PCE Working Group                                                  C. Li
Internet-Draft                                                   M. Chen
Intended status: Standards Track                     Huawei Technologies
Expires: 13 March 2022                                          W. Cheng
                                                            China Mobile
                                                               R. Gandhi
                                                     Cisco Systems, Inc.
                                                                Q. Xiong
                                                         ZTE Corporation
                                                        9 September 2021


 Path Computation Element Communication Protocol (PCEP) Extensions for
          Associated Bidirectional Segment Routing (SR) Paths
                    draft-ietf-pce-sr-bidir-path-08

Abstract

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.
   Segment routing (SR) leverages the source routing and tunneling
   paradigms.  The Stateful PCEP extensions allow stateful control of
   Segment Routing Traffic Engineering (TE) Paths.  Furthermore, PCEP
   can be used for computing SR TE paths in the network.

   This document defines PCEP extensions for grouping two unidirectional
   SR Paths (one in each direction in the network) into a single
   associated bidirectional SR Path.  The mechanisms defined in this
   document can also be applied using a stateful PCE for both PCE-
   initiated and PCC-initiated LSPs or when using a stateless PCE.


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."




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   This Internet-Draft will expire on 13 March 2022.

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
     1.1.  Bidirectional SR Policy Association . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   3.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Double-Sided Bidirectional with Reverse LSP
           Association . . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  Bidirectional LSP Association Group TLV . . . . . . .   6
   4.  PCEP Procedures . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  PCE-Initiated Associated Bidirectional SR Paths . . . . .   7
     4.2.  PCC-Initiated Associated Bidirectional SR Paths . . . . .   8
     4.3.  Stateless PCE . . . . . . . . . . . . . . . . . . . . . .  11
     4.4.  Bidirectional (B) Flag  . . . . . . . . . . . . . . . . .  11
     4.5.  PLSP-ID Usage . . . . . . . . . . . . . . . . . . . . . .  11
     4.6.  State Synchronization . . . . . . . . . . . . . . . . . .  12
     4.7.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  12
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .  12
     5.1.  Huawei's Commercial Delivery  . . . . . . . . . . . . . .  13
     5.2.  ZTE's Commercial Delivery . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  14
     7.1.  Control of Function and Policy  . . . . . . . . . . . . .  14
     7.2.  Information and Data Models . . . . . . . . . . . . . . .  14
     7.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  14
     7.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  14
     7.5.  Requirements On Other Protocols . . . . . . . . . . . . .  14
     7.6.  Impact On Network Operations  . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Association Type  . . . . . . . . . . . . . . . . . . . .  15
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15



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     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Segment routing (SR) [RFC8402] leverages the source routing and
   tunneling paradigms.  SR supports steering packets onto an explicit
   forwarding path at the ingress node.  SR is specified for
   unidirectional paths.  However, some applications require
   bidirectional paths in SR networks, for example, in mobile backhaul
   transport networks.  The requirement for bidirectional SR Paths is
   specified in [I-D.ietf-spring-mpls-path-segment] and
   [I-D.ietf-spring-srv6-path-segment].

   [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 Traffic Engineering (TE) Label Switched
   Paths (LSP).  [RFC8231] specifies a set of extensions to PCEP to
   enable stateful control of TE LSPs within and across PCEP sessions.
   The mode of operation where LSPs are initiated from the PCE is
   described in [RFC8281].

   [RFC8408] specifies extensions to the Path Computation Element
   Protocol (PCEP) [RFC5440] for SR networks, that allow a stateful PCE
   to compute and initiate SR TE paths, as well as a PCC to request,
   report or delegate them.

   [RFC8697] introduces a generic mechanism to create a grouping of
   LSPs.  This grouping can then be used to define associations between
   sets of LSPs or between a set of LSPs and a set of attributes, and it
   is equally applicable to the stateful PCE (active and passive modes)
   [RFC8231] and the stateless PCE [RFC5440].

   For bidirectional SR paths, there are use-cases such as directed BFD
   [I-D.ietf-mpls-bfd-directed] and Performance Measurement (PM)
   [I-D.ietf-spring-stamp-srpm] those require ingress node (PCC) to be
   aware of the reverse direction SR Path.  For such use-cases, the
   reverse SR Paths need to be communicated to the ingress node (PCCs)
   using PCEP mechanisms.  This allows both endpoint ingress nodes to be
   aware of the SR Paths in both directions, including their status and
   all other path related information.






