



Internet Engineering Task Force (IETF)                    R. Parekh, Ed.
Request for Comments: 9960                                        Arrcus
Updates: 9524                                              D. Voyer, Ed.
Category: Standards Track                                    C. Filsfils
ISSN: 2070-1721                                      Cisco Systems, Inc.
                                                              H. Bidgoli
                                                                   Nokia
                                                                Z. Zhang
                                                        Juniper Networks
                                                              April 2026


               Segment Routing Point-to-Multipoint Policy

Abstract

   The Point-to-Multipoint (P2MP) Policy enables creation of P2MP trees
   for efficient multipoint packet delivery in a Segment Routing (SR)
   domain.  This document specifies the architecture, signaling, and
   procedures for SR P2MP Policies with Segment Routing over MPLS (SR-
   MPLS) and Segment Routing over IPv6 (SRv6).  It defines the SR P2MP
   Policy construct, candidate paths (CPs) of an SR P2MP Policy, and the
   instantiation of the P2MP tree instances (PTIs) of a CP using
   Replication segments.  Additionally, it describes the required
   extensions for a controller to support P2MP path computation and
   provisioning.  This document updates RFC 9524.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9960.

Copyright Notice

   Copyright (c) 2026 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
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   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 Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Terminology
     1.2.  Requirements Language
   2.  SR P2MP Policy
     2.1.  SR P2MP Policy Identification
     2.2.  Components of an SR P2MP Policy
     2.3.  Candidate Paths and P2MP Tree Instances
   3.  Steering Traffic into an SR P2MP Policy
   4.  P2MP Tree Instance
     4.1.  Replication Segments at Leaf Nodes
     4.2.  Shared Replication Segments
     4.3.  Packet Forwarding in a P2MP Tree Instance
   5.  Using a Controller to Build a P2MP Tree
     5.1.  SR P2MP Policy on a Controller
     5.2.  Controller Functions
     5.3.  P2MP Tree Compute
     5.4.  SID Management
     5.5.  Instantiating P2MP Tree Instance on Nodes
     5.6.  Protection
       5.6.1.  Local Protection
       5.6.2.  Path Protection
   6.  IANA Considerations
   7.  Security Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Appendix A.  Illustration of the SR P2MP Policy and P2MP Tree
     A.1.  P2MP Tree with Non-Adjacent Replication Segments
       A.1.1.  SR-MPLS
       A.1.2.  SRv6
     A.2.  P2MP Tree with Adjacent Replication Segments
       A.2.1.  SR-MPLS
       A.2.2.  SRv6
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   [RFC9524] defines a Replication segment that enables a SR node to
   replicate traffic to multiple downstream nodes in an SR domain
   [RFC8402].  A Point-to-Multipoint (P2MP) service can be realized by a
   single Replication segment spanning from the ingress node to the
   egress nodes of the service.  This effectively achieves ingress
   replication, which is inefficient since the traffic of the P2MP
   service may traverse the same set of nodes and links in the SR domain
   on its path from the ingress node to the egress nodes.

   A multipoint service delivery can be efficiently realized with a P2MP
   tree in a SR domain.  A P2MP tree spans from a Root node to a set of
   Leaf nodes via intermediate Replication nodes.  It consists of a
   Replication segment at the Root node, and that Replication segment is
   stitched to one or more Replication segments between the Leaf nodes
   and intermediate Replication nodes.  A Bud node [RFC9524] is a node
   that is both a Replication node and a Leaf node.  Any mention of
   "Leaf node(s)" in this document should be considered as referring to
   "Leaf or Bud node(s)".

   An SR P2MP Policy defines the Root and Leaf nodes of a P2MP tree.  It
   has one or more CPs provisioned with optional constraints and/or
   optimization objectives.

   A controller computes PTIs of the CPs using the constraints and
   objectives specified in the CP.  The controller then instantiates a
   PTI in the SR domain by signaling Replication segments to the Root,
   Replication, and Leaf nodes.  A Path Computation Element (PCE)
   [RFC4655] is one example of such a controller.  In other cases, a PTI
   can be installed using the Network Configuration Protocol (NETCONF) /
   YANG or the Command Line Interface (CLI) on the Root, Replication,
   and Leaf nodes.

   The Replication segments of a PTI can be instantiated for SR-MPLS
   [RFC8660] and SRv6 [RFC8986] data planes, enabling efficient packet
   replication within an SR domain.

   This document updates the Replication-ID portion of the Replication
   segment identifier (Replication-SID) specified in Section 2 of
   [RFC9524].

1.1.  Terminology

   This section defines terms used frequently in this document.  Refer
   to the Terminology section of [RFC9524] for the definitions of
   Replication segment and other terms associated with it and the
   definitions of Root, Leaf, and Bud nodes.

   SR P2MP Policy:  An SR P2MP Policy is a framework to construct P2MP
      trees in an SR domain by specifying Root and Leaf nodes.

   Tree-ID:  An identifier of an SR P2MP Policy in context of the Root
      node.

   Candidate path (CP):  A CP of the SR P2MP Policy defines topological
      or resource constraints and optimization objectives that are used
      to compute and construct PTIs.

   P2MP tree instance (PTI):  A PTI of a CP is constructed by stitching
      Replication segments between the Root and Leaf nodes of an SR P2MP
      Policy.  Its topology is determined by the constraints and
      optimization objective of the CP.

   Instance-ID:  An identifier of a PTI in context of the SR P2MP
      Policy.

   Tree-SID:  The Replication-SID of the Replication segment at the Root
      node of a PTI.

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  SR P2MP Policy

   An SR P2MP Policy is used to instantiate P2MP trees between Root and
   Leaf nodes in an SR domain.  Note that multiple SR P2MP Policies can
   have identical Root nodes and identical sets of Leaf nodes.  An SR
   P2MP Policy has one or more CPs [RFC9256].

2.1.  SR P2MP Policy Identification

   An SR P2MP Policy is uniquely identified by the tuple <Root, Tree-
   ID>, where:

   *  Root: The IP address of the Root node of P2MP trees instantiated
      by the SR P2MP Policy.

   *  Tree-ID: A 32-bit unsigned integer that uniquely identifies the SR
      P2MP Policy in the context of the Root node.

