Advertising p2mp policies in BGP
draft-hb-idr-sr-p2mp-policy-04

Network Working Group                                    H. Bidgoli, Ed.
Internet-Draft                                                     Nokia
Intended status: Standards Track                                V. Voyer
Expires: 10 April 2022                                       Bell Canada
                                                                A. Stone
                                                                   Nokia
                                                               R. Parekh
                                                            Cisco System
                                                                S. Krier
                                                        A. Venkateswaran
                                                      Cisco System, Inc.
                                                          7 October 2021

                    Advertising p2mp policies in BGP
                     draft-hb-idr-sr-p2mp-policy-04

Abstract

   SR P2MP policies are set of policies that enable architecture for
   P2MP service delivery.

   A P2MP policy consists of candidate paths that connects the Root of
   the Tree to a set of Leaves.  The P2MP policy is composed of
   replication segments.  A replication segment is a forwarding
   instruction for a candidate path which is downloaded to the Root,
   transit nodes and the leaves.

   This document specifies a new BGP SAFI with a new NLRI in order to
   advertise P2MP policy from a controller to a set of nodes.

   This document introduces three new route types within this NLRI, one
   for P2MP policy and its candidate paths that need to be programmed on
   the Root node, one for the replication segment incoming SID which
   uniquely will identify the cross connect and another for each
   outgoing interface that the packets get replicated to.  The last two
   route types are forwarding instructions that needs to be programmed
   on the Root, and optionally on Transit and Leaf nodes.

   It should be noted that this document does not specify how the Root
   and the Leaves are discovered on the controller, it only describes
   how the P2MP Policy and Replication Segments are programmed from the
   controller to the nodes.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   4
   3.  P2MP Policy and Replication Segment Encoding  . . . . . . . .   4
     3.1.  P2MP Policy SAFI and NLRI . . . . . . . . . . . . . . . .   4
       3.1.1.  P2MP Policy Route - Route Type TBD1 . . . . . . . . .   5
       3.1.2.  Replication segment Route Binding SID- Route type TBD
               2 . . . . . . . . . . . . . . . . . . . . . . . . . .   6
       3.1.3.  Replication segment Route OIF- Route type TBD 3 . . .   8
     3.2.  Tunnel Encapsulation Attribute  . . . . . . . . . . . . .   9
       3.2.1.  SR P2MP policy encoding . . . . . . . . . . . . . . .   9
       3.2.2.  Replication segment Binding SID encoding  . . . . . .  10
       3.2.3.  Replication segment OIF encoding  . . . . . . . . . .  10
     3.3.  P2MP Policy Sub-TLVs  . . . . . . . . . . . . . . . . . .  11
       3.3.1.  preference Sub-TLV  . . . . . . . . . . . . . . . . .  11
       3.3.2.  leaf-list Sub-TLV . . . . . . . . . . . . . . . . . .  11
       3.3.3.  path-instance Sub-TLV . . . . . . . . . . . . . . . .  12
         3.3.3.1.  active instance-id Sub-TLV  . . . . . . . . . . .  12
         3.3.3.2.  instance-id Sub-TLV . . . . . . . . . . . . . . .  13
     3.4.  Replication segment Sub-TLVs  . . . . . . . . . . . . . .  13
       3.4.1.  Segment list Sub-TLV  . . . . . . . . . . . . . . . .  14

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       3.4.2.  Weight sub-tlv  . . . . . . . . . . . . . . . . . . .  14
       3.4.3.  Protection sub-tlv  . . . . . . . . . . . . . . . . .  14
       3.4.4.  Segment Sub-TLV . . . . . . . . . . . . . . . . . . .  15
   4.  P2MP Policy Operation . . . . . . . . . . . . . . . . . . . .  15
     4.1.  Configuration and advertisement of P2MP Policies  . . . .  16
     4.2.  Reception of an P2MP Policy NLRI  . . . . . . . . . . . .  16
     4.3.  Global Optimization for P2MP LSPs . . . . . . . . . . . .  17
   5.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . .  17
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   The draft [draft-ietf-pim-sr-p2mp-policy] defines a variant of the SR
   Policy [draft-ietf-spring-segment-routing-policy] for constructing a
   P2MP segment to support multicast service delivery.

