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Versions: (draft-vandevelde-idr-bgp-ls-segment-routing-rld) 00 01 02 03 04 05

IDR Working Group                                   G. Van de Velde, Ed.
Internet-Draft                                             W. Henderickx
Intended status: Standards Track                                M. Bocci
Expires: February 21, 2020                                         Nokia
                                                                K. Patel
                                                                  Arrcus
                                                         August 20, 2019


                      Signalling ERLD using BGP-LS
              draft-ietf-idr-bgp-ls-segment-routing-rld-05

Abstract

   This document defines the attribute encoding to use for BGP-LS to
   expose ERLD "Entropy capable Readable Label Depth" from a node 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].

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 https://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 February 21, 2020.

Copyright Notice

   Copyright (c) 2019 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



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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Advertising of ERLD in BGP-LS . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   When Segment Routing tunnels are computed by a centralised
   controller, it is beneficial that the controller knows the ERLD
   (Entropy 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 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 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.

2.  Conventions used in this document







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2.1.  Terminology

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

   ERLD: Entropy capable Readable Label Depth

   ELC: Entropy Label Capability

   MSD: Maximum SID Depth

   SID: Segment Identifier

3.  Problem Statement

   For Segment Routing technology both ISIS [7] and OSPF [6] have
   proposed extensions to signal the ERLD (Entropy Readable Label Depth)
   and ELC (Entropy Label Capability) of a node.  However, if a network
   SDN controller is connected to the network through a BGP-LS session
   and not through either ISIS or OSPF technology, then both ERLD and
   ELC needs to be signalled using BGP-LS encoding.  This document
   describes the extension BGP-LS requires to signal ERLD.

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

4.  Advertising of ERLD in BGP-LS

   Both ISIS [7] and OSPF [6] have proposed extensions to signal the
   ERLD (Entropy Readable Label Depth) and ELC (Entropy Label
   Capability) using new MSD-type of the Node MSD sub-Type TLV RFC8491
   [4] or RFC8476 [3].

   This document defines a new node BGP MSD sub-type TLV from draft-
   ietf-idr-bgp-ls-segment-routing-msd [5] to signal the ERLD.

   A BGP-LS router exporting the IGP LSDB, MUST NOT encode the IGP ERLD
   value in an BGP-LS ERLD attribute, if the associated ELC is not
   signalled.








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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | MSD-Type=TBD  |   ERLD-Value  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                                 Figure 1

   The BGP-LS ERLD is encoded as a node MSD sub-type defined in the IANA
   registry titled "IGP MSD-Types" under the "Interior Gateway Protocol
   (IGP) Parameters" registry created by RFC8491 [4].

   The ERLD-Value field in the range between 0 to 255 is set to the BGP-
   LS imported IGP ERLD.  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.  Security Considerations

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

6.  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.

7.  IANA Considerations

   This document requests assigning new BGP MSD sub-TLV code-points as
   described in section 4.

   Note: placeholder IANA request

8.  References

8.1.  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>.






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   [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>.

   [3]        Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
              "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
              DOI 10.17487/RFC8476, December 2018,
              <https://www.rfc-editor.org/info/rfc8476>.

   [4]        Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,
              <https://www.rfc-editor.org/info/rfc8491>.

   [5]        Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
              and N. Triantafillis, "draft-ietf-idr-bgp-ls-segment-
              routing-msd", June 2019.

8.2.  Informative References

   [6]        Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "draft-ietf-ospf-mpls-elc", May 2019.

   [7]        Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "draft-ietf-isis-mpls-elc", May 2019.

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








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   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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