Signaling Maximum SID Depth (MSD) Using IS-IS
RFC 8491

Document Type RFC - Proposed Standard (November 2018; No errata)
Last updated 2018-11-14
Replaces draft-tantsura-isis-segment-routing-msd
Stream IETF
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Reviews
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
Shepherd write-up Show (last changed 2018-06-16)
IESG IESG state RFC 8491 (Proposed Standard)
Consensus Boilerplate Yes
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Responsible AD Alvaro Retana
Send notices to Christian Hopps <chopps@chopps.org>, aretana.ietf@gmail.com
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
Internet Engineering Task Force (IETF)                       J. Tantsura
Request for Comments: 8491                                  Apstra, Inc.
Category: Standards Track                                    U. Chunduri
ISSN: 2070-1721                                      Huawei Technologies
                                                               S. Aldrin
                                                            Google, Inc.
                                                             L. Ginsberg
                                                           Cisco Systems
                                                           November 2018

             Signaling Maximum SID Depth (MSD) Using IS-IS

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

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8491.

Tantsura, et al.             Standards Track                    [Page 1]
RFC 8491                Signaling MSD Using IS-IS          November 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
   (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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   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.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  10
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   When Segment Routing (SR) paths are computed by a centralized
   controller, it is critical that the controller learn the Maximum SID
   Depth (MSD) that can be imposed at each node/link of a given SR path.
   This ensures that the Segment Identifier (SID) stack depth of a
   computed path does not exceed the number of SIDs the node is capable
   of imposing.

   [PCEP-EXT] 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 the controller does not participate in IGP routing, it has
   no way of learning the MSD of nodes and links.  BGP-LS (Distribution

Tantsura, et al.             Standards Track                    [Page 2]
RFC 8491                Signaling MSD Using IS-IS          November 2018

   of Link-State and TE Information Using Border Gateway Protocol)
   [RFC7752] defines a way to expose topology and associated attributes
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