IDR Working Group                                   G. Van de Velde, Ed.
Internet-Draft                                             W. Henderickx
Intended status: Standards Track                                M. Bocci
Expires: December 20, 2019 February 21, 2020                                         Nokia
                                                                K. Patel
                                                                  Arrcus
                                                           June 18,
                                                         August 20, 2019

                      Signalling ERLD using BGP-LS
              draft-ietf-idr-bgp-ls-segment-routing-rld-04
              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

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   This Internet-Draft will expire on December 20, 2019. February 21, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3   2
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Origination  Advertising of ERLD in BGP-LS . . . . . . . . . . . . . . . .   3
   5.  ERLD support by a node  . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   9.
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.   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 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 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
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

   ELC: Entropy Label Capability

   MSD: Maximum SID Depth

   SID: Segment Identifier

   SR: Segment routing

3.  Problem Statement

   In existing

   For Segment Routing technology both ISIS [4] [7] and OSPF [3] [6] have
   proposed extensions to signal the RLD (Readable 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 RLD ERLD and
   ELC needs to be signalled using BGP-LS encoding.  This document
   describes the extension BGP-LS requires to transport the combined RLD and ELC into an ERLD (Entropy
   capable Readable Label Depth) attribute. 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
   entropy label cannot be processed by the node at the ingress to the
   link.

4.  Origination  Advertising of ERLD in BGP-LS

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

   This document defines a node. 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 RLD ERLD
   value in an BGP-LS ERLD attribute, if the associated node ELC is not
   signalled.

5.  ERLD support by a node

   Node ERLD is encoded in a new Node 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 MSD-Type=TBD  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     ERLD   ERLD-Value  |
     +-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1

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

   The 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 encoded as a number 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 of 0-254. 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.

6.

5.  Security Considerations

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

7.

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.

8.

7.  IANA Considerations

   This document requests assigning a new BGP MSD sub-TLV code-points from the BGP-LS
   Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
   TLVs registry as specified
   described in section 5. 4.

   Note: placeholder IANA request
   Request Node ERLD codepoint

   BGP-LS TLV Code Point: TBD1

   ISIS TLV 242/TBD2

   Note: There is nothing in IANA from draft draft-ietf-isis-mpls-elc

   Note: Draft talks only about ELC/RLD and that is mismatch with ERLD

   OSPF RI TLV TBD5

   OSPF ELC in Non-OSPF functionality Capability Bits (TBD6)

9.

8.  References

9.1.

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>.

   [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.

   [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

   [3]

   [6]        Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "draft-ietf-ospf-mpls-elc", January 2018.

   [4] May 2019.

   [7]        Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "draft-ietf-isis-mpls-elc", January 2018. 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
   Matthew Bocci
   Nokia
   Shoppenhangers Road
   Maidenhead, Berks
   UK

   Email: matthew.bocci@nokia.com

   Keyur Patel
   Arrcus
   USA

   Email: keyur@arrcus.com