Explicit Tracking with Wild Card Routes in Multicast VPN
draft-ietf-bess-mvpn-expl-track-03

Document Type Active Internet-Draft (bess WG)
Last updated 2017-09-29 (latest revision 2017-09-22)
Replaces draft-dolganow-bess-mvpn-expl-track
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BESS WG                                                      A. Dolganow
Internet-Draft                                               J. Kotalwar
Updates: 6625 (if approved)                                        Nokia
Intended status: Standards Track                           E. Rosen, Ed.
Expires: March 26, 2018                                         Z. Zhang
                                                  Juniper Networks, Inc.
                                                      September 22, 2017

        Explicit Tracking with Wild Card Routes in Multicast VPN
                   draft-ietf-bess-mvpn-expl-track-03

Abstract

   The MVPN specifications provide procedures to allow a multicast
   ingress node to invoke "explicit tracking" for a multicast flow or
   set of flows, thus learning the egress nodes for that flow or set of
   flows.  However, the specifications are not completely clear about
   how the explicit tracking procedures work in certain scenarios.  This
   document provides the necessary clarifications.  It also specifies a
   new, optimized explicit tracking procedure.  This new procedure
   allows an ingress node, by sending a single message, to request
   explicit tracking of each of a set of flows, where the set of flows
   is specified using a wildcard mechanism.  This document updates
   RFC6625.

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
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   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 March 26, 2018.

Copyright Notice

   Copyright (c) 2017 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
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The Explicit Tracking Flags . . . . . . . . . . . . . . . . .   5
   3.  Match for Tracking vs. Match for Reception  . . . . . . . . .   5
   4.  Ingress Node Initiation of Tracking . . . . . . . . . . . . .   7
   5.  Egress Node Response to the Match for Tracking  . . . . . . .   8
     5.1.  General Egress Node Procedures  . . . . . . . . . . . . .   8
     5.2.  Responding to the LIR-pF Flag . . . . . . . . . . . . . .   9
     5.3.  When the Egress Node is an ABR or ASBR  . . . . . . . . .  12
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   [RFC6513] and [RFC6514] define the "Selective Provider Multicast
   Service Interface Auto-Discovery route" (S-PMSI A-D route).  By
   originating one of these BGP routes, an ingress node advertises that
   it is transmitting a particular multicast flow.  In the terminology
   of those RFCs, each flow is denoted by (C-S,C-G), where C-S is an IP
   source address and C-G is an IP multicast address, both in the
   address space of a VPN customer.  The (C-S,C-G) of the multicast flow
   is encoded into the Network Layer Reachability Information (NLRI) of
   the S-PMSI A-D route.

   Additionally, each S-PMSI A-D route contains a PMSI Tunnel attribute
   (PTA), which identifies a tunnel through the provider backbone
   network (a "P-tunnel").  If a P-tunnel is identified in the PTA of a
   given S-PMSI A-D route, the originator of that route is advertising
   that it will transmit the flow identified in the NLRI through the
   tunnel identified in the PTA.

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   [RFC6513] and [RFC6514] also define a procedure that allows an
   ingress node to determine the set of egress nodes that have requested
   to receive a particular flow from that ingress node.  The ability of
   an ingress node to identify the egress nodes for a particular flow is
   known as "explicit tracking".  An ingress node requests explicit
   tracking by setting a flag (the "Leaf Information Required" flag, or
   LIR) in the PTA.  When an egress node receives an S-PMSI A-D route
   with LIR set, the egress node originates a Leaf A-D route whose NLRI
   contains the NLRI from the corresponding S-PMSI A-D route.  In this
   way, the egress node advertises that it has requested to receive the
   particular flow identified in the NLRI of that S-PMSI A-D route.

   [RFC6513] and [RFC6514] also allow an ingress node to originate an
   S-PMSI A-D route whose PTA has LIR set, but which does not identify
   any P-tunnel.  This mechanism can be used when it is desired to do
   explicit tracking of a flow without at the same time binding that
   flow to a particular P-tunnel.

