PCE Q. Xiong Internet-Draft S. Peng Intended status: Standards Track ZTE Corporation Expires: 3 March 2023 F. Qin China Mobile August 2022 PCEP Extension for SR-MPLS Entropy Label Position draft-peng-pce-entropy-label-position-08 Abstract This document proposes a set of extensions for PCEP to configure the entropy label position for SR-MPLS networks. 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 2 February 2023. Copyright Notice Copyright (c) 2022 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. Xiong, et al. Expires 3 March 2023 [Page 1] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions used in this document . . . . . . . . . . . . . . 3 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 3. Entropy Labels in SR-MPLS Scenario with PCE . . . . . . . . . 3 4. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 5 4.2. The LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . . 5 4.3. The SR-ERO Object . . . . . . . . . . . . . . . . . . . . 5 5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8.1. New SR PCE Capability Flag Registry . . . . . . . . . . . 6 8.2. New LSP-EXTENDED-FLAG Flag Registry . . . . . . . . . . . 6 8.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction [RFC5440] describes the Path Computation Element Protocol (PCEP) which is used between a Path Computation Element (PCE) and a Path Computation Client (PCC) (or other PCE) to enable computation of Multi-protocol Label Switching (MPLS) for Traffic Engineering Label Switched Path (TE LSP). PCEP Extensions for the Stateful PCE Model [RFC8231] describes a set of extensions to PCEP to enable active control of MPLS-TE and Generalized MPLS (GMPLS) tunnels. [RFC8281] describes the setup and teardown of PCE-initiated LSPs under the active stateful PCE model, without the need for local configuration on the PCC, thus allowing for dynamic centralized control of a network. Segment Routing (SR) leverages the source routing paradigm. Segment Routing can be instantiated on MPLS data plane which is referred to as SR-MPLS [RFC8660]. SR-MPLS leverages the MPLS label stack to construct the SR path. PCEP Extensions for Segment Routing [RFC8664] specifies extensions to the PCEP that allow a stateful PCE to compute and initiate TE paths, as well as a PCC to request a path subject to certain constraint(s) and optimization criteria in SR networks. Entropy label (EL) [RFC6790] is a technique used in the MPLS data plane to improve load-balancing. Entropy Label Indicator (ELI) can be immediately preceding an EL in the MPLS label stack. The idea Xiong, et al. Expires 3 March 2023 [Page 2] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 behind the EL is that the ingress router computes a hash based on several fields from a given packet and places the result in an additional label, named "entropy label". Then, this entropy label can be used as part of the hash keys used by an LSR. Using the entropy label as part of the hash keys reduces the need for deep packet inspection in the LSR while keeping a good level of entropy in the load-balancing. When the entropy label is used, the keys used in the hashing functions are still a local configuration matter and an LSR may use solely the entropy label or a combination of multiple fields from the incoming packet. [RFC8662] proposes to use entropy labels for SR-MPLS networks and mutiple pairs SHOULD be inserted in the SR-MPLS label stack. The ingress node may decide the number and place of the ELI/ ELs which need to be inserted into the label stack. The extensions for Border Gateway Protocol (BGP) to indicate the entropy label position in the SR-MPLS label stack has been proposed in [I-D.zhou-idr-bgp-srmpls-elp]. In some cases, the the controller(e.g. PCE) could be used to perform the TE path computation as well as the Entropy Label Position (ELP) which is useful for inter-domain scenarios. This document proposes a set of extensions for PCEP to configure the ELP information for SR- MPLS networks. 2. Conventions used in this document 2.1. Terminology The terminology is defined as [RFC5440], [RFC6790], [RFC8664] and [RFC8662]. 2.2. 