   A Point-to-Multipoint (P2MP) Policy contains a set of candidate paths
   and identifies a Root node and a set of Leaf nodes in a Segment
   Routing Domain.  The draft also defines a Replication segment, which
   corresponds to the state of a P2MP segment on a particular node.  The
   Replication segment is the forwarding instruction for a P2MP LSP at
   the Root, Transit and Leaf nodes.

   For a P2MP segment, a controller may be used to compute a tree from a
   Root node to a set of Leaf nodes, optionally via a set of replication
   nodes.  A packet is replicated at the root node and optionally on
   Replication nodes towards each Leaf node.

   We define two types of a P2MP segment: Ingress Replication (aka
   Spray) and Downstream Replication (aka TreeSID).

   A Point-to-Multipoint service delivery could be via Ingress
   Replication (aka Spray in some SR context), i.e., the root unicasts
   individual copies of traffic to each leaf.  The corresponding P2MP
   segment consists of replication segments only for the root and the
   leaves.

   A Point-to-Multipoint service delivery could also be via Downstream
   Replication (aka TreeSID in some SR context), i.e., the root and some
   downstream replication nodes replicate the traffic along the way as
   it traverses closer to the leaves.

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   It should be noted that two replication nodes can be connected
   directly, or they can be connected via unicast SR segment or a
   segment list.

   The leaves and the root of a p2mp policy can be discovered via the
   multicast protocols or procedures like NG-MVPN [RFC6513] or manually
   configured on the PCC (CLI) or the PCE.

   Based on the discovered root and leaves, the controller builds a P2MP
   policy and advertise it to the head-end router (i.e. the root of the
   P2MP Tree).  The advertisement uses BGP extensions defined in this
   document.  The controller also calculates the tree path and builds
   the replication segments on each segment of the tree, Root, Transit
   and Leaf nodes and downloads the forwarding instructions to the nodes
   via BGP extensions defined in this document.

   SR p2mp policy is a variant of the SR policy and as such it reuses
   the concept of a candidate path.  This draft reuses some of the
   concepts and TLVs mentioned in
   [draft-ietf-idr-segment-routing-te-policy]

   A candidate path with in the P2MP policy can contain multiple path-
   instances.  A path-instance can be viewed as a P2MP LSP.  For
   candidate path global optimization purposes, two or more path-
   instances can be used to execute make before break procedures.

   Each path-instance is a P2MP LSP as such each path-instance needs a
   set of replication segments to construct its forwarding instructions.

2.  Conventions used in this document

   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 RFC 2119 [RFC2119].

3.  P2MP Policy and Replication Segment Encoding

3.1.  P2MP Policy SAFI and NLRI

   This document defines a new BGP NLRI, called the P2MP-POLICY NLRI.

   A new SAFI is defined: the SR P2MP Policy SAFI, (Codepoint tbd
   assigned by IANA).  The following is the format of the P2MP-POLICY
   NLRI:

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         +-----------------------------------+
         |             route type            | 1 octet
         +-----------------------------------+
         |               length              | 1 octet
         +-----------------------------------+
         |    route type specific (variable) |
         +-----------------------------------+

   *  The Route type field defines the encoding of the rest of the P2MP-
      POLICY NLRI.

   *  The length field indicates the length in octets of the route type
      specific data, excluding route type and length

   *  This document defines the following route types:

      -  P2MP Policy route: TBD1, this is the actually P2MP policy on
         the root which contains the candidate paths, its prefrence and
         path instances.

      -  Replication Segment Binding SID: TBD2, this is part of the
         replication segment and it is used for programming the incoming
         SID used to identify a P2MP cross connect.

      -  Replication Segment OIF: TBD3, this is a single Outgoing
         Interface for the P2MP cross connect.  It also contains the
         outgoing SID.

   The NLRI containing the SR P2MP Policy is carried in a BGP UPDATE
   message [RFC4271] using BGP multiprotocol extensions [RFC4760] with
   an AFI of 1 or 2 (IPv4 or IPv6) and with a SAFI of "TBD" (assigned by
   IANA from the "Subsequent Address Family Identifiers (SAFI)
   Parameters" registry).

