draft-ietf-pce-stateful-flags-01.txt   rfc8786.txt 
PCE Working Group A. Farrel Internet Engineering Task Force (IETF) A. Farrel
Internet-Draft Old Dog Consulting Request for Comments: 8786 Old Dog Consulting
Updates: 8231 (if approved) January 23, 2020 Updates: 8231 May 2020
Intended status: Standards Track Category: Standards Track
Expires: July 26, 2020 ISSN: 2070-1721
Updated Rules for Processing Stateful PCE Request Parameters Flags Updated Rules for Processing Stateful PCE Request Parameters Flags
draft-ietf-pce-stateful-flags-01
Abstract Abstract
Extensions to the Path Computation Element Communication Protocol Extensions to the Path Computation Element Communication Protocol
(PCEP) to support stateful Path Computation Elements (PCEs) are (PCEP) to support stateful Path Computation Elements (PCEs) are
defined in RFC 8231. One of the extensions is the Stateful PCE defined in RFC 8231. One of the extensions is the Stateful PCE
Request Parameters (SRP) object. That object includes a Flags field 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 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 for tracking assigned flags. However, RFC 8231 does not explain how
an implementation should set unassigned flags in transmitted an implementation should set unassigned flags in transmitted
messages, nor how an implementation should process unassigned, messages, nor how an implementation should process unassigned,
unknown, or unsupported flags in received messages. unknown, or unsupported flags in received messages.
This document updates RFC 8231 by defining the correct behaviors. This document updates RFC 8231 by defining the correct behaviors.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on July 26, 2020. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8786.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language
3. Updated Procedures . . . . . . . . . . . . . . . . . . . . . 3 3. Updated Procedures
3.1. Advice for Specification of New Flags . . . . . . . . . . 3 3.1. Advice for Specification of New Flags
3.2. Flags Field of the SRP Object . . . . . . . . . . . . . . 4 3.2. Flags Field of the SRP Object
4. Compatibility Considerations . . . . . . . . . . . . . . . . 4 4. Compatibility Considerations
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 5 5. Management Considerations
6. Management Considerations . . . . . . . . . . . . . . . . . . 5 6. Security Considerations
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. References
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.2. Informative References
10.1. Normative References . . . . . . . . . . . . . . . . . . 6 Acknowledgements
10.2. Informative References . . . . . . . . . . . . . . . . . 6 Author's Address
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
[RFC5440] describes the Path Computation Element Communication [RFC5440] describes the Path Computation Element Communication
Protocol (PCEP). PCEP defines the communication between a Path Protocol (PCEP). PCEP defines the communication between a Path
Computation Client (PCC) and a Path Computation Element (PCE), or Computation Client (PCC) and a Path Computation Element (PCE), or
between PCEs, enabling computation of Multiprotocol Label Switching between PCEs, enabling computation of Multiprotocol Label Switching
(MPLS) for Traffic Engineering Label Switched Path (TE LSP) (MPLS) for Traffic Engineering Label Switched Path (TE LSP)
characteristics. characteristics.
skipping to change at page 3, line 18 skipping to change at line 105
specifications about how to describe the interaction between flags specifications about how to describe the interaction between flags
that have already been defined and flags being defined in the new that have already been defined and flags being defined in the new
specifications. specifications.
This document updates RFC 8231 by defining the correct behaviors. This document updates RFC 8231 by defining the correct behaviors.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Updated Procedures 3. Updated Procedures
3.1. Advice for Specification of New Flags 3.1. Advice for Specification of New Flags
Section 7 of [RFC8231] introduces changes to existing PCEP objects Section 7 of [RFC8231] introduces changes to existing PCEP objects
and the definition of new PCEP objects and TLVs in support of and defines new PCEP objects and TLVs in support of stateful PCE
stateful PCE functionality. That text does not advise future functionality. That text does not advise future specifications on
specifications how to describe the interaction between flags that may how to describe the interaction between flags that may be defined.
be defined.
The text in Section 7 is updated to read as follows: The text in Section 7 of [RFC8231] is updated to read as follows:
The PCEP objects defined in this document are compliant with the The PCEP objects defined in this document are compliant with the
PCEP object format defined in [RFC5440]. The P and I flags of the PCEP object format defined in [RFC5440]. The P and I flags of the
PCEP objects defined in the current document MUST be set to 0 on PCEP objects defined in the current document MUST be set to 0 on
transmission and SHOULD be ignored on receipt since they are transmission and SHOULD be ignored on receipt since they are
exclusively related to path computation requests. exclusively related to path computation requests.
The sections that follow define PCEP objects and TLVs that contain The sections that follow define PCEP objects and TLVs that contain
flags fields, and some flag values are defined. Future Flags fields, and some flag values are defined. Future
specifications may define further flags, and each new specifications may define further flags, and each new
specification that defines additional flags is expected to specification that defines additional flags is expected to
describe the interaction between these new flags and any existing describe the interaction between these new flags and any existing
flags. In particular, new specifications are expected to explain flags. In particular, new specifications are expected to explain
how to handle the cases when both new and pre-existing flags are how to handle the cases when both new and pre-existing flags are
set. set.
3.2. Flags Field of the SRP Object 3.2. Flags Field of the SRP Object
Section 7.2 of [RFC8231] defines the PCEP SRP object. It describes Section 7.2 of [RFC8231] defines the PCEP SRP object. It describes
the flags field as: the Flags field as:
Flags (32 bits): None defined yet. Flags (32 bits): None defined yet.
This document updates that text as follows: This document updates that text as follows:
Flags (32 bits): This document does not define any flags. Flags (32 bits): This document does not define any flags.