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   [RFC9059] defines PCEP extensions for grouping two unidirectional
   Resource Reservation Protocol - Traffic Engineering (RSVP-TE) LSPs
   into an associated bidirectional LSP when using a stateful PCE for
   both PCE-initiated and PCC-initiated LSPs as well as when using a
   stateless PCE.  Specifically, it defines the procedure for 'Double-
   Sided Bidirectional LSP Association', where the PCE creates the
   association and provisions the forward LSPs at their ingress nodes.
   The RSVP-TE signals the forward LSPs to the egress nodes.  Thus, both
   endpoints learn the reverse LSPs forming the bidirectional LSP
   association.

   This document extends the bidirectional LSP association to SR paths
   by specifying PCEP extensions for grouping two unidirectional SR
   Paths into an associated bidirectional SR Path.  Note that the
   procedure for using the association group defined in this document is
   specific to the associated bidirectional SR Paths.  Associating an
   unidirectional SR Path with a reverse direction unidirectional RSVP-
   TE LSP to form a bidirectional LSP and vice versa, are outside the
   scope of this document.

1.1.  Bidirectional SR Policy Association

   An SR Policy contains one or more SR Policy Candidate Paths (CPs)
   [I-D.ietf-spring-segment-routing-policy] where one or more such paths
   can be computed via PCE.  Each Candidate Path maps to a unique PLSP-
   ID in PCEP.  Multiple Candidate Paths can be associated together into
   a single SR Policy, via the use of the PCEP Association object with
   the "SR Policy Association" type as specified in
   [I-D.ietf-pce-segment-routing-policy-cp].  The two unidirectional
   Candidate Paths can be associated to form a bidirectional Candidate
   Path using the procedure defined in this document.

   Each Candidate Path of an SR Policy contains one or more Segment
   Lists (SLs) [I-D.ietf-spring-segment-routing-policy].  If the
   Candidate Path is computed by the PCE, it means that the PCE computed
   all SLs of that Candidate Path.  [I-D.ietf-pce-multipath] defines
   procedure for carrying multiple SLs in a Candidate Path.  The
   procedure works at the SL level to identify the forward and the
   reverse direction SLs in a Candidate Path as shown in an Example in
   Section 7.4 (Opposite Direction Tunnels) in [I-D.ietf-pce-multipath].
   The procedure defined in this document allows to identify the forward
   and reverse direction Candidate Paths in a bidirectional SR Policy.

2.  Terminology

   This document makes use of the terms defined in [RFC8408].  The
   reader is assumed to be familiar with the terminology defined in
   [RFC5440], [RFC8231], [RFC8281], [RFC8697], and [RFC9059].



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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.  PCEP Extensions

   As per [RFC8697], TE LSPs are associated by adding them to a common
   association group by a PCEP peer.  [RFC9059] uses the association
   group object and the procedures as specified in [RFC8697] to group
   two unidirectional RSVP-TE LSPs.  Similarly, two SR Paths can also be
   associated using similar technique.  This document extends these
   association mechanisms for bidirectional SR Paths.  Two
   unidirectional SR Paths (one in each direction in the network) can be
   associated together by using the association group defined in this
   document for PCEP messages.

   [I-D.ietf-pce-sr-path-segment] defines a mechanism for communicating
   Path Segment Identifier (PSID) in PCEP for SR.  The SR-MPLS PSID is
   defined in [I-D.ietf-spring-mpls-path-segment] and SRv6 PSID is
   defined in [I-D.ietf-spring-srv6-path-segment].  The PSID can be used
   for identifying the SR Path of an associated bidirectional SR Path.
   The PATH-SEGMENT TLV MAY be included for the SR Path in the LSP
   object to support the use-cases as required.  The PATH-SEGMENT TLV
   MUST be handled as defined in [I-D.ietf-pce-sr-path-segment] and is
   not modified for associated bidirectional SR Path.

