Point-to-Multipoint Transport Using Chain Replication in Segment Routing

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Internet Engineering Task Force                               Yimin Shen
Internet-Draft                                             Zhaohui Zhang
Intended status: Standards Track                        Juniper Networks
Expires: October 3, 2020                                  Rishabh Parekh
                                                           Cisco Systems
                                                          Hooman Bidgoli
                                                             Yuji Kamite
                                                      NTT Communications
                                                           April 1, 2020

Point-to-Multipoint Transport Using Chain Replication in Segment Routing


   This document specifies a point-to-multipoint (P2MP) transport
   mechanism based on chain replication.  It can be used in segment
   routing to achieve traffic optimization.

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Table of Contents

   1.  Introduction
   2.  Specification of Requirements
   3.  Applicability
   4.  P2MP Transport Using Chain Replication
     4.1.  Bud Segment
     4.2.  P2MP Chain
     4.3.  Example
   5.  Path Computation for P2MP Chains
   6.  IGP and BGP-LS Extensions for Bud Segment
   7.  Bud Segments for Special Processing
   8.  IANA Considerations
   9.  Security Considerations
   10. Acknowledgements
   11. Contributors
   12. References
     12.1.  Normative References
     12.2.  Informative References
   Authors' Addresses

1.  Introduction

   The Segment Routing Architecture [RFC8402] describes segment routing
   (SR) and its instantiation in two data planes, i.e. MPLS and IPv6.
   In SR, point-to-multipoint (P2MP) transport is currently achieved by
   using ingress replication, where a point-to-point (P2P) SR tunnel is
   constructed from a root node to each leaf node, and every ingress
   packet is replicated and sent via a bundle of such P2P SR tunnels to
   all the leaf nodes.  Although this approach provides P2MP
   reachability, it does not consider traffic optimization across the
   tunnels, as the path of each tunnel is computed or decided

   An alternative approach would be to use P2MP-tree based transport.
   Such approach can achieve maximum traffic optimization, but it relies
   a controller or path computation element (PCE) to dynamically
   provision and manage "replication segments" on branch nodes.  The
   replication segments are essentially per-P2MP-tree (i.e. per-tunnel)
   state on transit routers.  Therefore, this approach is not fully
   aligned with SR's principles of single-point (i.e. ingress router)
   provisioning and stateless core.

   This document introduces a new solution for P2MP transport in SR,
   based on "chain replication".  In this solution, P2MP transport is
   achieved by constructing a set of "P2MP chain tunnels" (or simply
   "P2MP chains") from a root node to leaf nodes.  Each P2MP chain is a
   tunnel with a leaf node at tail end and some transit leaf nodes along
   the path, resembling a chain.  The leaf node at the tail end behaves
   as a normal receiver.  Each transit leaf node replicates a packet
   once for local processing off the chain, and also forwards the
   original packet down the chain.  The root node replicates and sends
   packets via the set of P2MP chains to all the leaf nodes.

   As a P2MP chain can reach multiple leaf nodes, it is considered to be
   more efficient than the multiple P2P tunnels which would be needed in
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