Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-09

Document Type Active Internet-Draft (isis WG)
Last updated 2018-01-10
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: July 14, 2018                               Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                             L. Ginsberg
                                                           Cisco Systems
                                                        January 10, 2018

             Signaling MSD (Maximum SID Depth) using IS-IS
                 draft-ietf-isis-segment-routing-msd-09

Abstract

   This document defines a way for an IS-IS Router to advertise multiple
   types of supported Maximum SID Depths (MSDs) at node and/or link
   granularity.  Such advertisements allow entities (e.g., centralized
   controllers) to determine whether a particular SID stack is
   supportable in a given network.  This document only defines one type
   of MSD (maximum label imposition) - but defines an encoding which can
   support other MSD types.

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 July 14, 2018.

Copyright Notice

   Copyright (c) 2018 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

Tantsura, et al.          Expires July 14, 2018                 [Page 1]
Internet-Draft                                              January 2018

   (https://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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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

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.  Node MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   3.  Link MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   4.  Using Node and Link MSD Advertisements  . . . . . . . . . . .   5
   5.  Base MPLS Imposition MSD  . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   When Segment Routing(SR) paths are computed by a centralized
   controller, it is critical that the controller learns the Maximum SID
   Depth(MSD) which can be imposed at the node/link a given SR path is
   applied so as to insure that the SID stack depth of a computed path
   doesn't exceed the number of SIDs the node is capable of imposing.

   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
   configured.  BGP-LS [RFC7752] defines a way to expose topology and
   associated attributes and capabilities of the nodes in that topology
   to a centralized controller.  MSD signaling by BGP-LS has been
   defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd].  Typically,
   BGP-LS is configured on a small number of nodes, that do not
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