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Versions: (draft-barth-pce-association-bidir) 00 01 02 03 04 05 06

PCE Working Group                                         R. Gandhi, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                                C. Barth
Expires: August 7, 2020                                 Juniper Networks
                                                                  B. Wen
                                                                 Comcast
                                                        February 4, 2020


PCEP Extensions for Associated Bidirectional Label Switched Paths (LSPs)
                  draft-ietf-pce-association-bidir-05

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.
   The Stateful PCE extensions allow stateful control of Multiprotocol
   Label Switching (MPLS) Traffic Engineering (TE) Label Switched Paths
   (LSPs) using PCEP.

   This document defines PCEP extensions for grouping two unidirectional
   MPLS TE LSPs (one in each direction in the network) into an
   Associated Bidirectional LSP.  The mechanisms defined in this
   document can be applied using a Stateful PCE for both PCE-Initiated
   and PCC-Initiated LSPs, as well as when using a Stateless PCE.  The
   procedures defined are applicable to the LSPs using Resource
   Reservation Protocol (RSVP) for signaling.

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 7, 2020.






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Copyright Notice

   Copyright (c) 2020 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
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   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.  Conventions Used in This Document . . . . . . . . . . . . . .   4
     2.1.  Key Word Definitions  . . . . . . . . . . . . . . . . . .   4
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Single-sided Initiation . . . . . . . . . . . . . . . . .   5
     3.2.  Double-sided Initiation . . . . . . . . . . . . . . . . .   6
     3.3.  Co-routed Associated Bidirectional LSP  . . . . . . . . .   7
   4.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  ASSOCIATION Object  . . . . . . . . . . . . . . . . . . .   8
     4.2.  Bidirectional LSP Association Group TLV . . . . . . . . .   9
   5.  PCEP Procedure  . . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  PCE Initiated LSPs  . . . . . . . . . . . . . . . . . . .  10
     5.2.  PCC Initiated LSPs  . . . . . . . . . . . . . . . . . . .  10
     5.3.  Stateless PCE . . . . . . . . . . . . . . . . . . . . . .  11
     5.4.  Bidirectional (B) Flag  . . . . . . . . . . . . . . . . .  11
     5.5.  PLSP-ID Usage . . . . . . . . . . . . . . . . . . . . . .  11
     5.6.  State Synchronization . . . . . . . . . . . . . . . . . .  12
     5.7.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  12
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  13
     6.1.  Implementation  . . . . . . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  14
     8.1.  Control of Function and Policy  . . . . . . . . . . . . .  14
     8.2.  Information and Data Models . . . . . . . . . . . . . . .  14
     8.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  14
     8.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  14
     8.5.  Requirements On Other Protocols . . . . . . . . . . . . .  14
     8.6.  Impact On Network Operations  . . . . . . . . . . . . . .  14
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Association Types . . . . . . . . . . . . . . . . . . . .  14



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     9.2.  Bidirectional LSP Association Group TLV . . . . . . . . .  15
       9.2.1.  Flag Fields in Bidirectional LSP Association Group
               TLV . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.3.  PCEP Errors . . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     10.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   [RFC5440] describes the Path Computation Element Protocol (PCEP) as a
   communication mechanism between a Path Computation Client (PCC) and a
   Path Control Element (PCE), or between PCE and PCC, that enables
   computation of Multiprotocol Label Switching (MPLS) Traffic
   Engineering (TE) Label Switched Paths (LSPs).

   [RFC8231] specifies extensions to PCEP to enable stateful control of
   MPLS TE LSPs.  It describes two modes of operation - Passive Stateful
   PCE and Active Stateful PCE.  In [RFC8231], the focus is on Active
   Stateful PCE where LSPs are provisioned on the PCC and control over
   them is delegated to a PCE.  Further, [RFC8281] describes the setup,
   maintenance and teardown of PCE-Initiated LSPs for the Stateful PCE
   model.

   [RFC8697] introduces a generic mechanism to create a grouping of LSPs
   which can then be used to define associations between a set of LSPs
   and/or a set of attributes, for example primary and secondary LSP
   associations, and is equally applicable to the active and passive
   modes of a Stateful PCE [RFC8231] or a stateless PCE [RFC5440].

   The MPLS Transport Profile (MPLS-TP) requirements document [RFC5654]
   specifies that MPLS-TP MUST support associated bidirectional point-
   to-point LSPs.  [RFC7551] defines RSVP signaling extensions for
   binding two reverse unidirectional LSPs [RFC3209] into an associated
   bidirectional LSP.  The fast reroute (FRR) procedures for associated
   bidirectional LSPs are described in [RFC8537].