2.2.  Components of an SR P2MP Policy

   An SR P2MP Policy consists of the following elements:

   *  Leaf nodes: A set of nodes that terminate the P2MP trees of the SR
      P2MP Policy.

   *  Candidate paths: A set of possible paths that define constraints
      and optimization objectives for PTIs of the SR P2MP Policy.

   An SR P2MP Policy and its CPs are provisioned on a controller (see
   Section 5) or the Root node or both, depending upon the provisioning
   model.  After provisioning, the Policy and its CPs are instantiated
   on the Root node or the controller by using a signaling protocol.

2.3.  Candidate Paths and P2MP Tree Instances

   An SR P2MP Policy has one or more CPs.  The tuple <Protocol-Origin,
   Originator, Discriminator>, as specified in Section 2.6 of [RFC9256],
   uniquely identifies a CP in the context of an SR P2MP Policy.  The
   semantics of Protocol-Origin, Originator, and Discriminator fields of
   the identifier are the same as in Sections 2.3, 2.4, and 2.5 of
   [RFC9256], respectively.

   The Root node of the SR P2MP Policy selects the active CP based on
   the tiebreaking rules defined in Section 2.9 of [RFC9256].

   A CP may include topological and/or resource constraints and
   optimization objectives that influence the computation of the PTIs of
   the CP.

   A CP has zero or more PTIs.  A CP does not have a PTI when the
   controller cannot compute a P2MP tree from the network topology based
   on the constraints and/or optimization objectives of the CP.  A CP
   can have more than one PTI, e.g., during the Make-Before-Break (see
   Section 5.3) procedure to handle a network state change.  However,
   one and only one PTI MUST be the active instance of the CP.  If more
   than one PTI of a CP is active at same time, and that CP is the
   active CP of the SR P2MP Policy, then duplicate traffic may be
   delivered to the Leaf nodes.

   A PTI is identified by an Instance-ID.  This is an unsigned 16-bit
   number that is unique in context of the SR P2MP Policy of the CP.

   PTIs are instantiated using Replication segments.  Section 2 of
   [RFC9524] specifies the Replication-ID of the Replication segment
   control plane identifier tuple as a variable length field that can be
   modified as required based on the use of a Replication segment.
   However, length is an imprecise indicator of the actual structure of
   the Replication-ID.  This document updates the Replication-ID of the
   control plane identifier of a Replication segment [RFC9524] to be the
   tuple: <Root, Tree-ID, Instance-ID>, where <Root, Tree-ID> identifies
   the SR P2MP Policy and Instance-ID identifies the PTI within that SR
   P2MP Policy.  The Replication segments used to instantiate a PTI are
   thus identified in the control plane by the tuple: <Root, Tree-ID,
   Instance-ID, Node-ID>.  As per Section 2 of [RFC9524], for a simple
   use case, the Replication-ID is a 32-bit number.  To map this use
   case to the tuple for the control plane identifier of a Replication
   segment as defined in this document, the Root MUST be zero (0.0.0.0
   for IPv4 and :: for IPv6), the Instance-ID MUST be zero, and the
   32-bit Tree-ID to effectively make the tuple <[0.0.0.0 or ::], Tree-
   ID, 0, Node-ID>.

   PTIs may have different tree topologies due to possibly differing
   constraints and optimization objectives of the CPs in an SR P2MP
   Policy and across different policies.  Even within a given CP, two
   PTIs of that CP, say during the Make-Before-Break procedure, are
   likely to have different tree topologies due to a change in the
   network state.  Since the PTIs may have different tree topologies,
   their replication states also differ at various nodes in the SR
   domain.  Therefore, each PTI has its own Replication segment and a
   unique Replication-SID in the data plane at a given node in the SR
   domain.

   A controller designates an active instance of a CP at the Root node
   of the SR P2MP Policy by signaling this state through the protocol
   used to instantiate the Replication segment of the instance.

   This document focuses on the use of a controller to compute and
   instantiate PTIs of SR P2MP Policy CPs.  It is also feasible to
   provision an explicit CP in an SR P2MP Policy with a static tree
   topology using NETCONF/YANG or CLI.  Note that a static tree topology
   will not adapt to any changes in the network state of an SR domain.
   The explicit CPs may be provisioned on the controller or the Root
   node.  When an explicit CP is provisioned on the controller, the
   controller bypasses the compute stage and directly instantiates the
   PTIs in the SR domain.  When an explicit CP is provisioned on the
   Root node, the Root node instantiates the PTIs in the SR domain.  The
   exact procedures for provisioning an explicit CP and the signaling
   from the Root node to instantiate the PTIs are outside the scope of
   this document.

3.  Steering Traffic into an SR P2MP Policy

   The Replication-SID of the Replication segment at the Root node is
   referred to as the Tree-SID of a PTI.  It is RECOMMENDED that the
   Tree-SID is also used as the Replication-SID for the Replication
   segments at the intermediate Replication nodes and the Leaf nodes of
   the PTI as it simplifies operations and troubleshooting.  However,
   the Replication-SIDs of the Replication segments at the intermediate
   Replication nodes and the Leaf nodes MAY differ from the Tree-SID.
   For SRv6, Replication-SID is the FUNCT portion of the SRv6 segment ID
   (SID) [RFC8986] [RFC9524].  Note that even if the Tree-SID is the
   Replication-SID of all the Replication segments of a PTI, the locator
   (LOC) portion of the SRv6 SID [RFC8986] differs for the Root node,
   the intermediate Replication nodes, and the Leaf nodes of the PTI.

   An SR P2MP Policy has a Binding SID (BSID).  The BSID is used to
   steer traffic into an SR P2MP Policy, as described below, when the
   Root node is not the ingress node of the SR domain where the traffic
   arrives.  The packets are steered from the ingress node to the Root
   node using a segment list with the BSID as the last segment in the
   list.  In this case, it is RECOMMENDED that the BSID of an SR P2MP
   Policy SHOULD be constant throughout the lifetime of the policy so
   the steering of traffic to the Root node remains unchanged.  The BSID
   of an SR P2MP Policy MAY be the Tree-SID of the active P2MP instance
   of the active CP of the policy.  In this case, the BSID of an SR P2MP
   Policy changes when the active CP or the active PTI of the SR P2MP
   Policy changes.  Note that the BSID is not required to steer traffic
   into an SR P2MP Policy when the Root node of an SR P2MP Policy is
   also the ingress node of the SR domain where the traffic arrives.