   All other recommendations of
   [draft-ietf-idr-segment-routing-te-policy] section SR Policy SAFI and
   NLRI, should be taken into account for P2MP policy.

3.1.1.  P2MP Policy Route - Route Type TBD1

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        +-----------------------------------+
        |            Root-ID Length         | 1 octets
        +-----------------------------------+
        ~             Root-ID               ~ 4 or 16 octets (ipv4/ipv6)
        +-----------------------------------+
        |               Tree-ID             | 4 octets
        +-----------------------------------+
        |            Distinguisher          | 4 octets
        +-----------------------------------+

   *  Root-ID: IPv4/IPv6 address of the head-end (Root) of the p2mp
      tree, based on AFI.

   *  Tree-ID: a unique 4 octets identifier of the p2mp tree on the
      head- end (root)router.

   *  Distinguisher: 4-octets value uniquely identifying the policy in
      the context of <Tree-ID, Originating Router's IP> tuple.  The
      distinguisher has no semantic value and is solely used by the SR
      P2MP Policy originator to make unique (from an NLRI perspective)
      multiple occurrences of the same SR P2MP Policy.

3.1.2.  Replication segment Route Binding SID- Route type TBD 2

   There can be two type of replication segment, shared and non-shared.
   A shared replication segment can carry multiple MVPN services or it
   can be used for Facility Fast reroute protecting multiple P2MP trees.
   A non-shared tree is used when the label field of the PMSI Tunnel
   Attribute (PTA) is set to 0 as per
   [draft-ietf-bess-mvpn-evpn-sr-p2mp].  The Binding SID route type
   Programs the incoming replication SID on the replication node.  Since
   a replication cross connect has a single incoming replication SID
   with a set of Outgoing Interfaces, this route type can be used to
   download the replication SID once for the cross connect.

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        +-----------------------------------+
        |            Root-ID Length         | 1 octets
        +-----------------------------------+
        ~             Root-ID               ~ 4 or 16 octets (ipv4/ipv6)
        +-----------------------------------+
        |               Tree-ID             | 4 octets
        +-----------------------------------+
        |           Distinguisher           | 4 octets
        +-----------------------------------+
        |             instance-ID           | 2 octets
        +-----------------------------------+
        |            Node-ID Length         | 1 octets
        +-----------------------------------+
        ~              Node-ID              ~ 4 or 16 octets
        +-----------------------------------+
        |        Replication SID Length     | 1 octets
        +-----------------------------------+
        ~          Replication SID          ~ 4 or 16 octets
        +-----------------------------------+

   *  Root-ID: IPv4/IPv6 address of the head-end (Root) of the p2mp tree
      based on AFI.

   *  Tree-ID: a unique 4 octets identifier of the p2mp tree on the
      head- end router (Root)

   *  instance-id, identifies the path-instance with in the p2mp-
      policy.  Each candidate path can have one, two or more path-
      instance.  Path-instance is used for global optimization of the
      candidate path via make before break procedures.  Instance-ID can
      be used

   *  Distinguisher: 4-octets value uniquely identifying the policy in
      the context of <Root-ID, Tree-ID> tuple.  The distinguisher has no
      semantic value and is solely used by the SR P2MP Policy originator
      to make unique (from an NLRI perspective) multiple occurrences of
      the same SR P2MP Policy.

   *  Node-ID: This Node's IPv4/IPv6 address

   *  Replication SID: the incoming replication SID used to identify
      this replication point (MPLS or SRv6).  Note the replication SID
      is not part of the NLRI key.

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3.1.3.  Replication segment Route OIF- Route type TBD 3

   This route type is used to identify and program each out going
   interface individually for a replication cross connect.  Downloading
   each OIF individually ensures easier modification and programming and
   will keep the programming of each OIF in par with
   [draft-ietf-idr-segment-routing-te-policy] . Note: this route type
   can be used for shared and non-shared replication segment as it was
   explained in previous sections.

