PCEP extensions for Circuit Style Policies
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|Authors||Samuel Sidor , Zafar Ali , Praveen Maheshwari , Reza Rokui , Andrew Stone , Luay Jalil , Shuping Peng , Tarek Saad , Daniel Voyer|
|Last updated||2023-07-06 (Latest revision 2023-01-09)|
|Stream||Stream state||(No stream defined)|
|RFC Editor Note||(None)|
|IESG||IESG state||I-D Exists|
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PCE Working Group S. Sidor Internet-Draft Z. Ali Intended status: Standards Track Cisco Systems, Inc. Expires: 7 January 2024 P. Maheshwari Airtel India R. Rokui Ciena A. Stone Nokia L. Jalil Verizon S. Peng Huawei Technologies T. Saad Juniper Networks D. Voyer Bell Canada 6 July 2023 PCEP extensions for Circuit Style Policies draft-sidor-pce-circuit-style-pcep-extensions-04 Abstract This document proposes a set of extensions for Path Computation Element Communication Protocol (PCEP) for Circuit Style Policies - Segment-Routing Policy designed to satisfy requirements for connection-oriented transport services. New TLV is introduced to control path recomputation and new flag to add ability to request path with strict hops only. 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. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Sidor, et al. Expires 7 January 2024 [Page 1] Internet-Draft PCEP extensions for CS Policies July 2023 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 7 January 2024. Copyright Notice Copyright (c) 2023 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Overview of Extensions to PCEP . . . . . . . . . . . . . . . 4 3.1. LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . . . 4 3.2. PATH-RECOMPUTATION TLV . . . . . . . . . . . . . . . . . 4 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Strict path enforcement . . . . . . . . . . . . . . . . . 5 4.2. Path recomputation . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6.1. LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . . . 6 6.2. PATH-RECOMPUTATION TLV . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 7.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Sidor, et al. Expires 7 January 2024 [Page 2] Internet-Draft PCEP extensions for CS Policies July 2023 1. Introduction Usage of Segment-routing and PCEP in connection-oriented transport services require path persistancy and hop-by-hop behavior for PCE computed paths. Circuit-Style Policy introduced in [I-D.ietf-spring-cs-sr-policy] requires PCEP extensions, which are covered in this document. This document: * Introduces possibility to request strict path from the PCE by extending LSP-EXTENDED-FLAG TLV * Adding new TLV to encode information about disabling path recomputation for specific path to the PCE, to be carried inside the LSPA object, which is defined in [RFC5440]. * Clarifies usage of existing O-flag from RP object in Segment- routing PCEP extensions described in this document are applicable to RSVP-TE and SR-TE. 2. Terminology The following terminologies are used in this document: ERO: Explicit Route Object IGP: Interior Gateway Protocol LSP: Label Switched Path. LSPA: Label Switched Path Attributes. OTN: Optical Transport Network. PCC: Path Computation Client PCE: Path Computation Element PCEP: Path Computation Element Protocol. SDH: Synchronous Digital Hierarchy SID: Segment Identifier Sidor, et al. Expires 7 January 2024 [Page 3] Internet-Draft PCEP extensions for CS Policies July 2023 SONET: Synchronous Optical Network SR: Segment Routing. SR-TE: Segment Routing Traffic Engineering. 3. Overview of Extensions to PCEP 3.1. LSP-EXTENDED-FLAG TLV O-flag is proposed in the LSP-EXTENDED-FLAG TLV, which was introduced in 3.1 of [RFC9357] and extended with E-flag in [I-D.peng-pce-entropy-label-position]. TLV format will be added after assigning O flag bit position by IANA. Type (16 bits): the value is TBD1 by IANA. Length (16 bits): multiple of 4 octets. O (Strict-Path): If set to 1, this indicates to the PCE that a path exclusively made of strict hops is required. Strict hop definition is described in Section 4.1 3.2. PATH-RECOMPUTATION TLV This document defines new TLV for the LSPA Object for encoding information whether path recomputation is allowed for delegated LSP. The TLV is optional. If the TLV is included in LSPA object, the PCE MUST NOT recompute path in cases specified by flags in the TLV. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = TBD2 | Length = 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags |P|F| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type (16 bits): the value is TBD2 by IANA. Length (16 bits): 4 octets Reserved: MUST be set to zero by the sender and MUST be ignored by the receiver. Flags: This document defines the following flag bits. The other bits MUST be set to zero by the sender and MUST be ignored by the receiver. Sidor, et al. Expires 7 January 2024 [Page 4] Internet-Draft PCEP extensions for CS Policies July 2023 * P (Permanent): If set to 1, the PCE MUST NOT recompute path even if current path is not satisfying path computation constraints. Otherwise, if this flag is cleared, then the PCE MAY recompute path if original path is invalidated. * F (Force): If set to 1, the PCE MUST NOT update path. If flag is cleared, the PCE MAY update path based on explicit request from operator. 