   The Root node can steer an incoming packet into an SR P2MP Policy in
   one of following methods:

   *  Local-policy-based forwarding: The Root node maps the incoming
      packet to the active PTI of the active CP of an SR P2MP Policy
      based on local forwarding policy, and it is replicated with the
      encapsulated Replication-SIDs of the downstream nodes.  The
      procedures to map an incoming packet to an SR P2MP Policy are out
      of scope of this document.  It is RECOMMENDED that an
      implementation provide a mechanism to examine the result of
      application of the local forwarding policy, i.e., provide
      information about the traffic mapped to an SR P2MP Policy and the
      active CP and active PTI of the policy.

   *  Tree-SID-based forwarding: The BSID, which may be the Tree-SID of
      the active PTI, in an incoming packet is used to map the packet to
      the active PTI.  The BSID in the incoming packet is replaced with
      the Tree-SID of the active PTI of the active CP, and the packet is
      replicated with the Replication-SIDs of the downstream nodes.

   For local-policy-based forwarding with SR-MPLS, the TTL for the Root
   node SHOULD set the TTL in the encapsulating MPLS header so that the
   replicated packet can reach the furthest Leaf node.  The Root MAY set
   the TTL in the encapsulating MPLS header from the payload.  In this
   case, the TTL may not be sufficient for the replicated packet to
   reach the furthest node.  For SRv6, Section 2.2 of [RFC9524] provides
   guidance to set the IPv6 Hop Limit of the encapsulating IPv6 header.

4.  P2MP Tree Instance

   A PTI within an SR domain establishes a forwarding structure that
   connects a Root node to a set of Leaf nodes via a series of
   intermediate Replication nodes.  The tree consists of:

   *  A Replication segment at the Root node.

   *  Zero or more Replication segments at intermediate Replication
      nodes.

   *  Replication segments at the Leaf nodes.

4.1.  Replication Segments at Leaf Nodes

   A specific service is identified by a service context in a packet.  A
   PTI is usually associated with one and only one multipoint service.
   On a Leaf node of such a multipoint service, the transport
   identifier, which is the Tree-SID or Replication-SID of the
   Replication segment at a Leaf node, is also associated with the
   service context because it is not always feasible to separate the
   transport and service context with efficient replication in core
   since a) multipoint services may have differing sets of endpoints and
   b) downstream allocation of a service context cannot be encoded in
   packets replicated in the core.

   A PTI can be associated with one or more multipoint services on the
   Root and Leaf nodes.  In SR-MPLS deployments, if it is known a priori
   that multipoint services mapped to an SR-MPLS PTI can be uniquely
   identified with their service label, a controller MAY opt to not
   instantiate Replication segments at Leaf nodes.  In such cases,
   Replication nodes upstream of the Leaf nodes can remove the Tree-SID
   from the packet before forwarding it.  A multipoint service context
   allocated from an upstream assigned label or Domain-wide Common Block
   (DCB), as specified in [RFC9573], is an example of a globally unique
   context that facilitates this optimization.

   In SRv6 deployments, Replication segments of a PTI MUST be
   instantiated on Leaf nodes of the tree since behavior like
   Penultimate Hop Popping (PHP) is not feasible because the Tree-SID is
   carried in the IPv6 Destination Address field of the outer IPv6
   header.  If two or more multipoint services are mapped to one SRv6
   PTI, an SRV6 SID representing the service context is assigned by the
   Root node or assigned from the DCB.  This SRv6 SID MUST be encoded as
   the last segment in the Segment List of the Segment Routing Header
   [RFC8754] by the Root node to derive the packet processing context
   (PPC) for the service, as described in Section 2.2 of [RFC9524], at a
   Leaf node.

4.2.  Shared Replication Segments

   A Replication segment MAY be shared across different PTIs.  One
   simple use of a shared Replication segment is for local protection on
   a Replication node.  Assume a Replication node, say node X, has
   multiple PTIs.  Assume the Replications segments of these PTIs
   replicate to a downstream node, say node Y, amongst other downstream
   nodes.  This node Y is a common downstream node of these Replication
   segments at node X.  A Replication segment is established to protect
   the adjacency or path between node X and node Y; this Replication
   segment can be shared across all the Replication segments of the PTIs
   replicating from node X to node Y.

   A shared Replication segment MUST be identified using a Root set to
   zero (0.0.0.0 for IPv4 and :: for IPv6), an Instance-ID set to zero,
   and a Tree-ID that is unique within the context of the node where the
   Replication segment is instantiated.  The Root is zero because a
   shared Replication segment is not associated with a particular SR
   P2MP Policy or a PTI.  Note that the shared Replication-SID conforms
   with the updated Replication-ID definition in Section 2.3.

   It is possible for different PTIs to share a P2MP tree at a
   Replication node.  This allows a common sub-tree to be shared across
   PTIs whose tree topologies are identical in some portion of an SR
   domain.  The procedures to share a P2MP tree across PTIs are outside
   the scope of this document.

4.3.  Packet Forwarding in a P2MP Tree Instance

   When a packet is steered into a PTI, the Replication segment at the
   Root node performs packet replication and forwards copies to
   downstream nodes.

   *  Each replicated packet carries the Replication-SID of the
      Replication segment at the downstream node.

   *  A downstream node can be either:

      -  A Leaf node, in which case the replication process terminates,
         or

      -  An intermediate Replication node, which further replicates the
         packet through its associated Replication segments until it
         reaches all Leaf nodes.

   A Replication node and a downstream node can be non-adjacent.  In
   this case, the replicated packet has to traverse a path to reach the
   downstream node.  For SR-MPLS, this is achieved by inserting one or
   more SIDs before the downstream Replication-SID.  For SRv6, the LOC
   [RFC8986] of the downstream Replication-SID can guide the packet to
   the downstream node or an optional segment list may be used to steer
   the replicated packet on a specific path to the downstream node.  For
   details of SRv6 replication to a non-adjacent downstream node and
   IPv6 Hop Limit considerations, refer to Section 2.2 of [RFC9524].

