PCEP Extensions to support LSP parameters

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 5 June 2023.¶

Copyright Notice

Copyright (c) 2022 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

Table of Contents

1. Introduction

Path Computation Element (PCE) Communication Protocol (PCEP) [[RFC5440]] enables the communication between a Path Computation Client (PCC) and a Path Computation Element (PCE), or between two PCEs based on the PCE architecture [[RFC4655]].¶

PCEP Extensions for the Stateful PCE Model [[RFC8231]] describes a set of extensions to PCEP to enable active control of Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS) tunnels. [[RFC8281]] describes the setup and teardown of PCE-initiated LSPs under the active stateful PCE model, without the need for local configuration on the PCC, thus allowing for dynamic centralized control of a network.¶

PCEP Extensions for Segment Routing [[RFC8664]] specifies extensions to the Path Computation Element Protocol (PCEP) that allow a stateful PCE to compute and initiate Traffic Engineering (TE) paths, as well as a PCC to request a path subject to certain constraint(s) and optimization criteria in SR networks.¶

PCEP Extensions for Establishing Relationships Between Sets of LSPs [[RFC8697]] 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 behaviors) and is equally applicable to stateful PCE (active and passive modes) and stateless PCE.¶

Segment Routing Policy for Traffic Engineering details the concepts of SR Policy and approaches to steering traffic into an SR Policy. This document specifies PCEP extensions to signal additional information to configure LSP attributes. This is accomplished via the use of the existing LSPA object, by defining a new capability and new TLVs.¶

2. Terminology

The following terminologies are used in this document:¶

• PCC: Path Computation Client. Any client application requesting a path computation to be performed by a Path Computation Element.¶
• PCE: 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.¶
• PCEP: Path Computation Element Protocol. PCEP Tunnel: The entity identified by the PLSP-ID, as per [I-D.koldychev-pce- operational].¶

3. Motivation

S-BFD protocol is used for detecting failures in SR-TE tunnels. There are several protocol parameters that need to be configured and exchanged between PCEP speakers. As the parameters are associated to SR-TE tunnels, they are exchanged via PCEP. The LSPS-BFD-Capability TLV, the LSP-SBFD TLV and its sub-TLVs, defined in this document, allow PCEP speakers to exchange additional information about S-BFD.¶

4. Overview of Protocol Extensions

      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved                          |B|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: TBD1
Length: 4
B: A PCEP speaker sets this bit to 1 to indicate that it is capable
of S-BFD, and it supports configuring the S-BFD via PCEP

    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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Reserved                          |B|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Optional sub-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              |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Min Tx Interval                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Reserved                 |   Multiplier |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: TBD3
Length: 8
Min Tx Interval: 32 bits - Specify the Minimal Transmit Interval
(microseconds). Default "1000000".
Multiplier: 1..255

     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            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Remote Discriminator                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: TBD4
Length: 4
Remote Discriminator: 32 bits

5. Error Handling

If a PCEP speaker has not received S-BFD-Capability TLV from a peer in the Open object, and it received an LSP S-BFD TLV (see Section 4.3.2.1) from that peer, then it MUST ignore the content of the LSP S-BFD TLV, and it MUST return a PCErr message with Error-Type=19 "Invalid Operation" with Error-value = TBD5 "SBFD capability is not negotiated".¶

If Multiplier value in the LSP-SBFD-Parameters sub-TLV is not in the legal range (1..255), then the PCEP Speaker MUST return a PCErr message with Error-Type=23 "Bad parameter value" and Error-value = TBD6 "Multiplier is out of range".¶

If Remote Discriminator value in the PCEP LSP-SBFD-Discriminator sub-TLV is not in the legal range (i.e., it is zero), then the PCEP Speaker MUST return a PCErr message with Error-Type=23 "Bad parameter value" and Error-value = TBD8 "Remote Discriminator is out of range".¶

6. Implementation Note

In some implementations there is limitation that LSPs in the same association group must have same S-BFD parameter values. If either the Min Tx Interval, the Multiplier or the Remote Discriminator values received in the LSP-BFD Parameters sub-TLVs for LSPs that are members in the same Association Group are not identical, then the PCEP Speaker SHOULD return a PCErr message with Error-Type=26 "Association Error" with Error-value TBD7 "Invalid S-BFD parameter value"¶

7. IANA Considerations

     +=======+================================+===============+
     | Value | Description                    | Reference     |
     +=======+================================+===============+
     | TBD1  | LSP-SBFD-Capability TLV        | This document |
     +-------+--------------------------------+---------------+
     | TBD2  | LSP-SBFD TLV                   | This document |
     +-------+--------------------------------+---------------+
     | TBD3  | LSP-BFD-Parameters sub-TLV     | This document |
     +-------+--------------------------------+---------------+
     | TBD4  | LSP-SBFD-DISCRIMINATOR sub-TLV | This document |
     +-------+--------------------------------+---------------+

This document defines new Error-Values within the different Error-Types.
IANA is requested to allocate new types:</t>
        <figure anchor="ure-2">
          <artwork name="" type="" align="left" alt=""><![CDATA[
 +============+=============+======================+===========+
 | Error Type | Error Value | Meaning              | Reference |
 +============+=============+======================+===========+
 | 19         | TBD5        | SBFD capability is   | This      |
 |            |             | not negotiated       | document  |
 +------------+-------------+----------------------+-----------+
 | 23         | TBD6        | Multiplier is out of | This      |
 |            |             | range                | document  |
 +------------+-------------+----------------------+-----------+
 | 26         | TBD7        | Invalid S-BFD        | This      |
 |            |             | parameter value      | document  |
 +------------+-------------+----------------------+-----------+
 | 26         | TBD8        | Remote Discriminator | This      |
 |            |             | is out of range      | document  |
 +------------+-------------+----------------------+-----------+

8. Security Considerations

This document defines one new type for association, which does
not add any new security concerns beyond those discussed in
[<xref target="RFC5440" format="default"/>],
[<xref target="RFC8231" format="default"/>],
[<xref target="RFC8664" format="default"/>],
[<xref target="RFC5880" format="default"/>] and
[<xref target="RFC8697" format="default"/> ]
in itself.

9. Acknowledgement

Would like to thank Avantika Sushil, Alexander Ferdman, Itay Katz and Galina Mintz for review and suggestions.¶

Appendix A. Contributors

Dhruv Dhody

Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India¶

Email: dhruv.ietf@gmail.com¶

Authors' Addresses