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Versions: 00                                                            
BESS                                                            Z. Zhang
Internet-Draft                                          Juniper Networks
Updates: 6513, 6514, 7524 (if approved)                           J. Xie
Intended status: Standards Track                                  Huawei
Expires: June 23, 2019                                 December 20, 2018

                MVPN/EVPN Segmentated Forwarding Options


   [RFC6513] and [RFC6514] specify MVPN Inter-AS Segmentation
   procedures.  [RFC7524] specifies MVPN Inter-Area Segmentation
   procedures.  [I-D.ietf-bess-evpn-bum-procedure-updates] specifies
   EVPN BUM Inter-Region Segmentation Procedures.  Several other
   documents also touch upon the segmentation topic.  The forwarding at
   the segmentation points has been assumed to be label switching,
   subject to certain limitations.  The purpose of this document is to
   provide a review of segmentation points' available forwarding options
   and limitations, and to clarify and expand some procedures.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 June 23, 2019.

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Copyright Notice

   Copyright (c) 2018 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 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.  MPLS Label Switching at Segmentation Points . . . . . . .   3
     2.2.  IP Processing at Segmentation Points  . . . . . . . . . .   5
   3.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Terminology

   This document uses terminology from MVPN and EVPN.  It is expected
   that the audience is familiar with the concepts and procedures
   defined in [RFC6513], [RFC6514], [RFC7524], [RFC7432], [I-D.ietf-
   bess-evpn-bum-procedure-updates], and [I-D.ietf-bess-evpn-igmp-mld-
   proxy].  Some terms are listed below for references.

   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.  A PMSI A-D route is a BGP MVPN/EVPN auto-discovery
      route that announces the PMSI and optionally the tunnel that
      instantiates the PMSI.

   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.

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   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

2.  Introduction

   [RFC6513] and [RFC6514] specify MVPN Inter-AS Segmentation
   procedures.  [RFC7524] specifies MVPN Inter-Area Segmentation
   procedures.  [I-D.ietf-bess-evpn-bum-procedure-updates] specifies
   EVPN BUM Inter-Region Segmentation Procedures.  Several other
   documents also touch upon the segmentation topic.

2.1.  MPLS Label Switching at Segmentation Points

   It has been assumed that the forwarding across a segmentation point
   is label based.  The upstream segment of a PMSI tunnel is stitched to
   the downstream segment via label switching and no IP processing is
   done.  This is true even if the segmentation point also has a VRF
   with PE-CE interfaces, where IP processing is done to decide if a
   packet should be forwarded out of a PE-CE interface but label
   switching is used for forwarding traffic to receivers connected by
   downstream segments.

   This label switching is based on the assumption/requirement that each
   PMSI tunnel has its own unique label (in the simpliest case - this
   can be relaxed as specified in [RFC7988] in case of Ingress
   Relication).  The following is a breakdown of the various situations:

   o  If an aggregated RSVP-TE or mLDP P2MP tunnel, or BIER is used for
      the upstream (or downstream) segment, the x-PMSI A-D route
      received (or re-advertised, in case of downstream segment) by the
      segmentation point carries a per-PMSI label in the PMSI Tunnel
      Attribute (PTA).  The BIER case is specified in
      [I-D.ietf-bier-mvpn] and [I-D.ietf-bier-evpn].

   o  If a unique RSVP-TE or mLDP P2MP tunnel is used for for each
      upstream segment, the segmentation point advertises a unique label
      for each tunnel to the upstream node on the tunnel.  Similarly, in
      the downstream segment case, the segmenation point must receive a
      unique tunnel label.

   o  If Ingress Replication is used for the upstream segment, the
      segmentatation point may either simply advertise a different label
      in each Leaf A-D route that it advertises, or use a more elaborate
      procedure to decide how labels could be advertised while still

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      allow correct label switching procedure, as specified in
      Section 7.2 of [RFC7988].