5.  Using a Controller to Build a P2MP Tree

   A controller is instantiated or provisioned with the SR P2MP Policy
   and its CPs to compute and instantiate PTIs in an SR domain.  The
   procedures for provisioning or instantiation of these constructs on a
   controller are outside the scope of this document.

5.1.  SR P2MP Policy on a Controller

   An SR P2MP Policy is provisioned on a controller by an entity that
   can be an operator, a network node, or a machine by specifying the
   addresses of the Root, the set of Leaf nodes, and the CPs.  In this
   case, the policy and its CPs are instantiated on the Root node using
   a signaling protocol.  An SR P2MP Policy, its Leaf nodes, and the CPs
   may also be provisioned on the Root node and then instantiated on the
   controller using a signaling protocol.  The procedures and mechanisms
   for provisioning and instantiation of an SR P2MP Policy and its CPS
   on a controller or a Root node are outside the scope of this
   document.

   The possible set of constraints and optimization objective of a CP
   are described in Section 3 of [SR-POLICY].  Other constraints and
   optimization objectives MAY be used for P2MP tree computation.

5.2.  Controller Functions

   A controller performs the following functions in general:

   *  Topology Discovery: A controller discovers network topology across
      Interior Gateway Protocol (IGP) areas, levels, or Autonomous
      Systems (ASes).

   *  Capability Exchange: A controller discovers a node's capability to
      participate in an SR P2MP Policy as well as advertise its
      capability to support the SR P2MP Policy.

5.3.  P2MP Tree Compute

   A controller computes one or more PTIs for CPs of an SR P2MP Policy.
   A CP may not have any PTIs if a controller cannot compute a P2MP tree
   for it.

   A controller MUST compute a P2MP tree such that there are no loops in
   the tree at steady state as required by [RFC9524].

   A controller SHOULD modify a PTI of a CP on detecting a change in the
   network topology if the change affects the tree instance or when a
   better path can be found based on the new network state.
   Alternatively, the controller MAY decide to implement a Make-Before-
   Break approach to minimize traffic loss.  The controller can do this
   by creating a new PTI, activating the new instance once it is
   instantiated in the network, and then removing the old PTI.

5.4.  SID Management

   The controller assigns the Replication-SIDs for the Replication
   segments of the PTI.

   The Replication-SIDs of a PTI of a CP of an SR P2MP Policy can be
   either dynamically assigned by the controller or statically assigned
   by the entity provisioning the SR P2MP Policy.

   For SR-MPLS, a Replication-SID may be assigned from the SR Local
   Block (SRLB) or the SR Global Block (SRGB) [RFC8402].  It is
   RECOMMENDED to assign a Replication-SID from the SRLB since
   Replication segments are local to each node of the PTI.  It is NOT
   RECOMMENDED to allocate a Replication-SID from the SRGB since this
   block is globally significant in the SR domain any it may get
   depleted if a significant number of PTIs are instantiated in the SR
   domain.

   Section 3 recommends that the Tree-SID be used as the Replication-
   SIDs for all the Replication segments of a PTI.  It may be feasible
   to allocate the same Tree-SID value for all the Replication segments
   if the blocks used for allocation are not identical on all the nodes
   of the PTI or if the particular Tree-SID value in the block is
   assigned to some other SID on some node.

   A BSID is also assigned for the SR P2MP Policy.  The controller MAY
   decide to not assign a BSID and allow the Root node of the SR P2MP
   Policy to assign the BSID.  It is RECOMMENDED to assign the BSID of
   an SR P2MP Policy from the SRLB for SR-MPLS.

   The controller MAY be provisioned with a reserved block or multiple
   reserved blocks for assigning Replication-SIDs and/or the BSIDs for
   SR P2MP Policies.  A single block maybe be reserved for the whole SR
   domain, or dedicated blocks can be reserved for each node or a group
   of nodes in the SR domain.  These blocks MAY overlap with either the
   SRGB, the SRLB, or both.  The procedures for provisioning these
   reserved blocks and procedures for deconflicting assignments from
   these reserved blocks with overlapping SRLB or SRGB blocks are
   outside the scope of this document.

   A controller may not be aware of all the assignments of SIDs from the
   SRGB or the SRLB of the SR domain.  If reserved blocks are not used,
   the assignment of Replication-SIDs or BSIDs of SR P2MP Policies from
   these blocks may conflict with other SIDs.

5.5.  Instantiating P2MP Tree Instance on Nodes

   After computing P2MP trees, the controller instantiates the
   Replication segments that compose the PTIs in the SR domain using
   signaling protocols such as the Path Computation Element
   Communication Protocol (PCEP) [SR-P2MP-PCEP], BGP [P2MP-BGP], or
   other mechanisms such as NETCONF/YANG [SR-P2MP-YANG], etc.  The
   procedures for the instantiation of the Replication segments in an SR
   domain are outside the scope of this document.

   A node SHOULD report a successful instantiation of a Replication
   segment.  The exact procedure for reporting this is outside the scope
   of this document.

   The instantiation of a Replication segment on a node may fail, e.g.,
   when the Replication-SID conflicts with another SID on the node.  The
   node SHOULD report this, preferably with a reason for the failure,
   using a signaling protocol.  The exact procedure for reporting this
   failure is outside the scope of this document.

   If the instantiation of a Replication segment on a node fails, the
   controller SHOULD attempt to re-instantiate the Replication segment.
   There SHOULD be an upper bound on the number of attempts.  If the
   instantiation of a Replication segment ultimately fails after the
   allowed number of attempts, the controller SHOULD generate an alert
   via mechanisms like syslog.  These alerts SHOULD be rate-limited to
   protect the logging facility in case Replication segment
   instantiation fails on multiple nodes.  The controller MAY decide to
   tear down the PTI if the instantiations of some of the Replication
   segments of the instance fail.  The controller is RECOMMENDED to tear
   down the PTI if the instantiation of the Replication segment on the
   Root node fails.  The controller can employ different strategies to
   retry instantiating a PTI after a failure.  These are out of scope of
   this document.

