< draft-ietf-pce-stateful-flags-00.txt   draft-ietf-pce-stateful-flags-01.txt >
PCE Working Group A. Farrel PCE Working Group A. Farrel
Internet-Draft Old Dog Consulting Internet-Draft Old Dog Consulting
Updates: 8231 (if approved) November 7, 2019 Updates: 8231 (if approved) January 23, 2020
Intended status: Standards Track Intended status: Standards Track
Expires: May 10, 2020 Expires: July 26, 2020
Updated Rules for Processing Stateful PCE Request Parameters Flags Updated Rules for Processing Stateful PCE Request Parameters Flags
draft-ietf-pce-stateful-flags-00 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
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Copyright Notice Copyright Notice
Copyright (c) 2019 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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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Updated Procedures . . . . . . . . . . . . . . . . . . . . . 3 3. Updated Procedures . . . . . . . . . . . . . . . . . . . . . 3
4. Compatibility Considerations . . . . . . . . . . . . . . . . 3 3.1. Advice for Specification of New Flags . . . . . . . . . . 3
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 4 3.2. Flags Field of the SRP Object . . . . . . . . . . . . . . 4
6. Management Considerations . . . . . . . . . . . . . . . . . . 4 4. Compatibility Considerations . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. Management Considerations . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 5 10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 5 10.2. Informative References . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 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.
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path computations within and across PCEP sessions. path computations within and across PCEP sessions.
One of the extensions defined in [RFC8231] is the Stateful PCE One of the extensions defined in [RFC8231] 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 or messages, nor how an implementation should process unassigned or
unknown flags in received messages. unknown flags in received messages.
Furthermore, [RFC8231] gives no guidance to the authors of future
specifications about how to describe the interaction between flags
that have already been defined and flags being defined in the new
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 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
Section 7 of [RFC8231] introduces changes to existing PCEP objects
and the definition of new PCEP objects and TLVs in support of
stateful PCE functionality. That text does not advise future
specifications how to describe the interaction between flags that may
be defined.
The text in Section 7 is updated to read as follows:
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 objects defined in the current document MUST be set to 0 on
transmission and SHOULD be ignored on receipt since they are
exclusively related to path computation requests.
The sections that follow define PCEP objects and TLVs that contain
flags fields, and some flag values are defined. Future
specifications may define further flags, and each new
specification that defines additional flags is expected to
describe the interaction between these new flags and any existing
flags. In particular, new specifications are expected to explain
how to handle the cases when both new and pre-existing flags are
set.
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
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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 of RFC 8231 that might set any of the unassigned flags, and current
(such as [RFC8281]) and future (such as (such as [RFC8281]) and future (such as
[I-D.ietf-pce-lsp-control-request]) specifications that assign
[I-D.ietf-pce-lsp-control-request]) specifications. That problem specific meanings to flags if set. That problem cannot be fixed in
cannot be fixed in old implementations by any amount of old implementations by any amount of documentation, and can only be
documentation, and can only be handled for future specifications by handled for future specifications by obsoleting the Flags field and
obsoleting the Flags field and using a new technique. Fortunately, using a new technique. Fortunately, however, most implementations
however, most implementations will have been constructed to set will have been constructed to set unused flags to zero which is
unused flags to zero which is consistent with the behavior described consistent with the behavior described in this document and so the
in this document. risk of bad interactions is sufficiently small that there is no need
to obsolete the existing Flags field.
5. Implementation Status 5. Implementation Status
[NOTE TO RFC EDITOR: Please remove this section before publication as [NOTE TO RFC EDITOR: Please remove this section before publication as
an RFC.] an RFC.]
While this document describes changes to [RFC8231] that are important While this document describes changes to [RFC8231] that are important
for implementation, and while the document gives advice to for implementation, and while the document gives advice to
implementations, there is nothing specific in this document to implementations, there is nothing specific in this document to
implement. implement.
A private and unscientific poll of implementers of RFC 8231 conducted A private and unscientific poll of implementers of RFC 8231 conducted
by the author suggests that existing implementations already abide by by the author suggests that existing implementations already abide by
the modification set out in this document. the modification set out in this document.
6. Management Considerations 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 the fact. 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 7. 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. attack surface. That is, by reminding implementations to ignore
unset bits, it is less possible to attack them by randomly tweaking
bits. Furthermore, by reminding implementations to leave undefined
bits unset, the network is future-proofed against new definitions of
previously undefined bits.
8. IANA Considerations 8. 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 is requested to update the Reference in
that subregistry to include a reference to this document in addition that subregistry to include a reference to this document in addition
to [RFC8281]. to [RFC8281].
9. Acknowledgements 9. Acknowledgements
Thanks to the authors of [I-D.ietf-pce-lsp-control-request] for 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 exposing the need for this work. Thanks to Dhruv Dhody and Julien
Meuric for discussing the solution. Additional thanks to Hariharan Meuric for discussing the solution. Additional thanks to Hariharan
Ananthakrishnan for his Shepherd's review. Ananthakrishnan for his Shepherd's review. Thanks to Benjamin Kaduk
and Alvaro Retana for helpful comments during IESG review.
10. References 10. References
10.1. Normative References 10.1. 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>.
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