3.1.  Double-Sided Bidirectional with Reverse LSP Association

   For associating two unidirectional SR Paths, this document defines a
   new Association Type called 'Double-Sided Bidirectional with Reverse
   LSP Association' for Association Group object (Class-Value 40) as
   follows:

   *  Association Type (TBD1 to be assigned by IANA) = Double-Sided
      Bidirectional with Reverse LSP Association

   The bidirectional association is considered to be both dynamic and
   operator-configured in nature.  As per [RFC8697], the association
   group could be manually created by the operator on the PCEP peers,
   and the LSPs belonging to this association are conveyed via PCEP
   messages to the PCEP peer; alternately, the association group could
   be created dynamically by the PCEP speaker, and both the association
   group information and the LSPs belonging to the association group are
   conveyed to the PCEP peer.  The Operator-configured Association Range



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   MUST be set for this Association Type to mark a range of Association
   Identifiers that are used for operator-configured associations to
   avoid any Association Identifier clash within the scope of the
   Association Source (Refer to [RFC8697]).  Specifically, for the PCE-
   initiated associated bidirectional SR Paths, the Association Type is
   dynamically created by the PCE on the PCE peers.

   The handling of the Association ID, Association Source, optional
   Global Association Source and optional Extended Association ID in
   this association are set in the same way as [RFC9059].

   [RFC8697] specifies the mechanism for the capability advertisement of
   the Association Types supported by a PCEP speaker by defining an
   ASSOC-Type-List TLV (value 35) to be carried within an OPEN object.
   This capability exchange for the Bidirectional Association MUST be
   done before using the Bidirectional Association Type.  Thus, the PCEP
   speaker MUST include the bidirectional Association Type in the ASSOC-
   Type-List TLV and MUST receive the same from the PCEP peer before
   using the Bidirectional Association in PCEP messages.

   A member of the 'Double-Sided Bidirectional with Reverse LSP
   Association' can take the role of a forward or reverse direction SR
   Path and follow the similar rules defined in [RFC9059] for LSPs.

   *  An SR Path (forward or reverse) MUST NOT be part of more than one
      'Double-Sided Bidirectional with Reverse LSP Association'.

   *  The endpoint nodes of the SR Paths in 'Double-Sided Bidirectional
      with Reverse LSP Association' MUST be matching in the reverse
      directions.

3.1.1.  Bidirectional LSP Association Group TLV

   In 'Double-Sided Bidirectional with Reverse LSP Association', for
   properties such as forward and reverse direction and co-routed path,
   it uses the 'Bidirectional LSP Association Group TLV' defined in
   [RFC9059].  All fields and processing rules are as per [RFC9059].

4.  PCEP Procedures

   For an associated bidirectional SR Path, an ingress node PCC is aware
   of the forward direction SR Path beginning from itself to the egress
   node PCC using the existing PCEP procedures.  For the use-cases which
   require the ingress node PCC to be aware of the reverse direction SR
   Path, PCE informs the reverse SR Path to the ingress node PCC.  To
   achieve this, a PCInitiate message for the reverse SR Path is sent to
   the ingress node PCC and a PCInitiate message for the forward SR Path
   is sent to the egress node PCC (with the matching association group).



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   These PCInitiate message MUST NOT trigger initiation of SR Paths on
   PCCs.

   The PCEP procedure defined in this document is applicable to the
   following three scenarios:

   *  Neither unidirectional LSP exists, and both must be established.

   *  Both unidirectional LSPs exist, but the association must be
      established.

   *  One LSP exists, but the reverse associated LSP must be
      established.

4.1.  PCE-Initiated Associated Bidirectional SR Paths

   As specified in [RFC8697], associated bidirectional SR Paths can be
   created and updated by a Stateful PCE as shown in Figure 1.

   *  Stateful PCE MAY create and update the forward and reverse SR
      Paths independently for the 'Double-Sided Bidirectional with
      Reverse LSP Association'.

   *  Stateful PCE MAY establish and remove the association relationship
      on a per SR Path basis.

   *  Stateful PCE MUST create and update the SR Path and the
      association on a PCC via PCInitiate and PCUpd messages,
      respectively, using the procedures described in [RFC8697].

   *  The reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node
      D as shown in Figure 1) SHOULD be informed by the PCE via
      PCInitiate message with the matching association group for the
      use-cases which require the PCC to be aware of the reverse
      direction SR Path.
















