BGP trigger Segment Routing ODN

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Network Working Group                                        Yuanchao Su
Internet-Draft                                               Cisco Systems, Inc.
Intended status: Standards Track                             October 1,2018 
Expires: January 3, 2019                                    

              BGP trigger Segment Routing ODN


   This document defines an extension to the BGP SR Policy NLRI
   (draft-ietf-idr-segment-routing-te-policy) in order to use BGP to trigger 
   Segment Routing ODN, without using PCEP.
   The goal is to consolidate the SR Policy provision(BGP-TE), collection(BGP-LS)
   and ODN-trigger protocol for device to be BGP only, thus remove the need
   for PCEP and reduce the network complexity and potential bugs cause by
   different protocol interactions.

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1.  Introduction

   Segment Routing (SR) allows a headend node to steer a packet flow
   along any path.  Intermediate per-flow states are eliminated thanks
   to source routing [I-D.ietf-spring-segment-routing].

   The headend node is said to steer a flow into a Segment Routing
   Policy (SR Policy).

   The header of a packet steered in an SR Policy is augmented with the
   ordered list of segments associated with that SR Policy.

   [I-D.ietf-spring-segment-routing-policy] details the concepts of SR
   Policy and steering into an SR Policy.  These apply equally to the
   MPLS and SRv6 instantiations of segment routing.

   [I-D.ietf-idr-segment-routing-te-policy] specifies the way to use BGP
   to distribute one or more of the candidate paths of an SR Policy to the
   headend of that policy.
   This document specifies a way for headend to trigger SR ODN with BGP SR Policy NLRI UPDATE messages.
   BGP can then be used to replace PCEP as the signal protocol for ODN.
   This special UPDATE message SHOULD NOT be used for BGP best path selection.
   When controller receives this specific UPDATE message from headend, it checks whether it's PCE,
   if yes, it processed the payload of the message, otherwise it drops the message.
   If controller is PCE, it retrieves the color, link affinity, association
   information from the message and starts the path calculation.
   Once the path calculation is done, the controller uses BGP SR Policy NLRI UPDATE message
   to distribute the candidate path to headend.If the calculation is failed, 
   for example, the constrains expressed by the link affinity TLV can't be met, 
   the controller MUST sends a BGP SR Policy NLRI with Segment List TLV empty and Bing-SID empty.
   When headend receives the update from controller, it processed the update
   as specified in [I-D.ietf-idr-segment-routing-te-policy]

   The extensions to SR Policy NLRI include:

   o  Distinguisher field SR Policy NLRI: special address FF:FF:FF:FF as the signal for ODN

   o  Two new sub-TLVs belong to Tunnel Encaps Attribute with Tunnel-Type set to 15(SR Policy) 
      o Metric sub-TLV to specify the metric that the PCE should use for the path calculation
      o Link Affinity sub-TLV to specify the link constrains
      o Association sub-TLV to specify the disjointness and protection constrains

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  BGP trigger ODN Encoding
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