Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-12
IS-IS Working Group J. Tantsura
Internet-Draft Nuage Networks
Intended status: Standards Track U. Chunduri
Expires: November 17, 2018 Huawei Technologies
S. Aldrin
Google, Inc
L. Ginsberg
Cisco Systems
May 16, 2018
Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-12
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 can be
supported in a given network. This document only defines one type of
MSD maximum label imposition, but defines an encoding that can
support other MSD types.
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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. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 5
4. Using Node and Link MSD Advertisements . . . . . . . . . . . 6
5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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 a given SR path 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 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 [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 necessarily act as
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