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rfc:rfc8281

Internet Engineering Task Force (IETF) E. Crabbe Request for Comments: 8281 Individual Contributor Category: Standards Track I. Minei ISSN: 2070-1721 Google, Inc.

                                                          S. Sivabalan
                                                   Cisco Systems, Inc.
                                                              R. Varga
                                             Pantheon Technologies SRO
                                                         December 2017

Path Computation Element Communication Protocol (PCEP) Extensions for

          PCE-Initiated LSP Setup in a Stateful PCE Model

Abstract

 The Path Computation Element Communication Protocol (PCEP) provides
 mechanisms for Path Computation Elements (PCEs) to perform path
 computations in response to Path Computation Client (PCC) requests.
 The extensions for stateful PCE provide active control of
 Multiprotocol Label Switching (MPLS) Traffic Engineering Label
 Switched Paths (TE LSPs) via PCEP, for a model where the PCC
 delegates control over one or more locally configured LSPs to the
 PCE.  This document describes the creation and deletion of
 PCE-initiated LSPs under the stateful PCE model.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8281.

Crabbe, et al. Standards Track [Page 1] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

Copyright Notice

 Copyright (c) 2017 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.

Crabbe, et al. Standards Track [Page 2] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
 3.  Architectural Overview  . . . . . . . . . . . . . . . . . . .   5
   3.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.2.  Operation Overview  . . . . . . . . . . . . . . . . . . .   6
 4.  Support of PCE-Initiated LSPs . . . . . . . . . . . . . . . .   7
   4.1.  STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . .   8
 5.  PCE-Initiated LSP Instantiation and Deletion  . . . . . . . .   8
   5.1.  The LSP Initiate Request  . . . . . . . . . . . . . . . .   8
   5.2.  The R Flag in the SRP Object  . . . . . . . . . . . . . .  10
   5.3.  LSP Instantiation . . . . . . . . . . . . . . . . . . . .  10
     5.3.1.  The Create Flag . . . . . . . . . . . . . . . . . . .  12
     5.3.2.  The SPEAKER-ENTITY-ID TLV . . . . . . . . . . . . . .  13
   5.4.  LSP Deletion  . . . . . . . . . . . . . . . . . . . . . .  13
 6.  LSP Delegation and Cleanup  . . . . . . . . . . . . . . . . .  14
 7.  LSP State Synchronization . . . . . . . . . . . . . . . . . .  15
 8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   8.1.  PCEP Messages . . . . . . . . . . . . . . . . . . . . . .  15
   8.2.  LSP Object  . . . . . . . . . . . . . . . . . . . . . . .  15
   8.3.  SRP object  . . . . . . . . . . . . . . . . . . . . . . .  16
   8.4.  STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . .  16
   8.5.  PCEP-Error Object . . . . . . . . . . . . . . . . . . . .  17
 9.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   9.1.  Malicious PCE . . . . . . . . . . . . . . . . . . . . . .  18
   9.2.  Malicious PCC . . . . . . . . . . . . . . . . . . . . . .  18
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
   10.1.  Normative References . . . . . . . . . . . . . . . . . .  19
   10.2.  Informative References . . . . . . . . . . . . . . . . .  19
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  20
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

Crabbe, et al. Standards Track [Page 3] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

1. Introduction

 [RFC5440] describes the Path Computation Element Communication
 Protocol (PCEP).  PCEP defines the communication between a Path
 Computation Client (PCC) and a Path Computation Element (PCE), or
 between PCE and PCE, enabling computation of Multiprotocol Label
 Switching (MPLS) for Traffic Engineering Label Switched Path (TE LSP)
 characteristics.
 [RFC8231] specifies a set of extensions to PCEP to enable stateful
 control of TE LSPs between and across PCEP sessions in compliance
 with [RFC4657].  It includes:
 o  mechanisms to effect LSP State Synchronization between PCCs and
    PCEs
 o  delegation of control of LSPs to PCEs
 o  PCE control of timing and sequence of path computations within and
    across PCEP sessions
 It focuses on a model where LSPs are configured on the PCC, and
 control over them is delegated to the PCE.
 This document describes the setup, maintenance, and teardown of
 PCE-initiated LSPs under the stateful PCE model, without the need for
 local configuration on the PCC, thus allowing for a dynamic network
 that is centrally controlled and deployed.

