Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-04

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Last updated 2017-06-04
Replaces draft-tantsura-isis-segment-routing-msd
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IS-IS Working Group                                          J. Tantsura
Internet-Draft                                                Individual
Intended status: Standards Track                             U. Chunduri
Expires: December 6, 2017                            Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                             L. Ginsberg
                                                           Cisco Systems
                                                           June 04, 2017

             Signaling MSD (Maximum SID Depth) using IS-IS
                 draft-ietf-isis-segment-routing-msd-04

Abstract

   This document proposes a way to signal Maximum SID Depth (MSD)
   supported by a node at node and/or link granularity by an IS-IS
   Router.  In a Segment Routing (SR) enabled network a centralized
   controller that programs SR tunnels needs to know the MSD supported
   by the head-end at node and/or link granularity to push the SID stack
   of an appropriate depth.  MSD is relevant to the head-end of a SR
   tunnel or Binding-SID anchor node where Binding-SID expansions might
   result in creation of a new SID stack.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on December 6, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Tantsura, et al.        Expires December 6, 2017                [Page 1]
Internet-Draft                                                 June 2017

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions used in this document . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Node MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   4.  LINK MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   5.  Node MSD vs Link MSD conflict resolution  . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   When Segment Routing tunnels are computed by a centralized
   controller, it is critical that the controller learns the MSD
   "Maximum SID Depth" of the node or link SR tunnel exits over, so the
   SID stack depth of a path computed doesn't exceed the number of SIDs
   the node is capable of imposing.  This document describes how to use
   IS-IS to signal the MSD of a node or link to a centralized
   controller.

   PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD
   in SR PCE Capability TLV and METRIC Object.  However, if PCEP is not
   supported/configured on the head-end of a SR tunnel or a Binding-SID
   anchor node and controller does not participate in IGP routing, it
   has no way to learn the MSD of nodes and links which has been
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