PCE Working Group H. Ananthakrishnan
Internet-Draft Netflix
Intended status: Standards Track S. Sivabalan
Expires: August 7, 2019 Cisco
C. Barth
R. Torvi
Juniper Networks
I. Minei
Google, Inc
E. Crabbe
Individual Contributor
M. Negi
Huawei Technologies
February 3, 2019

PCEP Extensions for Associating Working and Protection LSPs with Stateful PCE


A stateful Path Computation Element (PCE) is capable of computing as well as controlling via Path Computation Element Protocol (PCEP) Multiprotocol Label Switching Traffic Engineering Label Switched Paths (MPLS LSP). Furthermore, it is also possible for a stateful PCE to create, maintain, and delete LSPs. This document describes PCEP extension to associate two or more LSPs to provide end-to-end path protection.

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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on August 7, 2019.

Copyright Notice

Copyright (c) 2019 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 (https://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.

Table of Contents

1. Introduction

[RFC5440] describes PCEP for communication between a Path Computation Client (PCC) and a PCE or between one a pair of PCEs as per [RFC4655]. A PCE computes paths for MPLS-TE LSPs based on various constraints and optimization criteria.

Stateful pce [RFC8231] specifies a set of extensions to PCEP to enable stateful control of paths such as MPLS TE LSPs between and across PCEP sessions in compliance with [RFC4657]. It includes mechanisms to effect LSP state synchronization between PCCs and PCEs, delegation of control of LSPs to PCEs, and PCE control of timing and sequence of path computations within and across PCEP sessions and focuses on a model where LSPs are configured on the PCC and control over them is delegated to the PCE. Furthermore, a mechanism to dynamically instantiate LSPs on a PCC based on the requests from a stateful PCE or a controller using stateful PCE, is specified in [RFC8281].

Path protection [RFC4427] refers to a paradigm in which the working LSP is protected by one or more protection LSP(s). When the working LSP fails, protection LSP(s) is/are activated. When the working LSPs are computed and controlled by the PCE, there is benefit in a mode of operation where protection LSPs are as well.

This document specifies a stateful PCEP extension to associate two or more LSPs for the purpose of setting up path protection. The proposed extension covers the following scenarios: [RFC4427] or a Primary LSP [RFC4872]) or post failure of the corresponding working LSP according to the operator choice/policy (known as secondary LSP [RFC4872]).

Note that protection LSP can be established (signaled) prior to the failure (in which case the LSP is said to be in standby mode

[I-D.ietf-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 that is equally applicable to stateful PCE (active and passive modes) and stateless PCE.

This document specifies a PCEP extension to associate one working LSP with one or more protection LSPs using the generic association mechanism.

This document describes a PCEP extension to associate protection LSPs by creating Path Protection Association Group (PPAG) and encoding this association in PCEP messages for stateful PCEP sessions.

1.1. 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.

2. Terminology

The following terminologies are used in this document:

Explicit Route Object.
Label Switched Path.
Path Computation Client.
Path Computation Element
Path Computation Element Protocol.
Path Protection Association Group.
Type, Length, and Value.

3. PCEP Extensions

3.1. Path Protection Association Type

LSPs are not associated by listing the other LSPs with which they interact, but rather by making them belong to an association group referred to as "Path Protection Association Group" (PPAG) in this document. All LSPs join a PPAG individually. PPAG is based on the generic Association object used to associate two or more LSPs specified in [I-D.ietf-pce-association-group]. A member of a PPAG can take the role of working or protection LSP. This document defines a new association type called "Path Protection Association Type" of value TBD1. A PPAG can have one working LSP and/or one or more protection LSPs. The source, destination and Tunnel ID (as carried in LSP-IDENTIFIERS TLV [RFC8231], with description as per [RFC3209]) of all LSPs within a PPAG MUST be the same. As per [RFC3209], TE tunnel is used to associate a set of LSPs during reroute or to spread a traffic trunk over multiple paths.

The format of the Association object used for PPAG is specified in [I-D.ietf-pce-association-group].

