Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-08
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OSPF Working Group J. Tantsura
Internet-Draft Individual
Intended status: Standards Track U. Chunduri
Expires: June 17, 2018 Huawei Technologies
S. Aldrin
Google, Inc
P. Psenak
Cisco Systems
December 14, 2017
Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-08
Abstract
This document proposes a way to signal Maximum SID Depth (MSD)
supported by a node at node and/or link granularity by an OSPF
Router. In a Segment Routing (SR) enabled network a centralized
controller that programs SR tunnels needs to know the MSD supported
by the head-end at node and/or link granularity to impose the SID
stack of an appropriate depth. MSD is relevant to the head-end of a
SR tunnel or Binding-SID anchor node where Binding-SID expansions
might result in creation of a new SID stack. Here the term OSPF
means both OSPFv2 and OSPFv3.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 17, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
Tantsura, et al. Expires June 17, 2018 [Page 1]
Internet-Draft December 2017
This document is subject to BCP 78 and the IETF Trust's Legal
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Node MSD TLV . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Link MSD sub-TLV . . . . . . . . . . . . . . . . . . . . . . 5
5. Node MSD vs Link MSD conflict resolution . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
When Segment Routing tunnels are computed by a centralized
controller, it is critical that the controller learns the MSD
"Maximum SID Depth" of the node or link SR tunnel exits over, so the
SID stack depth of a path computed doesn't exceed the number of SIDs
the node is capable of imposing. This document describes how to use
OSPF to signal the MSD of a node or link to a centralized controller.
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 a 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 which has been
configured. BGP-LS [RFC7752] defines a way to expose topology and
associated attributes and capabilities of the nodes in that topology
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