IDR Working Group J. Tantsura
Internet-Draft Individual
Intended status: Standards Track G. Mirsky
Expires: January 9, 2017 Ericsson
S. Sivabalan
Cisco
U. Chunduri
Ericsson
July 8, 2016
Signaling Maximum SID Depth using Border Gateway Protocol Link-State
draft-tantsura-idr-bgp-ls-segment-routing-msd-01
Abstract
This document discusses use of BGP-LS to expose node and/or link on a
node MSD "Maximum SID Depth" to a centralized controller (PCE/SDN).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 2
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 2
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. MSD supported by a node . . . . . . . . . . . . . . . . . . . 3
4. MSD supported on a link . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative References . . . . . . . . . . . . . . . . . . 4
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
When Segment Routing tunnels are computed by a centralized
controller, it is crucial that the controller knows MSD "Maximum SID
Depth" of the node or link SR tunnel exits over, so it doesn't
download a path with SID (label stack) of a depth more than the node
or link configured is capable of imposing.This document describes how
to use BGP-LS to expose the MSD of the node or link configured to a
centralized controller.
1.1. Conventions used in this document
1.1.1. Terminology
BGP-LS: Distribution of Link-State and TE Information using Border
Gateway Protocol
MSD: Maximum SID Depth
PCC: Path Computation Client
PCE: Path Computation Element
PCEP: Path Computation Element Protocol
SID: Segment Identifier
SR: Segment routing
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1.1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
2. Problem Statement
In existing technology only PCEP has extension to signal the MSD (SR
PCE Capability TLV/ METRIC Object as defined in
[I-D.ietf-pce-segment-routing],If PCEP is not supported by the node
(head-end of the SR tunnel) controller has no way to learn the MSD of
the node/link configured. OSPF and IS-IS extensions are defined in:
[I-D.tantsura-ospf-segment-routing-msd]
[I-D.tantsura-isis-segment-routing-msd]
3. MSD supported by a node
Node MSD is encoded in a new Node Attribute TLV, as defined in
[RFC7752]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD |
+-+-+-+-+-+-+-+-+
Figure 1: Node attribute format
Type : A 2-octet field specifiying code-point of the new TLV type.
Code-point: TBA (suggested 1050) from BGP-LS Node Descriptor, Link
Descriptor, Prefix Descriptor, and Attribute TLVs registry
Length: A 2-octet field that indicates the length of the value
portion
MSD: Node MSD is a number in the range of 0-254. The vaule of 0
represents lack of ability to push MSD of any depth, any other value
represents that of the node.
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4. MSD supported on a link
Link MSD is encoded in a New Link Attribute TLV, as defined in
[RFC7752]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD |
+-+-+-+-+-+-+-+-+
Figure 2: Link attribute format
Type : A 2-octet field specifiying code-point of the new TLV type.
Code-point: TBA (suggested 1110) from BGP-LS Node Descriptor, Link
Descriptor, Prefix Descriptor, and Attribute TLVs registry
Length: A 2-octet field that indicates the length of the value
portion
MSD: Link MSD is a number in the range of 0-254. The vaule of 0
represents lack of ability to push MSD of any depth, any other value
represents that of the link.
5. IANA Considerations
This document requests assigning 2 new code-points from the BGP-LS
Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs registry as specified in sections 3 and 4.
6. Security Considerations
This document does not introduce security issues beyond those
discussed in [RFC7752]
7. Acknowledgements
We like to thank Nikos Triantafillis for the valuable comments.
8. References
8.1. Normative References
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[I-D.ietf-pce-segment-routing]
Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick,
"PCEP Extensions for Segment Routing", draft-ietf-pce-
segment-routing-07 (work in progress), March 2016.
[I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
and E. Crabbe, "Segment Routing with MPLS data plane",
draft-ietf-spring-segment-routing-mpls-04 (work in
progress), March 2016.
[I-D.tantsura-isis-segment-routing-msd]
Tantsura, J. and U. Chunduri, "Signaling MSD (Maximum SID
Depth) using IS-IS", draft-tantsura-isis-segment-routing-
msd-01 (work in progress), July 2016.
[I-D.tantsura-ospf-segment-routing-msd]
Tantsura, J. and U. Chunduri, "Signaling MSD (Maximum SID
Depth) using OSPF", draft-tantsura-ospf-segment-routing-
msd-00 (work in progress), March 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<http://www.rfc-editor.org/info/rfc7752>.
8.2. Informative References
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
Extensions for Segment Routing", draft-ietf-isis-segment-
routing-extensions-07 (work in progress), June 2016.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-09 (work in progress), July 2016.
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Authors' Addresses
Jeff Tantsura
Individual
Email: jefftant.ietf@gmail.com
Greg Mirsky
Ericsson
Email: gregory.mirsky@ericsson.com
Siva Sivabalan
Cisco
Email: msiva@cisco.com
Uma Chunduri
Ericsson
Email: uma.chunduri@ericsson.com
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