   A PTI should be instantiated within a reasonable time, especially if
   it is the active PTI of an SR P2MP Policy.  One approach is the
   controller instantiates the Replication segments in a batch.  For
   example, the controller instantiates the Replication segments of the
   Leaf nodes and the intermediate Replication nodes first.  If all of
   these Replication segments are successfully instantiated, the
   controller then proceeds to instantiate the Replication segment at
   the Root node.  If the Replication segment instantiation at the Root
   node succeeds, the controller can immediately activate the instance
   if it needs to carry traffic of the SR P2MP Policy.  A controller can
   adopt a similar approach when instantiating the new PTI for the Make-
   Before-Break procedure.

5.6.  Protection

5.6.1.  Local Protection

   A network link, node, or replication branch on a PTI can be protected
   using SR Policies [RFC9256].  The backup SR Policies are associated
   with replication branches of a Replication segment and are programmed
   in the data plane in order to minimize traffic loss when the
   protected link/node fails.  The segment list of the backup SR Policy
   is imposed on the downstream Replication-SID of a replication branch
   to steer the traffic on the backup path.

   It is also possible to use a node local Loop-Free Alternate [RFC5286]
   or Topology Independent Loop-Free Alternate (TI-LFA) [RFC9855]
   protection and a Micro-Loop [RFC5715] or SR Micro-Loop [SR-LOOP]
   prevention mechanism to protect the links/nodes of a PTI.

5.6.2.  Path Protection

   A controller can create a disjoint backup tree instance for providing
   end-to-end tree protection if the topology permits.  This can be
   achieved by having a backup CP with constraints and/or optimization
   objectives that ensure its PTIs are disjoint from the PTIs of the
   primary/active CP.

6.  IANA Considerations

   This document has no IANA actions.

7.  Security Considerations

   This document describes how a PTI can be created in an SR domain by
   stitching Replication segments together.  Some security
   considerations for Replication segments outlined in [RFC9524] are
   also applicable to this document.  Following is a brief reminder of
   those security considerations.

   An SR domain needs protection from outside attackers as described in
   [RFC8402], [RFC8754], and [RFC8986].

   Failure to protect the SR-MPLS domain by correctly provisioning MPLS
   support per interface permits attackers from outside the domain to
   send packets to receivers of the multipoint services that use the SR
   P2MP Policies provisioned within the domain.

   Failure to protect the SRv6 domain with inbound Infrastructure Access
   Control Lists (IACLs) on external interfaces, combined with failure
   to implement the method described in RFC 2827 [BCP38] or apply IACLs
   on nodes provisioning SIDs, permits attackers from outside the SR
   domain to send packets to the receivers of multipoint services that
   use the SR P2MP Policies provisioned within the domain.

   Incorrect provisioning of Replication segments by a controller that
   computes SR PTI can result in a chain of Replication segments forming
   a loop.  In this case, replicated packets can create a storm until
   MPLS TTL (for SR-MPLS) or IPv6 Hop Limit (for SRv6) decrements to
   zero.

   The control plane protocols (like PCEP, BGP, etc.) used to
   instantiate Replication segments of SR PTI can leverage their own
   security mechanisms such as encryption, authentication filtering,
   etc.

   For SRv6, [RFC9524] describes an exception for the ICMPv6 Parameter
   Problem message with Code 2.  If an attacker is able to inject a
   packet into a multipoint service with the source address of a node
   and with an extension header using an unknown option type marked as
   mandatory, then a large number of ICMPv6 Parameter Problem messages
   can cause a denial-of-service attack on the source node.

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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.

   [RFC9524]  Voyer, D., Ed., Filsfils, C., Parekh, R., Bidgoli, H., and
              Z. Zhang, "Segment Routing Replication for Multipoint
              Service Delivery", RFC 9524, DOI 10.17487/RFC9524,
              February 2024, <https://www.rfc-editor.org/info/rfc9524>.

8.2.  Informative References

   [BCP38]    Best Current Practice 38,
              <https://www.rfc-editor.org/info/bcp38>.
              At the time of writing, this BCP comprises the following:

              Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
              May 2000, <https://www.rfc-editor.org/info/rfc2827>.

   [P2MP-BGP] Bidgoli, H., Voyer, D., Stone, A., Parekh, R., Krier, S.,
              and S. Agrewal, "Advertising p2mp policies in BGP", Work
              in Progress, Internet-Draft, draft-ietf-idr-sr-p2mp-
              policy-01, 29 April 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
              p2mp-policy-01>.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [RFC5715]  Shand, M. and S. Bryant, "A Framework for Loop-Free
              Convergence", RFC 5715, DOI 10.17487/RFC5715, January
              2010, <https://www.rfc-editor.org/info/rfc5715>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

   [RFC9573]  Zhang, Z., Rosen, E., Lin, W., Li, Z., and IJ. Wijnands,
              "MVPN/EVPN Tunnel Aggregation with Common Labels",
              RFC 9573, DOI 10.17487/RFC9573, May 2024,
              <https://www.rfc-editor.org/info/rfc9573>.

   [RFC9855]  Bashandy, A., Litkowski, S., Filsfils, C., Francois, P.,
              Decraene, B., and D. Voyer, "Topology Independent Fast
              Reroute Using Segment Routing", RFC 9855,
              DOI 10.17487/RFC9855, October 2025,
              <https://www.rfc-editor.org/info/rfc9855>.

   [SR-LOOP]  Bashandy, A., Filsfils, C., Litkowski, S., Decraene, B.,
              Francois, P., and P. Psenak, "Loop avoidance using Segment
              Routing", Work in Progress, Internet-Draft, draft-
              bashandy-rtgwg-segment-routing-uloop-18, 19 April 2026,
              <https://datatracker.ietf.org/doc/html/draft-bashandy-
              rtgwg-segment-routing-uloop-18>.

   [SR-P2MP-PCEP]
              Bidgoli, H., Voyer, D., Budhiraja, A., Parekh, R., and S.
              Sivabalan, "PCEP extensions for SR P2MP Policy", Work in
              Progress, Internet-Draft, draft-ietf-pce-sr-p2mp-policy-
              14, 23 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-sr-
              p2mp-policy-14>.

