PCE Working Group U. Palle
Internet-Draft D. Dhody
Intended status: Standards Track Huawei Technologies
Expires: December 8, 2014 Y. Tanaka
Y. Kamite
NTT Communications
Z. Ali
Cisco Systems
June 6, 2014

PCEP Extensions for PCE-initiated Point-to-Multipoint LSP Setup in a Stateful PCE Model


The Path Computation Element (PCE) has been identified as an appropriate technology for the determination of the paths of point-to-multipoint (P2MP) TE LSPs. The extensions described in [I-D.ietf-pce-stateful-pce] provide stateful control of Multiprotocol Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE LSP) via PCE communication Protocol (PCEP), for a model where the Path Computation Client (PCC) delegates control over one or more locally configured LSPs to the PCE. Further [I-D.ietf-pce-pce-initiated-lsp] describes the creation and deletion of PCE-initiated LSPs under the stateful PCE model. This document provides extensions required for PCEP so as to enable the usage of a stateful PCE initiation capability in recommending point-to-multipoint (P2MP) TE LSP instantiation.

Status of This Memo

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Table of Contents

1. Introduction

As per [RFC4655], the Path Computation Element (PCE) is an entity that is capable of computing a network path or route based on a network graph, and applying computational constraints. A Path Computation Client (PCC) may make requests to a PCE for paths to be computed.

[RFC4857]describes how to set up point-to-multipoint (P2MP) Traffic Engineering Label Switched Paths (TE LSPs) for use in Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks. The PCE has been identified as a suitable application for the computation of paths for P2MP TE LSPs ( [RFC5671]).

The PCEP is designed as a communication protocol between PCCs and PCEs for point-to-point (P2P) path computations and is defined in [RFC5440]. The extensions of PCEP to request path computation for P2MP TE LSPs are described in [RFC6006].

Stateful PCEs are shown to be helpful in many application scenarios, in both MPLS and GMPLS networks, as illustrated in [I-D.ietf-pce-stateful-pce-app]. These scenarios apply equally to P2P and P2MP TE LSPs. [I-D.ietf-pce-stateful-pce] provides the fundamental extensions needed for stateful PCE to support general functionality for P2P TE LSP. Further [I-D.palle-pce-stateful-pce-p2mp] focuses on the extensions that are necessary in order for the deployment of stateful PCEs to support P2MP TE LSPs. It includes mechanisms to effect P2MP LSP state synchronization between PCCs and PCEs, delegation of control of P2MP LSPs to PCEs, and PCE control of timing and sequence of P2MP path computations within and across PCEP sessions and focuses on a model where P2MP LSPs are configured on the PCC and control over them is delegated to the PCE.

[I-D.ietf-pce-pce-initiated-lsp] provides the fundamental extensions needed for stateful PCE-initiated P2P TE LSP recommended instantiation.

This document describes the setup, maintenance and teardown of PCE- initiated P2MP LSPs under the stateful PCE model, without the need for local configuration on the PCC, thus allowing for a dynamic network that is centrally controlled and deployed.

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

Terminology used in this document is same as terminology used in [I-D.ietf-pce-stateful-pce], [I-D.ietf-pce-pce-initiated-lsp] and [RFC6006].

3. Architectural Overview

3.1. Motivation

[I-D.palle-pce-stateful-pce-p2mp] provides stateful control over P2MP TE LSPs that are locally configured on the PCC. This model relies on the Ingress taking an active role in delegating locally configured P2MP TE LSPs to the PCE, and is well suited in environments where the P2MP TE LSP placement is fairly static. However, in environments where the P2MP TE LSP placement needs to change in response to application demands, it is useful to support dynamic creation and tear down of P2MP TE LSPs. The ability for a PCE to trigger the creation of P2MP TE LSPs on demand can be seamlessly integrated into a controller-based network architecture, where intelligence in the controller can determine when and where to set up paths.

Section 3 of [I-D.ietf-pce-pce-initiated-lsp] further describes the motivation behind the PCE-Initiation capability, which are equally applicable for P2MP TE LSPs.

3.2. Operation Overview

A PCC or PCE indicates its ability to support PCE provisioned dynamic P2MP LSPs during the PCEP Initialization Phase via mechanism described in Section 4.

As per section 5.1 of [I-D.ietf-pce-pce-initiated-lsp], the PCE sends a Path Computation LSP Initiate Request (PCInitiate) message to the PCC to suggest instantiation or deletion of a P2P TE LSP. This document extends the PCInitiate message to support P2MP TE LSP (see details in Section 5.1).

P2MP TE LSP suggested instantiation and deletion operations are same as P2P LSP as described in section 5.3 and 5.4 of [I-D.ietf-pce-pce-initiated-lsp]. This document focuses on extensions needed for further handling of P2MP TE LSP (see details in Section 5.2).

