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Versions: 00                                                            
Inter-Domain Routing Working Group                            Y. Wang
Internet-Draft                                                  H. Li
Intended status: Standards Track                               Y. Qiu
Expires: August 2, 2021                                       L. Yang
                                                              M. Chen
                                                     H3C Technologies
                                                     February 2, 2021


                Segment Routing PCE Delegation in BGP
              draft-wang-idr-sr-policy-pce-delegation-00

Abstract

   Segment Routing is a source routing paradigm that explicitly
   indicates the forwarding path for packets at the ingress node. An
   SR policy is a set of candidate SR paths consisting of one or more
   segment lists with necessary path attributes. The headend of an SR
   Policy may learn multiple candidate paths for an SR Policy.
   Candidate paths may be learned via a number of different mechanisms,
   e.g., CLI, NetConf, PCEP, or BGP.

   The Path Computation Element (PCE) provides path computation
   functions in support of traffic engineering in Multi Protocol Label
   Switching (MPLS) and Generalized MPLS (GMPLS) networks.

   Currently, when a controller uses BGP to deploy an SR Policy, there
   is no way to encode PCE delegation related options. The only way to
   import a PCE delegation is through local configuration management,
   e.g., Netconf, CLI or gRPC.

   This document defines extensions to BGP to distribute PCE
   delegation information within an SR policy.

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 August 2, 2021.



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Copyright Notice

   Copyright (c) 2021 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  SR Policy for PCE Delegation. . . . . . . . . . . . . . . . .   4
     3.1.  PCE Delegation Sub-TLV  . . . . . . . . . . . . . . . . .   6
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
      9.1.  Normative References . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10




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1.  Introduction

   Segment routing (SR) [RFC8402] is a source routing paradigm that
   explicitly indicates the forwarding path for packets at the
   ingress node.  The ingress node steers packets into a specific
   path according to the Segment Routing Policy (SR Policy) as
   defined in[I-D.ietf-spring-segment-routing-policy].  In order
   to distribute SR policies to the headend,
   [I-D.ietf-idr-segment-routing-te-policy] specifies a mechanism by
   using BGP.

   [RFC5440] describes the Path Computation Element (PCE) Communication
   Protocol (PCEP). PCEP enables the communication between a Path
   Computation Client (PCC) and a PCE, or between PCE and PCE, for the
   purpose of computation of Multi protocol Label Switching (MPLS) as
   well as Generalized MPLS (GMPLS) Traffic Engineering Label Switched
   Path (TE LSP) characteristics.

   When a controller uses BGP deploy an SR Policy, The only way to
   import a PCE delegation is through configuration management e.g.,
   Netconf, CLI or gRPC. It's inconvenient for a controller to use
   separate channels to deploy SR policies.

   This document defines extensions to BGP to distribute PCE delegation
   information within SR policies.

2.  Terminology

   PCE delegation : An operation to grant a PCE temporary rights to
   modify a subset of LSP parameters on one or more PCC's LSPs.  LSPs
   are delegated from a PCC to a PCE, and are referred to as delegated
   LSPs.  The PCC who owns the PCE state for the LSP has the right to
   delegate it.  An LSP is owned by a single PCC at any given point
   in time.  For intra-domain LSPs, this PCC SHOULD be the PCC of the
   LSP head end.



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2.1.  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.

3.  SR Policy for PCE Delegation

      As defined in [I-D.ietf-idr-segment-routing-te-policy] , the SR
    policy encoding structure is as follows:

         SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
      Attributes:
         Tunnel Encaps Attribute (23)
            Tunnel Type: SR Policy
                Binding SID
                Preference
                Priority
                Policy Name
                Explicit NULL Label Policy (ENLP)
                Segment List
                    Weight
                    Segment
                    Segment
                    ...
                ...

   As introduced in Section 1, SR Policy could use PCE to calculate
   path. SR policy with PCE delegation information is expressed as
   below:



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         SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
      Attributes:
         Tunnel Encaps Attribute (23)
            Tunnel Type: SR Policy
                Binding SID
                Preference
                Priority
                Policy Name
                PCE Delegation
                Explicit NULL Label Policy (ENLP)
                Segment List
                    Weight
                    Segment
                    Segment
                    ...
                ...