   [SR-P2MP-YANG]
              Bidgoli, H., Voyer, D., Parekh, R., Saad, T., and T.
              Kundu, "YANG Data Model for p2mp sr policy", Work in
              Progress, Internet-Draft, draft-hb-spring-sr-p2mp-policy-
              yang-02, 30 October 2020,
              <https://datatracker.ietf.org/doc/html/draft-hb-spring-sr-
              p2mp-policy-yang-02>.

   [SR-POLICY]
              Filsfils, C., Talaulikar, K., Król, P. G., Horneffer, M.,
              and P. Mattes, "SR Policy Implementation and Deployment
              Considerations", Work in Progress, Internet-Draft, draft-
              filsfils-spring-sr-policy-considerations-09, 24 April
              2022, <https://datatracker.ietf.org/doc/html/draft-
              filsfils-spring-sr-policy-considerations-09>.

Appendix A.  Illustration of the SR P2MP Policy and P2MP Tree

   Consider the following topology:

                                      R3------R6
                         Controller--/         \
                             R1----R2----R5-----R7
                                     \         /
                                      +--R4---+

                           Figure 1: SR Topology

   In these examples, the Node-SID of a node Rn is N-SIDn and the
   Adjacency-SID from node Rm to node Rn is A-SIDmn.  The interface
   between Rm and Rn is Lmn.

   For SRv6, the reader is expected to be familiar with SRv6 Network
   Programming [RFC8986] to follow the examples.

   *  2001:db8::/32 is an IPv6 block allocated by a Regional Internet
      Registry (RIR) to the operator.

   *  2001:db8:0::/48 is dedicated to the internal address space.

   *  2001:db8:cccc::/48 is dedicated to the internal SRv6 SID space.

   *  We assume a location is expressed in 64 bits and a function is
      expressed in 16 bits.

   *  Node k has a classic IPv6 loopback address 2001:db8::k/128, which
      is advertised in the IGP.

   *  Node k has 2001:db8:cccc:k::/64 for its local SID space.  Its SIDs
      will be explicitly assigned from that block.

   *  Node k advertises 2001:db8:cccc:k::/64 in its IGP.

   *  Function :1:: (function 1, for short) represents the End function
      with Penultimate Segment Pop (PSP) support.

   *  Function :Cn:: (function Cn, for short) represents the End.X
      function to node n.

   *  Function :C1n: (function C1n for short) represents the End.X
      function to node n with Ultimate Segment Decapsulation (USD).

   Each node k has:

   *  An explicit SID instantiation 2001:db8:cccc:k:1::/128 bound to an
      End function with additional support for PSP

   *  An explicit SID instantiation 2001:db8:cccc:k:Cj::/128 bound to an
      End.X function to neighbor J with additional support for PSP

   *  An explicit SID instantiation 2001:db8:cccc:k:C1j::/128 bound to
      an End.X function to neighbor J with additional support for USD

   Assume a controller is provisioned with the following SR P2MP Policy
   at Root R1 with Tree-ID T-ID:

   SR P2MP Policy <R1,T-ID>:
    Leaf nodes: {R2, R6, R7}
    candidate-path 1:
      Optimize: IGP metric
      Tree-SID: T-SID1

   The controller is responsible for computing a PTI of the CP.  In this
   example, we assume one active PTI with Instance-ID I-ID1.  Assume the
   controller instantiates PTIs by signaling Replication segments, i.e.,
   the Replication-ID of these Replication segments is <Root, Tree-ID,
   Instance-ID>.  All Replication segments use the Tree-SID T-SID1 as
   the Replication-SID.  For SRv6, assume the Replication-SID at node k,
   bound to an End.Replicate function, is 2001:db8:cccc:k:fa::/128.

A.1.  P2MP Tree with Non-Adjacent Replication Segments

   Assume the controller computes a PTI with Root node R1, Intermediate
   and Leaf node R2, and Leaf nodes R6 and R7.  The controller
   instantiates the instance by stitching Replication segments at R1,
   R2, R6, and R7.  The Replication segment at R1 replicates to R2.  The
   Replication segment at R2 replicates to R6 and R7.  Note that nodes
   R3, R4, and R5 do not have any Replication segment state for the
   tree.

A.1.1.  SR-MPLS

   The Replication segment state at nodes R1, R2, R6, and R7 is shown
   below.

   Replication segment at R1:

   Replication segment <R1,T-ID,I-ID1,R1>:
    Replication-SID: T-SID1
    Replication State:
      R2: <T-SID1->L12>

   Replication to R2 steers a packet directly to the node on interface
   L12.

   Replication segment at R2:

   Replication segment <R1,T-ID,I-ID1,R2>:
    Replication-SID: T-SID1
    Replication State:
      R2: <Leaf>
      R6: <N-SID6, T-SID1>
      R7: <N-SID7, T-SID1>

   R2 is a Bud node.  It performs the role of a Leaf as well as a
   transit node replicating to R6 and R7.  Replication to R6, using
   N-SID6, steers a packet via IGP shortest path to that node.
   Replication to R7, using N-SID7, steers a packet via IGP shortest
   path to R7 via either R5 or R4 based on ECMP hashing.

   Replication segment at R6:

   Replication segment <R1,T-ID,I-ID1,R6>:
    Replication-SID: T-SID1
    Replication State:
      R6: <Leaf>

   Replication segment at R7:

   Replication segment <R1,T-ID,I-ID1,R7>:
    Replication-SID: T-SID1
    Replication State:
      R7: <Leaf>

   When a packet is steered into the active instance CP 1 of the SR P2MP
   Policy at R1:

   *  Since R1 is directly connected to R2, R1 performs the PUSH
      operation with just the <T-SID1> label for the replicated copy and
      sends it to R2 on interface L12.

   *  R2, as a Leaf, performs the NEXT operation, pops the T-SID1 label,
      and delivers the payload.  For replication to R6, R2 performs a
      PUSH operation of N-SID6 to send the <N-SID6,T-SID1> label stack
      to R3.  R3 is the penultimate hop for N-SID6; it performs PHP,
      which corresponds to the NEXT operation, and the packet is then
      sent to R6 with <T-SID1> in the label stack.  For replication to
      R7, R2 performs a PUSH operation of N-SID7 to send the
      <N-SID7,T-SID1> label stack to R4, which is one of the IGP ECMP
      next hops (R5 is other) towards R7.  R4 is the penultimate hop for
      N-SID7; it performs PHP, which corresponds to the NEXT operation,
      and the packet is then sent to R7 with <T-SID1> in the label
      stack.