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                                  +-----+
                                  | PCE |
                                  +-----+
     PCInitiate:                  /     \     PCInitiate:
     Tunnel 1 (F)                /       \    Tunnel 2 (F)
     LSP1 (F,0), LSP2 (R,0)     /         \   LSP2 (F,0), LSP1 (R,0)
     Association #1            /           \  Association #1
                              /             \
                             v               v
                        +-----+    LSP1     +-----+
                        |  S  |------------>|  D  |
                        |     |<------------|     |
                        +-----+    LSP2     +-----+
                              <no signaling>

         Legends: F = Forward LSP, R = Reverse LSP, (0) = PLSP-IDs

         Figure 1a: PCE-Initiated Associated Bidirectional SR Path
                    with Forward and Reverse Direction SR Paths


                                  +-----+
                                  | PCE |
                                  +-----+
     PCRpt:                       ^     ^     PCRpt:
     Tunnel 1 (F)                /       \    Tunnel 2 (F)
     LSP1 (F,100), LSP2 (R,300) /         \   LSP2 (F,200), LSP1 (R,400)
     Association #1            /           \  Association #1
                              /             \
                             /               \
                        +-----+    LSP1     +-----+
                        |  S  |------------>|  D  |
                        |     |<------------|     |
                        +-----+    LSP2     +-----+
                              <no signaling>

     Legends: F=Forward LSP, R = Reverse LSP, (100,200,300,400)=PLSP-IDs

         Figure 1b: PCC-Reported Bidirectional SR Path
                    with Forward and Reverse Direction SR Paths

4.2.  PCC-Initiated Associated Bidirectional SR Paths

   As specified in [RFC8697], associated bidirectional SR Paths can also
   be created and updated by a PCC as shown in Figure 2a and 2b.






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   *  PCC MAY create and update the forward SR Path and update the
      reverse SR Path independently for the 'Double-Sided Bidirectional
      with Reverse LSP Association'.

   *  PCC MUST NOT instantiate a reverse SR Path in a bidirectional SR
      Path.

   *  PCC MAY establish and remove the association relationship on a per
      SR Path basis.

   *  PCC MUST report the change in the association group of an SR Path
      to PCE(s) via PCRpt message.

   *  PCC reports the forward and reverse SR Paths independently to
      PCE(s) via PCRpt message.

   *  PCC MAY delegate the forward and reverse SR Paths independently to
      a Stateful PCE, where PCE would control the SR Paths.

   *  Stateful PCE updates the SR Paths in the 'Double-Sided
      Bidirectional with Reverse LSP Association' via PCUpd message,
      using the procedures described in [RFC8697].

   *  The reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node
      D as shown in Figure 2b) SHOULD be informed by the PCE via
      PCInitiate message with the matching association group for the
      use-cases which require the PCC to be aware of the reverse
      direction SR Path.

                                 +-----+
                                 | PCE |
                                 +-----+
        Report/Delegate:         ^     ^        Report/Delegate:
        Tunnel 1 (F)            /       \       Tunnel 2 (F)
        LSP1 (F,100)           /         \      LSP2 (F,200)
        Association #2        /           \     Association #2
                             /             \
                            /               \
                       +-----+    LSP1     +-----+
                       |  S  |------------>|  D  |
                       |     |<------------|     |
                       +-----+    LSP2     +-----+
                             <no signaling>

     Legends: F = Forward LSP, R = Reverse LSP, (100,200) = PLSP-IDs

     Figure 2a: Step 1: PCC-Initiated Associated Bidirectional SR
                        Path with Forward Direction SR Paths



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                                 +-----+
                                 | PCE |
                                 +-----+
    PCInitiate:                  /     \     PCInitiate:
    Tunnel 1 (F)                /       \    Tunnel 2 (F)
    LSP1 (F,100), LSP2 (R,0)   /         \   LSP2 (F,200), LSP1 (R,0)
    Association #2            /           \  Association #2
                             /             \
                            v               v
                       +-----+    LSP1     +-----+
                       |  S  |------------>|  D  |
                       |     |<------------|     |
                       +-----+    LSP2     +-----+
                             <no signaling>

     Legends: F = Forward LSP, R = Reverse LSP, (0,100,200) = PLSP-IDs

     Figure 2b: Step 2: PCE-Initiated Associated Bidirectional SR
                       Path with Reverse Direction SR Paths


                                 +-----+
                                 | PCE |
                                 +-----+
    PCRpt:                       ^     ^     PCRpt:
    Tunnel 1 (F)                /       \    Tunnel 2 (F)
    LSP1 (F,100), LSP2 (R,300) /         \   LSP2 (F,200), LSP1 (R,400)
    Association #2            /           \  Association #2
                             /             \
                            /               \
                       +-----+    LSP1     +-----+
                       |  S  |------------>|  D  |
                       |     |<------------|     |
                       +-----+    LSP2     +-----+
                             <no signaling>

     Legends: F=Forward LSP, R = Reverse LSP, (100,200,300,400)=PLSP-IDs

     Figure 2c: Step 3: PCC-Reported Associated Bidirectional SR
                        Path with Reverse Direction SR Paths











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4.3.  Stateless PCE

   As defined in [RFC9059], for a stateless PCE, it might be useful to
   associate a path computation request to an association group, thus
   enabling it to associate a common set of configuration parameters or
   behaviors with the request [RFC8697].  A PCC can request co-routed or
   non-co-routed forward and reverse direction paths from a stateless
   PCE for a bidirectional SR Path.