4. Support of PCE Initiated P2MP TE LSPs

During PCEP Initialization Phase, as per Section 7.1.1 of [I-D.ietf-pce-stateful-pce], PCEP speakers advertises Stateful capability via Stateful PCE Capability TLV in open message. A new flag is defined for the STATEFUL-PCE-CAPABILITY TLV defined in [I-D.ietf-pce-stateful-pce]. Its format 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            |            Length=4           |
|                             Flags             |P|M|N|D|T|I|S|U|


The U (LSP-UPDATE-CAPABILITY) bit is defined in [I-D.ietf-pce-stateful-pce]. The I (LSP-INSTANTIATION-CAPABILITY) bit is defined in [I-D.ietf-pce-pce-initiated-lsp]. The S (INCLUDE-DB-VERSION), T (TRIGGERED-SYNC) and D (DELTA-LSP-SYNC-CAPABILITY) bits are defined in [I-D.ietf-pce-stateful-sync-optimizations]. The N (P2MP-CAPABILITY) and M (P2MP-LSP-UPDATE-CAPABILITY) bits are defined in [I-D.palle-pce-stateful-pce-p2mp]. A new bit P (P2MP-LSP-INSTANTIATION-CAPABILITY) is added in this document:

If set to 1 by a PCC, the P Flag indicates that the PCC allows suggested instantiation of an P2MP LSP by a PCE. If set to 1 by a PCE, the P flag indicates that the PCE will suggest P2MP LSP instantiation. The P2MP-LSP-INSTANTIATION-CAPABILITY flag must be set by both PCC and PCE in order to support PCE-initiated P2MP LSP instantiation.

A PCEP speaker should continue to advertise the basic P2MP capability via mechanisms as described in [RFC6006].

5. PCE-initiated P2MP TE LSP Operations

5.1. The PCInitiate message

As defined in section 5.1 of [I-D.ietf-pce-pce-initiated-lsp], PCE sends a PCInitiate message to a PCC to recommend instantiation of a P2P TE LSP, this document extends the format of PCInitiate message for the creation of P2MP TE LSPs but the creation and deletion operations of P2MP TE LSP are same to the P2P TE LSP.

The format of PCInitiate message is as follows:

<PCInitiate Message> ::= <Common Header>

<PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>

<PCE-initiated-lsp-request> ::= 

<PCE-initiated-lsp-instantiation> ::= <SRP>

<PCE-initiated-lsp-deletion> ::= <SRP>



<path> ::= (<ERO>|<SERO>) 
<attribute-list> is defined in [RFC5440] and extended
by PCEP extensions.	                              

The PCInitiate message with an LSP object with N bit (P2MP) set is used to convey operation on a P2MP TE LSP. The SRP object is used to correlate between initiation requests sent by the PCE and the error reports and state reports sent by the PCC as described in [I-D.ietf-pce-stateful-pce].

5.2. P2MP TE LSP Instantiation

The Instantiation operation of P2MP TE LSP is same as defined in section 5.3 of [I-D.ietf-pce-pce-initiated-lsp] including handling of PLSP-ID, SYMBOLIC-PATH-NAME etc. Rules of processing and error codes remains unchanged. Further, as defined in section 6.1 of [I-D.palle-pce-stateful-pce-p2mp], N bit MUST be set in LSP object in PCInitiate message by PCE to specify the instantiation is for P2MP TE LSP and the PCC or PCE MUST follow the mechanism defined in [I-D.palle-pce-stateful-pce-p2mp] for delegation and updation of P2MP TE LSPs.

Though N bit is set in the LSP object, P2MP-LSP-IDENTIFIER TLV defined in section 6.2 of [I-D.palle-pce-stateful-pce-p2mp] MUST NOT be included in the LSP object in PCIntiitate message as it SHOULD be generated by PCC and carried in PCRpt message.

5.3. P2MP TE LSP Deletion

The deletion operation of P2MP TE LSP is same as defined in section 5.4 of [I-D.ietf-pce-pce-initiated-lsp] by sending an LSP Initiate Message with an LSP object carrying the PLSP-ID of the LSP to be removed and an SRP object with the R flag set (LSP-REMOVE as per section 5.2 of [I-D.ietf-pce-pce-initiated-lsp]). Rules of processing and error codes remains unchanged.

5.4. Adding and Pruning Leaves for the P2MP TE LSP

Adding of new leaves and Pruning of old Leaves for the PCE initiated P2MP TE LSP MUST be carried in PCUpd message and SHOULD refer [I-D.palle-pce-stateful-pce-p2mp] for P2MP TE LSP extensions. As defined in [RFC6006], leaf type = 1 for adding of new leaves, leaf type = 2 for pruning of old leaves of P2MP END-POINTS Object are used in PCUpd message.

PCC MAY use the Incremental State Update mechanims as described in [RFC4875] to signal adding and pruning of leaves.

5.5. P2MP TE LSP Delegation and Cleanup

P2MP TE LSP delegation and cleanup operations are same as defined in section 6 of [I-D.ietf-pce-pce-initiated-lsp]. Rules of processing and error codes remains unchanged.

6. PCIntiate Message Fragmentation

The total PCEP message length, including the common header, is 16 bytes. In certain scenarios the P2MP LSP Initiate may not fit into a single PCEP message (initial PCInitiate message). The F-bit is used in the LSP object to signal that the initial PCInitiate was too large to fit into a single message and will be fragmented into multiple messages.