Unassigned flags MUST be set to zero on transmission and MUST be Unassigned flags MUST be set to zero on transmission and MUST be
ignored on receipt. Implementations that do not understand any ignored on receipt. Implementations that do not understand any
particular flag MUST ignore the flag. particular flag MUST ignore the flag.
4. Compatibility Considerations 4. Compatibility Considerations
While one of the main objectives of the changes made by this document While one of the main objectives of the changes made by this document
is to enable backward compatibility, there remains an issue of is to enable backward compatibility, there remains an issue of
compatibility between existing implementations of RFC 8231 and compatibility between existing implementations of RFC 8231 and
implementations that are consistent with this document. implementations that are consistent with this document.
It should be noted that common behavior for flags fields is as It should be noted that common behavior for Flags fields is as
described by the updated text presented in Section 3. Thus, many described by the updated text presented in Section 3. Thus, many
implementations, lacking guidance from RFC 8231, will still have implementations, lacking guidance from RFC 8231, will still have
implemented a consistent and future-proof approach. However, for implemented a consistent and future-proof approach. However, for
completeness it is worth noting how behaviors might interact between completeness, it is worth noting how behaviors might interact between
implementations. implementations.
SRP objects generated by an implementation of this document will set SRP objects generated by an implementation of this document will set
all unknown flag bits to zero and will therefore cause no issues to all unknown flag bits to zero and will therefore cause no issues to
an older implementation even if it inspects those bits. Similarly, an older implementation even if it inspects those bits. Similarly,
an implementation of this document will not inspect any unknown flag an implementation of this document will not inspect any unknown flag
bits and will therefore be unaffected by older implementations no bits and will therefore be unaffected by older implementations no
matter how they set the flags. matter how they set the flags.
There will remain an issue with compatibility between implementations There will remain an issue with compatibility between implementations
of RFC 8231 that might set any of the unassigned flags, and current and how they set the flags. An implementation of RFC 8231 might set
(such as [RFC8281]) and future (such as any of the unassigned flags, but an implementation of a future or
[I-D.ietf-pce-lsp-control-request]) specifications that assign current specification (such as [RFC8281] or [RFC8741]) assigns
specific meanings to flags if set. That problem cannot be fixed in specific meanings to a flag if set. That problem cannot be fixed in
old implementations by any amount of documentation, and can only be old implementations by any amount of documentation and can only be
handled for future specifications by obsoleting the Flags field and handled for future specifications by obsoleting the Flags field and
using a new technique. Fortunately, however, most implementations using a new technique. Fortunately, however, most implementations
will have been constructed to set unused flags to zero which is will have been constructed to set unused flags to zero, which is
consistent with the behavior described in this document and so the consistent with the behavior described in this document, and so the
risk of bad interactions is sufficiently small that there is no need risk of bad interactions is sufficiently small that there is no need
to obsolete the existing Flags field. to obsolete the existing Flags field.
5. Implementation Status 5. Management Considerations
[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 Implementations receiving set SRP flags that they do not recognize
MAY log this. That could be helpful for diagnosing backward MAY log this. That could be helpful for diagnosing backward
compatibility issues with future features that utilize those flags. compatibility issues with future features that utilize those flags.
7. Security Considerations 6. Security Considerations
[RFC8231] sets out security considerations for PCEP when used for [RFC8231] sets out security considerations for PCEP when used for
communication with a stateful PCE. This document does not change communication with a stateful PCE. This document does not change
those considerations. those considerations.
However, by defining the expected behavior of implementations, this However, by defining the expected behavior of implementations, this
document may improve the stability of networks and thus reduce the document may improve the stability of networks and thus reduce the
attack surface. That is, by reminding implementations to ignore attack surface. That is, by reminding implementations to ignore
unset bits, it is less possible to attack them by randomly tweaking unset bits, it is less possible to attack them by randomly tweaking
bits. Furthermore, by reminding implementations to leave undefined bits. Furthermore, by reminding implementations to leave undefined
bits unset, the network is future-proofed against new definitions of bits unset, the network is future-proofed against new definitions of
previously undefined bits. previously undefined bits.
8. IANA Considerations 7. IANA Considerations
IANA maintains a registry called the "Path Computation Element IANA maintains a registry called the "Path Computation Element
Protocol (PCEP) Numbers" registry with a subregistry called " SRP Protocol (PCEP) Numbers" registry with a subregistry called "SRP
Object Flag Field". IANA is requested to update the Reference in Object Flag Field". IANA has updated the reference for that
that subregistry to include a reference to this document in addition subregistry to list this document in addition to [RFC8281].
to [RFC8281].
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. Thanks to Benjamin Kaduk
and Alvaro Retana for helpful comments during IESG review.
10. References 8. References
10.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
skipping to change at page 6, line 32 skipping to change at line 235
Extensions for Stateful PCE", RFC 8231, Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017, DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>. <https://www.rfc-editor.org/info/rfc8231>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP) Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>. <https://www.rfc-editor.org/info/rfc8281>.
10.2. Informative References 8.2. 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 [RFC4657] Ash, J., Ed. and J.L. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <https://www.rfc-editor.org/info/rfc4657>. 2006, <https://www.rfc-editor.org/info/rfc4657>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440, Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009, DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>. <https://www.rfc-editor.org/info/rfc5440>.
[RFC8741] 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)", RFC 8741, DOI 10.17487/RFC8741, March 2020,
<https://www.rfc-editor.org/info/rfc8741>.
Acknowledgements
Thanks to the authors of [RFC8741] 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. Thanks to Benjamin Kaduk and Alvaro Retana for
helpful comments during IESG review.
Author's Address Author's Address
Adrian Farrel Adrian Farrel
Old Dog Consulting Old Dog Consulting
Email: adrian@olddog.co.uk Email: adrian@olddog.co.uk
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