        +-----------------------------------+
        |            Root-ID Length         | 1 octets
        +-----------------------------------+
        ~             Root-ID               ~ 4 or 16 octets (ipv4/ipv6)
        +-----------------------------------+
        |               Tree-ID             | 4 octets
        +-----------------------------------+
        |           Distinguisher           | 4 octets
        +-----------------------------------+
        |            instance-ID            | 2 octets
        +-----------------------------------+
        |            Node-ID Length         | 1 octets
        +-----------------------------------+
        ~              Node-ID              ~ 4 or 16 octets
        +-----------------------------------+
        |       Downstream-Node Length      | 1 octets
        +-----------------------------------+
        ~          Downstream-Node          ~ 4 or 16 octets
        +-----------------------------------+
        |      Outgoing-TreeSID Length      | 1 octets
        +-----------------------------------+
        ~         Outgoing-TreeSID          ~ 4 or 16 octets
        +-----------------------------------+

   *  Root-ID: IPv4/IPv6 address of the head-end (Root) of the p2mp tree
      based on AFI.

   *  Tree-ID: a unique 4 octets identifier of the p2mp tree on the
      head- end router (Root)

   *  instance-id, identifies the path-instance with in the p2mp-
      policy.  Each candidate path can have one, two or more path-
      instance.  Path-instance is used for global optimization of the
      candidate path via make before break procedures.  Instance-ID can
      be used

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   *  Distinguisher: 4-octets value uniquely identifying the policy in
      the context of <Root-ID, Tree-ID> tuple.  The distinguisher has no
      semantic value and is solely used by the SR P2MP Policy originator
      to make unique (from an NLRI perspective) multiple occurrences of
      the same SR P2MP Policy.

   *  Node-ID: Node's IPv4/IPv6 address

   *  Downstream Node: Downstream Node Identifier

   *  Outgoing TreeSID: The outgoing SID for this branch (MPLS or SRv6).
      Note the outgoing-TreeSID is not part of the NLRI Key.

3.2.  Tunnel Encapsulation Attribute

   The content of this new NLRI is encoded in the tunnel Encapsulation
   Attribute originally defined in [ietf-idr-tunnel-encaps] using two
   new Tunnel-Type TLV (codepoint is TBD, assigned by IANA from the "BGP
   Tunnel Encapsulation Attribute Tunnel Types" registry) one for P2MP
   Policy and another for Replication segment.

3.2.1.  SR P2MP policy encoding

         SR P2MP Policy SAFI NLRI: <route-type p2mp-policy>
         Attributes:
            Tunnel Encaps Attribute (23)
               Tunnel Type: (TBD, P2MP-Policy)
                   Preference
                   Policy Name
                   Policy Candidate Path Name
                   leaf-list (optional)
                        remote-end point
                        remote-end point
                        ...
                   path-instance
                       active-instance-id
                       instance-id
                       instance-id
                       ...

   *  Relevant only at the Root.

   *  SR P2MP-POLICY NLRI and P2MP Policy route type.

   *  Tunnel Encapsulation Attribute is defined in
      [ietf-idr-tunnel-encaps]

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   *  Tunnel-Type is set to P2MP-Policy Tunnel-Type TBD (assigned by
      IANA from the "BGP Tunnel Encapsulation Attribute Tunnel Types"
      registry).

   *  Policy Name, Policy Candidate Path Name are defined in
      [draft-ietf-idr-segment-routing-te-policy]

   *  Preference, leaf-list, remote-end point and path- instance,
      instance-ids are defined in this document.

   *  Additional sub-TLVs may be defined in the future.

3.2.2.  Replication segment Binding SID encoding

replication segment Binding SID SAFI NLRI: <route-type non-sahred/shared
                                tree replication-segment-binding-sid>

   This route type has no additional sub-TLVs, and it is only meant to
   download the incoming SID for the replication cross connect.

3.2.3.  Replication segment OIF encoding

replication segment SAFI NLRI: <route-type non-sahred/shared
                                tree replication-segment-oif>
     Attributes:
         Tunnel Encaps Attribute (23)
            Tunnel Type: (TBD Replication-Segment-oif)
                    segment-list
                        weight (optional)
                        protection (optional, must be present when protection flag is enabled for downstream-nodes)
                        segment
                        segment
                        ...
                    segment-list
                        weight (optional)
                        protection (optional, must be present when protection flag is enabled for downstream-nodes)
                        segment
                        segment
                        ...
                   segment-list (protection segment list)
                        protection (protecting the first segment list, can't have weight sub-tlv)
                        segment
                        segment
                        ...
                   ...
                ...