This document defines a new Association type, the Path Protection Association type, value will be assigned by IANA (TBD1).

[I-D.ietf-pce-association-group] specify the mechanism for the capability advertisement of the association types supported by a PCEP speaker by defining a ASSOC-Type-List TLV to be carried within an OPEN object. This capability exchange for the association type described in this document (i.e. Path Protection Association Type) MAY be done before using the policy association, i.e., the PCEP speaker MAY include the Path Protection Association Type (TBD1) in the ASSOC-Type-List TLV before using the PPAG in the PCEP messages.

This Association-Type is dynamic in nature and created by the PCC or PCE for the LSPs belonging to the same TE tunnel (as described in [RFC3209]) originating at the same head node and terminating at the same destination. These associations are conveyed via PCEP messages to the PCEP peer. Operator-configured Association Range MUST NOT be set for this association-type and MUST be ignored.

3.2. Path Protection Association TLV

The Path Protection Association TLV is an optional TLV for use with the Path Protection Association Object Type. The Path Protection Association TLV MUST NOT be present more than once. If it appears more than once, only the first occurrence is processed and any others MUST be ignored.

The Path Protection Association TLV follows the PCEP TLV format of [RFC5440].

The type (16 bits) of the TLV is to be assigned by IANA. The length field is 16 bit-long and has a fixed value of 4.

The value comprises of a single field, the Path Protection Association Flags (32 bits), where each bit represents a flag option.

The format of the Path Protection Association TLV is as follows:

  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 = TBD2         |              Length             |
  |   PT      |     Path Protection Association Flags         |S|P|


Figure 1: Path Protection Association TLV format

Path Protection Association Flags (32 bits) - Following flags are currently defined -

If the TLV is missing, it is considered that the LSP is the working LSP (i.e. P bit is unset).

4. Operation

An LSP is associated with other LSPs with which they interact by adding them to a common association group via the ASSOCIATION object. All procedures and error-handling for the ASSOCIATION object is as per [I-D.ietf-pce-association-group].

4.1. State Synchronization

During state synchronization, a PCC MUST report all the existing path protection association groups as well as any path protection flags to PCE(s) as per [I-D.ietf-pce-association-group].

4.2. PCC Initiated LSPs

A PCC can associate a set of LSPs under its control for path protection purpose. Similarly, the PCC can remove on or more LSPs under its control from the corresponding PPAG. In both cases, the PCC would report the change in association to PCE(s) via PCRpt message. A PCC can also delegate the working and protection LSPs to a stateful PCE, where PCE would control the LSPs. The stateful PCE could update the paths and attributes of the LSPs in the association group via PCUpd message. A PCE could also update the association to PCC via PCUpd message. These procedures are described in [I-D.ietf-pce-association-group].

It is expected that both working and protection LSP are delegated together (and to the same PCE) to avoid any race conditions. Refer [I-D.litkowski-pce-state-sync] for the problem description.

4.3. PCE Initiated LSPs

A PCE can create/update working and protection LSPs independently. As specified in [I-D.ietf-pce-association-group], Association Groups can be created by both PCE and PCC. Further, a PCE can remove a protection LSP from a PPAG as specified in [I-D.ietf-pce-association-group]. The PCE uses PCUpd or PCInitiate message to communicate the association information to the PCC.

4.4. Session Termination

As per [I-D.ietf-pce-association-group] the association information is cleared along with the LSP state information. When a PCEP session is terminated, after expiry of State Timeout Interval at PCC, the LSP state associated with that PCEP session is reverted to operator-defined default parameters or behaviors as per [RFC8231]. Same procedure is also followed for the association information. On session termination at the PCE, when the LSP state reported by PCC is cleared, the association information is also cleared as per [I-D.ietf-pce-association-group]. Where there are no LSPs in a association group, the association is considered to be deleted..

4.5. Error Handling

As per the processing rules specified in section 5.4 of [I-D.ietf-pce-association-group], if a PCEP speaker does not support this Path Protection association-type, it would return a PCErr message with Error-Type 26 (Early allocation by IANA) "Association Error" and Error-Value 1 "Association-type is not supported".