4. Operation 4.1. Strict path enforcement PCC MAY set the O flag in LSP-EXTENDED-FLAG TLV in PCRpt message to the PCE to indicate that a path exclusively made of strict hops is required. O flag cleared or LSP-EXTENDED-FLAG TLV not included indicates that a loose path is acceptable. In PCUpdate or PCInitiate messages, PCE MAY set O bit if strict path is provided. The flag is applicable only for stateful messages. Existing O flag in RP object MAY be used to indicate similar behavior in PCReq and PCRep messages as described in as described in Section 7.4.1 of [RFC5440]. If O flag is set to 1 for both stateful and stateless messages for SR paths introduced in [RFC8664], PCE MUST use only SIDs, which will use explicitly specified adjacencies for packet forwarding. For example Adjacency SIDs MAY be used, but Prefix SIDs MUST NOT be used (even if there is only one adjacency). the PCE MUST use Adjacency SIDs only. 4.2. Path recomputation PCC MAY set flags in PATH-RECOMPUTATION TLV to control path computation behavior on PCE side. If TLV is not included, then the PCE MAY use local policy to trigger path-computation or LSP path update. The presence of the TLV is blocking path recomputation based on various triggers like topology update, any periodic update or changed state of other LSPs in the network. LSP path MAY be modified if forwarded packets will still use same path - for example if same path can be encoded using Adjacency and Prefix SIDs, then PCE MAY switch between various representations of same path. Sidor, et al. Expires 7 January 2024 [Page 5] Internet-Draft PCEP extensions for CS Policies July 2023 If P flag is cleared, the PCE MAY recompute if current path is not considered valid, for example after topology update resulting in path not satisfying LSP's path constraints, but it MUST NOT recompute path if current path is not optimal. If P flag is set, the PCE MUST NOT recompute path during LSP lifetime even if path is invalidated. Only exception is explicit request from operator to recompute path If F flag is cleared, path update triggered manually by operator or any northbound interface of PCE MAY be done. If flag is set the PCE CAN update path only to tear down LSP by sending PCUpdate message with empty ERO. TLV MAY be included in PCInitiate and PCUpdate messages to indicate, which triggers will be disabled on the PCE. PCC should reflect flag values in PCRpt messages to forward requirement to other PCEs in the network. 5. Security Considerations No additional security measure is required. 6. IANA Considerations 6.1. LSP-EXTENDED-FLAG TLV [RFC9357] defines the LSP-EXTENDED-FLAG TLV. IANA is requested to make the following assignment from the "LSP-EXTENDED-FLAG TLV Flag Field" registry: +======+======================+===============+ | Bit | Description | Reference | +======+======================+===============+ | TBD1 | Strict-Path Flag (O) | This document | +------+----------------------+---------------+ Table 1 6.2. PATH-RECOMPUTATION TLV IANA is requested to make the assignment of a new value for the existing "PCEP TLV Type Indicators" registry as follows: Sidor, et al. Expires 7 January 2024 [Page 6] Internet-Draft PCEP extensions for CS Policies July 2023 +==========+========================+===============+ | TLV Type | TLV Name | Reference | +==========+========================+===============+ | TBD2 | PATH-RECOMPUTATION TLV | This document | +----------+------------------------+---------------+ Table 2 7. References 7.1. Normative References [I-D.peng-pce-entropy-label-position] Xiong, Q., Peng, S., and F. Qin, "PCEP Extension for SR- MPLS Entropy Label Position", Work in Progress, Internet- Draft, draft-peng-pce-entropy-label-position-09, 5 March 2023, <https://www.ietf.org/archive/id/draft-peng-pce- entropy-label-position-09.txt>. [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>. [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>. [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>. [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, December 2019, <https://www.rfc-editor.org/info/rfc8664>. [RFC9357] Xiong, Q., "Label Switched Path (LSP) Object Flag Extension for Stateful PCE", RFC 9357, February 2023, <https://www.rfc-editor.org/info/rfc9357>. Sidor, et al. Expires 7 January 2024 [Page 7] Internet-Draft PCEP extensions for CS Policies July 2023 7.2. Informative References [I-D.ietf-spring-cs-sr-policy] Schmutzer, C., Ali, Z., Maheshwari, P., Rokui, R., and A. Stone, "Circuit Style Segment Routing Policies", Work in Progress, Internet-Draft, draft-ietf-spring-cs-sr-policy- 00, 16 June 2023, <https://www.ietf.org/archive/id/draft- ietf-spring-cs-sr-policy-00.txt>. [SDH] International Telecommunication Union, "Network node interface for the synchronous digital hierarchy (SDH)", ITU-T Recommendation G.707, October 2020. [SONET] American National Standards Institute, "Synchronous Optical Network (SONET) Basic Description including Multiplex Structure, Rates, and Formats", ANSI T1.105, January 1995. Authors' Addresses Samuel Sidor Cisco Systems, Inc. Eurovea Central 3. Pribinova 10 811 09 Bratislava Slovakia Email: email@example.com Zafar Ali Cisco Systems, Inc. Email: firstname.lastname@example.org Praveen Maheshwari Airtel India Email: Praveen.Maheshwari@airtel.com Reza Rokui Ciena Email: email@example.com Andrew Stone Nokia Email: firstname.lastname@example.org Sidor, et al. Expires 7 January 2024 [Page 8] Internet-Draft PCEP extensions for CS Policies July 2023 Luay Jalil Verizon Email: email@example.com Shuping Peng Huawei Technologies Email: firstname.lastname@example.org Tarek Saad Juniper Networks Email: email@example.com Daniel Voyer Bell Canada Email: firstname.lastname@example.org Sidor, et al. Expires 7 January 2024 [Page 9]