Network Working Group                                      D. Voyer, Ed.
Internet-Draft                                               Bell Canada
Intended status: Standards Track                             C. Filsfils
Expires: April 13, 2020                                        R. Parekh
                                                     Cisco Systems, Inc.
                                                              H. Bidgoli
                                                                Z. Zhang
                                                        Juniper Networks
                                                        October 11, 2019

        SR Replication Segment for Multi-point Service Delivery


   This document describes the SR Replication segment for Multi-point
   service delivery.  A SR Replication segment allows a packet to be
   replicated from a Replication node to downstream nodes.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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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   This Internet-Draft will expire on April 13, 2020.

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Copyright Notice

   Copyright (c) 2019 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
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   ( in effect on the date of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Replication segment . . . . . . . . . . . . . . . . . . . . .   2
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   We define a new type of segment for Segment Routing [RFC8402], called
   Replication segment, which allows a node (henceforth called as
   Replication node) to replicate packets to a set of other nodes
   (called Downstream nodes) in a Segment Routing Domain.  Replication
   segments provide building blocks for Point-to-Multi-point Service
   delivery.  A Replication segment at ingress node of Multi-point
   service replicates packets directly to each egress node of the
   service, without need for any state in the core of SR domain.
   Multiple Replication segments can be stitched together to build a
   tree in SR domain for Multi-point service; this is outside the scope
   of this document.

2.  Replication segment

   In a Segment Routing Domain, a Replication segment is a logical
   segment which connects a Replication node to a set of Downstream
   nodes.  A Replication segment can be either provisioned locally on a
   node or programmed by a PCE.  Replication segments apply equally to
   both SR-MPLS and SRv6 instantiations of Segment Routing.

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   A Replication segment is identified by the tuple <Replication-ID,
   Node-ID>, where:

   o  Replication-ID: An identifier for a Replication segment that is
      unique in context of the Replication node.  This is an unsigned
      32-bit number.

   o  Node-ID: The address of a node at which a Replication segment is
      instantiated.  Replication segment is instantiated at Downstream
      nodes and at the Replication node.

   The Replicaion-ID can be extended or modified as required based on
   specific use of a Replication segment.

   A Replication segment is defined by following elements:

   o  Replication SID: The Segment Identifier of a Replication Segment.
      This is a SR-MPLS label or a SRv6 SID [RFC8402].

   o  Downstream Nodes: Set of nodes in Segment Routing domain to which
      a packet is replicated by the Replication segment.

   o  Replication State: See below.

   Replication state is a list of Replication branches to the Downstream
   nodes.  In this document, each branch is abstracted to a <Downstream
   Node, Downstream Replication-SID> tuple.  A Replication branch to a
   particular Downstream Node could be represented by the node's Node
   SID (i.e. it does not matter how traffic gets to the Downstream node,
   whether it's directly connected or not), or in case of a directly
   connected node it could be represented by the Adjacency SID (for the
   interface connecting to the directly connected Leaf Node).
   Alternatively, the Downstream Node could also be expanded to a SID-
   list that partially/fully specifies the explicit path to it.  A
   Replication branch can also use a Segment Routing Policy
   [I-D.ietf-spring-segment-routing-policy], if available, from the
   Replication node to the Downstream node.

   Replication SID identifies the Replication Segment in the forwarding
   plane.  The Replication SID SHOULD be considered to be the equivalent
   of Binding SID [I-D.ietf-spring-segment-routing-policy] of a Segment
   Routing Policy, when Replication Segment is instantiated at Ingress
   node of a Multi-point service.  At Downstream nodes, the Replication
   SID MAY be used to identify the Multi-point service.

   A packet steered into a Replication Segment at a node is replicated
   to each Downstream node with the Downstream Replication SID that is

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   relevant at that node . A packet is steered into a Replication
   Segment in two ways:

   o  Based on a local policy-based routing at Replication node.

   o  When the Active Segment [RFC8402] at Replication node is the
      Replication SID.

3.  IANA Considerations

   This document makes no request of IANA.

4.  Security Considerations

   There are no additional security risks introduced by this design.

5.  Acknowledgements

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

6.  Contributors

   Clayton Hassen
   Bell Canada


   Kurtis Gillis
   Bell Canada


   Arvind Venkateswaran
   Cisco Systems, Inc.
   San Jose


   Zafar Ali
   Cisco Systems, Inc.

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   Swadesh Agrawal
   Cisco Systems, Inc.
   San Jose


   Jayant Kotalwar
   Mountain View


   Tanmoy Kundu
   Mountain View


   Tarek Saad
   Juniper Networks

7.  Normative References

              Filsfils, C., Sivabalan, S.,, d.,
    , b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
              policy-03 (work in progress), May 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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, <>.

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Authors' Addresses

   Daniel Voyer (editor)
   Bell Canada


   Clarence Filsfils
   Cisco Systems, Inc.


   Rishabh Parekh
   Cisco Systems, Inc.
   San Jose


   Hooman Bidgoli


   Zhaohui Zhang
   Juniper Networks


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