Simulating Partial Mesh of Multipoint-to-Multipoint (MP2MP) Provider Tunnels with Ingress Replication
RFC 7740

Internet Engineering Task Force (IETF)                          Z. Zhang
Request for Comments: 7740                                    Y. Rekhter
Category: Standards Track                               Juniper Networks
ISSN: 2070-1721                                              A. Dolganow
                                                          Alcatel-Lucent
                                                            January 2016

      Simulating Partial Mesh of Multipoint-to-Multipoint (MP2MP)
               Provider Tunnels with Ingress Replication

Abstract

   RFC 6513 ("Multicast in MPLS/BGP IP VPNs") describes a method to
   support bidirectional customer multicast flows using a partial mesh
   of Multipoint-to-Multipoint (MP2MP) tunnels.  This document specifies
   how a partial mesh of MP2MP tunnels can be simulated using Ingress
   Replication.  This solution enables a service provider to use Ingress
   Replication to offer transparent bidirectional multicast service to
   its VPN customers.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7740.

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Copyright Notice

   Copyright (c) 2016 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
   (http://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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Control State . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Forwarding State  . . . . . . . . . . . . . . . . . . . .   6
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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1.  Introduction

   Section 11.2 of RFC 6513 ("Partitioned Sets of PEs") describes two
   methods of carrying Bidirectional PIM (BIDIR-PIM) [RFC5015] C-flow
   traffic over a provider core without using the core as the Rendezvous
   Point Link (RPL) or requiring Designated Forwarder election.

   With these two methods, all Provider Edges (PEs) of a particular VPN
   are separated into partitions, with each partition being all the PEs
   that elect the same PE as the Upstream PE with respect to the C-RPA
   (the Rendezvous Point Address in the customer's address space).  A PE
   must discard bidirectional C-flow traffic from PEs that are not in
   the same partition as the PE itself.

   In particular, Section 11.2.3 of RFC 6513 ("Partial Mesh of MP2MP
   P-Tunnels") guarantees the above discard behavior without using an
   extra PE Distinguisher Label by having all PEs in the same partition
   join a single MP2MP tunnel dedicated to that partition and use it to
   transmit traffic.  All traffic arriving on the tunnel will be from
   PEs in the same partition, so it will be always accepted.

   RFC 6514 specifies BGP encodings and procedures used to implement
   Multicast VPN (MVPN) as specified in RFC 6513, while the details
   related to MP2MP tunnels are specified in [RFC7582].

   RFC 7582 assumes that an MP2MP P-tunnel is realized either via BIDIR-
   PIM [RFC5015] or via MP2MP mLDP (Multipoint extensions for LDP)
   [RFC6388].  Each would require signaling and state not just on PEs,
   but on the P routers as well.  This document describes how the MP2MP
   tunnel can be simulated with a mesh of P2MP tunnels, each of which is
   instantiated by Ingress Replication (IR) [RFC6513] [RFC6514].  The
   procedures in this document are different from the procedures that
   are used to set up the mesh of Ingress Replication tunnels as
   described in RFC 6514; the procedures in this document do not require
   each PE on the MP2MP tunnel to send a Selective P-Multicast Service
   Interface (S-PMSI) auto-discovery route (A-D route) for the P2MP
   tunnel that the PE is the root for, nor do they require each PE to
   send a Leaf A-D route to the root of each P2MP tunnel in the mesh.

   Because it uses Ingress Replication, this scheme has both the
   advantages and the disadvantages of Ingress Replication in general.

1.1.  Terminology

   This document uses terminology from [RFC5015], [RFC6513], [RFC6514],
   and [RFC7582].

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1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Operation

   In the following sections, the originator of an S-PMSI A-D route or
   Leaf A-D route is determined from the "originating router's IP
   address" field of the corresponding route.

2.1.  Control State

   If a PE, say PEx, is connected to a site of a given VPN and PEx's
   next-hop interface to some C-RPA is a VPN Routing and Forwarding
   (VRF) interface, then PEx MUST advertise a (C-*,C-*-BIDIR) S-PMSI A-D
   route, regardless of whether it has any local BIDIR-PIM join states
   corresponding to the C-RPA learned from its Customer Edges (CEs).  It
   MAY also advertise one or more (C-*,C-G-BIDIR) S-PMSI A-D routes, if
   selective distribution trees are needed for those C-G-BIDIR groups
   and the corresponding C-RPA is in the site that the PEx connects to.
   For example, the (C-*,C-G-BIDIR) S-PMSI A-D routes could be triggered
   when the (C-*,C-G-BIDIR) traffic rate goes above a threshold (this
   may require measuring the traffic in both directions, due to the
   nature of BIDIR-PIM), and fan-out could also be taken into account.