4.4.  Bidirectional (B) Flag

   The Bidirectional (B) flag in Request Parameters (RP) object
   [RFC5440] and Stateful PCE Request Parameter (SRP) object
   [I-D.ietf-pce-pcep-stateful-pce-gmpls] follow the procedure defined
   in [RFC9059].

4.5.  PLSP-ID Usage

   For a bidirectional LSP computation when using both direction LSPs on
   a node, the same LSP would need to be identified using 2 different
   PLSP-IDs based on the PCEP session to the ingress or the egress node.
   Note that the PLSP-ID space is independent at each PCC, the PLSP-ID
   allocated by the egress PCC cannot be used for the LSP at the ingress
   PCC (PLSP-ID conflict may occur).  As per normal PCInitiate
   operations, PCC assigns the PLSP-IDs for the local LSPs.  Hence, when
   the PCE notifies an ingress PCC of the reverse LSP, it does so by
   using PCInitiate operations and sets PLSP-ID to zero and sets the R
   bit in the 'Bidirectional LSP Association Group TLV' in the
   association object to indicate that this PCInitiate LSP is a reverse
   LSP.  The PCC upon receiving the PCInitiate MUST locally assign a new
   PLSP-ID and it MUST issue a PCRpt to PCE for this LSP containing the
   new PLSP-ID.  This reverse direction LSP MUST NOT be instantiated on
   the PCC.

   In other words, a given LSP will be identified by PLSP-ID A at the
   ingress node while it will be identified by PLSP-ID B at the egress
   node.  The PCE will maintain two PLSP-IDs for the same LSP.  For
   example, ingress PCC1 may report to PCE an LSP1 with PLSP-ID 100.
   Egress PCC2 may report to PCE an LSP2 with PLSP-ID 200.  Both of
   these LSPs are part of a bidirectional association.  When PCE
   notifies PCC1 of the reverse direction LSP2, it does so by sending a
   PCInitiate to PCC1 with PLSP-ID set to zero and R bit set in the
   'Bidirectional LSP Association Group TLV'.  PCC1 upon reception of
   this generates a new PLSP-ID (example PLSP-ID 300) and issues a PCRpt
   to PCE.  Thus there would two PLSP-ID associated for LSP2 (300 at
   PCC1 and 200 at PCC2).





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   For an associated bidirectional SR Path, LSP-IDENTIFIERS TLV
   [RFC8231] MUST be included in all forward and reverse LSPs.

4.6.  State Synchronization

   During state synchronization, a PCC MUST report all the existing
   Bidirectional Associations to the Stateful PCE as per [RFC8697].
   After the state synchronization, the PCE MUST remove all stale
   Bidirectional Associations.

4.7.  Error Handling

   The error handling as described in section 5.7 of [RFC9059] continue
   to apply.

   The PCEP Path Setup Type (PST) for SR is set to 'TE Path is Setup
   using Segment Routing' [RFC8408] or 'Path is setup using SRv6'
   [I-D.ietf-pce-segment-routing-ipv6].

   If a PCEP speaker receives a different PST value for the 'Double-
   Sided Bidirectional with Reverse LSP Association', the PCE speaker
   MUST return a PCErr message with Error-Type = 26 (Association Error)
   and Error-value = '16: Path Setup Type not supported' defined in
   [RFC9059].

5.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to [RFC7942].

   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.









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   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".


5.1.  Huawei's Commercial Delivery

   The feature is developing based on Huawei VRP8.

   *  Organization: Huawei

   *  Implementation: Huawei's Commercial Delivery implementation based
      on VRP8.

   *  Description: The implementation is under development.

   *  Maturity Level: Product

   *  Contact: tanren@huawei.com


5.2.  ZTE's Commercial Delivery

   *  Organization: ZTE

   *  Implementation: ZTE's Commercial Delivery implementation based on
      Rosng v8.

   *  Description: The implementation is under development.

