Conveying Vendor-Specific Information in the Path Computation Element (PCE) Communication Protocol (PCEP) extensions for Stateful PCE.

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Table of Contents

1. Introduction

The Path Computation Element Communication Protocol (PCEP) [RFC5440] provides mechanisms for a Path Computation Element (PCE) to perform path computation in response to a Path Computation Client (PCC) request.¶

A Stateful PCE is capable of considering, for the purposes of the path computation, not only the network state in terms of links and nodes (referred to as the Traffic Engineering Database or TED) but also the status of active services (previously computed paths, and currently reserved resources, stored in the Label Switched Paths Database (LSP-DB)). [RFC8051] describes general considerations for a Stateful PCE deployment and examines its applicability and benefits, as well as its challenges and limitations through a number of use cases.¶

[RFC8231] describes a set of extensions to PCEP to provide stateful control. A Stateful PCE has access to not only the information carried by the network's Interior Gateway Protocol (IGP), but also the set of active paths and their reserved resources for its computations. The additional state allows the PCE to compute constrained paths while considering individual LSPs and their interactions. [RFC8281] describes the setup, maintenance, and teardown of PCE-initiated LSPs under the Stateful PCE model. These extensions add new messages in PCEP for Stateful PCE.¶

[RFC7470] defines the Vendor Information object that can be used to carry arbitrary, proprietary information such as vendor-specific constraints in stateless PCEP. It also defines the VENDOR-INFORMATION-TLV that can be used to carry arbitrary information within any existing or future PCEP object that supports TLVs.¶

The Vendor Information Object and the VENDOR-INFORMATION-TLV are also valuable in the Stateful PCE model. The VENDOR-INFORMATION-TLV can be included within any of the new objects introduced in PCEP for Stateful PCE as defined in [RFC7470]. This document extends stateful PCEP messages to incorporate the Vendor Information Object.¶

2. Procedures for the Vendor Information Object

A Path Computation LSP State Report message (also referred to as PCRpt message) [RFC8231] is a PCEP message sent by a PCC to a PCE to report the current state of an LSP. A PCC that wants to convey proprietary or vendor-specific information or metrics to a PCE does so by including a Vendor Information object in the PCRpt message. The contents and format of the object, including the VENDOR-INFORMATION object and the VENDOR-INFORMATION-TLV, are described in Section 4 of [RFC7470]. The PCE determines how to interpret the information in the Vendor Information object by examining the Enterprise Number it contains.¶

The Vendor Information object is OPTIONAL in a PCRpt message. Multiple instances of the object MAY be contained in a single PCRpt message. Different instances of the object MAY have different Enterprise Numbers.¶

The message formats in this document are specified using Routing Backus-Naur Format (RBNF) encoding as specified in [RFC5511].¶

The format of the PCRpt message (with [RFC8231] as the base) is updated as follows:¶

      <PCRpt Message> ::= <Common Header>
                          <state-report-list>
   Where:

      <state-report-list> ::= <state-report>[<state-report-list>]

      <state-report> ::= [<SRP>]
                         <LSP>
                         <path>
                         [<vendor-info-list>]
    Where:
      <vendor-info-list> ::= <VENDOR-INFORMATION>
                             [<vendor-info-list>]

      <path> is defined in [RFC8231].

A Path Computation LSP Update Request message (also referred to as PCUpd message) [RFC8231] is a PCEP message sent by a PCE to a PCC to update the attributes of an LSP. The Vendor Information object can be included in a PCUpd message to convey proprietary or vendor-specific information.¶

The format of the PCUpd message (with [RFC8231] as the base) is updated as follows:¶

      <PCUpd Message> ::= <Common Header>
                          <update-request-list>
   Where:

      <update-request-list> ::= <update-request>
                          [<update-request-list>]

      <update-request> ::= <SRP>
                           <LSP>
                           <path>
                           [<vendor-info-list>]
   Where:
      <vendor-info-list> ::= <VENDOR-INFORMATION>
                             [<vendor-info-list>]

      <path> is defined in [RFC8231].

A Path Computation LSP Initiate Message (also referred to as PCInitiate message) [RFC8281] is a PCEP message sent by a PCE to a PCC to trigger an LSP instantiation or deletion. The Vendor Information object can be included in a PCInitiate message to convey proprietary or vendor-specific information.¶

The format of the PCInitiate message (with [RFC8281] as the base) is updated as follows:¶

     <PCInitiate Message> ::= <Common Header>
                              <PCE-initiated-lsp-list>
  Where:

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

     <PCE-initiated-lsp-request> ::=
                          (<PCE-initiated-lsp-instantiation>|
                           <PCE-initiated-lsp-deletion>)

     <PCE-initiated-lsp-instantiation> ::= <SRP>
                                           <LSP>
                                           [<END-POINTS>]
                                           <ERO>
                                           [<attribute-list>]
                                           [<vendor-info-list>]

     Where:

     <vendor-info-list> ::= <VENDOR-INFORMATION>
                            [<vendor-info-list>]

     <PCE-initiated-lsp-deletion> and <attribute-list> is as per
     [RFC8281].

A legacy implementation that does not recognize the Vendor Information object will act according to the procedures set out in [RFC8231] and [RFC8281]. An implementation that supports the Vendor Information object, but receives one carrying an Enterprise Number that it does not support, MUST ignore the object in the same way as described in [RFC7470].¶

3. Procedures for the Vendor Information TLV

The Vendor Information TLV can be used to carry vendor-specific information that applies to a specific PCEP object by including the TLV in the object. This includes objects used in Stateful PCE extensions such as Stateful PCE Request Parameter (SRP) and LSP objects. All the procedures are as per section 3 of [RFC7470].¶

5. IANA Considerations

There are no IANA actions in this document, only a clarification. [RFC7470] defines the Enterprise Numbers allocated by IANA and managed through an IANA registry [RFC2578]. This document clarifies the Private Enterprise Numbers (PEN) as described in the IANA registry. The registration procedures and the registry location are described by [RFC9371].¶

6. Implementation Status

[NOTE TO RFC EDITOR : This whole section and the reference to RFC 7942 is to be removed before publication as an RFC]¶

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".¶

7. Security Considerations

The protocol extensions defined in this document do not change the nature of PCEP. Therefore, the security considerations set out in [RFC5440], [RFC7470], [RFC8231] and [RFC8281] apply unchanged.¶

As per [RFC8231] it is RECOMMENDED that these PCEP extensions only be activated on authenticated and encrypted sessions across PCEs and PCCs using Transport Layer Security (TLS) [RFC8253], as per the recommendations and best current practices in RFC 9325 [BCP195] (unless explicitly set aside in [RFC8253]).¶

The use of vendor-specific information as defined in [RFC7470] and in this document may provide a covert channel that could be misused by PCEP speaker implementations or by malign software at PCEP speakers. There is little protection against this, however, an operator that monitors the PCEP sessions can determine that vendor-specific information is being used and ask their suppliers (the PCE and PCC implementers) to provide a mechanism to decode the vendor-specific information.¶

8. Acknowledgments

Thanks to Adrian Farrel, Avantika, Mahendra Singh Negi, Udayasree Palle, and Swapna K for their suggestions.¶

Authors' Addresses