Signaling Maximum SID Depth (MSD) Using OSPF
RFC 8476
Internet Engineering Task Force (IETF) J. Tantsura
Request for Comments: 8476 Apstra, Inc.
Category: Standards Track U. Chunduri
ISSN: 2070-1721 Huawei Technologies
S. Aldrin
Google, Inc.
P. Psenak
Cisco Systems
December 2018
Signaling Maximum SID Depth (MSD) Using OSPF
Abstract
This document defines a way for an Open Shortest Path First (OSPF)
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 Identifier (SID) stack can be supported in a given
network. This document only refers to the Signaling MSD as defined
in RFC 8491, but it defines an encoding that can support other MSD
types. Here, the term "OSPF" means both OSPFv2 and OSPFv3.
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/rfc8476.
Tantsura, et al. Standards Track [Page 1]
RFC 8476 Signaling MSD Using OSPF December 2018
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Table of Contents
1. Introduction ....................................................3
1.1. Terminology ................................................4
1.2. Requirements Language ......................................4
2. Node MSD Advertisement ..........................................5
3. Link MSD Sub-TLV ................................................6
4. Procedures for Defining and Using Node and Link MSD
Advertisements ..................................................7
5. IANA Considerations .............................................7
6. Security Considerations .........................................8
7. References ......................................................9
7.1. Normative References .......................................9
7.2. Informative References ....................................10
Acknowledgements ..................................................11
Contributors ......................................................11
Authors' Addresses ................................................11
Tantsura, et al. Standards Track [Page 2]
RFC 8476 Signaling MSD Using OSPF December 2018
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 on a given SR path.
This ensures that the Segment Identifier (SID) stack depth of a
computed path doesn't 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
of Link-State and TE Information Using BGP) [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 [MSD-BGP]. Typically, BGP-LS is
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