All LSPs (working or protection) within a PPAG MUST belong to the same TE Tunnel (as described in [RFC3209]) and have the same source and destination. If a PCEP speaker attempts to add an LSP to a PPAG and the Tunnel ID (as carried in LSP-IDENTIFIERS TLV [RFC8231], with description as per [RFC3209]) or source or destination of the LSP is different from the LSP(s) in the PPAG, the PCC MUST send PCErr with Error-Type= 29 (Early allocation by IANA) (Association Error) [I-D.ietf-pce-association-group] and Error-Value = TBD3 (Tunnel ID or End points mismatch for Path Protection Association). In case of Path Protection, LSP-IDENTIFIERS TLV SHOULD be included for all LSPs (including segment routing (SR) [I-D.ietf-pce-segment-routing].

When the protection type is set to 1+1 or 1:N (with N=1), there MUST be only one working LSP and protection LSP within a PPAG. If a PCEP Speaker attempts to add another working/protection LSP, the PCEP peer MUST send PCErr with Error-Type=29 (Early allocation by IANA) (Association Error) [I-D.ietf-pce-association-group] and Error-Value = TBD4 (Attempt to add another working/protection LSP for Path Protection Association).

All processing as per section 5.4 of [I-D.ietf-pce-association-group] continue to apply.

5. Other considerations

The working and protection LSPs are typically resource disjoint (e.g., node, SRLG disjoint). This ensures that a single failure will not affect both the working and protection LSPs.The disjoint requirement for a group of LSPs is handled via another association type called "Disjointness Association", as described in [I-D.ietf-pce-association-diversity]. The diversity requirements for the the protection LSP are also handled by including both ASSOCIATION object identifying both the protection association group and disjoint association group for the group of LSPs.

6. IANA considerations

6.1. Association Type

This document defines a new association type, originally defined in [I-D.ietf-pce-association-group], for path protection. IANA is requested to make the assignment of a new value for the sub-registry "ASSOCIATION Type Field" (request to be created in [I-D.ietf-pce-association-group]), as follows:

Association Type Value Association Name Reference
TBD1 Path Protection Association This document


This document defines a new TLV for carrying additional information of LSPs within a path protection association group. IANA is requested to make the assignment of a new value for the existing "PCEP TLV Type Indicators" registry as follows:

TLV Type Value TLV Name Reference
TBD2 Path Protection Association Group TLV This document

This document requests that a new sub-registry, named "Path protection Association Group TLV Flag Field", is created within the "Path Computation Element Protocol (PCEP) Numbers" registry to manage the Flag field in the Path Protection Association Group TLV. New values are to be assigned by Standards Action [RFC8126]. Each bit should be tracked with the following qualities:

Each bit should be tracked with the following qualities:

Bit Number Name Reference
31 P - PROTECTION-LSP This document
30 S - STANDBY This document
0-5 Protection Type Flags This document

6.3. PCEP Errors

This document defines new Error-Type and Error-Value related to path protection association. IANA is requested to allocate new error values within the "PCEP-ERROR Object Error Types and Values" sub-registry of the PCEP Numbers registry, as follows:

Error-Type Meaning Reference
29 Association error [I-D.ietf-pce-association-group]
Error-value=TBD3: Tunnel ID or End points mismatch for Path Protection Association This document
Error-value=TBD4: Attempt to add another working/protection LSP for Path Protection Association This document

7. Security Considerations

The security considerations described in [RFC8231], [RFC8281], and [RFC5440] apply to the extensions described in this document as well. Additional considerations related to associations where a malicious PCEP speaker could be spoofed and could be used as an attack vector by creating associations is described in [I-D.ietf-pce-association-group]. Thus securing the PCEP session using Transport Layer Security (TLS) [RFC8253], as per the recommendations and best current practices in [RFC7525], is RECOMMENDED.

8. Manageability Considerations

8.1. Control of Function and Policy

Mechanisms defined in this document do not imply any control or policy requirements in addition to those already listed in [RFC5440], [RFC8231], and [RFC8281].