   *  R6, as a Leaf, performs the NEXT operation, pops the T-SID1 label,
      and delivers the payload.

   *  R7, as a Leaf, performs the NEXT operation, pops the T-SID1 label,
      and delivers the payload.

A.1.2.  SRv6

   For SRv6, the replicated packet from R2 to R7 has to traverse R4
   using an SR Policy, Policy27.  The policy has one SID in the segment
   list: End.X function with USD of R4 to R7.  The Replication segment
   state at nodes R1, R2, R6, and R7 is shown below.

   Policy27: <2001:db8:cccc:4:c17::>

   Replication segment at R1:

   Replication segment <R1,T-ID,I-ID1,R1>:
    Replication-SID: 2001:db8:cccc:1:fa::
    Replication State:
      R2: <2001:db8:cccc:2:fa::->L12>

   Replication to R2 steers a packet directly to the node on interface
   L12.

   Replication segment at R2:

   Replication segment <R1,T-ID,I-ID1,R2>:
    Replication-SID: 2001:db8:cccc:2:fa::
    Replication State:
      R2: <Leaf>
      R6: <2001:db8:cccc:6:fa::>
      R7: <2001:db8:cccc:7:fa:: -> Policy27>

   R2 is a Bud node.  It performs the role of a Leaf as well as a
   transit node replicating to R6 and R7.  Replication to R6 steers a
   packet via IGP shortest path to that node.  Replication to R7, via an
   SR Policy, first encapsulates the packet using H.Encaps and then
   steers the outer packet to R4.  End.X USD on R4 decapsulates the
   outer header and sends the original inner packet to R7.

   Replication segment at R6:

   Replication segment <R1,T-ID,I-ID1,R6>:
    Replication-SID: 2001:db8:cccc:6:fa::
    Replication State:
      R6: <Leaf>

   Replication segment at R7:

   Replication segment <R1,T-ID,I-ID1,R7>:
    Replication-SID: 2001:db8:cccc:7:fa::
    Replication State:
      R7: <Leaf>

   When a packet (A,B2) is steered into the active instance of CP 1 of
   the SR P2MP Policy at R1 using H.Encaps.Replicate behavior:

   *  Since R1 is directly connected to R2, R1 sends the replicated copy
      (2001:db8::1, 2001:db8:cccc:2:fa::) (A,B2) to R2 on interface L12.

   *  R2, as a Leaf, removes the outer IPv6 header and delivers the
      payload.  R2, as a Bud node, also replicates the packet.

   *  -  For replication to R6, R2 sends (2001:db8::1,
         2001:db8:cccc:6:fa::) (A,B2) to R3.  R3 forwards the packet
         using the 2001:db8:cccc:6::/64 packet to R6.

      -  For replication to R7 using Policy27, R2 encapsulates and sends
         (2001:db8::2, 2001:db8:cccc:4:C17::) (2001:db8::1,
         2001:db8:cccc:7:fa::) (A,B2) to R4.  R4 performs End.X USD
         behavior, decapsulates the outer IPv6 header, and sends
         (2001:db8::1, 2001:db8:cccc:7:fa::) (A,B2) to R7.

   *  R6, as a Leaf, removes the outer IPv6 header and delivers the
      payload.

   *  R7, as a Leaf, removes the outer IPv6 header and delivers the
      payload.

A.2.  P2MP Tree with Adjacent Replication Segments

   Assume the controller computes a PTI with Root node R1, Intermediate
   and Leaf node R2, Intermediate nodes R3 and R5, and Leaf nodes R6 and
   R7.  The controller instantiates the PTI by stitching Replication
   segments at R1, R2, R3, R5, R6, and R7.  The Replication segment at
   R1 replicates to R2.  The Replication segment at R2 replicates to R3
   and R5.  The Replication segment at R3 replicates to R6.  The
   Replication segment at R5 replicates to R7.  Note that node R4 does
   not have any Replication segment state for the tree.

A.2.1.  SR-MPLS

   The Replication segment state at nodes R1, R2, R3, R5, R6, and R7 is
   shown below.

   Replication segment at R1:

   Replication segment <R1,T-ID,I-ID1,R1>:
    Replication-SID: T-SID1
    Replication State:
      R2: <T-SID1->L12>

   Replication to R2 steers a packet directly to the node on interface
   L12.

   Replication segment at R2:

   Replication segment <R1,T-ID,I-ID1,R2>:
    Replication-SID: T-SID1
    Replication State:
      R2: <Leaf>
      R3: <T-SID1->L23>
      R5: <T-SID1->L25>

   R2 is a Bud node.  It performs the role of a Leaf as well as a
   transit node replicating to R3 and R5.  Replication to R3 steers a
   packet directly to the node on L23.  Replication to R5 steers a
   packet directly to the node on L25.

   Replication segment at R3:

   Replication segment <R1,T-ID,I-ID1,R3>:
    Replication-SID: T-SID1
    Replication State:
      R6: <T-SID1->L36>

   Replication to R6 steers a packet directly to the node on L36.

   Replication segment at R5:

   Replication segment <R1,T-ID,I-ID1,R5>:
    Replication-SID: T-SID1
    Replication State:
      R7: <T-SID1->L57>

   Replication to R7 steers a packet directly to the node on L57.

   Replication segment at R6:

   Replication segment <R1,T-ID,I-ID1,R6>:
    Replication-SID: T-SID1
    Replication State:
      R6: <Leaf>

   Replication segment at R7:

   Replication segment <R1,T-ID,I-ID1,R7>:
    Replication-SID: T-SID1
    Replication State:
      R7: <Leaf>

   When a packet is steered into the SR P2MP Policy at R1:

   *  Since R1 is directly connected to R2, R1 performs the PUSH
      operation with just the <T-SID1> label for the replicated copy and
      sends it to R2 on interface L12.