   [RFC6625] (and other RFCs that update it) extends the specification
   of S-PMSI A-D routes, and allows an S-PMSI A-D route to encode a
   wildcard in its NLRI.  Either the C-S or the C-G or both can be
   replaced by wildcards.  These routes are known as (C-*,C-S) S-PMSI
   A-D routes, or as (C-S,C-*) S-PMSI A-D routes, or as (C-*,C-*) S-PMSI
   A-D routes, depending on whether the C-S or C-G or both have been
   replaced by wildcards.  These routes are known jointly as "wildcard
   S-PMSI A-D routes".

   One purpose of this document is to clarify the way that the explicit
   tracking procedures of [RFC6513] and [RFC6514] are applied when
   wildcard S-PMSI A-D routes are used.

   In addition, this document addresses the following scenario, which is
   not addressed in [RFC6513], [RFC6514], or [RFC6625].  Suppose an
   ingress node originates an S-PMSI A-D route whose NLRI specifies, for
   example, (C-*,C-*) (i.e., both C-S and C-G are replaced by
   wildcards), and whose PTA identifies a particular P-tunnel.  Now
   suppose that the ingress node wants explicit tracking for each
   individual flow that it transmits (following the procedures of
   [RFC6625] on that P-tunnel.

   In this example, if the ingress node sets LIR in the PTA of the
   wildcard S-PMSI A-D route, each egress node that needs to receive a
   flow from the ingress node will respond with a Leaf A-D route whose
   NLRI specifies contains the (C-*,C-*) wildcard.  This allows the
   ingress node to determine the set of egress nodes that are receiving
   flows from the ingress node.  However, it does not allow the ingress
   node to determine which flows are being received by which egress
   nodes.

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   If the ingress node needs to determine which egress nodes are
   receiving which flows, it needs to originate an S-PMSI A-D route for
   each individual (C-S,C-G) flow that it is transmitting, and it needs
   to set LIR in the PTA of each such route.  However, since all the
   flows are being sent through the tunnel identified in the (C-*,C-*)
   S-PMSI A-D route, there is no need to identify a tunnel in the PTA of
   each (C-S,C-G) S-PMSI A-D route.  Per [RFC6514], the PTA of the
   (C-S,C-G) S-PMSI A-D routes can specify "no tunnel information".
   This procedure allows explicit tracking of individual flows, even
   though all those flows are assigned to tunnels in widlcard S-PMSI A-D
   routes.

   Howver, this procedure requires several clarifications:

   o  The procedures of [RFC6625] do not clearly state how to handle an
      S-PMSI A-D route if its NLRI contains wild cards, but its PTA
      specifies "no tunnel info".

   o  If it is desired to send a set of flows through the same tunnel
      (where that tunnel is advertised in a wildcard S-PMSI A-D route),
      but it is also desired to explicitly track each individual flow
      transmitted over that tunnel, one has to send an S-PMSI A-D route
      (with LIR set in the PTA) for each individual flow.  It would be
      more optimal if the ingress node could just send a single wildcard
      S-PMSI A-D route binding the set of flows to a particular tunnel,
      and have the egress nodes respond with Leaf A-D routes for each
      individual flow.

   o  [RFC6513] and [RFC6514] support the notion of "segmented
      P-tunnels", where "segmentation" occurs at ASBRs; [RFC7524]
      extends the notion segmented P-tunnels so that segmentation can
      occur at ABRs.  One can think of a segmented P-tunnel as passing
      through a number of "segmentation domains".  In each segmentation
      domain, a given P-tunnel has an ingress node and a set of egress
      nodes.  The explicit tracking procedures allow an ingress node of
      a particular segmentation domain to determine, for a particular
      flow or set of flows, the egress nodes of that segmentation
      domain.  This has given rise to two further problems:

      *  The explicit tracking procedures do not allow an ingress node
         to "see" past the boundaries of the segmentation domain.

         This particular problem is not further addressed in this
         revision of this document.

      *  The prior specifications do not make it very clear whether an
         egress node, upon receiving an S-PMSI A-D route whose PTA
         specifies "no tunnel information", is expected to forward the

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         S-PMSI A-D route, with the same PTA, to the next segmentation
         domain.  This document provides the necessary clarifications.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL", when and only when appearing in all capital letters, are
   to be interpreted as described in [RFC2119].

