PCE Working Group D. Dhody
Internet-Draft Q. Wu
Intended status: Standards Track Huawei Technologies
Expires: January 6, 2016 July 5, 2015

Path Computation Element communication Protocol extension for relationship between LSPs and Attributes


The Path Computation Element (PCE) provides functions of path computation in support of traffic engineering in networks controlled by Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS).

This document defines a mechanism to create associations between a set of LSPs and a set of attributes (such as configuration parameters, policy or behaviours).

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Table of Contents

1. Introduction

[RFC5440] describes the Path Computation Element communication Protocol (PCEP) which 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].

[I-D.minei-pce-association-group] introduces a generic mechanism to create a grouping of LSPs which can then be used to define associations between a set of LSPs and a set of attributes (such as configuration parameters or behaviours) and is equally applicable to the active and passive modes of a stateful PCE and a stateless PCE.

This document specifies a PCEP extension to associate one or more LSPs with a set of attributes, which includes, but not limited to -

1.1. Requirements Language

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 [RFC2119].

2. Terminology

The following terminology is used in this document.

Attribute Association Group.
Label Switch Router.
Multiprotocol Label Switching.
Path Computation Client. Any client application requesting a path computation to be performed by a Path Computation Element.
Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints.
Path Computation Element Communication Protocol.

3. Motivation

This section discusses in more detail the motivation and use cases for such an association including but not limited to -

3.1. Opaque Identifier

An opaque identifier may represent attributes such as configured parameters or constraints that a PCEP speaker may invoke on a peer. Thus a PCEP speaker may only need an opaque identifier to invoke these attributes (parameters or constraints) rather than encoding them explicitly in each PCEP message.

3.2. Policy based Constraints

In the context of policy-enabled path computation [RFC5394], path computation policies may be applied at both a PCC and a PCE. Consider an Label Switch Router (LSR) with a policy enabled PCC, it receives a service request via signaling, including over a Network-Network Interface (NNI) or User Network Interface (UNI) reference point, or receives a configuration request over a management interface to establish a service. The PCC may also apply user- or service-specific policies to decide how the path selection process should be constrained, that is, which constraints, diversities, optimization criterion, and constraint relaxation strategies should be applied in order for the service LSP(s) to have a likelihood to be successfully established and provide necessary QoS and resilience against network failures. The user- or service-specific policies applied to PCC and are then passed to the PCE along with the Path computation request, in the form of constraints [RFC5394].

PCEP speaker can use the generic mechanism as per [I-D.minei-pce-association-group] to associate a set of LSPs with policy and its resulting path computation constraints. This simplified the path computation message exchanges.

3.3. Bundled requests

In some scenarios(e.g.,the topology example described in Section 4.6 of [RFC6805]), there is a need to send multiple requests with the same constraints and attributes to the PCE. Currently these requests are either sent in a separate path computation request (PCReq) messages or bundled together in one (or more) PCReq messages. In either case, the constraints and attributes need to be encoded separately for each request even though they are exactly identical.

If a association is used to identify these constraints and attributes shared by multiple requests and grouped together via association mechanism, thus simplifying the path computation message exchanges.

4. Overview

As per [I-D.minei-pce-association-group], LSPs are associated with other LSPs with which they interact by adding them to a common association group. This grouping can then be used to define associations between sets of LSPs or between a set of LSPs and a set of attributes (such as configuration parameters or behaviors). A new optional Association Object is defined. This document uses the same association for attributes, called Attribute Association Group (AAG) based on the generic Association object. This document defines a new association type called "Attribute Association Type" of value TBD. An AAG can have one or more LSPs and its associated attributes. The scope and handling of AAG identifier is similar to the generic association identifier defined in [I-D.minei-pce-association-group].

One or more LSP are grouped via a single group identifier as defined in [I-D.minei-pce-association-group]. The attributes that may be associated with this set of LSPs may either are -

Error handling would be taken up in future revision.

5. Attribute Association Group

The format of the generic Association object used for AAG is shown in Figure 1:

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
|  Type |            Flags    |R|          Reserved             |
|                   Association ID                              |
|              IPv4 Association Source                          |
//                   Optional TLVs                            //

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
|  Type |            Flags    |R|          Reserved             |
|                   Association ID                              |
|                                                               |
|                    IPv6 Association Source                    |
|                                                               |
|                                                               |
//                   Optional TLVs                            //

Figure 1: The Association Object formats

Type - TBD for the Attribute Association Type.

