SR Policy for Reverse Path
draft-lp-spring-sr-policy-reverse-path-00

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SPRING WG                                                         Y. Liu
Internet-Draft                                                   S. Peng
Intended status: Standards Track                         ZTE Corporation
Expires: July 31, 2021                                  January 27, 2021

                       SR Policy for Reverse Path
               draft-lp-spring-sr-policy-reverse-path-00

Abstract

   This document introduces a method of dynamically configuring the
   return path for an SR path.

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   This Internet-Draft will expire on July 31, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  SR Policy for Bidirectional Path  . . . . . . . . . . . . . .   2
     2.1.  BGP Extensions for Advertising Segment List . . . . . . .   3
     2.2.  Illustration  . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Difference from Path Segment  . . . . . . . . . . . . . .   5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Echo-BFD [RFC5880] can be used to monitor an SR Policy between the
   local and the remote BFD peers.  As defined in [RFC5880], the remote
   BFD system does not process the payload of an Echo BFD.

   A BSID can be used to specify the return path of an Echo BFD packet.

   As introduced in [I-D.ietf-spring-bfd], the sender MAY use a Binding
   SID (BSID) [RFC8402] that has been bound with the SR Policy that
   ensures the return of a packet to that particular node and a BSID MAY
   be associated with the SR Policy that is the reverse to the SR Policy
   programmed onto the BFD Echo packet by the sender.

   One way to implement this is through static configuration, e.g,
   configure the BSID corresponding to the return path for each segment
   list when enable BFD for an SR policy or an segment list.

   This document introduces a method of dynamically configuring the
   return path for an SR path, which can be used to specify the return
   path in Echo BFD for SR, ICMPv6 for SRv6, etc.

2.  SR Policy for Bidirectional Path

   In order to specify the return path for an segment list when
   delivering the SR Policy, and the tail node can return the packet
   according to the specified return path, this document proposes
   extensions of SR Policy.  It allows the segment list to have its own
   BSID.

   When delivering SR policy, the BSID of the segment list and the
   corresponding BSID of the return segment list can be carried
   together.

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2.1.  BGP Extensions for Advertising Segment List

   Segment List sub-TLV is introduced in
   [I-D.ietf-idr-segment-routing-te-policy] and it includes the elements
   of the paths (i.e., segments).

   This document introduces two optional sub-sub-tlvs of Segment List
   sub-TLV, Binding SID Sub-TLV and Reverse Binding SID Sub-TLV.

   The Binding SID sub-TLV has the following format:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+