2.  The Explicit Tracking Flags

   Prior specifications define one flag in the PTA, the "Leaf Info
   Required" (LIR) flag, that is used for explicit tracking.

   This document defines a new flag in the flags field of the PMSI
   Tunnel attribute.  This new flag is known as the "Leaf Info Required
   per Flow" bit (LIR-pF).  This flag MAY be set in the PTA of a
   (C-*,C-*), (C-*,C-G), or (C-S,C-*) S-PMSI A-D route.  (Use of this
   flag in a PTA carried by other routes is outside the scope of this
   document.)  Support for this flag is OPTIONAL.

   The action taken by an egress node when the LIR-pF bit is set is
   detailed in Section 5.

   If the LIR-pF flag is set in a given PTA, the LIR flag of that PTA
   SHOULD also be set.  (By setting LIR as well as LIR-pF, one forces a
   a response to be sent an egress node that does not support LIR-pF,
   and it is possible to tell from that response that the egress node
   does not support LIR-pF.)

3.  Match for Tracking vs. Match for Reception

   RFC6625 (and other RFCs or RFCs-to-be that update RFC6625) specify a
   set of rules for finding the S-PMSI A-D route that is the "match for
   reception" for a given (C-S,C-G) or (C-*,C-G) state.  These rules do
   not take into account the fact that some S-PMSI A-D routes may not be
   carrying PTAs at all, or may be carrying PTAs that do not identify
   any P-tunnel.  (A PTA that does not identify any P-tunnel is one
   whose "tunnel type" field has been set to "no tunnel information", as
   specified in Section 5 of [RFC6514].)

   The definition of "match for reception" in [RFC6625] is hereby
   modified as follows:

      When finding the "match for reception" for a given (C-S,C-G) or
      (C-*,C-G), ignore any S-PMSI A-D route that has no PTA, or whose
      PTA specifying "no tunnel information".

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   We also introduce a new notion: the "match for tracking".  This
   differs from the "match for reception" as follows:

      For a given C-flow ((C-S,C-G) or (C-*,C-G)) the "match for
      tracking" is chosen as follows.  Ignore any S-PMSI A-D route that
      has no PTA.  Also ignore any S-PMSI A-D route whose PTA specifies
      "no tunnel information", but does not have either LIR or LIR-pF
      set.  (In particular, DO NOT ignore an S-PMSI A-D route that has a
      PTA specifying "no tunnel information", but whose LIR or LIR-pF
      bits are set).  Then apply the rules (from [RFC6625] and other
      documents that that update it) for finding the "match for
      reception".  The result (if any) is the match for tracking".

   We will clarify this with a few examples.  In these examples, we
   assume that there is only one segmentation domain.  In this case, the
   ingress and egress nodes are Provider Edge (PE) routers.

   Suppose a given PE router, PE1, has chosen PE2 as the "upstream PE"
   ([RFC6513]) for a given flow (C-S1,C-G1).  And suppose PE1 has
   installed the following two routes that were originated by PE2:

   o  Route1: A (C-*,C-*) S-PMSI A-D route, whose PTA specifies a
      tunnel.

   o  Route2: A (C-S1,C-G1) S-PMSI A-D route, whose PTA specifies "no
      tunnel info" and has LIR set.

   Route1 is (C-S1,C-G1)'s match for reception, and Route2 is
   (C-S1,C-G1)'s match for tracking.

   Continuing this example, suppose:

   o  PE1 has chosen PE2 as the upstream PE for a different flow,
      (C-S2,C-G2).

   o  PE2 has not originated an S-PMSI A-D route for (C-S2,C-G2).

   In this case, PE1 would consider Route1 to be (C-S2,C-G2)'s match for
   tracking as well as its match for reception.

   Also note that if a match for tracking does not have the LIR flag or
   the LIR-pF flag set, no explicit tracking information will be
   generated.  See Section 5.