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   *  SR P2MP-POLICY NLRI and non-shared tree Replication segment route
      type or shared tree Replication segment route type.

   *  Tunnel Encapsulation Attribute is defined in
      [ietf-idr-tunnel-encaps].

   *  Tunnel-Type is set to Replication Segment OIF Tunnel Type, TBD
      (assigned by IANA from the "BGP Tunnel Encapsulation Attribute
      Tunnel Types" registry).

   *  segment-list are defined in this document.

   *  Additional sub-TLVs may be defined in the future.

3.3.  P2MP Policy Sub-TLVs

   EACH P2MP policy NLRI represents a candidate path for a P2MP policy.
   A P2MP policy can have multiple candidate paths and would need
   multiple P2MP policy NRLI to download all the candidate paths.

3.3.1.  preference Sub-TLV

   As defined in preference Sub-TLV section in
   [draft-ietf-idr-segment-routing-te-policy] the candidate path with
   highest preference is the active candidate path.

3.3.2.  leaf-list Sub-TLV

   The leaf list sub-tlv identifies a set of leaves for the tree.  Each
   leaf is a remote endpoint as defined in [ietf-idr-tunnel-encaps] The
   leaf-list sub-tlv is optional.  The PCE can choose to download the
   leaf list every time it is configured or learns a new leaf.  If the
   PCE chooses to download this optional sub-tlv it should download the
   entire set of the end-points every time the endpoint list has been
   modified.  The leaf list has informational value only hence why it is
   optonal and it is not required for the root PE to operate.  However,
   it must be noted that in some cases the end-points list can become
   very large with 100s of leaves.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |             Length            |   RESERVED    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                           sub-TLVs                          //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   *  Type: TBD, 1 octet

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   *  Length: 2 octets, the total length (not including the Type and
      Length fields) of the sub-TLVs encoded within the leaf-list sub-
      TLV.

   *  RESERVED: 1 octet of reserved bits.  SHOULD be unset on
      transmission and MUST be ignored on receipt.

   *  sub-TLVs: One or more remote endpoint sub-TLVs.  Note the remote
      endpoint object is defined in [ietf-idr-tunnel-encaps]

3.3.3.  path-instance Sub-TLV

   The path instance sub-tlv contains a set of instance-ids (P2MP LSPs).
   These LSPs can be used for MBB procedure under a candidate path.
   Each LSP Instance-id has a unique id (4 octets) with in the <root
   node, P2MP policy>, in other word it is unique per <root node,tree-
   id>.  The PCE SHOULD always download all instance-ids to the node.
   The active instance is identified via the active instance-id sub-tlv.

   The P2MP LSP and its replication segments should be configured from
   root to the leaves first before the PCE switches that active
   instance-id to this new instance.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |             Length            |   RESERVED    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                           Sub-TLVs                          //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   *  Type: TBD, 1 octet

   *  Length: 2 octets, the total length (not including the Type and
      Length fields) of the sub-TLVs encoded within the Segment List
      sub-TLV.

   *  RESERVED: 1 octet of reserved bits.  SHOULD be unset on
      transmission and MUST be ignored on receipt

   *  sub-TLVs: * active instance-id * one or more instance-id

3.3.3.1.  active instance-id Sub-TLV

   The Active instance-id is used to identify the P2MP LSP which should
   be active amongst the collection of instances.

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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |             Length            |   RESERVED    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           active instance-id                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   *  Type: TBD.

   *  Length: the total length (not including the Type and Length
      fields) of the sub-TLVs encoded within the Segment List sub-TLV.

   *  RESERVED: 1 octet of reserved bits.  SHOULD be unset on
      transmission and MUST be ignored on receipt.

   *  active instant-id: The identifier of the active instance-id

3.3.3.2.  instance-id Sub-TLV

   Multiple Instance-ids can be programmed for a candidate path.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |             Length            |   RESERVED    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           instance-id                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   *  Type: TBD

   *  Length: the total length (not including the Type and Length
      fields) of the sub-TLVs encoded within the Segment List sub-TLV.