   This document defines PCEP extensions for grouping two unidirectional
   MPLS-TE LSPs into an Associated Bidirectional LSP for both single-
   sided and double-sided initiation cases when using a Stateful PCE for
   both PCE-Initiated and PCC-Initiated LSPs as well as when using a
   Stateless PCE.  The procedures defined are applicable to the LSPs
   using Resource Reservation Protocol (RSVP) for signaling [RFC3209].
   The PCEP extensions cover the following cases:





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   o  A PCC initiates the forward and/ or reverse LSP of a single-sided
      or double-sided bidirectional LSP and retains the control of the
      LSP.  The PCC computes the path itself or makes a request for path
      computation to a PCE.  After the path setup, it reports the
      information and state of the path to the PCE.  This includes the
      association group identifying the bidirectional LSP.  This is the
      Passive Stateful mode defined in [RFC8051].

   o  A PCC initiates the forward and/ or reverse LSP of a single-sided
      or double-sided bidirectional LSP and delegates the control of the
      LSP to a Stateful PCE.  During delegation the association group
      identifying the bidirectional LSP is included.  The PCE computes
      the path of the LSP and updates the PCC with the information about
      the path as long as it controls the LSP.  This is the Active
      Stateful mode defined in [RFC8051].

   o  A PCE initiates the forward and/ or reverse LSP of a single-sided
      or double-sided bidirectional LSP on a PCC and retains the control
      of the LSP.  The PCE is responsible for computing the path of the
      LSP and updating the PCC with the information about the path as
      well as the association group identifying the bidirectional LSP.
      This is the PCE-Initiated mode defined in [RFC8281].

   o  A PCC requests co-routed or non co-routed paths for forward and
      reverse LSPs of a bidirectional LSP from a Stateless PCE
      [RFC5440].

2.  Conventions Used in This Document

2.1.  Key Word Definitions

   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.

2.2.  Terminology

   The reader is assumed to be familiar with the terminology defined in
   [RFC5440], [RFC7551], [RFC8231], and [RFC8697].

3.  Overview

   As shown in Figure 1, two reverse unidirectional LSPs can be grouped
   to form an associated bidirectional LSP.  There are two methods of
   initiating the bidirectional LSP association, single-sided and




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   double-sided, as defined in [RFC7551] and described in the following
   sections.

               LSP1 -->          LSP1 -->          LSP1 -->
      +-----+           +-----+           +-----+           +-----+
      |  A  +-----------+  B  +-----------+  C  +-----------+  D  |
      +-----+           +--+--+           +--+--+           +-----+
               <-- LSP2    |                 |     <-- LSP2
                           |                 |
                           |                 |
                        +--+--+           +--+--+
                        |  E  +-----------+  F  |
                        +-----+           +-----+
                                 <-- LSP2

             Figure 1: Example of Associated Bidirectional LSP

3.1.  Single-sided Initiation

   As specified in [RFC7551], in the single-sided case, the
   bidirectional tunnel is provisioned only on one endpoint node (PCC)
   of the tunnel.  Both forward and reverse LSPs of this tunnel are
   initiated with the Association Type set to "Single-sided
   Bidirectional LSP Association" on the originating endpoint node.  The
   forward and reverse LSPs are identified in the Bidirectional LSP
   Association Group TLV of their PCEP ASSOCIATION Objects.

   The originating endpoint node signals the properties for the revere
   LSP in the RSVP REVERSE_LSP Object [RFC7551] of the forward LSP Path
   message.  The remote endpoint then creates the corresponding reverse
   tunnel and signals the reverse LSP in response to the received RSVP
   Path message.  Similarly, the remote endpoint node deletes the
   reverse LSP when it receives the RSVP Path delete message [RFC3209]
   for the forward LSP.

   The originating endpoint (PCC) node may report/ delegate the forward
   and reverse direction LSPs to a PCE.  The remote endpoint (PCC) node
   may report its forward direction LSP to a PCE.