   As another example, suppose PE1 has installed the following two
   routes that were originated by PE2:

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   o  Route1: A (C-*,C-*) S-PMSI A-D route (irrespective of whether the
      PTA specifies a tunnel)

   o  Route2: A (C-S1,C-G1) S-PMSI A-D route whose PTA specifies a
      tunnel.

   Then Route2 is both the "match for reception" and the "match for
   tracking" for (C-S1,C-G1).

   Note that for a particular C-flow, PE1's match for reception might be
   the same route as its match for tracking, or its match for reception
   might be a "less specific" route than its match for tracking.  But
   its match for reception can never be a "more specific" route than its
   match for tracking.

4.  Ingress Node Initiation of Tracking

   An ingress node that needs to initiate explicit tracking for a
   particular flow or set of flows can do so by performing one of the
   following procedures:

   1.  An ingress node can initiate explicit tracking for (C-S1,C-G1) by
       originating an S-PMSI A-D route that identifies (C-S1,C-G1) in
       its NLRI, including a PTA in that route, and setting the LIR flag
       in that PTA.  The PTA may specify a particular tunnel, or may
       specify "no tunnel info".

       However, the PTA of the (C-S1,C-G1) S-PMSI A-D route SHOULD NOT
       specify "no tunnel info" unless the ingress node also originates
       an A-D route carrying a PTA that specifies the tunnel to be used
       for carrying (C-S1,C-G1) traffic.  Such a route could be an
       I-PMSI A-D route, a (C-*,C-G1) S-PMSI A-D route, a (C-S1,C-*)
       S-PMSI A-D route, or a (C-*,C-*) S-PMSI A-D route.  (There is no
       point in requesting explicit tracking for a given flow if there
       is no tunnel on which the flow is being carried.)

       Further, if the ingress node originates a wildcard S-PMSI A-D
       route carrying a PTA specifying the tunnel to be used for
       carrying (C-S1,C-G1) traffic, and if that PTA has the LIR-pF bit
       set, then explicit tracking for (C-S1,C-G1) is requested by that
       S-PMSI A-D route.  Thus the ingress node SHOULD NOT originate a
       (C-S1,C-G1) S-PMSI A-D route whose PTA specifies "no tunnel
       info"; such a route would not provide any additional
       functionality.

       To terminate explicit tracking that has been initiated by an
       S-PMSI A-D route whose PTA specifies "no tunnel info", the
       ingress node withdraws the route.

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       To terminate explicit tracking that has been initiated by an
       S-PMSI A-D route whose PTA specifies a tunnel, the ingress node
       re-originates the route without the LIR flag set.

   2.  The following procedure can be used if (and only if) it is known
       that the egress nodes support the optional LIR-pF flag.  If the
       ingress node originates a wildcard S-PMSI A-D route, it can
       initiate explicit tracking for the individual flows that match
       the wildcard route by setting the LIR-pF flag in the PTA of the
       wildcard route.  If an egress node needs to receive one or more
       flows for which that wildcard route is a match for tracking, the
       egress node will originate a Leaf A-D route for each such flow,
       as specified in Section 5.2).

       When following this procedure, the PTA of the S-PMSI A-D route
       may specify a tunnel, or may specify "no tunnel info".  The
       choice between these two options is determined by considerations
       that are outside the scope of this document.

       To terminate explicit tracking that has been initiated by an
       S-PMSI A-D route whose PTA specifies "no tunnel info", the
       ingress node withdraws the route.

       To terminate explicit tracking that has been initiated by an
       S-PMSI A-D route whose PTA specifies a tunnel, the ingress node
       re-originates the route without the LIR flag set

5.  Egress Node Response to the Match for Tracking

5.1.  General Egress Node Procedures

   There are four cases to consider:

   1.  With regard to a particular (C-S,C-G) or (C-*,C-G) multicast
       state, the egress node's match for tracking is same as its match
       for reception, and neither LIR nor LIR-pF flags are on.

       In this case, the egress node does not originate a Leaf A-D route
       in response to the match for reception/tracking, and there is no
       explicit tracking of the flow.  This document specifies no new
       procedures for this case.

   2.  With regard to a particular (C-S,C-G) or (C-*,C-G) multicast
       state, the egress node's match for tracking is the same as its
       match for reception, LIR is set, but LIR-pF is not set.