   The S-PMSI A-D routes include a PMSI Tunnel Attribute (PTA) with
   tunnel type set to Ingress Replication, with the Leaf Information
   Required flag set, with a downstream allocated MPLS label that other
   PEs in the same partition MUST use when sending relevant C-BIDIR
   flows to this PE, and with the Tunnel Identifier field in the PTA set
   to a routable address of the originator.  This specification does not
   prevent sharing of labels between P-tunnels, such as a label being
   shared by a (C-*,C-*-BIDIR) and a (C-*,C-G-BIDIR) S-PMSI A-D route
   originated by a given PE (note that other specifications put
   constraints on how that can be done, e.g., [MVPN-EXTRANET]).

   If some other PE, PEy, receives and imports into one of its VRFs any
   (C-*,C-*-BIDIR) S-PMSI A-D route whose PTA specifies an IR P-tunnel
   and the VRF has any local BIDIR-PIM join state that PEy has received
   from its CEs and if PEy chooses PEx as its Upstream PE with respect
   to the C-RPA for those states, PEy MUST advertise a Leaf A-D route in
   response.  Or, if PEy has received and imported into one of its VRFs
   a (C-*,C-*-BIDIR) S-PMSI A-D route from PEx before, then upon
   receiving in the VRF any local BIDIR-PIM join state from its CEs with
   PEx being the Upstream PE for those states' C-RPA, PEy MUST advertise
   a Leaf A-D route.

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   The encoding of the Leaf A-D route is as specified in RFC 6514,
   except that the Route Targets are set to the same value as in the
   corresponding S-PMSI A-D route so that the Leaf A-D route will be
   imported by all VRFs that import the corresponding S-PMSI A-D route.
   This is irrespective of whether or not the originator of the S-PMSI
   A-D route is the Upstream PE from a receiving PE's perspective.  The
   label in the PTA of the Leaf A-D route originated by PEy MUST be
   allocated specifically for PEx, so that when traffic arrives with
   that label, the traffic can associate with the partition (represented
   by the PEx).  This specification does not prevent sharing of labels
   between P-tunnels, such as a label being shared by a (C-*,C-*-BIDIR)
   and a (C-*,C-G-BIDIR) Leaf A-D route originated by a given PE (note
   that other specifications put constraints on how that can be done,
   e.g., [MVPN-EXTRANET]).

   Note that RFC 6514 requires that a PE or an ASBR (Autonomous System
   Border Router) take no action with regard to a Leaf A-D route unless
   that Leaf A-D route carries an IP-address-specific Route Target
   identifying the PE/ASBR.  This document removes that requirement when
   the route key of a Leaf A-D route identifies a (C-*,C-*-BIDIR) or a
   (C-*,C-G-BIDIR) S-PMSI.

   To speed up convergence (so that PEy starts receiving traffic from
   its new Upstream PE immediately instead of waiting until the new Leaf
   A-D route corresponding to the new Upstream PE is received by sending
   PEs), PEy MAY advertise a Leaf A-D route even if it does not choose
   PEx as its Upstream PE with respect to the C-RPA.  With that, it will
   receive traffic from all PEs, but some will arrive with the label
   corresponding to its choice of Upstream PE while some will arrive
   with a different label; the traffic in the latter case will be
   discarded.

   Similar to the (C-*,C-*-BIDIR) case, if PEy receives and imports into
   one of its VRFs any (C-*,C-G-BIDIR) S-PMSI A-D route whose PTA
   specifies an IR P-tunnel, PEy chooses PEx as its Upstream PE with
   respect to the C-RPA, and it has corresponding local (C-*,C-G-BIDIR)
   join state that it has received from its CEs in the VRF, PEy MUST
   advertise a Leaf A-D route in response.  Or, if PEy has received and
   imported into one of its VRFs a (C-*,C-G-BIDIR) S-PMSI A-D route
   before, then upon receiving its local (C-*,C-G-BIDIR) join state from
   its CEs in the VRF, it MUST advertise a Leaf A-D route.

   The encoding of the Leaf A-D route is similar to the (C-*,C-*-BIDIR)
   case.  Similarly, PEy MAY advertise a Leaf A-D route even if it does
   not choose PEx as its Upstream PE with respect to the C-RPA.

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   PEy MUST withdraw the corresponding Leaf A-D route if any of the
   following conditions are true:

   o  the (C-*,C-*-BIDIR) or (C-*,C-G-BIDIR) S-PMSI A-D route is
      withdrawn.

   o  PEy no longer chooses the originator PEx as its Upstream PE with
      respect to C-RPA and PEy only advertises Leaf A-D routes in
      response to its Upstream PE's S-PMSI A-D route.

   o  if relevant local join state is pruned.