   *  RESERVED: 1 octet of reserved bits.  SHOULD be unset on
      transmission and MUST be ignored on receipt.

   *  instan-id: a 32 bit unique identifier.  The instance-id is unique
      with in the context of the <root node, p2mp policy>

3.4.  Replication segment Sub-TLVs

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3.4.1.  Segment list Sub-TLV

   The segment list Sub-TLV is defined in
   [ietf-spring-segment-routing-policy].  The segment-list Sub-TLV
   contains one or more segment Sub-TLVs.  Two replication segments can
   be directly connected via a replication sid or can be connected via a
   unicast segment list and a replication sid.  In the later case the
   replication sid needs to be at the bottom of the unicast segment
   list.

3.4.2.  Weight sub-tlv

   The Weight sub-TLV is optional and is as defined in
   [draft-ietf-idr-segment-routing-te-policy].  With in the downstream
   node sub-tlv, there can be one or more segment list used for ECMP.
   In this case the weight sub-tlv can provide weighted ECMP.

3.4.3.  Protection sub-tlv

   Protection sub-tlv is optional, if FRR is desired for the downstream
   node this sub-tlv can be used to identify the protection segment
   list.  To identify protection segment list this sub-tlv provides a
   segment list identifier.  If protection is desired under the endpoint
   all the segment lists should have this sub-tlv.  A protection segment
   list can not have a weight sub-tlv and it can not participate in
   ECMP.  That said a segment list that is being protected can have a
   weight sub-tlv and participate in ECMP.

   In general protection segment list is used only if replication
   segments are directly connected and there is no unicast segment list
   connecting two replication segment.  If there is a unicast
   replication segment connecting the two replication sid, then the
   unicast protection mechanism can be exercise and there is no need for
   this protection sub-tlv, hence why this sub-tlv is optional.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |   Length      |     Flags   |P|   RESERVED    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           segment list id     |  protection segment list id   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   *  Type : tbd, 1 octet.

   *  Length: 8

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   *  Flag: 1 octet, the P bit is set when this segment list is
      protected by another segment list for the downstream node

   *  segment list id: the segment list id

   *  protection segment list id: the segment list id that is being used
      as protection.

3.4.4.  Segment Sub-TLV

   The segment sub-Tlv is identified in
   [draft-ietf-idr-segment-routing-te-policy].  As it was mentioned
   before two replication segments can be connected directly to each
   other or via a segment list.  If they are connected directly to each
   other then the segment list can be constructed via:

   *  If the replication segment is steered via IPv4 or IPv6 nexthops or
      interface then the segment type E or G can be used with the new R
      flag set.

   *  If the replication segment is steered via a SR Unicast node or
      adjacency SID then segment type A can be used with the new R flag
      set.  Unicast SR segment types can also be configured for
      steering.

   If they are connected via SR domain then the segment list can contain
   multiple different types of SIDs, such as Node, Adjacency or Binding
   SIDe.  In this case the replication sid is at the bottom of the stack
   and of type A with the R flag set.  The SR node/adjacency or binding
   sids steer the packet through a SR domain until it reaches another
   replication segment. where the bottom of the stack replication sid
   identifies the forwarding information on that replication segment.

   It should be noted that the segment sub-TLV is only used to program
   the unicast SR Segment or outgoing interface for the replication SID
   outgoing interface.  The outgoing tree SID it self is programmed in
   the appropriate route type.

4.  P2MP Policy Operation

   Inline with [draft-ietf-idr-segment-routing-te-policy] the consumer
   of an P2MP Policy is not the BGP process.  The BGP process is used
   for distributing the P2MP policy NLRI and its route-types but its
   installation and use is outside the scope of BGP.  The detail for
   P2MP Policy can be found in [draft-ietf-pim-sr-p2mp-policy]

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4.1.  Configuration and advertisement of P2MP Policies

   The controller usually is connected to the receivers via a route
   reflector.  As such one or more route-target SHOULD be attached to
   the advertisement of P2MP Policy NLRI and its route-type.  Each route
   target identifies one head-end (root nodes) for P2MP Policy route or
   one or more head-end, transit and leaf nodes for the Non- Shared/
   Shared Tree Replication Segment route, for the advertised P2MP
   Policy.