2. Terminology

 This document uses the following terms defined in [RFC5440]: PCC,
 PCE, and PCEP Peer.
 This document uses the following terms defined in [RFC8051]: Stateful
 PCE and Delegation.
 This document uses the following terms defined in [RFC8231]:
 Redelegation Timeout Interval, State Timeout Interval, LSP State
 Report, and LSP Update Request.
 The following terms are defined in this document:
 PCE-initiated LSP:  LSP that is instantiated as a result of a request
    from the PCE.
 The message formats in this document are specified using Routing
 Backus-Naur Form (RBNF) encoding as specified in [RFC5511].

Crabbe, et al. Standards Track [Page 4] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

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. Architectural Overview

3.1. Motivation

 [RFC8231] provides active control over LSPs that are locally
 configured on the PCC.  This model relies on the Label Edge Router
 (LER) taking an active role in delegating locally configured LSPs to
 the PCE and is well suited in environments where the LSP placement is
 fairly static.  However, in environments where the LSP placement
 needs to change in response to application demands, it is useful to
 support dynamic creation and teardown of LSPs.  The ability for a PCE
 to trigger the creation of LSPs on demand can be seamlessly
 integrated into a controller-based network architecture, where
 intelligence in the controller can determine when and where to set up
 paths.
 A possible use case is a software-defined network, where applications
 request network resources and paths from the network infrastructure.
 For example, an application can request a path with certain
 constraints between two Label Switching Routers (LSRs) by contacting
 the PCE.  The PCE can compute a path satisfying the constraints, and
 instruct the head end LSR to instantiate and signal it.  When the
 path is no longer required by the application, the PCE can request
 its teardown.
 Another use case is dynamically adjusting aggregate bandwidth between
 two points in the network using multiple LSPs.  This functionality is
 very similar to auto-bandwidth, but it allows for providing the
 desired capacity through multiple LSPs.  This approach overcomes two
 of the limitations auto-bandwidth can experience: 1) growing the
 capacity between the endpoints beyond the capacity of individual
 links in the path and 2) achieving good bin packing through use of
 several small LSPs instead of a single large one.  The number of LSPs
 varies based on the demand, and LSPs are created and deleted
 dynamically to satisfy the bandwidth requirements.

Crabbe, et al. Standards Track [Page 5] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

 Another use case is demand engineering, where a PCE with visibility
 into both the network state and the demand matrix can anticipate and
 optimize how traffic is distributed across the infrastructure.  Such
 optimizations may require creating new paths across the
 infrastructure.

3.2. Operation Overview

 This document defines the new I flag in the STATEFUL-PCE-CAPABILITY
 TLV to indicate that the sender supports PCE-initiated LSPs (see
 details in Section 4.1).  A PCC or PCE sets this flag in the Open
 message during the PCEP initialization phase to indicate that it
 supports the procedures of this document.
 This document defines a new PCEP message, the LSP Initiate Request
 (PCInitiate) message, which a PCE can send to a PCC to request the
 initiation or deletion of an LSP.  The decision when to instantiate
 or delete a PCE-initiated LSP is out of the scope of this document.
 The PCE sends a PCInitiate message to the PCC to request the
 initiation of an LSP.  The PCC creates the LSP using the attributes
 communicated by the PCE and local values for any unspecified
 parameters.  The PCC generates a Path Computation State Report
 (PCRpt) for the LSP, carrying a newly assigned PLSP-ID for the LSP
 and delegating the LSP to the PCE via the Delegate flag in the LSP
 object.
 The PCE can update the attributes of the LSP by sending subsequent
 Path Computation Update Request (PCUpd) messages.  Subsequent PCRpt
 and PCUpd messages that the PCC and PCE, respectively, send for the
 LSP will carry the PCC-assigned PLSP-ID, which uniquely identifies
 the LSP.  See details in Section 5.3.
 The PCE sends a PCInitiate message to the PCC to request the deletion
 of an LSP.  To indicate a delete operation, this document defines the
 new R flag in the Stateful PCE Request Parameter (SRP) object in the
 PCInitiate message, as described in Section 5.2.  As a result of the
 deletion request, the PCC removes the LSP and sends a PCRpt for the
 removed state.  See details in Section 5.4.
 Figure 1 illustrates these message exchanges.