   Notice that in the case of P2MP tunnel, x-PMSI A-D routes are
   required to advertise the tunnel identification and in case of tunnel
   aggregation (BIER or aggregated P2MP tunnel) the x-PMSI A-D routes
   are required to advertise the per-PMSI label.  However, [I-D.ietf-
   bess-mvpn-expl-track] introduces a "Leaf Information Required per
   Flow" bit (LIR-pF) in the flags field of the PTA of wildcard S-PMSI
   A-D routes, so that an ingress PE does not have to advertise
   individual more specific S-PMSI A-D routes even if it wants to
   explicitly track the leaves for more specific flows.  This can be
   used for RSVP-TE P2MP, Ingress Replication and BIER.

   For EVPN, explicit tracking is based on unsolicited Selective
   Multicast Ethernet Tag (SMET) A-D routes and LIR-pF is not used.
   However, that is as if the LIR-pF flag was set in an implicit (C-*,
   C-*) wildcard S-PMSI A-D route.

   Both [I-D.ietf-bier-mvpn] and [I-D.ietf-bier-evpn] specify that the
   LIR-pF flag MUST not be used with segmentation.  That's because with
   LIR-pF while an ingress PE can send a flow to only leaves tracked for
   the flow, it does not advertise the label bound to the corresponding
   PMSI for the flow (as the LIR-pF removes the need to advertise the
   more specific S-PMSI routes).

   The same restriction also applies if aggregated RSVP-TE P2MP tunnels
   are used (the same tunnel could be used for multiple more specific
   S-PMSIs but a per-PMSI label would be associated with each S-PMSI).
   The LIR-pF flag removes the need for those more specific S-PMSI A-D
   routes so no S-PMSI specific labels could be advertised for the
   segmentation points to do label switching with.

   The restriction does not apply to Ingress Replication because the
   per-PMSI label is advertised in the Leaf A-D routes.

   The restriction with BIER and aggregated RSVP-TE P2MP tunnel can be
   lifted if the LIR-pF triggered more specific MVPN Leaf A-D routes or
   the unsolicited EVPN SMET routes can trigger corresponding S-PMSI A-D
   routes, so that the per-PMSI labels can be advertised.  The concept
   of triggering S-PMSI A-D routes by Leaf/SMET A-D routes is already
   present in [RFC7524] and

   It may be argued that triggering S-PMSI A-D route from Leaf/SMET A-D
   routes for mroe specific flows has the following concerns (which
   leads to the consideration for forwarding option described in
   Section 2.2):

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   o  Flooding of those extra more specific S-PMSI A-D routes

   o  Delay in setting up the forwarding state (as the segmentation
      points now have to wait for the corresponding S-PMSI A-D route
      from its upstream).

   The first concern can be discounted that the burden of those extra
   S-PMSI A-D routes are mainly in the control plane.  The forwarding
   plane does need to maintain addtional per-PMSI labels but it's much
   better than the alertnative described in the following section.

   The second concern can be mitigated by having the ingress PE delay
   switching traffic over to the more specific S-PSMI.  That way,
   traffic will continue to be forwarded on the less specific PMSI (and
   label switched by segmentation points) for a short period before
   being moved to the more specific S-PMSI.

2.2.  IP Processing at Segmentation Points

   If the above mentioned discount/mitigation are not enough to address
   the two concerns, IP processing can be used at segmentation points.
   This will allow the use of LIR-pF with segemntation without
   triggering those more specific S-PMSI A-D routes
   [I-D.xie-bier-mvpn-segmented] .

   Basically, a segmentation point will create an IP multicast
   forwarding table for each "context", which could be for an EVPN
   Broadcast Domain (BD), a L3 VPN, an L3 VPN Extranet, or even
   something of smaller scope.  An incoming packet on an upstream
   segment is decapsulated and a corresponding IP multicat forwarding
   table is identified.  An IP lookup is performed and forwarded into
   downstream segments accordingly.

   While this does not require the S-PMSI A-D routes triggered by Leaf/
   SMET routes (and corresponding label forwarding state), additional IP
   forwarding tables and lookup are needed, which requires additional
   memory and cycles in the forwarding path, additional code to maintain
   the RIB/FIB tables, and additional OPEX to monitor them.