   *  R2, as a Leaf, performs the NEXT operation, pops the T-SID1 label,
      and delivers the payload.  It also performs the PUSH operation on
      T-SID1 for replication to R3 and R5.  For replication to R6, R2
      sends the <T-SID1> label stack to R3 on interface L23.  For
      replication to R5, R2 sends the <T-SID1> label stack to R5 on
      interface L25.

   *  R3 performs the NEXT operation on T-SID1, performs a PUSH
      operation for replication to R6, and sends the <T-SID1> label
      stack to R6 on interface L36.

   *  R5 performs the NEXT operation on T-SID1, performs a PUSH
      operation for replication to R7, and sends the <T-SID1> label
      stack to R7 on interface L57.

   *  R6, as a Leaf, performs the NEXT operation, pops the T-SID1 label,
      and delivers the payload.

   *  R7, as a Leaf, performs the NEXT operation, pops the T-SID1 label,
      and delivers the payload.

A.2.2.  SRv6

   The Replication segment state at nodes R1, R2, R3, R5, R6, and R7 is
   shown below.

   Replication segment at R1:

   Replication segment <R1,T-ID,I-ID1,R1>:
    Replication-SID: 2001:db8:cccc:1:fa::
    Replication State:
      R2: <2001:db8:cccc:2:fa::->L12>

   Replication to R2 steers a packet directly to the node on interface
   L12.

   Replication segment at R2:

   Replication segment <R1,T-ID,I-ID1,R2>:
    Replication-SID: 2001:db8:cccc:2:fa::
    Replication State:
      R2: <Leaf>
      R3: <2001:db8:cccc:3:fa::->L23>
      R5: <2001:db8:cccc:5:fa::->L25>

   R2 is a Bud node.  It performs the role of a Leaf as well as a
   transit node replicating to R3 and R5.  Replication to R3 steers a
   packet directly to the node on L23.  Replication to R5 steers a
   packet directly to the node on L25.

   Replication segment at R3:

   Replication segment <R1,T-ID,I-ID1,R3>:
    Replication-SID: 2001:db8:cccc:3:fa::
    Replication State:
      R6: <2001:db8:cccc:6:fa::->L36>

   Replication to R6 steers a packet directly to the node on L36.

   Replication segment at R5:

   Replication segment <R1,T-ID,I-ID1,R5>:
    Replication-SID: 2001:db8:cccc:5:fa::
    Replication State:
      R7: <2001:db8:cccc:7:fa::->L57>

   Replication to R7 steers a packet directly to the node on L57.

   Replication segment at R6:

   Replication segment <R1,T-ID,I-ID1,R6>:
    Replication-SID: 2001:db8:cccc:6:fa::
    Replication State:
      R6: <Leaf>

   Replication segment at R7:

   Replication segment <R1,T-ID,I-ID1,R7>:
    Replication-SID: 2001:db8:cccc:7:fa::
    Replication State:
      R7: <Leaf>

   When a packet (A,B2) is steered into the active instance of CP 1 of
   the SR P2MP Policy at R1 using the H.Encaps.Replicate behavior:

   *  Since R1 is directly connected to R2, R1 sends the replicated copy
      (2001:db8::1, 2001:db8:cccc:2:fa::) (A,B2) to R2 on interface L12.

   *  R2, as a Leaf, removes the outer IPv6 header and delivers the
      payload.  R2, as a Bud node, also replicates the packet.  For
      replication to R3, R2 sends (2001:db8::1, 2001:db8:cccc:3:fa::)
      (A,B2) to R3 on interface L23.  For replication to R5, R2 sends
      (2001:db8::1, 2001:db8:cccc:5:fa::) (A,B2) to R5 on interface L25.

   *  R3 replicates and sends (2001:db8::1, 2001:db8:cccc:6:fa::) (A,B2)
      to R6 on interface L36.

   *  R5 replicates and sends (2001:db8::1, 2001:db8:cccc:7:fa::) (A,B2)
      to R7 on interface L57.

   *  R6, as a Leaf, removes the outer IPv6 header and delivers the
      payload.

   *  R7, as a Leaf, removes the outer IPv6 header and delivers the
      payload.

Acknowledgements

   The authors would like to acknowledge Siva Sivabalan, Mike Koldychev,
   and Vishnu Pavan Beeram for their valuable input.

Contributors

   Clayton Hassen
   Bell Canada
   Vancouver
   Canada
   Email: clayton.hassen@bell.ca


   Kurtis Gillis
   Bell Canada
   Halifax
   Canada
   Email: kurtis.gillis@bell.ca


   Arvind Venkateswaran
   Cisco Systems, Inc.
   San Jose,
   United States of America
   Email: arvvenka@cisco.com


   Zafar Ali
   Cisco Systems, Inc.
   United States of America
   Email: zali@cisco.com


   Swadesh Agrawal
   Cisco Systems, Inc.
   San Jose,
   United States of America
   Email: swaagraw@cisco.com


   Jayant Kotalwar
   Nokia
   Mountain View,
   United States of America
   Email: jayant.kotalwar@nokia.com


   Tanmoy Kundu
   Nokia
   Mountain View,
   United States of America
   Email: tanmoy.kundu@nokia.com


   Andrew Stone
   Nokia
   Ottawa
   Canada
   Email: andrew.stone@nokia.com


   Tarek Saad
   Juniper Networks
   Canada
   Email: tsaad@juniper.net


   Kamran Raza
   Cisco Systems, Inc.
   Canada
   Email: skraza@cisco.com


   Anuj Budhiraja
   Cisco Systems, Inc.
   United States of America
   Email: abudhira@cisco.com


   Mankamana Mishra
   Cisco Systems, Inc.
   United States of America
   Email: mankamis@cisco.com


Authors' Addresses

   Rishabh Parekh (editor)
   Arrcus
   San Jose,
   United States of America
   Email: rishabh@arrcus.com


   Daniel Voyer (editor)
   Cisco Systems, Inc.
   Montreal
   Canada
   Email: davoyer@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.
   Brussels
   Belgium
   Email: cfilsfil@cisco.com


   Hooman Bidgoli
   Nokia
   Ottawa
   Canada
   Email: hooman.bidgoli@nokia.com


   Zhaohui Zhang
   Juniper Networks
   Email: zzhang@juniper.net