4.2.  Reception of an P2MP Policy NLRI

   When a BGP speaker receives an P2MP Policy NLRI the following rules
   apply:

   *  The P2MP Policy update MUST have either the NO_ADVERTISE community
      or at least one route-target extended community in IPv4-address
      format.  If a router supporting this document receives an P2MP
      Policy update with no route-target extended communities and no
      NO_ADVERTISE community, the update MUST NOT be processed.
      Furthermore, it SHOULD be considered to be malformed, and the
      "treat-as-withdraw" strategy of [RFC7606] is applied.

   *  If one or more route-targets are present, then at least one route-
      target MUST match one of the BGP Identifiers of the receiver in
      order for the update to be considered usable.  The BGP Identifier
      is defined in [RFC4271] as a 4 octet IPv4 address.  Therefore the
      route- target extended community MUST be of the same format.

   *  If one or more route-targets are present and no one matches any of
      the local BGP Identifiers, then, while the P2MP Policy NLRI is
      acceptable, it is not usable on the receiver node.

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4.3.  Global Optimization for P2MP LSPs

   When a P2MP LSP needs to be optimized for any reason (i.e. it is
   taking on an FRR Path or new routers are added to the network) a
   global optimization is possible.  Note that optimization works per
   candidate path.  Each candidate path is capable of global
   optimization.  To do so each candidate path contains two or more
   path- instances.  Each path instance is a P2MP LSP, each P2MP LSP is
   identified via a path-instance-id (equivalent to an lsp-id
   [RFC3209]).  After calculating an optimized P2MP LSP path the PCE
   will program the candidate path with a 2nd path instance and its set
   of replication segments for this path-instance on the root, transit
   and leaf nodes.  After the optimized LSP replication segments are
   downloaded a MBB procedure is performed and the previous instance of
   the path instance is deleted and removed from head-end node and its
   corresponding replication segments from head-end, transit and leaves.

5.  IANA Consideration

   *  A new SAFI is defined: the SR P2MP Policy SAFI, (Codepoint tbd
      assigned by IANA)

   *  2 new Route type field defines the encoding of the rest of the
      P2MP- POLICY SAFI

      -  P2MP Policy Route

      -  Replication Segment Binding Sid

      -  Replication Segment OIF

   *  Two new Tunnel type to be assigned by IANA

6.  Security Considerations

   TBD

7.  Acknowledgments

8.  References

8.1.  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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8.2.  Informative References

   [draft-ietf-bess-mvpn-evpn-sr-p2mp]
              "".

   [draft-ietf-idr-segment-routing-te-policy]
              "".

   [draft-ietf-pim-sr-p2mp-policy]
              "D. Yoyer, C. Filsfils, R.Prekh, H.bidgoli, Z. Zhang,
              "draft-ietf-pim-sr-p2mp-policy"", October 2019.

   [draft-ietf-spring-segment-routing-policy]
              "".

   [draft-ietf-spring-sr-replication-segment]
              "D. Yoyer, C. Filsfils, R.Prekh, H.bidgoli, Z. Zhang,
              "draft-ietf-pim-sr-p2mp-policy "", July 2020.

   [ietf-idr-tunnel-encaps]
              "".

   [ietf-spring-segment-routing-policy]
              "".

   [RFC4271]  "".

   [RFC4760]  "".

   [RFC6513]  "".

   [RFC7606]  "".

Authors' Addresses

   Hooman Bidgoli (editor)
   Nokia
   Ottawa
   Canada

   Email: hooman.bidgoli@nokia.com

   Daniel Voyer
   Bell Canada
   Montreal
   Canada

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   Email: daniel.yover@bell.ca

   Andrew Stone
   Nokia
   Ottawa
   Canada

   Email: andrew.stone@nokia.com

   Rishabh Parekh
   Cisco System
   San Jose,
   United States of America

   Email: riparekh@cisco.com

   Serge Krier
   Cisco System, Inc.
   Rixensart
   Belgium

   Email: sekrier@cisco.com

   Arvind Venkateswaran
   Cisco System, Inc.
   Ottawa
   Canada

   Email: arvvenka@cisco.com

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