tree (MDT, or provider tunnel) is appropriate or

   It must be pointed out that, if PIM-SSM or other types of MDTs are
   desired, or if Inter-AS MDTs are needed, [RFC6037] requires a MDT
   SAFI to be used.  In that case, the BGP-MVPN approach as discussed in
   the previous section is recommended (since a new SAFI is needed
   anyway even with PIM-MVPN in this case).

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2.4.  Adapted [RFC6514] Procedures

   Notice that, an operator may have chosen to use EVPN Type-5 routes to
   signal L3VPN because they wanted to avoid signaling another BGP SAFI.
   Using [RFC6514] procedures as described in the previous section
   defeats that purpose because a new MCAST-VPN SAFI has to be used.

   That can be resolved by adapting the [RFC6514] procedures with EVPN
   SAFI, as described below.

   RFC6514 uses 7 route types and only the Source Active route does not
   already have a corresponding EVPN route type:

           MVPN                        EVPN
        Type  Name                  Type  Name
        ----  ----                  ----  ----
        1     Intra-AS I-PMSI       3     IMET
        2     Inter-AS I-PMSI       9     Per-Region I-PMSI
        3     S-PMSI                10    S-PMSI
        4     Leaf                  11    Leaf
        5     Source Active         TBD   Source Active (added in this spec)
        6     (*,G) C-Multicast     6     SMET
        7     (S,G) C-Multicast     7     SMET

   As pointed out in [zzhang-bess-mvpn-evpn-cmcast-enhancements], the
   MVPN Type-6/7 C-multicast routes don't have leaf tracking semantics
   while EVPN SMET route has built-in leaf tracking semantics.  Both
   have pros and cons depending on the situation.  This document will
   specify when SMET routes used for MVPN do or do not need leaf
   tracking semantics and the corresponding procedures.

   Also as pointed out in [zzhang-bess-mvpn-evpn-cmcast-enhancements],
   the MVPN Type-6/7 C-multicast routes are targeted while EVPN SMET
   routes are not.  This document specifies that the EVPN SMET routes
   used for MVPN purpose will be targeted, except in a special case as
   mentioned in [zzhang-bess-mvpn-evpn-cmcast-enhancements].

   With this, the MEG (MVPN/EVPN Gateway) [ietf-bess-evpn-irb-mcast]
   follows the adapted MVPN procedures as specified in this document
   instead of the [RFC6514] procedures on MVPN side.

   Detailed procedures are specified in the following section.

3.  Specifications

   Details to be added.

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4.  Security Considerations

   This document does not introduce new security risks.  Whatever
   security aspects that are applicable to [RFC7432], [RFC6513],
   [RFC6514] and [ietf-bess-evpn-prefix-advertisement] apply here.

5.  References

5.1.  Normative References

              Lin, W., Zhang, Z., Drake, J., Rosen, E., Rabadan, J., and
              A. Sajassi, "EVPN Optimized Inter-Subnet Multicast (OISM)
              Forwarding", draft-ietf-bess-evpn-irb-mcast-04 (work in
              progress), October 2019.

              Rabadan, J., Henderickx, W., Drake, J., Lin, W., and A.
              Sajassi, "IP Prefix Advertisement in EVPN", draft-ietf-
              bess-evpn-prefix-advertisement-11 (work in progress), May

              Zhang, Z., Kebler, R., Lin, W., and E. Rosen, "MVPN/EVPN
              C-Multicast Routes Enhancements", draft-zzhang-bess-mvpn-
              evpn-cmcast-enhancements-01 (work in progress), March

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

   [RFC6037]  Rosen, E., Ed., Cai, Y., Ed., and IJ. Wijnands, "Cisco
              Systems' Solution for Multicast in BGP/MPLS IP VPNs",
              RFC 6037, DOI 10.17487/RFC6037, October 2010,

   [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,

   [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>.

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5.2.  Informative References

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <https://www.rfc-editor.org/info/rfc6513>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks

   EMail: zzhang@juniper.net

   Wen Lin
   Juniper Networks

   EMail: wlin@juniper.net

   Jorge Rabadan

   EMail: jorge.rabadan@nokia.com

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