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                               +-----+
                               | PCE |
                               +-----+
         Initiates:             |    ^      Reports:
         Tunnel 1 (F)           |     \     Tunnel 2 (F)
         (LSP1 (F), LSP2 (R))   |      \    (LSP2 (F))
         Association #1         v       \   Association #1
                             +-----+    +-----+
                             |  A  |    |  D  |
                             +-----+    +-----+

     Figure 2: Example of PCE-Initiated Single-sided Bidirectional LSP

                               +-----+
                               | PCE |
                               +-----+
         Reports/Delegates:     ^    ^      Reports:
         Tunnel 1 (F)           |     \     Tunnel 2 (F)
         (LSP1 (F), LSP2 (R))   |      \    (LSP2 (F))
         Association #2         |       \   Association #2
                             +-----+    +-----+
                             |  A  |    |  D  |
                             +-----+    +-----+

     Figure 3: Example of PCC-Initiated Single-sided Bidirectional LSP

   As shown in Figures 2 and 3, the forward tunnel and both forward LSP1
   and reverse LSP2 are initiated on the originating endpoint node A,
   either by the PCE or the originating PCC, respectively.  The
   originating endpoint node A signals the properties of reverse LSP2 in
   the RSVP REVERSE_LSP Object in the Path message of the forward LSP1.
   The creation of reverse tunnel and reverse LSP2 on the remote
   endpoint node D is triggered by the RSVP signaled forward LSP1.

   As specified in [RFC8537], for fast reroute bypass tunnel assignment,
   the LSP starting from the originating node is identified as the
   forward LSP of the single-sided initiated bidirectional LSP.

3.2.  Double-sided Initiation

   As specified in [RFC7551], in the double-sided case, the
   bidirectional tunnel is provisioned on both endpoint nodes (PCCs) of
   the tunnel.  The forward and reverse LSPs of this tunnel are
   initiated with the Association Type set to "Double-sided
   Bidirectional LSP Association" on both endpoint nodes.  The forward
   and reverse LSPs are identified in the Bidirectional LSP Association
   Group TLV of their ASSOCIATION Objects.




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   The endpoint (PCC) nodes may report/ delegate the forward and reverse
   direction LSPs to a PCE.

                               +-----+
                               | PCE |
                               +-----+
                Initiates:      |    \      Initiates:
                Tunnel 1 (F)    |     \     Tunnel 2 (F)
                (LSP1 (F))      |      \    (LSP2 (F))
                Association #3  v       v    Association #3
                             +-----+    +-----+
                             |  A  |    |  D  |
                             +-----+    +-----+

     Figure 4: Example of PCE-Initiated Double-sided Bidirectional LSP

                               +-----+
                               | PCE |
                               +-----+
            Reports/Delegates:  ^    ^      Reports/Delegates:
            Tunnel 1 (F)        |     \     Tunnel 2 (F)
            (LSP1 (F))          |      \    (LSP2 (F))
            Association #4      |       \   Association #4
                             +-----+    +-----+
                             |  A  |    |  D  |
                             +-----+    +-----+

     Figure 5: Example of PCC-Initiated Double-sided Bidirectional LSP

   As shown in Figures 4 and 5, the forward tunnel and forward LSP1 are
   initiated on the endpoint node A and the reverse tunnel and reverse
   LSP2 are initiated on the endpoint node D, either by the PCE or the
   PCCs, respectively.

   As specified in [RFC8537], for fast reroute bypass tunnel assignment,
   the LSP with the higher Source Address [RFC3209] is identified as the
   forward LSP of the double-sided initiated bidirectional LSP.

3.3.  Co-routed Associated Bidirectional LSP

   In both single-sided and double-sided initiation cases, forward and
   reverse LSPs may be co-routed as shown in Figure 6, where both
   forward and reverse LSPs of a bidirectional LSP follow the same
   congruent path in the forward and reverse directions, respectively.







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               LSP3 -->          LSP3 -->          LSP3 -->
      +-----+           +-----+           +-----+           +-----+
      |  A  +-----------+  B  +-----------+  C  +-----------+  D  |
      +-----+           +-----+           +-----+           +-----+
              <-- LSP4          <-- LSP4          <-- LSP4

        Figure 6: Example of Co-routed Associated Bidirectional LSP

4.  Protocol Extensions

4.1.  ASSOCIATION Object

   As per [RFC8697], LSPs are associated by adding them to a common
   association group.  This document defines two new Bidirectional LSP
   Association Groups to be used by the associated bidirectional LSPs.
   A member of the Bidirectional LSP Association Group can take the role
   of a forward or reverse LSP and follows the following rules:

   o  An LSP (forward or reverse) can not be part of more than one
      Bidirectional LSP Association Group.  More than one forward LSP
      and/ or reverse LSP can be part of a Bidirectional LSP Association
      Group.

   o  The Tunnel (as defined in [RFC3209]) of forward and reverse LSPs
      of the Single-sided Bidirectional LSP Association on the
      originating node MUST be the same.

