IDR Working Group J. Tantsura
Internet-Draft Individual
Intended status: Standards Track U. Chunduri
Expires: December 6, 2017 Huawei Technologies
G. Mirsky
ZTE Corp.
S. Sivabalan
Cisco
June 04, 2017
Signaling Maximum SID Depth using Border Gateway Protocol Link-State
draft-tantsura-idr-bgp-ls-segment-routing-msd-05
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.
Status of This Memo
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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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by a path computation element/controller. In case, there are
additional labels (e.g. service) that are to be pushed to the stack -
this would be signaled with an another MSD type (TBD), no adjustment
to the Base MSD should be made. In the future, new MSD types could
be defined to signal additional capabilities: entropy labels, labels
that can be pushed thru recirculation, or another dataplane e.g IPv6.
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
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.ietf-ospf-segment-routing-msd]
[I-D.ietf-isis-segment-routing-msd]
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type and Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 1: Node attribute format
Type : A 2-octet field specifiying code-point of the new TLV type.
Code-point: 1050 (Suggested value - to be assigned by IANA) 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
Sub-Type and value fields are as defined in corresponding OSPF
[I-D.ietf-ospf-segment-routing-msd] and IS-IS
[I-D.ietf-isis-segment-routing-msd] extensions.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type and Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 2: Link attribute format
Type : A 2-octet field specifiying code-point of the new TLV type.
Code-point: 1110 (Suggested value - to be assigned by IANA) from BGP-
LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs registry
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Length: A 2-octet field that indicates the length of the value
portion
Sub-Type and value fields are as defined in corresponding OSPF
[I-D.ietf-ospf-segment-routing-msd] and IS-IS
[I-D.ietf-isis-segment-routing-msd] extensions.
5. IANA Considerations
This document requests IANA to assign 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, Stephane Litkowski and Bruno
Decraene for their reviews and valuable comments.
8. References
8.1. Normative References
[I-D.ietf-isis-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling MSD (Maximum SID Depth) using IS-IS", draft-
ietf-isis-segment-routing-msd-03 (work in progress), March
2017.
[I-D.ietf-ospf-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling MSD (Maximum SID Depth) using OSPF", draft-
ietf-ospf-segment-routing-msd-04 (work in progress), March
2017.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-09 (work in progress),
April 2017.
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[I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-08
(work in progress), March 2017.
[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. jefftant@gmail.com,
"IS-IS Extensions for Segment Routing", draft-ietf-isis-
segment-routing-extensions-12 (work in progress), April
2017.
[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-16 (work in progress), May 2017.
Authors' Addresses
Jeff Tantsura
Individual
Email: jefftant.ietf@gmail.com
Uma Chunduri
Huawei Technologies
Email: uma.chunduri@huawei.com
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Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Siva Sivabalan
Cisco
Email: msiva@cisco.com
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