Inter Stateful Path Computation Element (PCE) Communication Procedures.

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Last updated 2020-01-11
Replaces draft-dhody-pce-stateful-pce-lspdb-realtime-sync
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PCE Working Group                                           S. Litkowski
Internet-Draft                                              S. Sivabalan
Intended status: Standards Track                                   Cisco
Expires: July 14, 2020                                             C. Li
                                                                H. Zheng
                                                     Huawei Technologies
                                                        January 11, 2020

Inter Stateful Path Computation Element (PCE) Communication Procedures.


   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.
   The stateful PCE extensions allow stateful control of Multi-Protocol
   Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE
   LSPs) using PCEP.

   A Path Computation Client (PCC) can synchronize an LSP state
   information to a Stateful Path Computation Element (PCE).  The
   stateful PCE extension allows a redundancy scenario where a PCC can
   have redundant PCEP sessions towards multiple PCEs.  In such a case,
   a PCC gives control on a LSP to only a single PCE, and only one PCE
   is responsible for path computation for this delegated LSP.  The
   document does not state the procedures related to an inter-PCE
   stateful communication.

   There are some use cases, where an inter-PCE stateful communication
   can bring additional resiliency in the design, for instance when some
   PCC-PCE sessions fails.  The inter-PCE stateful communication may
   also provide a faster update of the LSP states when such an event
   occurs.  Finally, when, in a redundant PCE scenario, there is a need
   to compute a set of paths that are part of a group (so there is a
   dependency between the paths), there may be some cases where the
   computation of all paths in the group is not handled by the same PCE:
   this situation is called a split-brain.  This split-brain scenario
   may lead to computation loops between PCEs or suboptimal path

   This document describes the procedures to allow a stateful
   communication between PCEs for various use-cases and also the
   procedures to prevent computations loops.

Litkowski, et al.         Expires July 14, 2020                 [Page 1]
Internet-Draft                 state-sync                   January 2020

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

Status of This Memo

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Table of Contents

   1.  Introduction and Problem Statement  . . . . . . . . . . . . .   3
     1.1.  Reporting LSP changes . . . . . . . . . . . . . . . . . .   4
     1.2.  Split-brain . . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Applicability to H-PCE  . . . . . . . . . . . . . . . . .  12
   2.  Proposed solution . . . . . . . . . . . . . . . . . . . . . .  12
     2.1.  State-sync session  . . . . . . . . . . . . . . . . . . .  12

Litkowski, et al.         Expires July 14, 2020                 [Page 2]
Internet-Draft                 state-sync                   January 2020
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