IDR Working Group J. Tantsura
Internet-Draft Nuage Networks
Intended status: Standards Track U. Chunduri
Expires: February 14, 2019 Huawei USA
G. Mirsky
ZTE Corp.
S. Sivabalan
Cisco
August 13, 2018
Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link-
State
draft-ietf-idr-bgp-ls-segment-routing-msd-02
Abstract
This document defines a way for a Border Gateway Protocol Link-State
(BGP-LS) speaker to advertise multiple types of supported Maximum SID
Depths (MSDs) at node and/or link granularity.
Such advertisements allow logically centralized entities (e.g.,
centralized controllers) to determine whether a particular SID stack
can be supported in a given network.
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This Internet-Draft will expire on February 14, 2019.
Copyright Notice
Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . . . . . . . . . 7
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.
Other types of MSD are known to be useful. For example,
[I-D.ietf-ospf-mpls-elc] and [I-D.ietf-isis-mpls-elc] define Readable
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Label Depth Capability (RLDC) that is used by a head-end to insert an
Entropy Label (EL) at a depth that can be read by transit nodes.
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here .
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]
3. MSD supported by a node
Node MSD is encoded in a new Node Attribute TLV, as defined in
[RFC7752]
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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 specifying code-point of the new TLV type.
Code-point:(TBD1) 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 specifying code-point of the new TLV type.
Code-point:(TBD2) 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.
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5. IANA Considerations
We request IANA assign code points from the registry BGP-LS Node
Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs,
as follows: TLV Code Point Description IS-IS TLV/Sub-TLV Reference
TBD1 Node MSD 242/23 (this document) TBD2 Link MSD
(22,23,25,141,222,223)/15 (this document)
6. Security Considerations
Advertisement of the additional information defined in this document
that is false, e.g., an MSD that is incorrect, may result in a path
computation failing, having a service unavailable, or instantiation
of a path that can't be supported by the head-end (the node
performing the imposition).
This document does not introduce security issues beyond those
discussed in [RFC7752], [I-D.ietf-ospf-segment-routing-msd] and
[I-D.ietf-isis-segment-routing-msd]
7. Acknowledgements
We like to thank Nikos Triantafillis, Acee Lindem, Ketan Talaulikar,
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-13 (work in progress), July
2018.
[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-15 (work in progress), July
2018.
[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-12 (work in progress), June
2018.
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[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-14
(work in progress), June 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://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,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and Entropy
Readable Label Depth Using IS-IS", draft-ietf-isis-mpls-
elc-05 (work in progress), July 2018.
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., 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-19 (work in progress), July
2018.
[I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and Entropy
Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
mpls-elc-06 (work in progress), August 2018.
[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-25 (work in progress), April 2018.
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Authors' Addresses
Jeff Tantsura
Nuage Networks
Email: jefftant.ietf@gmail.com
Uma Chunduri
Huawei USA
Email: uma.chunduri@huawei.com
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Siva Sivabalan
Cisco
Email: msiva@cisco.com
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