PCEP Extensions to support BFD parameters

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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.¶

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 different tunnels path setup types. There are several protocol parameters that need to be configured and exchanged between PCEP speakers. As the parameters are associated to LSPs or 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

 The LSP-SBFD-Capability TLV is an optional TLV.  It MAY be carried
within an OPEN object sent by PCEP speaker in an Open message to a
PCEP peer to indicate it supports SBFD capability.
A legacy PCEP speaker (that does not recognize the
LSP-SBFD-Capability TLV) MUST ignore the TLV in accordance with
[ RFC5440].

 The LSP-SBFD-Capability TLV has the following format:

   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 flag: 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                       //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: TBD2

      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
(milliseconds).
Note: for YANG implementation of the S-BFD information model the value
needs to be converted to microseconds
Multiplier: 1..255

 Procedure

     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

Procedure

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  |
+------------+-------------+----------------------+-----------+
| 23         | 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 [RFC5440], [RFC8231], [RFC8664], [RFC5880] and [RFC8697] in itself.¶

9. Implementation Status [Note to the RFC Editor - remove this section before publication, as well as remove the reference to RFC 7942.]

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.¶

According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".¶

9.1. Ribbon Implementation
       Organization: Ribbon Communication
       Implementation: Head-end (PCC) and controller (PCE).
       Description: All features supported with limitation that LSPs in
   the same association group must have same S-BFD parameter values
       Maturity Level: Production.
       Coverage: Full.
       Contact: marina.fizgeer@rbbn.com

10. Acknowledgement

Would like to thank Avantika Sushil, Alexander Ferdman, Itay Katz, Galina Mintz and Boris Khasanov 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