       In this case, a Leaf A-D route is originated by the egress node,
       corresponding to the S-PMSI A-D route that is the match for

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       reception/tracking.  Construction of the Leaf A-D route is as
       specified in [RFC6514]; this document specifies no new procedures
       for this case.

   3.  With regard to a particular (C-S,C-G) or (C-*,C-G) multicast
       state, the egress node's match for tracking is the same as its
       match for reception, and LIR-pF is set.  The egress PE MUST
       follow whatever procedures are required by other specifications,
       based on the match for reception.  If the egress PE supports the
       LIR-pF flag, it MUST also follow the procedures of Section 5.2.

   4.  With regard to a particular (C-S,C-G) or (C-*,C-G) multicast
       state, the egress node's match for tracking is not the same as
       its match for reception.  This can only happen if the match for
       tracking has a PTA specifying "no tunnel info", with either LIR
       or LIR-pF set.  In this case, the egress node must respond,
       separately, BOTH to the match for tracking and to the match for
       reception.

       When responding to the match for reception, the egress node MUST
       ignore the LIR-pF flag.  However, the LIR flag is processed
       normally per the procedures for the match for reception.

       If the match for tracking has LIR set and if either (a) the
       egress node does not support LIR-pF, or (b) LIR-pF is not set,
       then the egress node must respond to the match for tracking,
       following procedures specified in other documents for the case
       where LIR is set.

       If the match for tracking has LIR-pF set, and the egress node
       supports the LIR-pF flag, the egress node must originate one or
       more Leaf A-D routes, as specified in Section 5.2.

       Note that if LIR is set in the PTA of the match for reception,
       the egress node may need to originate one or more Leaf A-D routes
       corresponding to the match for tracking, as well as originating a
       Leaf A-D route corresponding to the match for reception.

5.2.  Responding to the LIR-pF Flag

   To respond to a match for tracking that has LIR-pF set, an egress
   node originates one or more Leaf A-D routes.

   Suppose the egress node has multicast state for a (C-S,C-G) or a
   (C-*,C-G) flow, and has determined a particular S-PMSI A-D route,
   which has the LIR-pF flag set, to be the match for tracking for that
   flow.  Then if the egress node supports the LIR-pF flag, it MUST
   originate a Leaf A-D route whose NLRI identifies that particular

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   flow.  Note that if a single S-PMSI A-D route (with wild cards) is
   the match for tracking for multiple flows, the egress PE may need to
   originate multiple Leaf A-D routes, one for each such flow.  We say
   that, from the perspective of a given egress node, a given S-PMSI A-D
   route tracks the set of flows for which it is the match for tracking.
   Each of the Leaf A-D routes originated in response to that S-PMSI A-D
   route tracks a single such flow.

   The NLRI of each the Leaf A-D route that tracks a particular flow is
   constructed as follows.  The "route key" field of the NLRI will have
   the following format:

                   +-----------------------------------+
                   |      RD   (8 octets)              |
                   +-----------------------------------+
                   | Multicast Source Length (1 octet) |
                   +-----------------------------------+
                   |  Multicast Source (Variable)      |
                   +-----------------------------------+
                   |  Multicast Group Length (1 octet) |
                   +-----------------------------------+
                   |  Multicast Group   (Variable)     |
                   +-----------------------------------+
                   |  Ingress PE's IP address          |
                   +-----------------------------------+

                    Figure 1: NLRI of S-PMSI A-D Route

   o  The "ingress PE" address is taken from the "originating router"
      field of the NLRI of the S-PMSI A-D route that is the match for
      tracking.

   o  The multicast source and group fields specify the S and G of one
      of the flow being tracked by this Leaf A-D route.  If a (C-*,C-G)
      is being tracked by this Leaf A-D route, the source field is
      omitted, and its length is set to 0.

   o  The RD field is constructed as follows:

      *  Take the RD value from the NLRI of the S-PMSI A-D route.

      *  Add 16 to the second octet of the RD.