Crabbe, et al. Standards Track [Page 6] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

       +-+-+                            +-+-+
       |PCC|                            |PCE|
       +-+-+                            +-+-+
         |                                |
         |<--PCInitiate-------------------| (Initiate LSP)
         |                                |
         |---PCRpt, PLSP_ID=1, D=1------->| (Confirm initiation)
         |            .                   |
         |            .                   |
         |                                |
         |<--PCUpd, PLSP_ID=1-------------| (Update LSP)
         |                                |
         |---PCRpt, PLSP_ID=1, D=1------->| (Confirm update)
         |            .                   |
         |            .                   |
         |                                |
         |<--PCInitiate, PLSP_ID=1, R=1---| (Delete LSP)
         |                                |
         |---PCRpt, PLSP_ID=1, R=1------->| (Confirm delete)
                Figure 1: PCE-Initiated LSP Life Cycle

4. Support of PCE-Initiated LSPs

 A PCEP speaker indicates its ability to support PCE-initiated LSPs
 during the PCEP initialization phase, as follows.  When the PCEP
 session is created, it sends an Open message with an OPEN object that
 contains the STATEFUL-PCE-CAPABILITY TLV, as defined in [RFC8231].  A
 new flag, the I (LSP-INSTANTIATION-CAPABILITY) flag, is introduced to
 this TLV to indicate support for instantiation of PCE-initiated LSPs.
 A PCE can initiate LSPs only for PCCs that advertised this
 capability.  A PCC will follow the procedures described in this
 document only on sessions where the PCE advertised the I flag.

Crabbe, et al. Standards Track [Page 7] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

4.1. STATEFUL-PCE-CAPABILITY TLV

 The format of the STATEFUL-PCE-CAPABILITY TLV is defined in [RFC8231]
 and included here for easy reference with the addition of the new I
 flag.
    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=4           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Flags                                      |I|S|U|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+
             Figure 2: STATEFUL-PCE-CAPABILITY TLV Format
 A new flag is defined to indicate the sender's support for LSP
 instantiation by a PCE:
 I (LSP-INSTANTIATION-CAPABILITY -- 1 bit):  If set to 1 by a PCC, the
    I flag indicates that the PCC allows instantiation of an LSP by a
    PCE.  If set to 1 by a PCE, the I flag indicates that the PCE
    supports instantiating LSPs.  The LSP-INSTANTIATION-CAPABILITY
    flag must be set by both the PCC and PCE in order to enable
    PCE-initiated LSP instantiation.

5. PCE-Initiated LSP Instantiation and Deletion

 To initiate an LSP, a PCE sends a PCInitiate message to a PCC.  The
 message format, objects, and TLVs are discussed separately below for
 the creation and the deletion cases.

5.1. The LSP Initiate Request

 An LSP Initiate Request (PCInitiate) message is a PCEP message sent
 by a PCE to a PCC to trigger LSP instantiation or deletion.  The
 Message-Type field of the PCEP common header for the PCInitiate
 message is set to 12.  The PCInitiate message MUST include the SRP
 and the LSP objects and MAY contain other objects, as discussed later
 in this section.