Fragmentation procedure described below for PCInitiate message is similar to [RFC6006] which describes request and response message fragmentation.

6.1. PCIntiate Fragmentation Procedure

Once the PCE initiates to set up the P2MP TE LSP, a PCInitiate message is sent to the PCC. If the PCInitiate is too large to fit into a single PCInitiate message, the PCE will split the PCInitiate over multiple messages. Each PCInitiate message sent by the PCE, except the last one, will have the F-bit set in the LSP object to signify that the PCInitiate has been fragmented into multiple messages. In order to identify that a series of PCInitiate messages represents a single Initiate, each message will use the same PLSP-ID (in this case 0) and SRP-ID-number.

[Editor Note: P2MP message fragmentation errors associated with a P2MP path initiation will be defined in future version].

7. Non-Support of P2MP TE LSP Instantiation for Stateful PCE

The PCEP protocol extensions described in this document for PCC or PCE with instantiation capability for P2MP TE LSPs MUST NOT be used if PCC or PCE has not advertised its stateful capability with Instantiation and P2MP capability as per Section 4. If this is not the case and Stateful initiation operations on P2MP TE LSPs are attempted, then a PCErr with error-type 19 (Invalid Operation) and error-value TBD needs to be generated.

[Editor Note: more information on exact error value is needed]

8. Security Considerations


9. Manageability Considerations

9.1. Control of Function and Policy


9.2. Information and Data Models


9.3. Liveness Detection and Monitoring


9.4. Verify Correct Operations


9.5. Requirements On Other Protocols


9.6. Impact On Network Operations


10. IANA Considerations

This document requests IANA actions to allocate code points for the protocol elements defined in this document. Values shown here are suggested for use by IANA.


The following values are defined in this document for the Flags field in the STATEFUL-PCE-CAPABILITY-TLV in the OPEN object:

    Bit    Description           Reference

    25     P2MP-LSP-             This.I-D


11. Acknowledgments

Thanks to Quintin Zhao and Venugopal Reddy for his comments.

12. References

12.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009.
[I-D.ietf-pce-stateful-pce] Crabbe, E., Medved, J., Minei, I. and R. Varga, "PCEP Extensions for Stateful PCE", Internet-Draft draft-ietf-pce-stateful-pce-08, February 2014.
[I-D.ietf-pce-pce-initiated-lsp] Crabbe, E., Minei, I., Sivabalan, S. and R. Varga, "PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model", Internet-Draft draft-ietf-pce-pce-initiated-lsp-00, December 2013.
[I-D.palle-pce-stateful-pce-p2mp] Palle, U., Dhody, D., Tanaka, Y. and Y. Kamite, "Path Computation Element (PCE) Protocol Extensions for Stateful PCE usage for Point-to-Multipoint Traffic Engineering Label Switched Paths", Internet-Draft draft-palle-pce-stateful-pce-p2mp-02, February 2014.

12.2. Informative References

[RFC4655] Farrel, A., Vasseur, J. and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4857] Fogelstroem, E., Jonsson, A. and C. Perkins, "Mobile IPv4 Regional Registration", RFC 4857, June 2007.
[RFC4875] Aggarwal, R., Papadimitriou, D. and S. Yasukawa, "Extensions to Resource Reservation Protocol - Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5671] Yasukawa, S. and A. Farrel, "Applicability of the Path Computation Element (PCE) to Point-to-Multipoint (P2MP) MPLS and GMPLS Traffic Engineering (TE)", RFC 5671, October 2009.
[RFC6006] Zhao, Q., King, D., Verhaeghe, F., Takeda, T., Ali, Z. and J. Meuric, "Extensions to the Path Computation Element Communication Protocol (PCEP) for Point-to-Multipoint Traffic Engineering Label Switched Paths", RFC 6006, September 2010.
[I-D.ietf-pce-stateful-pce-app] Zhang, X. and I. Minei, "Applicability of Stateful Path Computation Element (PCE)", Internet-Draft draft-ietf-pce-stateful-pce-app-01, September 2013.
[I-D.ietf-pce-stateful-sync-optimizations] Crabbe, E., Medved, J., Minei, I., Varga, R., Zhang, X. and D. Dhody, "Optimizations of Label Switched Path State Synchronization Procedures for a Stateful PCE", Internet-Draft draft-ietf-pce-stateful-sync-optimizations-00, March 2014.

Authors' Addresses

Udayasree Palle Huawei Technologies Leela Palace Bangalore, Karnataka 560008 INDIA EMail: udayasree.palle@huawei.com
Dhruv Dhody Huawei Technologies Leela Palace Bangalore, Karnataka 560008 INDIA EMail: dhruv.ietf@gmail.com
Yosuke Tanaka NTT Communications Corporation Granpark Tower 3-4-1 Shibaura, Minato-ku Tokyo 108-8118 Japan EMail: yosuke.tanaka@ntt.com
Yuji Kamite NTT Communications Corporation Granpark Tower 3-4-1 Shibaura, Minato-ku Tokyo 108-8118 Japan EMail: y.kamite@ntt.com
Zafar Ali Cisco Systems EMail: zali@cisco.com