Internet Engineering Task Force (IETF) S. Yasukawa
Request for Comments: 5862 NTT Corporation
Category: Informational A. Farrel
ISSN: 2070-1721 Old Dog Consulting
June 2010
Path Computation Clients (PCC) - Path Computation Element (PCE)
Requirements for Point-to-Multipoint MPLS-TE
Abstract
The Path Computation Element (PCE) provides path computation
functions in support of traffic engineering in Multiprotocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) networks.
Extensions to the MPLS and GMPLS signaling and routing protocols have
been made in support of point-to-multipoint (P2MP) Traffic Engineered
(TE) Label Switched Paths (LSPs). The use of PCE in MPLS networks is
already established, and since P2MP TE LSP routes are sometimes
complex to compute, it is likely that PCE will be used for P2MP LSPs.
Generic requirements for a communication protocol between Path
Computation Clients (PCCs) and PCEs are presented in RFC 4657, "Path
Computation Element (PCE) Communication Protocol Generic
Requirements". This document complements the generic requirements
and presents a detailed set of PCC-PCE communication protocol
requirements for point-to-multipoint MPLS/GMPLS traffic engineering.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5862.
Yasukawa & Farrel Informational [Page 1]
RFC 5862 PCC-PCE and P2MP MPLS-TE June 2010
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
The Path Computation Element (PCE) defined in [RFC4655] is an entity
that is capable of computing a network path or route based on a
network graph, and applying computational constraints. The intention
is that the PCE is used to compute the path of Traffic Engineered
Label Switched Paths (TE LSPs) within Multiprotocol Label Switching
(MPLS) and Generalized MPLS (GMPLS) networks.
Requirements for point-to-multipoint (P2MP) MPLS TE LSPs are
documented in [RFC4461], and signaling protocol extensions for
setting up P2MP MPLS TE LSPs are defined in [RFC4875]. P2MP MPLS TE
networks are considered in support of various features, including
layer 3 multicast virtual private networks [RFC4834].
Path computation for P2MP TE LSPs presents a significant challenge,
and network optimization of multiple P2MP TE LSPs requires
considerable computational resources. PCE offers a way to offload
such path computations from Label Switching Routers (LSRs).
The applicability of the PCE-based path computation architecture to
P2MP MPLS TE is described in a companion document [RFC5671]. No
further attempt is made to justify the use of PCE for P2MP MPLS TE
within this document.
This document presents a set of PCC-PCE communication protocol
(PCECP) requirements for P2MP MPLS traffic engineering. It
supplements the generic requirements documented in [RFC4657].
Yasukawa & Farrel Informational [Page 2]
RFC 5862 PCC-PCE and P2MP MPLS-TE June 2010
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Although this document is not a protocol specification, this
convention is adopted for clarity of description of requirements.
3. PCC-PCE Communication Requirements for P2MP MPLS Traffic Engineering
This section sets out additional requirements specific to P2MP MPLS
TE that are not covered in [RFC4657].
3.1. PCC-PCE Communication
The PCC-PCE communication protocol MUST allow requests and replies
for the computation of paths for P2MP LSPs.
This requires no additional messages, but requires the addition of
the parameters described in the following sections to the existing
PCC-PCE communication protocol messages.
3.1.1. Indication of P2MP Path Computation Request
R1: Although the presence of certain parameters (such as a list of
more than one destination) MAY be used by a protocol
specification to allow an implementation to infer that a Path
Computation Request is for a P2MP LSP, an explicit parameter
SHOULD be placed in a conspicuous place within a Path
Computation Request message to allow a receiving PCE to easily
identify that the request is for a P2MP path.
3.1.2. Indication of P2MP Objective Functions
R2: [RFC4657] includes the requirement to be able to specify the
objective functions to be applied by a PCE during path
computation.
This document makes no change to that requirement, but it should
be noted that new and different objective functions will be used
for P2MP computation. Definitions for core objective functions
can be found in [RFC5541] together with usage procedures. New
objective functions for use with P2MP path computations will
need to be defined and allocated codepoints in a separate
document.
Yasukawa & Farrel Informational [Page 3]
RFC 5862 PCC-PCE and P2MP MPLS-TE June 2010
3.1.3. Non-Support of P2MP Path Computation
R3: PCEs are not required to support P2MP path computation.
Therefore, it MUST be possible for a PCE to reject a P2MP Path
Computation Request message with a reason code that indicates no
support for P2MP path computation.
3.1.4. Non-Support by Back-Level PCE Implementations
It is possible that initial PCE implementations will be developed
without support for P2MP path computation and without the ability to
recognize the explicit parameter described in