Network Working Group D. Voyer, Ed.
Internet-Draft C. Hassen
Intended status: Standards Track K. Gillis
Expires: December 31, 2018 Bell Canada
C. Filsfils
A. Venkateswaran
Cisco Systems, Inc.
June 29, 2018

SR Replication Policy for P2MP Service Delivery


This document describes the SR policy architecture for P2MP service delivery.

Requirements Language

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.

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 December 31, 2018.

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Table of Contents

1. Introduction

The document defines a variant of the SR Policy [I-D. ietf-spring-segment-routing-policy] which allows for replication for supporting point-to-multi-point service delivery. We call it an SR Replication Policy.

We illustrate its use in two use-cases known as Spray and TreeSID.

Spray uses an SR Replication Policy to replicate a packet, at a given node, along N SR paths to a set of leaf nodes.

In the TreeSID use-case, a controller computes a tree from a root to a set of leaves and then programs each replication node of the tree with an SR Replication Policy.

2. SR Replication Policy

This section is similar to section 2 of SR Policy draft [I-D.ietf-spring-segment-routing-policy] and holds information that applies equally to the Spray and TreeSID use-cases.

The SR Replication policy is a variant of an SR policy [I-D.ietf-spring-segment-routing-policy], which provides packet replication. A SR Replication Policy is identified through the tuple <headend, color>.

A SR Replication may comprise of multiple candidate paths. A candidate path is valid when all its SID-Lists are valid. The active candidate path is selected based on the tiebreaking rules amongst the valid candidate-paths.

Each SID-List is additionally identified by a endpoint where its SR path terminates. The endpoint could be the actual leaf of a P2MP service delivery tree or it could be the headend of another SR Replication Policy.

Any traffic steered into a SR Replication Policy is replicated along the SID-Lists of its selected path towards the Leaf node.

In the context of a SR Replication Policy, the selected path MAY have more than one SID-List. The weights of the SID-Lists is not applicable for a SR Replication Policy. They MUST be set to 1.

Like any SR policy, a SR Replication Policy has a BSID [I-D.ietf-spring-segment-routing-policy] instantiated into the forwarding plane.

A SR replication policy can be provisioned either locally or setup via controller.

Traffic is steered into a SR Replication Policy in two ways

3. Spray SR Policy

This is a use-case of the SR Replication Policy in which packet replication occurs only at the Root node. A Spray SR Replication policy is instantiated only at the Root node.

A packet, using this approach, is replicated directly to each Leaf node via a segment routed path from the Root to a given Leaf node.

4. TreeSID - Controller Instantiated SR Tree

This is a use-case of the SR Replication policy in which packet replication occurs at the Root node and on some downstream branch points towards the Leaf node.

A SR Replication policy instantiated on the Root node takes a packet from the Root node to a set of branch points towards the Leaf node. A branch point MAY also be a Leaf node.

Another SR Replication policy instantiated at each of these branch points take the packet down further to other branch points or Leaf nodes.

5. Illustration


6. IANA Considerations

This document makes no request of IANA.

7. Security Considerations

There are no additional security risks introduced by this design.

8. Acknowledgements

9. Contributors

10. Normative References

[I-D.ietf-spring-segment-routing-policy] Filsfils, C., Sivabalan, S.,, d.,, b. and P. Mattes, "Segment Routing Policy Architecture", Internet-Draft draft-ietf-spring-segment-routing-policy-01, June 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.

Authors' Addresses

Daniel Voyer (editor) Bell Canada Montreal, CA EMail:
Clayton Hassen Bell Canada Vancouver, CA EMail:
Kurtis Gillis Bell Canada Halifax, CA EMail:
Clarence Filsfils Cisco Systems, Inc. Brussels, BE EMail:
Arvind Venkateswaran Cisco Systems, Inc. San Jose, US EMail: