Internet-Draft | PCEP-UPDATE-OPEN | August 2024 |
Stone, et al. | Expires 20 February 2025 | [Page] |
- Workgroup:
- PCE Working Group
- Internet-Draft:
- draft-stone-pce-update-open-00
- Published:
- Intended Status:
- Standards Track
- Expires:
PCE Communication Protocol (PCEP) extensions for updating Open Message content
Abstract
This document describes extensions to the Path Computation Element (PCE) Communication Protocol (PCEP) to permit a PCEP Speaker to update information previously exchanged during PCEP session establishment via the Open message.¶
Discussion Venues
This note is to be removed before publishing as an RFC.¶
Discussion of this document takes place on the Path Computation Element Working Group mailing list (pce@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/pce/.¶
Source for this draft and an issue tracker can be found at https://github.com/astone282/draft-stone-pce-update-open.¶
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 working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any 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 20 February 2025.¶
Copyright Notice
Copyright (c) 2024 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
1. Introduction
The Path Computation Element (PCE) Communication Protocol (PCEP) [RFC5440] provides mechanisms for PCEs to perform path computations in response to requests from Path Computation Clients (PCCs).¶
[RFC5440] outlines the message exchange procedures that PCEP Speakers must follow upon initial connection to establish a PCEP Session. This procedure includes sending an Open Message containing an OPEN Object, which conveys various session characteristics such as protocol timers. The OPEN Object can be extended with TLVs to convey additional session characteristics, such as PCE capabilities (e.g., [RFC8408]) or specific values and ranges (e.g., [RFC8664] and [I-D.ietf-pce-controlled-id-space]). This information is exchanged only once per session and cannot be dynamically modified without tearing down and re-establishing the PCEP session, which can be operationally disruptive.¶
Additionally, [RFC5440] specify a Notification Message (PCNtf) containing a NOTIFICATION Object, which a PCEP Speaker may use to notify the other speaker of an event.¶
This document proposes a generic mechanism allowing a PCEP Speaker (PCC or PCE) to update previously exchanged Open Message information using a PCNtf Message with a new notification called "Open Refresh". This approach mitigates the need to terminate the session to modify any exchanged information.¶
Note that [I-D.ietf-pce-controlled-id-space] also proposes using PCNtf Message to relay Open Messages between PCEs about each PCE's connected peers. It is anticipated that [I-D.ietf-pce-state-sync] will use a similar notification mechanism with a unique notification type, as the semantics of a PCEP Speaker exchanging its information differ from exchanging information related to a connected state-sync PCEs.¶
This document describes a generic extension and mechanism to update Open Object content but future documents MAY describe further semantics on a per TLV basis.¶
1.1. 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.¶
2. Terminology
Open Refresh: The act of modifying content previously exchanged during PCEP Open Message in an ad-hoc manner without terminating the PCEP session.¶
Open Refresh Notification message: An Open Refresh notification message is a new Notification Type to be used in the PCNtf Message ([RFC5440]) that will also contain the open information to be refreshed.¶
3. Operational Considerations
This section discusses some high-level considerations that should be considered when supporting Open Refresh. While scenarios described here exist in present-day PCEP, they require explicitly tearing down the PCEP session which gives a clear indication of potential system impact. With ad-hoc manipulation of open information, the impact of a possible change may not be evident so this section attempts to describe some of these considerations.¶
3.1. Capability Change
One use case of the Open message is to exchange device software capabilities and feature enablement to determine whether a PCEP Speaker may support a given operation defined in PCEP extensions. If a PCEP speaker supports removal of a capability using Open Refresh, then all states related to the capability MUST be reset and removed and MUST follow the guidelines set out by the capability should the other PCEP speaker no longer support the capability. This may impact device-wide state and network traffic. For example, [RFC8281] defines the STATEFUL-PCE-CAPABILITY-TLV to indicate support for PCE-Initiated LSPs. The removal of this capability would result in PCE-Initiated LSPs being deleted from each PCEP Speaker.¶
3.2. Node-wide Property Change
One use case of the Open message is to exchange device-level configurations or settings. In the case of statefully delegated LSPs ([RFC8231], the modification of these values may trigger path calculations for established LSPs with a possibility of LSP tear down.¶