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. Entropy Labels in SR-MPLS Scenario with PCE [RFC8662] proposes to use entropy labels for SR-MPLS networks. The Entropy Readable Label Depth (ERLD) is defined as the number of labels which means that the router will perform load-balancing using the ELI/EL. An appropriate algorithm should consider the following criteria: Xiong, et al. Expires 3 March 2023 [Page 3] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 * a limited number of pairs SHOULD be inserted in the SR- MPLS label stack; * the inserted positions SHOULD be whithin the ERLD of a maximize number of transit LSRs; * a minimum number of pairs SHOULD be inserted while satisfying the above criteria. As described in [RFC8662] section 7, the ERLD value is important for inserting ELI/EL and the ingress node need to evaluate the minimum ERLD value along the node segment path. But it will add complexity in the ELI/EL insertion process. Moreover, the ingress node cannot find the minimum ERLD along the path and does not support the computation of the minimum ERLD especilly in inter-domain scenarios. As the Figure 1 shown, in SR-MPLS inter-domain scenario, the ingress node of the first domain could not get the ERLD information of other nodes of other domains. +-----+ +-----+ +-----+ |PCE-1| |PCE-2| |PCE-3| +--+--+ +--+--+ +--+--+ | | | .........+.......... .........+.......... .........+........... . . . . . . .+---+ +---+ . . +---+ +---+ . .+---+ +----+ . .| A |-------| B |------ | C |------| X |-------| Y |------| Z | . .+---+ +---+ . . +---+ +---+ . .+---+ +----+ . . SR-AS 1 . . SR-AS 2 . . SR-AS 3 . .................... .................... ..................... Figure 1: Entropy Labels in SR-MPLS Inter-Domain Scenario The PCEs could get the information of all nodes such as Maximum SID Depth (MSD) and ERLD through Interior Gateway Protocol (IGP) and can compute the minimum ERLD along the end-to-end path. For example, the ERLD value can be collected via IS-IS [I-D.ietf-isis-mpls-elc], and OSPF [I-D.ietf-ospf-mpls-elc]. IS-IS [RFC8491] and OSPF [RFC8476] provide examples of advertisement of the MSD. Moreover, the PCEs also can compute the Entropy Label Position (ELP) including the number and the places of the ELI/ELs. Then the ingress nodes MAY be required to support the capabilities of inserting multiple ELI/ELs and need to advertise the capabilities to the PCEs. Xiong, et al. Expires 3 March 2023 [Page 4] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 This document proposes the extensions for PCE to perform the computation of the end-to-end path as well as the positions of entropy labels in SR-MPLS networks. The ingress nodes can directly insert the ELI/ELs based on the positions. 4. PCEP Extensions 4.1. The OPEN Object As defined in [RFC8664], PCEP speakers use SR PCE Capability sub-TLV to exchange information about their SR capability when PST=1 in the PST List of the PATH-SETUP-TYPE-CAPABILITY TLV carried in Open object. This document defined a new flag (E-flag) for SR PCE Capability sub-TLV. E (Entropy Label Configuration is supported) : A PCE sets this flag bit to 1 carried in Open message to indicate that it supports the computation of SR path with ELP information. A PCC sets this flag to 1 to indicate that it supports the capability of inserting multiple ELI/EL pairs and and supports the results of SR path with ELP from PCE. 4.2. The LSP-EXTENDED-FLAG TLV The LSP Object is defined in Section 7.3 of [RFC8231]. This document defiend a new flag (E-flag) for the LSP-EXTENDED-FLAG TLV carried in LSP Object as defined in [I-D.ietf-pce-lsp-extended-flags]. E (Request for ELP Configuration) : If the bit is set to 1, it indicates that the PCC requests PCE to compute the SR path with ELP information. A PCE would also set this bit to 1 to indicate that the ELP information is included by PCE and encoded in the PCRep, PCUpd or PCInitiate message. 4.3. The SR-ERO Object SR-ERO subobject is used for SR-TE path which consists of one or more SIDs as defined in [RFC8664]. This document defiend a new flag (E-flag) for the SR-ERO subobject. E (ELP Configuration) : If this flag is set, it means that the position after this SR-ERO subobject is the position to insert , otherwise it cannot insert after this segment. Xiong, et al. Expires 3 March 2023 [Page 5] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 5. Operations The SR path is initiated by PCE or PCC with PCReq, PCInitiated or PCUpd messages and the E bit is set to 1 in LSP object to request the ELP configuration. The SR-TE path being recieved by PCC with SR-ERO segment list, for example, , especially S3 and S6 with E-flag set. It indicates that two pairs MUST be inserted into the label stack of the SR-TE forwarding entry, repectively after the label for S3 and label for S6. With EL information, the label stack for SR-MPLS would be . 