   Nonetheless, if IP processing on a segmentation point is desired for
   the reason of LIR-pF bit, the following could be done.

   o  Wildcard S-PMSI A-D routes with the LIR-pF flag are assigned with
      different labels from those in x-PMSI routes w/o the flag, and
      they lead to IP lookup.  The labels can either be upstream
      assigned or assigned from a Domain-wide Common Block (DCB)

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   o  Labels in x-PMSI routes w/o the LIR-pF flag, which are different
      from those in routes with the flag, lead to label switching.

   o  A Leaf A-D route with LIR-pF flag triggers corresponding (C-S,
      C-G) or (C-*, C-G) routes used for IP lookup, if there is no
      corresponding S-PMSI A-D route with LIR-pF flag.

   o  Upstream PE/ABR uses the label advertised in the matching x-PMSI
      routes to send traffic (so the packets will either be label
      switched or ip forwarded by segmentation points).

   On a PE, there are already VRFs or BDs configured so the IP RIBs/FIBs
   are just in those VRFs/BDs.  On a segmentation point, most likely
   there are no VRFs/BDs.  How IP RIBs/FIBs are managed is local
   behavior and implementation dependent.  While it is outside the scope
   of this document, one method could be to maintain one IP RIB/FIB for
   each label carried in a wildcard S-PMSI A-D route with the LIR-pF
   flag. .

3.  Specifications

   Detail specification for the above summary will be added in upcoming

4.  References

4.1.  Normative References

              Zhang, Z., Lin, W., Rabadan, J., Patel, K., and A.
              Sajassi, "Updates on EVPN BUM Procedures", draft-ietf-
              bess-evpn-bum-procedure-updates-05 (work in progress),
              December 2018.

              Sajassi, A., Thoria, S., Patel, K., Yeung, D., Drake, J.,
              and W. Lin, "IGMP and MLD Proxy for EVPN", draft-ietf-
              bess-evpn-igmp-mld-proxy-02 (work in progress), June 2018.

              Dolganow, A., Kotalwar, J., Rosen, E., and Z. Zhang,
              "Explicit Tracking with Wild Card Routes in Multicast
              VPN", draft-ietf-bess-mvpn-expl-track-13 (work in
              progress), November 2018.

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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,

   [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>.

   [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,

   [RFC7524]  Rekhter, Y., Rosen, E., Aggarwal, R., Morin, T.,
              Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area
              Point-to-Multipoint (P2MP) Segmented Label Switched Paths
              (LSPs)", RFC 7524, DOI 10.17487/RFC7524, May 2015,

4.2.  Informative References

              Zhang, Z., Rosen, E., Lin, W., Li, Z., and I. Wijnands,
              "MVPN/EVPN Tunnel Aggregation with Common Labels", draft-
              ietf-bess-mvpn-evpn-aggregation-label-02 (work in
              progress), December 2018.

              Zhang, Z., Przygienda, T., Sajassi, A., and J. Rabadan,
              "EVPN BUM Using BIER", draft-ietf-bier-evpn-01 (work in
              progress), April 2018.

              Rosen, E., Sivakumar, M., Aldrin, S., Dolganow, A., and T.
              Przygienda, "Multicast VPN Using BIER", draft-ietf-bier-
              mvpn-11 (work in progress), March 2018.

              Xie, J., Geng, L., Wang, L., McBride, M., and G. Yan,
              "Segmented MVPN Using IP Lookup for BIER", draft-xie-bier-
              mvpn-segmented-06 (work in progress), October 2018.

              Zhang, Z., Kebler, R., Lin, W., and E. Rosen, "MVPN/EVPN
              C-Multicast Routes Enhancements", draft-zzhang-bess-mvpn-
              evpn-cmcast-enhancements-00 (work in progress), July 2016.

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   [RFC7988]  Rosen, E., Ed., Subramanian, K., and Z. Zhang, "Ingress
              Replication Tunnels in Multicast VPN", RFC 7988,
              DOI 10.17487/RFC7988, October 2016,

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks

   EMail: zzhang@juniper.net

   Jingrong Xie

   EMail: xiejingrong@huawei.com

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