   *  Maturity Level: Product

   *  Contact: zhan.shuangping@zte.com.cn

6.  Security Considerations

   The security considerations described in [RFC5440], [RFC8231],
   [RFC8281], and [RFC8408] apply to the extensions defined in this
   document as well.









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   A new Association Type for the Association object, 'Double-Sided
   Bidirectional with Reverse LSP Association' is introduced in this
   document.  Additional security considerations related to LSP
   associations due to a malicious PCEP speaker are described in
   [RFC8697] and apply to this Association Type.  Hence, securing the
   PCEP session using Transport Layer Security (TLS) [RFC8253] is
   recommended.

7.  Manageability Considerations

   All manageability requirements and considerations listed in
   [RFC5440], [RFC8231], and [RFC8281] apply to PCEP protocol extensions
   defined in this document.  In addition, requirements and
   considerations listed in this section apply.

7.1.  Control of Function and Policy

   The mechanisms defined in this document do not imply any control or
   policy requirements in addition to those already listed in [RFC5440],
   [RFC8231], and [RFC8281].

7.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB, there are no new MIB Objects
   defined for 'Double-Sided Bidirectional with Reverse LSP
   Associations'.  The PCEP YANG module [I-D.ietf-pce-pcep-yang] defines
   data model for associated bidirectional SR Paths.

7.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440], [RFC8231], and [RFC8281].

7.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440], [RFC8231], and [RFC8408].

7.5.  Requirements On Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.







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7.6.  Impact On Network Operations

   Mechanisms defined in [RFC5440], [RFC8231], and [RFC8408] also apply
   to PCEP extensions defined in this document.

8.  IANA Considerations


8.1.  Association Type

   This document defines a new Association Type, originally described in
   [RFC8697].  IANA is requested to assign the following new value in
   the "ASSOCIATION Type Field" subregistry [RFC8697] within the "Path
   Computation Element Protocol (PCEP) Numbers" registry:


   Type    Name                                          Reference
   ---------------------------------------------------------------------
   TBD1    Double-Sided Bidirectional with Reverse       [This document]
           LSP Association

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, 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>.







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   [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,
              <https://www.rfc-editor.org/info/rfc8281>.

   [RFC8697]  Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "Path Computation Element
              Communication Protocol (PCEP) Extensions for Establishing
              Relationships between Sets of Label Switched Paths
              (LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
              <https://www.rfc-editor.org/info/rfc8697>.

   [RFC9059]  Gandhi, R., Ed., Barth, C., and B. Wen, "Path Computation
              Element Communication Protocol (PCEP) Extensions for
              Associated Bidirectional Label Switched Paths (LSPs)",
              RFC 9059, DOI 10.17487/RFC9059, June 2021,
              <https://www.rfc-editor.org/info/rfc9059>.

9.2.  Informative References

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,
              <https://www.rfc-editor.org/info/rfc8253>.

   [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>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [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,
              July 2018, <https://www.rfc-editor.org/info/rfc8408>.




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   [I-D.ietf-pce-sr-path-segment]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "Path Computation Element Communication Protocol (PCEP)
              Extension for Path Segment in Segment Routing (SR)", Work
              in Progress, Internet-Draft, draft-ietf-pce-sr-path-
              segment-04, 12 August 2021,
              <https://www.ietf.org/archive/id/draft-ietf-pce-sr-path-
              segment-04.txt>.

   [I-D.ietf-pce-segment-routing-ipv6]
              Li, C., Negi, M., Sivabalan, S., Koldychev, M.,
              Kaladharan, P., and Y. Zhu, "PCEP Extensions for Segment
              Routing leveraging the IPv6 data plane", Work in Progress,
              Internet-Draft, draft-ietf-pce-segment-routing-ipv6-09, 27
              May 2021, <https://www.ietf.org/internet-drafts/draft-
              ietf-pce-segment-routing-ipv6-09.txt>.

   [I-D.ietf-mpls-bfd-directed]
              Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
              "Bidirectional Forwarding Detection (BFD) Directed Return
              Path for MPLS Label Switched Paths (LSPs)", Work in
              Progress, Internet-Draft, draft-ietf-mpls-bfd-directed-18,
              20 August 2021, <https://www.ietf.org/archive/id/draft-
              ietf-mpls-bfd-directed-18.txt>.