   This document defines two new Association Types for the ASSOCIATION
   Object (Object-Class value 40) as follows:

   o  Association Type (TBD1) = Single-sided Bidirectional LSP
      Association Group

   o  Association Type (TBD2) = Double-sided Bidirectional LSP
      Association Group

   These Association Types are operator-configured associations in
   nature and statically created by the operator on the PCEP peers.  The
   LSP belonging to these associations is conveyed via PCEP messages to
   the PCEP peer.  Operator-configured Association Range TLV (Value 29)
   [RFC8697] MUST NOT be sent for these Association Types, and MUST be
   ignored, so that the entire range of association ID can be used for
   them.

   The Association ID, Association Source, optional Global Association
   Source and optional Extended Association ID in the Bidirectional LSP
   Association Group Object are initialized using the procedures defined
   in [RFC8697] and [RFC7551].



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4.2.  Bidirectional LSP Association Group TLV

   The Bidirectional LSP Association Group TLV is defined for use with
   the Single-sided and Double-sided Bidirectional LSP Association Group
   Object Types.

   o  The Bidirectional LSP Association Group TLV follows the PCEP TLV
      format from [RFC5440].

   o  The Type (16 bits) of the TLV is TBD3, to be assigned by IANA.

   o  The Length is 4 Bytes.

   o  The value comprises of a single field, the Bidirectional LSP
      Association Flags (32 bits), where each bit represents a flag
      option.

   o  If the Bidirectional LSP Association Group TLV is missing, it
      means the LSP is the forward LSP and it is not co-routed LSP.

   o  For co-routed LSPs, this TLV MUST be present.

   o  For reverse LSPs, this TLV MUST be present.

   o  The Bidirectional LSP Association Group TLV MUST NOT be present
      more than once.  If it appears more than once, only the first
      occurrence is processed and any others MUST be ignored.

   The format of the Bidirectional LSP Association Group TLV is shown in
   Figure 7:

    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 = TBD3           |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Reserved                          |C|R|F|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 7: Bidirectional LSP Association Group TLV format

   Bidirectional LSP Association Flags are defined as following.

   F (Forward LSP, 1 bit) - Indicates whether the LSP associated is the
   forward LSP of the bidirectional LSP.  If this flag is set, the LSP
   is a forward LSP.





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   R (Reverse LSP, 1 bit) - Indicates whether the LSP associated is the
   reverse LSP of the bidirectional LSP.  If this flag is set, the LSP
   is a reverse LSP.

   C (Co-routed Path, 1 bit) - Indicates whether the bidirectional LSP
   is co-routed.  This flag MUST be set for both the forward and reverse
   LSPs of a co-routed bidirectional LSP.

   The C flag is used by the PCE (for both Stateful and Stateless) to
   compute bidirectional paths of the forward and reverse LSPs of a co-
   routed bidirectional LSP.

   The Reserved flags MUST be set to 0 when sent and MUST be ignored
   when received.

5.  PCEP Procedure

5.1.  PCE Initiated LSPs

   As specified in [RFC8697], the Bidirectional LSP Association Groups
   can be created by a Stateful PCE.

   o  Stateful PCE can create and update the forward and reverse LSPs
      independently for both Single-sided and Double-sided Bidirectional
      LSP Association Groups.

   o  Stateful PCE can establish and remove the association relationship
      on a per LSP basis.

   o  Stateful PCE can create and update the LSP and the association on
      a PCC via PCInitiate and PCUpd messages, respectively, using the
      procedures described in [RFC8697].

5.2.  PCC Initiated LSPs

   As specified in [RFC8697], Bidirectional LSP Association Groups can
   also be created by a PCC.

   o  PCC can create and update the forward and reverse LSPs
      independently for both Single-sided and Double-sided Bidirectional
      LSP Association Groups.

   o  PCC can establish and remove the association relationship on a per
      LSP basis.

   o  PCC MUST report the change in the association group of an LSP to
      PCE(s) via PCRpt message.




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   o  PCC can report the forward and reverse LSPs independently to
      PCE(s) via PCRpt message.

   o  PCC can delegate the forward and reverse LSPs independently to a
      Stateful PCE, where PCE would control the LSPs.  For single-sided
      case, originating (PCC) node can delegate both forward and reverse
      LSPs of a tunnel together to a Stateful PCE in order to avoid any
      race condition.

   o  Stateful PCE can update the LSPs in the Bidirectional LSP
      Association Group via PCUpd message, using the procedures
      described in [RFC8697].

