Inter Stateful Path Computation Element (PCE) Communication Procedures.
draft-litkowski-pce-state-sync-07
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.
draft-litkowski-pce-state-sync-07
Abstract
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
computation.
This document describes the procedures to allow a stateful
communication between PCEs for various use-cases and also the
procedures to prevent computations loops.
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Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on July 14, 2020.
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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
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