Internet DRAFT - draft-farrel-pce-stateful-flags
draft-farrel-pce-stateful-flags
PCE Working Group A. Farrel
Internet-Draft Old Dog Consulting
Updates: 8231 (if approved) October 31, 2019
Intended status: Standards Track
Expires: May 3, 2020
Updated Rules for Processing Stateful PCE Request Parameters Flags
draft-farrel-pce-stateful-flags-03
Abstract
Extensions to the Path Computation Element Communication 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
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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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 May 3, 2020.
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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Updated Procedures . . . . . . . . . . . . . . . . . . . . . 3
4. Compatibility Considerations . . . . . . . . . . . . . . . . 3
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 4
6. Management Considerations . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
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.
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This document updates RFC 8231 by defining the correct behaviors.
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. Compatibility Considerations
While one of the main objectives of the changes made by this document
is to enable backward compatibility, there remains an issue of
compatibility between existing implementations of RFC 8231 and
implementations that are consistent with this document.
It should be noted that common behavior for flags fields is as
described by the updated text presented in Section 3. Thus, many
implementations, lacking guidance from RFC 8231, will still have
implemented a consistent and future-proof approach. However, for
completeness it is worth noting how behaviors might interact between
implementations.
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 unknown flag
bits and will therefore 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
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[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. Fortunately,
however, most implementations will have been constructed to set
unused flags to zero which is consistent with the behavior described
in this document.
5. Implementation Status
[NOTE TO RFC EDITOR: Please remove this section before publication as
an RFC.]
While this document describes changes to [RFC8231] that are important
for implementation, and while the document gives advice to
implementations, there is nothing specific in this document to
implement.
A private and unscientific poll of implementers of RFC 8231 conducted
by the author suggests that existing implementations already abide by
the modification set out in this document.
6. Management Considerations
Implementations receiving set SRP flags that they do not recognize
MAY log the fact. That could be helpful for diagnosing backward
compatibility issues with future features that utilize those flags.
7. 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 thus reduce the
attack surface.
8. IANA Considerations
IANA maintains a registry called the "Path Computation Element
Protocol (PCEP) Numbers" registry with a subregistry called " SRP
Object Flag Field". IANA is requested to update the Reference in
that subregistry to include a reference to this document in addition
to [RFC8281].
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9. 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. Additional thanks to Hariharan
Ananthakrishnan for his Shepherd's review.
10. References
10.1. 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>.
[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>.
10.2. 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-11 (work
in progress), October 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>.
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[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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