IS-IS Application-Specific Link Attributes
RFC 8919

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Internet Engineering Task Force (IETF)                       L. Ginsberg
Request for Comments: 8919                                     P. Psenak
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                               S. Previdi
                                                     Huawei Technologies
                                                           W. Henderickx
                                                                   Nokia
                                                                J. Drake
                                                        Juniper Networks
                                                            October 2020

               IS-IS Application-Specific Link Attributes

Abstract

   Existing traffic-engineering-related link attribute advertisements
   have been defined and are used in RSVP-TE deployments.  Since the
   original RSVP-TE use case was defined, additional applications (e.g.,
   Segment Routing Policy and Loop-Free Alternates) that also make use
   of the link attribute advertisements have been defined.  In cases
   where multiple applications wish to make use of these link
   attributes, the current advertisements do not support application-
   specific values for a given attribute, nor do they support indication
   of which applications are using the advertised value for a given
   link.  This document introduces new link attribute advertisements
   that address both of these shortcomings.

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/rfc8919.

Copyright Notice

   Copyright (c) 2020 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Requirements Language
   2.  Requirements Discussion
   3.  Legacy Advertisements
     3.1.  Legacy Sub-TLVs
     3.2.  Legacy SRLG Advertisements
   4.  Advertising Application-Specific Link Attributes
     4.1.  Application Identifier Bit Mask
     4.2.  Application-Specific Link Attributes Sub-TLV
       4.2.1.  Special Considerations for Maximum Link Bandwidth
       4.2.2.  Special Considerations for Reservable/Unreserved
               Bandwidth
       4.2.3.  Considerations for Extended TE Metrics
     4.3.  Application-Specific SRLG TLV
   5.  Attribute Advertisements and Enablement
   6.  Deployment Considerations
     6.1.  Use of Legacy Advertisements
     6.2.  Use of Zero-Length Application Identifier Bit Masks
     6.3.  Interoperability, Backwards Compatibility, and Migration
           Concerns
       6.3.1.  Multiple Applications: Common Attributes with RSVP-TE
       6.3.2.  Multiple Applications: All Attributes Not Shared with
               RSVP-TE
       6.3.3.  Interoperability with Legacy Routers
       6.3.4.  Use of Application-Specific Advertisements for RSVP-TE
   7.  IANA Considerations
     7.1.  Application-Specific Link Attributes Sub-TLV
     7.2.  Application-Specific SRLG TLV
     7.3.  Sub-sub-TLV Codepoints for Application-Specific Link
           Attributes Registry
     7.4.  Link Attribute Application Identifiers Registry
     7.5.  Sub-TLVs for TLV 238 Registry
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Advertisement of link attributes by the Intermediate System to
   Intermediate System (IS-IS) protocol in support of traffic
   engineering (TE) was introduced by [RFC5305] and extended by
   [RFC5307], [RFC6119], [RFC7308], and [RFC8570].  Use of these
   extensions has been associated with deployments supporting Traffic
   Engineering over Multiprotocol Label Switching (MPLS) in the presence
   of the Resource Reservation Protocol (RSVP), more succinctly referred
   to as RSVP-TE [RFC3209].

   For the purposes of this document, an application is a technology