   [I-D.ietf-spring-stamp-srpm]
              Gandhi, R., Filsfils, C., Voyer, D., Chen, M., Janssens,
              B., and R. Foote, "Performance Measurement Using Simple
              TWAMP (STAMP) for Segment Routing Networks", Work in
              Progress, Internet-Draft, draft-ietf-spring-stamp-srpm-01,
              6 July 2021, <https://www.ietf.org/archive/id/draft-ietf-
              spring-stamp-srpm-01.txt>.

   [I-D.ietf-spring-mpls-path-segment]
              Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
              "Path Segment in MPLS Based Segment Routing Network", Work
              in Progress, Internet-Draft, draft-ietf-spring-mpls-path-
              segment-05, 21 August 2021,
              <https://www.ietf.org/archive/id/draft-ietf-spring-mpls-
              path-segment-05.txt>.

   [I-D.ietf-spring-srv6-path-segment]
              Li, C., Cheng, W., Chen, M., Dhody, D., Gandhi, R., and Y.
              Zhu, "Path Segment for SRv6 (Segment Routing in IPv6)",
              Work in Progress, Internet-Draft, draft-ietf-spring-srv6-
              path-segment-02, 26 May 2021,
              <https://www.ietf.org/archive/id/draft-ietf-spring-srv6-
              path-segment-02.txt>.



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   [I-D.ietf-pce-pcep-yang]
              Dhody, D., Hardwick, J., Beeram, V. P., and J. Tantsura,
              "A YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-yang-16, 22 February
              2021, <https://www.ietf.org/archive/id/draft-ietf-pce-
              pcep-yang-16.txt>.

   [I-D.ietf-pce-pcep-stateful-pce-gmpls]
              Lee, Y., Zheng, H., Dios, O. G. D., Lopez, V., and Z. Ali,
              "Path Computation Element (PCE) Protocol Extensions for
              Stateful PCE Usage in GMPLS-controlled Networks", Work in
              Progress, Internet-Draft, draft-ietf-pce-pcep-stateful-
              pce-gmpls-15, 23 June 2021,
              <https://www.ietf.org/archive/id/draft-ietf-pce-pcep-
              stateful-pce-gmpls-15.txt>.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", Work in
              Progress, Internet-Draft, draft-ietf-spring-segment-
              routing-policy-13, 28 May 2021,
              <https://www.ietf.org/archive/id/draft-ietf-spring-
              segment-routing-policy-13.txt>.

   [I-D.ietf-pce-segment-routing-policy-cp]
              Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
              Bidgoli, "PCEP extension to support Segment Routing Policy
              Candidate Paths", Work in Progress, Internet-Draft, draft-
              ietf-pce-segment-routing-policy-cp-05, 23 May 2021,
              <https://www.ietf.org/archive/id/draft-ietf-pce-segment-
              routing-policy-cp-05.txt>.

   [I-D.ietf-pce-multipath]
              Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
              Bidgoli, H., Yadav, B., and S. Peng, "PCEP Extensions for
              Signaling Multipath Information", Work in Progress,
              Internet-Draft, draft-ietf-pce-multipath-01, 27 July 2021,
              <https://www.ietf.org/archive/id/draft-ietf-pce-multipath-
              01.txt>.

Acknowledgments

   Many thanks to Marina Fizgeer, Adrian Farrel, Andrew Stone, Tarek
   Saad, and Mike Koldychev for the detailed review of this document and
   providing many useful comments.





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Contributors

   The following people have substantially contributed to this document:

    Dhruv Dhody
    Huawei Technologies
    Divyashree Techno Park, Whitefield
    Bangalore, Karnataka  560066
    India

    Email: dhruv.ietf@gmail.com

    Zhenbin Li
    Huawei Technologies
    Huawei Campus, No. 156 Beiqing Rd.
    Beijing  100095
    China

    Email: lizhenbin@huawei.com


    Jie Dong
    Huawei Technologies
    Huawei Campus, No. 156 Beiqing Rd.
    Beijing  100095
    China

    Email: jie.dong@huawei.com

Authors' Addresses

   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China

   Email: c.l@huawei.com


   Mach(Guoyi) Chen
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China




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   Email: Mach.chen@huawei.com


   Weiqiang Cheng
   China Mobile
   China

   Email: chengweiqiang@chinamobile.com


   Rakesh Gandhi
   Cisco Systems, Inc.
   Canada

   Email: rgandhi@cisco.com


   Quan Xiong
   ZTE Corporation
   China

   Email: xiong.quan@zte.com.cn





























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