   Note that, per RFC4364, every RD begins with a two-octet type field
   that is either 0, 1, or 2.  By adding 16 to the second octet of the
   RD, we force the type field to be 16, 17, or 18.  The presence of one

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   of these values will indicate that the Leaf A-D route was constructed
   in response to a less specific S-PMSI A-D route that had the LIR-pF
   bit set.  (That is, it distinguishes the routes from "ordinary" MVPN
   Leaf A-D routes.)

   The encoding of these Leaf A-D routes is similar to the encoding of
   the Leaf A-D routes described in section 6.2.2 of [RFC7524], which
   were designed for the support of "global table multicast".  However,
   that document sets the RD to either 0 or -1; following the procedures
   of this document, the RD will never be 0 or -1.  Therefore Leaf A-D
   routes constructed according to the procedures of this section can
   always be distinguished from the Leaf A-D routes constructed
   according to the procedures of section 6.2.2 of [RFC7524].  Also,
   Leaf A-D routes constructed according to the procedures of this
   section are VPN-specific routes, and will always carry an IP-address-
   specific Route Target, as specified in [RFC6514].

   If a Leaf A-D route is originated as a response to a match for
   tracking whose PTA specifies "no tunnel info", a PTA SHOULD NOT be
   attached to the Leaf A-D route; if a PTA is attached, it MUST specify
   "no tunnel info".

   In the case where the match for tracking and the match for reception
   are the same, the PTA of the match may have both the LIR and the LIR-
   pF flags set.  This may cause the egress node to originate one Leaf
   A-D route in response to the LIR bit, and one or more Leaf A-D routes
   in response to the LIR-pF bit.  A PTA SHOULD NOT be attached to the
   Leaf A-D routes that are originated in response to the LIR-pF bit.

   When a Leaf A-D route constructed according to the procedures of this
   section is received, it MUST be processed by the node identified in
   its IP-address-specific Route Target, even though its "route key"
   field does not correspond to the NLRI of any S-PMSI A-D route.

   Of course, an egress node that originates such Leaf A-D routes needs
   to remember which S-PMSI A-D route caused these Leaf A-D routes to be
   originated; if that S-PMSI A-D route is withdrawn, those Leaf A-D
   routes MUST be withdrawn.

   Similarly, a Leaf A-D route needs to be withdrawn (either implicitly
   or explicitly) if the egress node changes its Upstream Multicast Hop
   (UMH) ([RFC6513]) for the flow that is identified in the Leaf A-D
   route's NLRI, or if the egress node that originated the route no
   longer needs to receive the flow identified in the NLRI of the route.

   Note that an egress node may acquire (C-S,C-G) state or (C-*,C-G)
   state after it has already received the S-PMSI A-D that is the match
   for tracking for that state.  In this case, a Leaf A-D route needs to

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   be originated at that time, and the egress node must remember that
   the new Leaf A-D route corresponds to that match for tracking.

   Note that if a particular S-PMSI A-D route is a match for tracking
   but not a match for reception, the LIR bit in its PTA is ignored if
   the LIR-pF bit is set.

5.3.  When the Egress Node is an ABR or ASBR

   When segmented P-tunnels are used, the ingress and egress nodes may
   be ABRs or ASBRs.  An egress ABR/ASBR that receives and installs an
   S-PMSI A-D route also forwards that route.  If the PTA of an
   installed S-PMSI A-D route specifies a tunnel, the egress ABR/ASBR
   MAY change the PTA to specify a different tunnel type (as discussed
   in [RFC6514] and/or [RFC7524]).

   However, if the PTA of the installed S-PMSI A-D route specifies "no
   tunnel info", the egress ABR/ASBR MUST pass the PTA along unchanged
   when it forwards the S-PMSI A-D route.  (That is, a PTA specifying
   "no tunnel info" MUST NOT be changed into a PTA specifying a tunnel.)
   Furthermore, if the PTA specifies "no tunnel info", the LIR and LIR-
   pF flags in the PTA MUST be passed along unchanged.