8.2. Information and Data Models

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

The PCEP YANG module [I-D.ietf-pce-pcep-yang] supports associations.

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], [RFC8231], and [RFC8281].

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], [RFC8231], and [RFC8281].

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], [RFC8231], and [RFC8281].

9. Acknowledgments

We would like to thank Jeff Tantsura, Xian Zhang and Greg Mirsky for their contributions to this document.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001.
[RFC4872] Lang, J., Rekhter, Y. and D. Papadimitriou, "RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery", RFC 4872, DOI 10.17487/RFC4872, May 2007.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009.
[RFC8126] Cotton, M., Leiba, B. and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8231] Crabbe, E., Minei, I., Medved, J. and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE", RFC 8231, DOI 10.17487/RFC8231, September 2017.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S. and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for PCE-Initiated LSP Setup in a Stateful PCE Model", RFC 8281, DOI 10.17487/RFC8281, December 2017.
[I-D.ietf-pce-association-group] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H., Dhody, D. and Y. Tanaka, "PCEP Extensions for Establishing Relationships Between Sets of LSPs", Internet-Draft draft-ietf-pce-association-group-07, December 2018.

10.2. Informative References

[RFC4427] Mannie, E. and D. Papadimitriou, "Recovery (Protection and Restoration) Terminology for Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4427, DOI 10.17487/RFC4427, March 2006.
[RFC4655] Farrel, A., Vasseur, J. and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006.
[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, DOI 10.17487/RFC4657, September 2006.
[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, DOI 10.17487/RFC7420, December 2014.
[RFC7525] Sheffer, Y., Holz, R. and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015.
[RFC8051] Zhang, X. and I. Minei, "Applicability of a Stateful Path Computation Element (PCE)", RFC 8051, DOI 10.17487/RFC8051, January 2017.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q. and D. Dhody, "PCEPS: Usage of TLS to Provide a Secure Transport for the Path Computation Element Communication Protocol (PCEP)", RFC 8253, DOI 10.17487/RFC8253, October 2017.
[I-D.ietf-pce-pcep-yang] Dhody, D., Hardwick, J., Beeram, V. and J. Tantsura, "A YANG Data Model for Path Computation Element Communications Protocol (PCEP)", Internet-Draft draft-ietf-pce-pcep-yang-09, October 2018.
[I-D.ietf-pce-association-diversity] Litkowski, S., Sivabalan, S., Barth, C. and D. Dhody, "Path Computation Element communication Protocol (PCEP) extension for signaling LSP diversity constraint", Internet-Draft draft-ietf-pce-association-diversity-05, December 2018.
[I-D.ietf-pce-segment-routing] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W. and J. Hardwick, "PCEP Extensions for Segment Routing", Internet-Draft draft-ietf-pce-segment-routing-14, October 2018.
[I-D.litkowski-pce-state-sync] Litkowski, S., Sivabalan, S. and D. Dhody, "Inter Stateful Path Computation Element communication procedures", Internet-Draft draft-litkowski-pce-state-sync-04, October 2018.

Appendix A. Contributor Addresses

Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka  560066

EMail: dhruv.ietf@gmail.com

Authors' Addresses

Hariharan Ananthakrishnan Netflix USA EMail: hari@netflix.com
Siva Sivabalan Cisco 2000 Innovation Drive Kananta, Ontaria K2K 3E8, Canada EMail: msiva@cisco.com
Colby Barth Juniper Networks 1194 N Mathilda Ave, Sunnyvale, CA, 94086, USA EMail: cbarth@juniper.net
Raveendra Torvi Juniper Networks 1194 N Mathilda Ave, Sunnyvale, CA, 94086, USA EMail: rtorvi@juniper.net
Ina Minei Google, Inc 1600 Amphitheatre Parkway Mountain View, CA, 94043, USA EMail: inaminei@google.com
Edward Crabbe Individual Contributor EMail: edward.crabbe@gmail.com
Mahendra Singh Negi Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India EMail: mahendrasingh@huawei.com