Local Protection Enforcement in PCEP

Document Type Active Internet-Draft (individual)
Last updated 2020-03-02
Replaces draft-stone-pce-path-protection-enforcement
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Network Working Group                                           A. Stone
Internet-Draft                                               M. Aissaoui
Intended status: Standards Track                                   Nokia
Expires: September 3, 2020                                  S. Sivabalan
                                                     Cisco Systems, Inc.
                                                           March 2, 2020

                  Local Protection Enforcement in PCEP


   This document aims to clarify existing usage of the local protection
   desired bit signalled in Path Computation Element Protocol (PCEP).
   This document also introduces a new flag for signalling protection
   strictness in PCEP.

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   This Internet-Draft will expire on September 3, 2020.

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Stone, et al.           Expires September 3, 2020               [Page 1]
Internet-Draft                     I-D                        March 2020

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   described in the Simplified BSD License.

1.  Introduction

   Path Computation Element (PCE) Communication Protocol (PCEP)
   [RFC5440] enables the communication between a Path Computation Client
   (PCC) and a Path Control Element (PCE), or between two PCEs based on
   the PCE architecture [RFC4655].

   PCEP [RFC5440] utilizes flags, values and concepts previously defined
   in RSVP-TE Extensions [RFC3209] and Fast Reroute Extensions to RSVP-
   TE [RFC4090].  One such concept in PCEP is the 'Local Protection
   Desired' (L-flag in the LSPA Object in RFC5440), which was originally
   defined in the SESSION-ATTRIBUTE Object in RFC3209.  In RSVP, this
   flag signals to downstream routers that local protection is desired,
   which indicates to transit routers that they may use a local repair
   mechanism.  The headend router calculating the path does not know
   whether a downstream router will or will not protect a hop during
   it's calculation.  Therefore, a local protection desired does not
   require the transit router to satisfy protection in order to
   establish the RSVP signalled path.  This flag is signalled in PCEP as
   an attribute of the LSP via the LSP Attributes object.

   PCEP Extensions for Segment Routing (draft-ietf-pce-segment-routing)
   extends support in PCEP for Segment Routed LSPs (SR-LSPs) as defined
   in the Segment Routing Architecture [RFC8402].  As per the Segment
   Routing Architecture, Adjacency Segment Identifiers(Adj-SID) may be
   eligible for protection (using IPFRR or MPLS-FRR).  The protection
   eligibility is advertised into IGP (draft-ietf-ospf-segment-routing-
   extensions and draft-ietf-isis-segment-routing-extensions) as the
   B-Flag part of the Adjacency SID sub-tlv and can be discovered by a
   PCE via BGP-LS [RFC7752] using the BGP-LS Segment Routing Extensions
   (draft-ietf-idr-bgp-ls-segment-routing-ext).  An Adjacency SID may or
   may not have protection eligibility and for a given adjacency between
   two routers there may be multiple Adjacency SIDs, some of which are
   protected and some which are not.

   A Segment Routed path calculated by PCE may contain various types of
   segments, as defined in [RFC8402] such as Adjacency, Node or Binding.
   The protection eligibility for Adjacency SIDs can be discovered by
   PCE, so therefore the PCE can take the protection eligibility into
   consideration as a path constraint.  If a path is calculated to
   include other segment identifiers which are not applicable to having
   their protection state advertised, as they may only be locally
   significant for each router processing the SID such as Node SIDs, it
   may not be possible for PCE to include the protection constraint as
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