Updated Rules for Processing Stateful PCE Request Parameters Flags
draft-farrel-pce-stateful-flags-00

PCE Working Group                                              A. Farrel
Internet-Draft                                        Old Dog Consulting
Updates: 8231 (if approved)                                June 24, 2019
Intended status: Standards Track
Expires: December 26, 2019

   Updated Rules for Processing Stateful PCE Request Parameters Flags
                   draft-farrel-pce-stateful-flags-00

Abstract

   Extensions to the Path Computation Element communications Protocol
   (PCEP) to support stateful Path Computation Elements (PCEs) are
   defined in RFC 8231.  One of the extensions is the Stateful PCE
   Request Parameters (SRP) object.  That object includes a Flags field
   that is a set of 32 bit flags, and RFC 8281 defines an IANA registry
   for tracking assigned flags.  However, RFC 8231 does not explain how
   an implementation should set unassigned flags in transmitted
   messages, nor how an implementation should process unassigned,
   unknown, or unsupported flags in received messages.

   This document updates RFC 8231 by defining the correct behaviors.

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
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   This Internet-Draft will expire on December 26, 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

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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Updated Procedures  . . . . . . . . . . . . . . . . . . . . .   3
   4.  Compatibliity Considerations  . . . . . . . . . . . . . . . .   3
   5.  Management Considerations . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   [RFC5440] describes the Path Computation Element Communication
   Protocol (PCEP).  PCEP defines the communication between a Path
   Computation Client (PCC) and a Path Computation Element (PCE), or
   between PCEs, enabling computation of Multiprotocol Label Switching
   (MPLS) for Traffic Engineering Label Switched Path (TE LSP)
   characteristics.

   [RFC8231] specifies a set of extensions to PCEP to enable stateful
   control of LSPs within and across PCEP sessions in compliance with
   [RFC4657].  It includes mechanisms to effect Label Switched Path
   (LSP) State Synchronization between PCCs and PCEs, delegation of
   control over LSPs to PCEs, and PCE control of timing and sequence of
   path computations within and across PCEP sessions.

   One of the extensions defined in [RFC8231] is the Stateful PCE
   Request Parameters (SRP) object.  That object includes a Flags field
   that is a set of 32 bit flags, and RFC 8281 defines an IANA registry
   for tracking assigned flags.  However, RFC 8231 does not explain how
   an implementation should set unassigned flags in transmitted
   messages, nor how an implementation should process unassigned or
   unknown flags in received messages.

   This document updates RFC 8231 by defining the correct behaviors.

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2.  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.

3.  Updated Procedures

   Section 7.2 of [RFC8231] defines the PCEP SRP object.  It describes
   the flags field as:

      Flags (32 bits): None defined yet.

   This document updates that text as follows:

      Flags (32 bits): This document does not define any flags.
      Unassigned flags MUST be set to zero on transmission and MUST be
      ignored on receipt.  Implementations that do not understand any
      particular flag MUST ignore the flag.

4.  Compatibliity Considerations

   While one of the main objectives of the changes made by this document
   is to enable backward compatibility, there remains an issue of
   compatiblity between existing implementations of RFC 8231 and
   implementations that are consistent with this document.

   SRP objects generated by an implementation of this document will set
   all unknown flag bits to zero and will therefore cause no issues to
   an older implementation even if it inspects those bits.  Similarly,
   an implementation of this document will not inspect any unknow flag
   bits and so will be unaffected by older implementations no matter how
   they set the flags.

   There will remain an issue with compatibility between implementations
   of RFC 8231 that might set any of the unassigned flags, and current
   (such as [RFC8281]) and future (such as
   [I-D.ietf-pce-lsp-control-request]) specifications.  That problem
   cannot be fixed in old implementations by any amount of
   documentation, and can only be handled for future specifications by
   obsoleting the Flags field and using a new technique.  Fortunatley,
   however, most implementations will have been constructed to set
   unused flags to zero which is consistent with the behavior described
   in this document.

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5.  Management Considerations

   Implementations receiving set SRP flags that they do not recognize
   MAY log the fact.  That could be helpful for diagnosing backward
   compatiblity issues with future features that utilise those flags.

6.  Security Considerations

   [RFC8231] sets out security considerations for PCEP when used for
   communication with a stateful PCE.  This document does not change
   those considerations.

   However, by defining the expected behavior of implementations, this
   document may improve the stability of networks and so reduce the
   attack surface.

7.  IANA Considerations

   This document makes no requests for IANA action.

8.  Acknowledgements

   Thanks to the authors of [I-D.ietf-pce-lsp-control-request] for
   exposing the need for this work.  Thanks to Dhruv Dhody and Julien
   Meuric for discussing the solution.

9.  References

9.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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,
              <https://www.rfc-editor.org/info/rfc8231>.

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   [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,
              <https://www.rfc-editor.org/info/rfc8281>.

9.2.  Informative References

   [I-D.ietf-pce-lsp-control-request]
              Raghuram, A., Goddard, A., Karthik, J., Sivabalan, S., and
              M. Negi, "Ability for a stateful Path Computation Element
              (PCE) to request and obtain control of a Label Switched
              Path (LSP)", draft-ietf-pce-lsp-control-request-05 (work
              in progress), June 2019.

   [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

Author's Address

   Adrian Farrel
   Old Dog Consulting

   Email: adrian@olddog.co.uk

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