   In the case where the egress node is a PE, it will know whether it
   needs to receive a given flow by virtue of its having received a PIM
   or IGMP Join for that flow from a CE.  In the case where the egress
   node is not a PE, but rather an ABR or ASBR, it will not know whether
   it needs to receive a given flow unless it receives a Leaf A-D route
   whose NLRI specifies that flow and whose IP-address-specific RT
   specifies an address of the egress node.  Therefore an egress ABR/
   ASBR MUST NOT originate a Leaf A-D route for a given flow UNLESS it
   has an installed Leaf A-D route for that flow, received from further
   downstream.

   This will ensure that an egress ABR/ASBR only sends a Leaf A-D route
   in response to a "match for tracking" if it is on the path to an
   egress PE for the flow(s) identified in the corresponding S-PMSI A-D
   route.

   Then we can establish the following rule for egress ABRs/ASBRs.
   Suppose an egress ABR/ASBR receives an S-PMSI A-D route whose NLRI is
   X, and whose PTA (a) specifies "no tunnel info" and (b) has LIR set.
   The egress ABR/ASBR should not immediately originate a Leaf A-D route
   in response.  Rather it should wait until it receives a Leaf A-D
   route whose NLRI contains X in the "route key" field.  If it receives
   such a Leaf A-D route, it redistributes that route, but first it
   changes that route's RT.  The "global administrator" field of the
   modified RT will be set to the IP address taken either from the

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   S-PMSI A-D route's next hop field, or from its Segmented P2MP Next
   Hop Extended Community.  (This is the same rule that is used for when
   the PTA does specify a tunnel type.)

6.  Acknowledgments

   The authors wish to thank Robert Kebler for his ideas and comments.

7.  IANA Considerations

   The LIR-pF flag needs to be added to the "P-Multicast Service
   Interface Tunnel (PMSI Tunnel) Attribute Flags" in the "Border
   Gateway Protocol (BGP) Parameters" registry.  This registry is
   defined in [RFC7902].  The requested value is Bit Position 2.  This
   document should be the reference.

   IANA is requested to allocate three new types from the Route
   Distinguisher Type Field registry:

   o  Administrator field is two-byte Autonomous System Number.  To be
      used only in certain MCAST-VPN Leaf A-D routes.

   o  Administrator field is four-byte IP Address.  To be used only in
      certain MCAST-VPN Leaf A-D routes.

   o  Administrator field is four-byte Autonomous System Number.  To be
      used only in certain MCAST-VPN Leaf A-D routes.

   The requested values are 16, 17, and 18 respectively.

8.  Security Considerations

   The Security Considerations of [RFC6513] and [RFC6514] apply.

   By setting the LIR-pF flag in a single wildcard S-PMSI A-D route, a
   large number of Leaf A-D routes can be elicited.  If this flag is set
   when not desired (through either error or malfeasance), a significant
   increase in control plane overhead can result.

9.  References

9.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [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,
              <https://www.rfc-editor.org/info/rfc6514>.

   [RFC6625]  Rosen, E., Ed., Rekhter, Y., Ed., Hendrickx, W., and R.
              Qiu, "Wildcards in Multicast VPN Auto-Discovery Routes",
              RFC 6625, DOI 10.17487/RFC6625, May 2012,
              <https://www.rfc-editor.org/info/rfc6625>.

   [RFC7902]  Rosen, E. and T. Morin, "Registry and Extensions for
              P-Multicast Service Interface Tunnel Attribute Flags",
              RFC 7902, DOI 10.17487/RFC7902, June 2016,
              <https://www.rfc-editor.org/info/rfc7902>.

9.2.  Informative References

   [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,
              <https://www.rfc-editor.org/info/rfc7524>.

Authors' Addresses

   Andrew Dolganow
   Nokia
   438B Alexandra Rd #08-07/10
   Alexandra Technopark
   Singapore  119968

   Email: andrew.dolganow@nokia.com

   Jayant Kotalwar
   Nokia
   701 East Middlefield Rd
   Mountain View, California  94043
   United States

   Email: jayant.kotalwar@nokia.com

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   Eric C. Rosen (editor)
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, Massachusetts  01886
   United States

   Email: erosen@juniper.net

   Zhaohui Zhang
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, Massachusetts  01886
   United States

   Email: zzhang@juniper.net

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