5.3.  Stateless PCE

   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.  A PCC can request co-routed or non co-routed forward
   and reverse direction paths from a stateless PCE for a Bidirectional
   LSP Association Group.

5.4.  Bidirectional (B) Flag

   As defined in [RFC5440], the Bidirectional (B) flag in the Request
   Parameters (RP) object is set when the PCC specifies that the path
   computation request is for a bidirectional TE LSP with the same TE
   requirements (e.g. latency) in each direction.  For an associated
   bidirectional LSP, the B-flag MAY be set when the PCC makes the path
   computation request for the same TE requirements in the forward and
   reverse directions.  When a stateful PCE initiates or updates the
   bidirectional LSPs, the B-flag in Stateful PCE Request Parameters
   (SRP) object [RFC8231] MAY also be set.

5.5.  PLSP-ID Usage

   As defined in [RFC8231], a PCEP-specific LSP Identifier (PLSP-ID) is
   created by a PCC to uniquely identify an LSP and it remains the same
   for the lifetime of a PCEP session.

   In case of Single-sided Bidirectional LSP Association, the reverse
   LSP of a bidirectional LSP created on the originating node is
   identified by the PCE using 2 different PLSP-IDs based on the PCEP
   session on the ingress or egress nodes for the LSP.  In other words,
   the reverse LSP on the originating node will have a PLSP-ID A at the
   ingress node while it will have a PLSP-ID B at the egress node.  This
   is not the case for the forward LSP of the Single-sided Bidirectional
   LSP on the originating node and there is no change in the PLSP-ID



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   allocation procedure for it.  In case of Double-sided Bidirectional
   LSP Association, there is no change in the PLSP-ID allocation
   procedure.

   For an Associated Bidirectional LSP, LSP-IDENTIFIERS TLV [RFC8231]
   MUST be included in all forward and reverse LSPs.

5.6.  State Synchronization

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

5.7.  Error Handling

   An LSP (forward or reverse) can not be part of more than one
   Bidirectional LSP Association Group.  If a PCE attempts to add an LSP
   not complying to this rule, the PCC MUST send PCErr with Error-Type =
   26 (Association Error) and Error-Value = TBD4 (Bidirectional LSP
   Association - Group Mismatch).  Similarly, if a PCC attempts to add
   an LSP at PCE not complying to this rule, the PCE MUST send this
   PCErr.

   The LSPs (forward or reverse) in a Single-sided Bidirectional
   Association Group MUST belong to the same TE Tunnel (as defined in
   [RFC3209]).  If a PCE attempts to add an LSP in a Single-sided
   Bidirectional LSP Association Group for a different Tunnel, the PCC
   MUST send PCErr with Error-Type = 26 (Association Error) and Error-
   Value = TBD5 (Bidirectional Association - Tunnel Mismatch).
   Similarly, if a PCC attempts to add an LSP to a Single-sided
   Bidirectional LSP Association Group at PCE not complying to this
   rule, the PCE MUST send this PCErr.

   The PCEP Path Setup Type (PST) MUST be set to 'Path is set up using
   the RSVP-TE signaling protocol' (Value 0) [RFC8408] for the LSP
   belonging to the Bidirectional LSP Association Groups defined in this
   document.  In case a PCEP speaker receives a different PST value for
   this association group, it MUST return a PCErr message with Error-
   Type = 26 (Association Error) and Error-Value = TBD6 (Bidirectional
   LSP Association - Path Setup Type Mismatch).

   The processing rules as specified in Section 6.4 of [RFC8697]
   continue to apply to the Association Types defined in this document.







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6.  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".

6.1.  Implementation

   The PCEP extensions defined in this document has been implemented by
   a vendor on their product.  No further information is available at
   this time.

7.  Security Considerations

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

   Two new Association Types for the ASSOCIATION Object, Single-sided
   Bidirectional LSP Association Group and Double-sided Bidirectional
   LSP Association Group are introduced in this document.  Additional
   security considerations related to LSP associations due to a
   malicious PCEP speaker is described in [RFC8697] and apply to these
   Association Types.  Hence, securing the PCEP session using Transport
   Layer Security (TLS) [RFC8253] is recommended.








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8.  Manageability Considerations

8.1.  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].

8.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB, there are no new MIB Objects
   defined for LSP associations.

   The PCEP YANG module [I-D.ietf-pce-pcep-yang] defines data model for
   LSP associations.

8.3.  Liveness Detection and Monitoring

   The 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].