6. Security Considerations Procedures and protocol extensions defined in this document do not introduce any new security considerations beyond those already listed in [RFC8662] and [RFC8664]. 7. Acknowledgements The authors would like to thank Stephane Litkowski, Dhruv Dhody, Tarek Saad, Zhenbin Li and Jeff Tantsura for their review, suggestions and comments to this document. 8. IANA Considerations 8.1. New SR PCE Capability Flag Registry SR PCE Capability TLV is defined in [RFC8664], and the registry to manage the Flag field of the SR PCE Capability TLV is requested in [RFC8664]. IANA is requested to make allocations from the registry, as follows: +=======+==============================================+===========+ | Value | Name | Reference | +=======+==============================================+===========+ | TBD11 | Entropy Label Configuration is supported (E) | [this | | | | document] | +-------+----------------------------------------------+-----------+ Table 1 8.2. New LSP-EXTENDED-FLAG Flag Registry [I-D.ietf-pce-lsp-extended-flags] defines the LSP-EXTENDED-FLAG TLV. IANA is requested to make allocations from the Flag field registry, as follows: Xiong, et al. Expires 3 March 2023 [Page 6] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 +=======+===================================+=================+ | Value | Name | Reference | +=======+===================================+=================+ | TBD | Request for ELP Configuration (E) | [this document] | +-------+-----------------------------------+-----------------+ Table 2 8.3. New SR-ERO Flag Registry SR-ERO subobject is defined in [RFC8664], and the registry to manage the Flag field of SR-ERO is requested in [RFC8664]. IANA is requested to make allocations from the registry, as follows: +=======+=======================+=================+ | Value | Name | Reference | +=======+=======================+=================+ | 36 | ELP Configuration (E) | [this document] | +-------+-----------------------+-----------------+ Table 3 9. References 9.1. Normative References [I-D.ietf-isis-mpls-elc] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., and M. Bocci, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using IS-IS", Work in Progress, Internet-Draft, draft-ietf-isis-mpls-elc-13, 28 May 2020, . [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S., and M. Bocci, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using OSPF", Work in Progress, Internet-Draft, draft-ietf-ospf-mpls-elc-15, 1 June 2020, . Xiong, et al. Expires 3 March 2023 [Page 7] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 [I-D.ietf-pce-lsp-extended-flags] Xiong, Q., "Label Switched Path (LSP) Object Flag Extension of Stateful PCE", Work in Progress, Internet- Draft, draft-ietf-pce-lsp-extended-flags-03, 7 June 2022, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, DOI 10.17487/RFC6790, November 2012, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [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, . [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, DOI 10.17487/RFC8476, December 2018, . [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, DOI 10.17487/RFC8491, November 2018, . Xiong, et al. Expires 3 March 2023 [Page 8] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 [RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing with the MPLS Data Plane", RFC 8660, DOI 10.17487/RFC8660, December 2019, . [RFC8662] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S., Shakir, R., and J. Tantsura, "Entropy Label for Source Packet Routing in Networking (SPRING) Tunnels", RFC 8662, DOI 10.17487/RFC8662, December 2019, . [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, . 9.2. Informative References [I-D.zhou-idr-bgp-srmpls-elp] Liu, Y. and S. Peng, "BGP Extension for SR-MPLS Entropy Label Position", Work in Progress, Internet-Draft, draft- zhou-idr-bgp-srmpls-elp-05, 7 June 2022, . Authors' Addresses Quan Xiong ZTE Corporation No.6 Huashi Park Rd Wuhan Hubei, 430223 China Email: xiong.quan@zte.com.cn Shaofu Peng ZTE Corporation No.50 Software Avenue Nanjing Jiangsu, 210012 China Email: peng.shaofu@zte.com.cn Xiong, et al. Expires 3 March 2023 [Page 9] Internet-Draft PCEP Extension for SR-MPLS Entropy Label August 2022 Fengwei Qin China Mobile Beijing China Email: qinfengwei@chinamobile.com Xiong, et al. Expires 3 March 2023 [Page 10]