draft-ietf-idr-bgp-ls-segment-routing-msd-03.txt   draft-ietf-idr-bgp-ls-segment-routing-msd-04.txt 
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G. Mirsky G. Mirsky
ZTE Corp. ZTE Corp.
S. Sivabalan S. Sivabalan
Cisco Cisco
N. Triantafillis N. Triantafillis
Apstra, Inc. Apstra, Inc.
February 19, 2019 February 19, 2019
Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link- Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link-
State State
draft-ietf-idr-bgp-ls-segment-routing-msd-03 draft-ietf-idr-bgp-ls-segment-routing-msd-04
Abstract Abstract
This document defines a way for a Border Gateway Protocol Link-State This document defines a way for a Border Gateway Protocol Link-State
(BGP-LS) speaker to advertise multiple types of supported Maximum SID (BGP-LS) speaker to advertise multiple types of supported Maximum SID
Depths (MSDs) at node and/or link granularity. Depths (MSDs) at node and/or link granularity.
Such advertisements allow logically centralized entities (e.g., Such advertisements allow logically centralized entities (e.g.,
centralized controllers) to determine whether a particular SID stack centralized controllers) to determine whether a particular SID stack
can be supported in a given network. can be supported in a given network.
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capitals, as shown here . capitals, as shown here .
2. Problem Statement 2. Problem Statement
In existing technology only PCEP has extension to signal the MSD (SR In existing technology only PCEP has extension to signal the MSD (SR
PCE Capability TLV/ METRIC Object as defined in PCE Capability TLV/ METRIC Object as defined in
[I-D.ietf-pce-segment-routing],If PCEP is not supported by the node [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 (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: the node/link configured. OSPF and IS-IS extensions are defined in:
[RFC8476] [RFC8476], [RFC8491]
[RFC8491]
3. MSD supported by a node 3. MSD supported by a node
Node MSD is encoded in a new Node Attribute TLV, as defined in Node MSD is encoded in a new Node Attribute TLV, as defined in
[RFC7752] [RFC7752]
0 1 2 3 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 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 | | Type | Length |
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5. IANA Considerations 5. IANA Considerations
We request IANA assign code points from the registry BGP-LS Node We request IANA assign code points from the registry BGP-LS Node
Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs, Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs,
as follows: TLV Code Point Description IS-IS TLV/Sub-TLV Reference as follows: TLV Code Point Description IS-IS TLV/Sub-TLV Reference
TBD1 Node MSD 242/23 (this document) TBD2 Link MSD TBD1 Node MSD 242/23 (this document) TBD2 Link MSD
(22,23,25,141,222,223)/15 (this document) (22,23,25,141,222,223)/15 (this document)
6. Security Considerations 6. Security Considerations
Advertisement of the additional information defined in this document The advertisement of an incorrect MSD value may have negative
that is false, e.g., an MSD that is incorrect, may result in a path consequences. If the value is smaller than supported, path
computation failing, having a service unavailable, or instantiation computation may fail to compute a viable path. If the value is
of a path that can't be supported by the head-end (the node larger than supported, an attempt to instantiate a path that can't be
performing the imposition). supported by the head-end (the node performing the SID imposition)
may occur. The presence of this information may also inform an
attacker of how to induce any of the aforementioned conditions.
This document does not introduce security issues beyond those This document does not introduce security issues beyond those
discussed in [RFC7752], [RFC8476] and [RFC8491] extensions. discussed in [RFC7752], [RFC8476] and [RFC8491]
7. Acknowledgements 7. Acknowledgements
We like to thank Acee Lindem, Ketan Talaulikar, Stephane Litkowski We like to thank Acee Lindem, Ketan Talaulikar, Stephane Litkowski
and Bruno Decraene for their reviews and valuable comments. and Bruno Decraene for their reviews and valuable comments.
8. References 8. References
8.1. Normative References 8.1. Normative References
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