3.1.  PCE Delegation Sub-TLV

   A PCE Delegation sub-TLV is an Optional sub-TLV.  When it appears,
   it must appear only once at most within a SR Policy Sub-TLV. If
   multiple PCE Delegation sub-TLVs appear within an SR Policy Sub-TLV,
   the NLRI MUST be treated as a malformed NLRI.

   As per [I-D.ietf-idr-segment-routing-te-policy], when the error
   determined allows for the router to skip the malformed NLRI(s) and
   continue processing of the rest of the update message, then it MUST
   handle such malformed NLRIs as 'Treat-as-withdraw'.  This document
   does not define new error handling rules for PCE Delegation sub-TLV,
   and the error handling rules defined in
   [I-D.ietf-idr-segment-routing-te-policy] apply to this document.

   PCE Delegation is a new sub-TLV of the BGP Tunnel Encapsulation
   Attribute [I-D.ietf-idr-tunnel-encaps].



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   A PCE Delegation sub-TLV is associated with an SR policy. The PCE
   Delegation sub-TLV has the following format:

      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     |    Length     |     Flags     |   RESERVED    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Figure 1. PCE Delegation sub-TLV

   Where:

   Type: to be assigned by IANA.

   Length: the total length of the value field not including Type and
   Length fields.

   Flags: 1 octet of flags.

    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
   |D|R|
   +-+-+-+-+-+-+-+-+

   where:
   * D-Flag:  The flag encode PCE delegation. When this flag is set, it
   indicates to enable PCE delegation function, otherwise it indicates
   to disable PCE delegation.

   * R-Flag:  The flag encode passive delegation report only. An
   implementation SHOULD report its the status of SR policies to PCE
   server without using PCE Server to calculate path.



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   To avoid confusion, D-Flag and R-Flag SHOULD NOT be set
   simultaneously.

   Unused bits in the Flag octet SHOULD be set to zero upon
   transmission and MUST be ignored upon receipt.

   Reserved: 8 bits reserved and MUST be set to 0 on transmission and
   MUST be ignored on receipt.

4.  Operations

   The document does not bring new operation beyond the description of
   operations defined in [I-D.ietf-idr-segment-routing-te-policy].  The
   existing operations defined in
   [I-D.ietf-idr-segment-routing-te-policy] can apply to this document
   directly.

   Typically but not limit to, the SR policies carrying PCE Delegation
   information are configured by a controller.

   After configuration, the SR policies carrying PCE Delegation
   information will be advertised by BGP update messages. The operation
   of advertisement is the same as defined in
   [I-D.ietf-idr-segment-routing-te-policy], as well as the reception.

   The consumer of the SR policies is not the BGP process.  The
   operation of sending information to consumers is out of scope of this
   document.



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5.  IANA Considerations

   This document defines a new Sub-TLV in registries "SR Policy List
   Sub- TLVs" [I-D.ietf-idr-segment-routing-te-policy]:

   Value    Description                                  Reference
   ---------------------------------------------------------------------
    TBA     PCE Delegation sub-TLV                       This document


6.  Security Considerations

   TBA

7.  Contributors

   Yang.Wang

   H3C Technology

   China

   Email: wang.a.yang@h3c.com

8.  Acknowledgements

   Authors would like to thank Changwang.Lin, Jinrong.Ye for their
   proprefessional comments and help.

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9.  References

9.1.  Normative References

   [I-D.ietf-idr-tunnel-encaps]
              Patel, K., Velde, G., Sangli, S., and J. Scudder, "The BGP
              Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-
              encaps-22 (work in progress), January 2021.

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
              Rosen, E., Jain, D., and S. Lin, "Advertising Segment
              Routing Policies in BGP", draft-ietf-idr-segment-routing-
              te-policy-11 (work in progress), May 2020.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-09 (work in progress),
              July 2020.

   [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>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.



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Authors' Addresses

   Yang Wang
   H3C Technologies
   China

   Email: wang.a.yang@h3c.com


   Hao Li
   H3C Technologies
   China

   Email: lihao@h3c.com


   Yuanxiang Qiu
   H3C Technologies
   China

   Email: qiuyuanxiang@h3c.com


   Liping Yang
   H3C Technologies
   China

   Email: liping_yang@h3c.com


   Mengxiao Chen
   H3C Technologies
   China

   Email: chen.mengxiao@h3c.com


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