Signalling ERLD using BGP-LS
draft-ietf-idr-bgp-ls-segment-routing-rld-01

IDR Working Group                                   G. Van de Velde, Ed.
Internet-Draft                                             W. Henderickx
Intended status: Standards Track                                M. Bocci
Expires: June 21, 2018                                             Nokia
                                                                K. Patel
                                                                  Arrcus
                                                       December 18, 2017

                      Signalling ERLD using BGP-LS
              draft-ietf-idr-bgp-ls-segment-routing-rld-01

Abstract

   This document defines the attributes to use for BGP-LS to expose ERLD
   "Entropy capable Readable Label Depth" from a node or link to a
   centralised controller (PCE/SDN).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

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   Copyright (c) 2017 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   4.  ERLD support by a node  . . . . . . . . . . . . . . . . . . .   3
   5.  ERLD support by a link  . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   When Segment Routing tunnels are computed by a centralised
   controller, it is beneficial that the controller knows the ERLD
   (Entropy capable Readable Label Depth) of each node or link a tunnel
   traverses.  A network node signalling an ERLD MUST support the
   ability to read the signalled number of labels before any action is
   done upon the packet and SHOULD support entropy awareness found
   within the signalled ERLD depth.

   ERLD awareness of each node and link will allow a network SDN
   controller to influence the path used for each tunnel.  The SDN
   controller may for example only create tunnels with a label stack
   smaller or equal as the ERLD of each node and link on the path.  This
   will allow the network to behave accordingly (e.g.  make use of
   Entropy Labels to improve ECMP) upon the imposed Segment Routing
   label stack on each packet.

   This document describes how to use BGP-LS to expose the ERLD of a
   node.

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2.  Conventions used in this document

2.1.  Terminology

   BGP-LS: Distribution of Link-State and TE Information using Border
   Gateway Protocol

   ERLD: Entropy capable Readable Label Depth

   PCC: Path Computation Client

   PCE: Path Computation Element

   PCEP: Path Computation Element Protocol

   SID: Segment Identifier

   SR: Segment routing

3.  Problem Statement

   In existing technology both ISIS [4] and OSPF [3] have proposed
   extensions to signal the RLD (Readable Label Depth) and ELC (Entropy
   Label Capability) of a node or link.  However, if a network SDN
   controller is connected to the network through a BGP-LS session and
   not through ISIS or OSPF technology, then both RLD and ELC needs to
   be signaled in BGP-LS accordingly.  This document describes the
   extension BGP-LS requires to transport the combination of RLD and ELC
   into according ERLD attributes for nodes and links.

   A network SDN controller having awareness of the ERLD Entropy capable
   Readable Label Depth can for example use it as a constraint on path
   computation so that it can make sure that high bandwidth LSPs are not
   placed on LAG (Link Aggregation Group) links with smaller member
   bandwidths if they know the Entropy Label cannot be processed by the
   node at the ingress to the link.

4.  ERLD support by a node

   Node ERLD is encoded in a new Node Attribute TLV, as defined in
   RFC7752 [2].

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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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     ERLD      |
     +-+-+-+-+-+-+-+-+

                                 Figure 1

      Type : A 2-octet field specifying code-point of the new TLV type.
      Code-point: TBA 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

      ERLD: Node ERLD is a number in the range of 0-254.  The value of 0
      represents lack of ability to read a label stack of any depth, any
      other value represents the readable label depth of the node.

5.  ERLD support by a link

   Link ERLD is encoded in a new Link Attribute TLV, as defined in
   RFC7752 [2].

      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     ERLD      |
     +-+-+-+-+-+-+-+-+

                                 Figure 2

      Type : A 2-octet field specifying code-point of the new TLV type.
      Code-point: TBA 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

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      ERLD: Link ERLD is a number in the range of 0-254.  The value of 0
      represents lack of ability to read a label stack of any depth, any
      other value represents the readable label depth of the link.

6.  Security Considerations

   This document does not introduce security issues beyond those
   discussed in RFC7752 [2]

7.  Acknowledgements

   Thanks to discussions with Acee Lindem, Jeff Tantsura, Stephane
   Litkowski, Bruno Decraene, Kireeti Kompella, John E.  Drake and
   Carlos Pignataro to bring the concept of combining ELC and RLD into a
   single ERLD signalled parameter more suitable for SDN controller
   based networks.

8.  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 4 and 5.

9.  References

9.1.  Normative References

   [1]        Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://xml.resource.org/public/rfc/html/rfc2119.html>.

   [2]        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>.

9.2.  Informative References

   [3]        Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "draft-ietf-ospf-mpls-elc", October 2016.

   [4]        Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "draft-ietf-isis-mpls-elc", October 2016.

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Authors' Addresses

   Gunter Van de Velde (editor)
   Nokia
   Antwerp
   BE

   Email: gunter.van_de_velde@nokia.com

   Wim Henderickx
   Nokia
   Belgium

   Email: wim.henderickx@nokia.com

   Matthew Bocci
   Nokia
   Shoppenhangers Road
   Maidenhead, Berks
   UK

   Email: matthew.bocci@nokia.com

   Keyur Patel
   Arrcus
   USA

   Email: keyur@arrcus.com

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