Signaling Maximum SID Depth using Border Gateway Protocol Link-State
draft-tantsura-idr-bgp-ls-segment-routing-msd-04
IDR Working Group J. Tantsura
Internet-Draft Individual
Intended status: Standards Track U. Chunduri
Expires: September 29, 2017 Huawei Technologies
G. Mirsky
ZTE Corp.
S. Sivabalan
Cisco
March 28, 2017
Signaling Maximum SID Depth using Border Gateway Protocol Link-State
draft-tantsura-idr-bgp-ls-segment-routing-msd-04
Abstract
This document proposes a way to signal Maximum SID Depth (MSD)
supported by a node at node and/or link granularity by a BGP-LS
speaker. 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 push 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.
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document authors. All rights reserved.
Tantsura, et al. Expires September 29, 2017 [Page 1]
Internet-Draft Signaling MSD Using BGP-LS March 2017
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. MSD supported by a node . . . . . . . . . . . . . . . . . . . 4
4. MSD supported on a link . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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
BGP-LS 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
to a centralized controller.
MSD of sub-type 1, called Base MSD as defined in Section 3 is used to
signal the number of SID's a node is capable of imposing, to be used
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