2.2.  Forwarding State

   The specification regarding forwarding state in this section matches
   the "When an S-PMSI is a 'Match for Transmission'" and "When an
   S-PMSI is a 'Match for Reception'" rules for the "Flat Partitioning"
   method in [RFC7582], except that the rules about (C-*,C-*) are not
   applicable, because this document requires that (C-*,C-*-BIDIR)
   S-PMSI A-D routes are always originated for a VPN that supports
   C-BIDIR flows.

   For the (C-*,C-G-BIDIR) S-PMSI A-D route that a PEy receives and
   imports into one of its VRFs from its Upstream PE with respect to the
   C-RPA, if PEy itself advertises the S-PMSI A-D route in the VRF, PEy
   maintains a (C-*,C-G-BIDIR) forwarding state in the VRF, with the
   Ingress Replication provider tunnel leaves being the originators of
   the S-PMSI A-D route and all relevant Leaf A-D routes.  The relevant
   Leaf A-D routes are the routes whose Route Key field contains the
   same information as the MCAST-VPN Network Layer Reachability
   Information (NLRI) of the (C-*,C-G-BIDIR) S-PMSI A-D route advertised
   by the Upstream PE.

   For the (C-*,C-*-BIDIR) S-PMSI A-D route that a PEy receives and
   imports into one of its VRFs from its Upstream PE with respect to a
   C-RPA, if PEy itself advertises the S-PMSI A-D route in the VRF, it
   maintains appropriate forwarding states in the VRF for the ranges of
   bidirectional groups for which the C-RPA is responsible.  The
   provider tunnel leaves are the originators of the S-PMSI A-D route
   and all relevant Leaf A-D routes.  The relevant Leaf A-D routes are
   the routes whose Route Key field contains the same information as the
   MCAST-VPN NLRI of the (C-*,C-*-BIDIR) S-PMSI A-D route advertised by
   the Upstream PE.  This is for the so-called "Sender Only Branches"
   where a router only has data to send upstream towards C-RPA but no
   explicit join state for a particular bidirectional group.  Note that
   the traffic must be sent to all PEs (not just the Upstream PE) in the

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   partition, because they may have specific (C-*,C-G-BIDIR) join states
   that this PEy is not aware of, while there are no corresponding
   (C-*,C-G-BIDIR) S-PMSI A-D and Leaf A-D routes.

   For a (C-*,C-G-BIDIR) join state that a PEy has received from its CEs
   in a VRF, if there is no corresponding (C-*,C-G-BIDIR) S-PMSI A-D
   route from its Upstream PE in the VRF, PEy maintains a corresponding
   forwarding state in the VRF, with the provider tunnel leaves being
   the originators of the (C-*,C-*-BIDIR) S-PMSI A-D route and all
   relevant Leaf A-D routes (same as the "Sender Only Branches" case
   above).  The relevant Leaf A-D routes are the routes whose Route Key
   field contains the same information as the MCAST-VPN NLRI of the
   (C-*,C-*-BIDIR) S-PMSI A-D route originated by the Upstream PE.  If
   there is also no (C-*,C-*-BIDIR) S-PMSI A-D route from its Upstream
   PE, then the provider tunnel has an empty set of leaves, and PEy does
   not forward relevant traffic across the provider network.

3.  Security Considerations

   This document raises no new security issues.  Security considerations
   for the base protocol are covered in [RFC6513] and [RFC6514].

4.  References

4.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
              2012, <http://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,
              <http://www.rfc-editor.org/info/rfc6514>.

   [RFC7582]  Rosen, E., Wijnands, IJ., Cai, Y., and A. Boers,
              "Multicast Virtual Private Network (MVPN): Using
              Bidirectional P-Tunnels", RFC 7582, DOI 10.17487/RFC7582,
              July 2015, <http://www.rfc-editor.org/info/rfc7582>.

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4.2.  Informative References

   [MVPN-EXTRANET]
              Rekhter, Y., Ed., Rosen, E., Ed., Aggarwal, R., Cai, Y.,
              and T. Morin, "Extranet Multicast in BGP/IP MPLS VPNs",
              Work in Progress, draft-ietf-bess-mvpn-extranet-06,
              January 2016.

   [RFC5015]  Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
              "Bidirectional Protocol Independent Multicast (BIDIR-
              PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
              <http://www.rfc-editor.org/info/rfc5015>.

   [RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
              Thomas, "Label Distribution Protocol Extensions for Point-
              to-Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
              <http://www.rfc-editor.org/info/rfc6388>.

Acknowledgements

   We would like to thank Eric Rosen for his comments and suggestions
   for some text used in the document.

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks
   10 Technology Park Dr.
   Westford, MA  01886
   United States

   Email: zzhang@juniper.net

   Yakov Rekhter
   Juniper Networks

   Andrew Dolganow
   Alcatel-Lucent
   600 March Rd.
   Ottawa, ON  K2K 2E6
   Canada

   Email: andrew.dolganow@alcatel-lucent.com

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