IDR Working Group J. Tantsura
Internet-Draft G. Mirsky
Intended status: Standards Track Ericsson
Expires: July 11, 2016 S. Sivabalan
Cisco
U. Chunduri
Ericsson
January 8, 2016

Signaling Maximum SID Depth using Border Gateway Protocol Link-State
draft-tantsura-bgp-ls-segment-routing-msd-02

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).

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on July 11, 2016.

Copyright Notice

Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.


Table of Contents

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

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.

3. MSD supported by a node

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.

Node MSD is encoded in the Opaque Node Attribute TLV, as defined in [I-D.ietf-idr-ls-distribution]

   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            | 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  //               Opaque node attributes (variable)             //
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	         

Figure 1: Opaque Node attribute format

4. MSD supported on a link

Link MSD is a number in the range of 0-254.The value of 0 represents lack of ability to push MSD of any depth, any other value represents that of the link.

Link MSD is encoded in the Opaque Link Attribute TLV, as defined in [I-D.ietf-idr-ls-distribution]

   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            | 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  //                Opaque link attributes (variable)            //
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              

Figure 2: Opaque link attribute format

5. IANA Considerations

TBA

6. Security Considerations

This document does not introduce security issues beyond those discussed in [I-D.ietf-idr-ls-distribution]

7. Acknowledgements

We like to thank Nikos Triantafillis for the valuable comments.

8. References

8.1. Normative References

[I-D.ietf-idr-ls-distribution] Gredler, H., Medved, J., Previdi, S., Farrel, A. and S. Ray, "North-Bound Distribution of Link-State and TE Information using BGP", Internet-Draft draft-ietf-idr-ls-distribution-13, October 2015.
[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", Internet-Draft draft-ietf-pce-segment-routing-06, August 2015.
[I-D.ietf-spring-segment-routing-mpls] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., rjs@rob.sh, r., Tantsura, J. and E. Crabbe, "Segment Routing with MPLS data plane", Internet-Draft draft-ietf-spring-segment-routing-mpls-02, October 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.

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", Internet-Draft draft-ietf-isis-segment-routing-extensions-06, December 2015.
[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", Internet-Draft draft-ietf-ospf-segment-routing-extensions-06, December 2015.

Authors' Addresses

Jeff Tantsura Ericsson EMail: jeff.tantsura@ericsson.com
Greg Mirsky Ericsson EMail: gregory.mirsky@ericsson.com
Siva Sivabalan Cisco EMail: msiva@cisco.com
Uma Chunduri Ericsson EMail: uma.chunduri@ericsson.com