AAG may carry optional TLVs including but not limited to -


The ATTRIBUTE-OBJECT-TLV(s) maybe included in AAG object to associate attributes encoded in PCEP objects.

The format of the ATTRIBUTE-OBJECT-TLV is shown in the following figure:

 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
|           Type=[TBD]          |           Length              |
| Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
|                                                               |
//                        (Object body)                        //
|                                                               |


The type of the TLV is [TBD] and it has a variable length. The value part consist of a PCEP object (including common header [RFC5440] identifying the object) that is associated with this AAG. This TLV identifies the attributes associated with this group. For each attribute a separate TLV is used. Future PCEP message exchanges may only carry the AAG.

6. Security Considerations

This document defines a new type for association and a new ATTRIBUTE-OBJECT-TLV which do not add any new security concerns beyond those discussed in [RFC5440], [I-D.ietf-pce-stateful-pce] and [I-D.minei-pce-association-group] in itself.

Some deployments may find these associations and their implications as extra sensitive and thus should employ suitable PCEP security mechanisms like TCP-AO or [I-D.ietf-pce-pceps].

7. IANA Considerations

7.1. Association object Type Indicators

This document defines the following new association type originally defined in [I-D.minei-pce-association-group].

Value     Name                        Reference
TBD       Attribute Association Type  [This I.D.]

7.2. PCEP TLV Type Indicators

This document defines the following new PCEP TLV; IANA is requested to make the following allocations from this registry. http://www.iana.org/assignments/pcep/pcep.xhtml#pcep-tlv-type-indicators

Value     Name                        Reference
TBD       ATTRIBUTE-OBJECT-TLV        [This I.D.]

8. Manageability Considerations

8.1. Control of Function and Policy

An operator MUST BE allowed to configure the attribute associations at PCEP peers and associate it with the LSPs.

8.2. Information and Data Models

[RFC7420] describes the PCEP MIB, there are no new MIB Objects for this document.

8.3. Liveness Detection and Monitoring

Mechanisms defined in this document do not imply any new liveness detection and monitoring requirements in addition to those already listed in [RFC5440].

8.4. Verify Correct Operations

Mechanisms defined in this document do not imply any new operation verification requirements in addition to those already listed in [RFC5440].

8.5. Requirements On Other Protocols

Mechanisms defined in this document do not imply any new requirements on other protocols.

8.6. Impact On Network Operations

Mechanisms defined in this document do not have any impact on network operations in addition to those already listed in [RFC5440].

9. Acknowledgments

A special thanks to author of [I-D.minei-pce-association-group], this document borrow some of the text from it.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4655] Farrel, A., Vasseur, J. and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009.
[I-D.minei-pce-association-group] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H., Zhang, X. and Y. Tanaka, "PCEP Extensions for Establishing Relationships Between Sets of LSPs", Internet-Draft draft-minei-pce-association-group-01, July 2015.
[I-D.ietf-pce-stateful-pce] Crabbe, E., Minei, I., Medved, J. and R. Varga, "PCEP Extensions for Stateful PCE", Internet-Draft draft-ietf-pce-stateful-pce-11, April 2015.

10.2. Informative References

[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L. and J. Ash, "Policy-Enabled Path Computation Framework", RFC 5394, December 2008.
[RFC6805] King, D. and A. Farrel, "The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS and GMPLS", RFC 6805, November 2012.
[RFC7150] Zhang, F. and A. Farrel, "Conveying Vendor-Specific Constraints in the Path Computation Element Communication Protocol", RFC 7150, March 2014.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D. and J. Hardwick, "Path Computation Element Communication Protocol (PCEP) Management Information Base (MIB) Module", RFC 7420, December 2014.
[I-D.ietf-pce-pceps] Lopez, D., Dios, O., Wu, W. and D. Dhody, "Secure Transport for PCEP", Internet-Draft draft-ietf-pce-pceps-04, May 2015.

Appendix A. Contributor Addresses

Xian Zhang
Huawei Technologies
Bantian, Longgang District
Shenzhen  518129

EMail: zhang.xian@huawei.com

Udayasree Palle
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka  560037

EMail: udayasree.palle@huawei.com


Authors' Addresses

Dhruv Dhody Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560037 India EMail: dhruv.ietf@gmail.com
Qin Wu Huawei Technologies 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China EMail: sunseawq@huawei.com