Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-19

Document Type Active Internet-Draft (lsr WG)
Last updated 2018-10-22 (latest revision 2018-10-09)
Replaces draft-tantsura-isis-segment-routing-msd
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Stream WG state Submitted to IESG for Publication (wg milestones: Jul 2018 - IS-IS Reverse Metric..., Jul 2018 - IS-IS Segment Routin... )
Document shepherd Christian Hopps
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Send notices to Christian Hopps <chopps@chopps.org>, aretana.ietf@gmail.com
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IS-IS Working Group                                          J. Tantsura
Internet-Draft                                              Apstra, Inc.
Intended status: Standards Track                             U. Chunduri
Expires: April 12, 2019                              Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                             L. Ginsberg
                                                           Cisco Systems
                                                         October 9, 2018

             Signaling MSD (Maximum SID Depth) using IS-IS
                 draft-ietf-isis-segment-routing-msd-19

Abstract

   This document defines a way for an Intermediate System to
   Intermediate System (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 (Segment ID) stack can be
   supported in a given network.  This document only defines one type of
   MSD (Base MPLS Imposition), but defines an encoding that can support
   other MSD types.  This document focuses on MSD use in a Segment
   Routing enabled network, but MSD may also be useful when Segment
   Routing is not enabled.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 12, 2019.

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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
   (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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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Node MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   3.  Link MSD Advertisement  . . . . . . . . . . . . . . . . . . .   5
   4.  Procedures for Defining and Using Node and Link MSD
       Advertisements  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Base MPLS Imposition MSD  . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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) that can be imposed at each node/link of a given SR path
   to ensure that the Segment Identifier (SID) stack depth of a computed
   path does not exceed the number of SIDs the node is capable of
   imposing.

   [I-D.ietf-pce-segment-routing] defines how to signal MSD in the Path
   Computation Element communication Protocol (PCEP).  However, if PCEP
   is not supported/configured on the head-end of an 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.  BGP-LS

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