3.3. Frequency of Open Refresh
A PCEP implementation should consider the impact on the entire network before sending frequent Open Refresh Notifications. It could consider applying some form of dampening or back-off mechanism.¶
4. Procedures
4.1. Capability Advertisement
A PCEP Speaker indicates support of Open Refresh during the PCEP Initialization phase ([RFC5440]). As per [RFC5440], a PCEP Speaker sends an Open Message with exactly one OPEN object. This document defines a new flag, OPEN-REFRESH-CAPABILITY (R-bit), in the Open Message Flags field to indicate the support of the Open Refresh feature.¶
-
R (OPEN-REFRESH-CAPABILITY - 1 bit - TBD1): If set to 1 by a PCEP speaker, the PCEP speaker indicates that the PCEP speaker supports updating the information in the Open message without resetting the session.¶
If a PCEP speaker receives an Open Message that does not set the OPEN-REFRESH-CAPABILITY flag, the PCEP Speaker MUST NOT send Open Refresh messages to the remote PCEP speaker.¶
4.2. Open Refresh
An Open Refresh is transmitted by sending a PCNtf Message ([RFC5440]) containing a NOTIFICATION Object with Notification-type=TBD2 (Open-Refresh):¶
-
Notification-value=1: Refresh the Open information. The NOTIFICATION Object encodes any TLV that can be encoded in an OPEN Object. The NOTIFICATION Object contains a snapshot of all unmodified and modified TLVs. Upon receiving an Open-Refresh Notification message, the PCEP Speaker compares the newly received TLVs with the previously received TLVs to determine what has changed. An omission of a TLV MUST be treated as a removal of the TLV and perform a necessary side effect(s) to the system state as if the TLV was never exchanged during session establishment via Open message.¶
4.2.1. Adding/removing values or Sub-TLVs
If the PCEP Speaker determines it cannot support the Open-Refresh differential change(s), the PCEP Speaker generates a PCEP Error (PCErr) with Error-type=TBD3 (Unsupported-Open-Refresh) and error-value TBD4 and it SHOULD terminate the PCEP session.¶
5. Security Considerations
TODO Security¶
7. Implementation Status
[Note to the RFC Editor - remove this section before publication, as well as remove the reference to RFC 7942.]¶
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".¶
8. IANA Considerations
8.1. Open Object Flag Field
IANA is requested to allocate a new bit value in the "Open Object Flag Field" registry:¶
Bit | Description | Reference |
---|---|---|
TBD1 | OPEN-REFRESH-CAPABILITY | This document |
8.2. NOTIFICATION Object
IANA is requested to allocate a new Notification-type value in the "Notification Object" registry:¶
Notification-type | Name | Reference |
---|---|---|
TBD2 | Open-Refresh | This document |
Notification-value | ||
1: Refresh the Open information |
8.3. PCEP Error
IANA is requested to allocate a new Error-type value in the "PCEP-ERROR Object Error Types and Values" registry:¶
Error-type | Meaning | Error-value | Reference |
---|---|---|---|
TBD3 | Open-Refresh Error | 1: Open-Refresh is not supported | This document |
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, , <https://www.rfc-editor.org/rfc/rfc2119>.
- [RFC5440]
- Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, , <https://www.rfc-editor.org/rfc/rfc5440>.
- [RFC8174]
- Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
9.2. Informative References
- [I-D.ietf-pce-controlled-id-space]
- Li, C., Shi, H., Wang, A., Cheng, W., and C. Zhou, "Path Computation Element Communication Protocol (PCEP) extension to advertise the PCE Controlled Identifier Space", Work in Progress, Internet-Draft, draft-ietf-pce-controlled-id-space-00, , <https://datatracker.ietf.org/doc/html/draft-ietf-pce-controlled-id-space-00>.
- [I-D.ietf-pce-state-sync]
- Litkowski, S., Sivabalan, S., Li, C., and H. Zheng, "Inter Stateful Path Computation Element (PCE) Communication Procedures.", Work in Progress, Internet-Draft, draft-ietf-pce-state-sync-07, , <https://datatracker.ietf.org/doc/html/draft-ietf-pce-state-sync-07>.
- [RFC7942]
- Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, , <https://www.rfc-editor.org/rfc/rfc7942>.
- [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, , <https://www.rfc-editor.org/rfc/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, , <https://www.rfc-editor.org/rfc/rfc8281>.
- [RFC8408]
- Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J. Hardwick, "Conveying Path Setup Type in PCE Communication Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408, , <https://www.rfc-editor.org/rfc/rfc8408>.
- [RFC8664]
- Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., and J. Hardwick, "Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing", RFC 8664, DOI 10.17487/RFC8664, , <https://www.rfc-editor.org/rfc/rfc8664>.
Acknowledgments
The authors would like to acknowledge Dhruv Dhody for the discussion and ideas related to this document.¶