8.4.  Verify Correct Operations

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

8.5.  Requirements On Other Protocols

   The mechanisms defined in this document do not add any new
   requirements on other protocols.

8.6.  Impact On Network Operations

   The mechanisms defined in this document do not have any impact on
   network operations in addition to those already listed in [RFC5440],
   [RFC8231], and [RFC8281].

9.  IANA Considerations

9.1.  Association Types

   This document adds new Association Types for the ASSOCIATION Object
   (Object-class value 40) defined [RFC8697].  IANA is requested to make
   the assignment of values for the sub-registry "ASSOCIATION Type
   Field" [RFC8697], as follows:




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   Type Name                                             Reference
   ---------------------------------------------------------------------
   TBD1 Single-sided Bidirectional LSP Association Group [This document]
   TBD2 Double-sided Bidirectional LSP Association Group [This document]

9.2.  Bidirectional LSP Association Group TLV

   This document defines a new TLV for carrying additional information
   of LSPs within a Bidirectional LSP Association Group.  IANA is
   requested to add the assignment of a new value in the existing "PCEP
   TLV Type Indicators" registry as follows:

   Value     Meaning                                   Reference
   -------------------------------------------------------------------
    TBD3     Bidirectional LSP Association Group TLV   [This document]

9.2.1.  Flag Fields in Bidirectional LSP Association Group TLV

   This document requests that a new sub-registry, named "Bidirectional
   LSP Association Group TLV Flag Field", is created within the "Path
   Computation Element Protocol (PCEP) Numbers" registry to manage the
   Flag field in the Bidirectional LSP Association Group TLV.  New
   values are to be assigned by Standards Action [RFC8126].  Each bit
   should be tracked with the following qualities:

   o  Bit number (count from 0 as the most significant bit)

   o  Description

   o  Reference

   The following values are defined in this document for the Flag field.

   Bit No.     Description                   Reference
   ---------------------------------------------------------
    31         F - Forward LSP               [This document]
    30         R - Reverse LSP               [This document]
    29         C - Co-routed Path            [This document]

9.3.  PCEP Errors

   This document defines new Error value for Error Type 26 (Association
   Error).  IANA is requested to allocate new Error value within the
   "PCEP-ERROR Object Error Types and Values" sub-registry of the PCEP
   Numbers registry, as follows:






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   Error Type  Description                  Reference
   ---------------------------------------------------------
    26         Association Error

               Error value: TBD4            [This document]
               Bidirectional LSP Association - Group Mismatch

               Error value: TBD5            [This document]
               Bidirectional LSP Association - Tunnel Mismatch

               Error value: TBD6            [This document]
               Bidirectional LSP Association - Path Setup Type Mismatch



10.  References

10.1.  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>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [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>.

   [RFC7551]  Zhang, F., Ed., Jing, R., and R. Gandhi, Ed., "RSVP-TE
              Extensions for Associated Bidirectional Label Switched
              Paths (LSPs)", RFC 7551, DOI 10.17487/RFC7551, May 2015,
              <https://www.rfc-editor.org/info/rfc7551>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.




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   [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>.

   [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>.

   [RFC8537]  Gandhi, R., Ed., Shah, H., and J. Whittaker, "Updates to
              the Fast Reroute Procedures for Co-routed Associated
              Bidirectional Label Switched Paths (LSPs)", RFC 8537,
              DOI 10.17487/RFC8537, February 2019,
              <https://www.rfc-editor.org/info/rfc8537>.

   [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>.

10.2.  Informative References

   [I-D.ietf-pce-pcep-yang]
              Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
              YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", draft-ietf-pce-pcep-
              yang-13 (work in progress), October 2019.

   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
              September 2009, <https://www.rfc-editor.org/info/rfc5654>.

   [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>.

   [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>.



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   [RFC8051]  Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
              Stateful Path Computation Element (PCE)", RFC 8051,
              DOI 10.17487/RFC8051, January 2017,
              <https://www.rfc-editor.org/info/rfc8051>.

   [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>.

   [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>.

Acknowledgments

   The authors would like to thank Dhruv Dhody for various discussions
   on association groups and inputs to this document.  The authors would
   also like to thank Dhruv Dhody, Mike Taillon, and Marina Fizgeer for
   reviewing this document and providing valuable comments.

Authors' Addresses

   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada

   Email: rgandhi@cisco.com


   Colby Barth
   Juniper Networks

   Email: cbarth@juniper.net


   Bin Wen
   Comcast

   Email: Bin_Wen@cable.comcast.com









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