Crabbe, et al. Standards Track [Page 8] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

 The format of a PCInitiate message is as follows:
   <PCInitiate Message> ::= <Common Header>
                            <PCE-initiated-lsp-list>
 Where:
   <Common Header> is defined in RFC 5440
   <PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
                                [<PCE-initiated-lsp-list>]
   <PCE-initiated-lsp-request> ::= (<PCE-initiated-lsp-instantiation>|
                                    <PCE-initiated-lsp-deletion>)
   <PCE-initiated-lsp-instantiation> ::= <SRP>
                                         <LSP>
                                         [<END-POINTS>]
                                         <ERO>
                                         [<attribute-list>]
   <PCE-initiated-lsp-deletion> ::= <SRP>
                                    <LSP>
 Where:
   <attribute-list> is defined in RFC 5440 and extended by
   PCEP extensions.
 The LSP object is defined in [RFC8231].  The END-POINTS and Explicit
 Route Objects (EROs) are defined in [RFC5440].
 The SRP object is defined in [RFC8231].  The SRP object contains an
 SRP-ID-number that is unique within a PCEP session.  The PCE
 increments the last-used SRP-ID-number before it sends each
 PCInitiate message.  The PCC MUST echo the value of the SRP-ID-number
 in PCEP Error (PCErr) and PCRpt messages that it sends as a result of
 the PCInitiate; this allows the PCE to correlate them with the
 corresponding PCInitiate message.

Crabbe, et al. Standards Track [Page 9] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

5.2. The R Flag in the SRP Object

 The format of the SRP object is defined in [RFC8231] and included
 here for easy reference with the addition of the new R flag.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Flags                              |R|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        SRP-ID-number                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    //                      Optional TLVs                          //
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 3: The SRP Object Format
 A new flag is defined to indicate a delete operation initiated by the
 PCE:
 R (LSP-REMOVE -- 1 bit):  If set to 0, it indicates a request to
    create an LSP.  If set to 1, it indicates a request to remove an
    LSP.

5.3. LSP Instantiation

 The LSP is instantiated by sending a PCInitiate message.  The LSP is
 set up using RSVP-TE.  Extensions for other setup methods are outside
 the scope of this document.
 The PCInitiate message, when used to instantiate an LSP, MUST contain
 an LSP object with the reserved PLSP-ID 0.  The LSP object MUST
 include the SYMBOLIC-PATH-NAME TLV, which is used to correlate
 between the PCC-assigned PLSP-ID and the LSP.
 The PCInitiate message, when used to instantiate an LSP, MUST contain
 an ERO for the LSP.
 For an instantiation request of an RSVP-signaled LSP, the destination
 address may be needed.  The PCC MAY determine it from a provided
 object (e.g., ERO) or a local decision.  Alternatively, the
 END-POINTS object MAY be included to explicitly convey the
 destination addresses to be used in the RSVP-TE signaling.  The
 source address MUST be either specified or left for the PCC to choose
 by setting it to "0.0.0.0" (if the destination is an IPv4 address) or
 "::" (if the destination is an IPv6 address).

Crabbe, et al. Standards Track [Page 10] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

 The PCE MAY include various attributes as per [RFC5440].  The PCC
 MUST use these values in the LSP instantiation and local values for
 unspecified parameters.  After the LSP setup, the PCC MUST send a
 PCRpt to the PCE, reflecting these values.  The SRP object in the
 PCRpt message MUST echo the value of the PCInitiate message that
 triggered the setup.  LSPs that were instantiated as a result of a
 PCInitiate message MUST have the Create flag (Section 5.3.1) set in
 the LSP object.
 If the PCC receives a PCInitiate message with a non-zero PLSP-ID and
 the R flag in the SRP object set to zero, then it MUST send a PCErr
 message with Error-type=19 (Invalid Operation) and Error-value=8
 (Non-zero PLSP-ID in the LSP Initiate Request).
 If the PCC receives a PCInitiate message without an ERO and the R
 flag in the SRP object set to zero, then it MUST send a PCErr message
 with Error-type=6 (Mandatory Object missing) and Error-value=9 (ERO
 object missing).
 If the PCC receives a PCInitiate message without a SYMBOLIC-PATH-NAME
 TLV, then it MUST send a PCErr message with Error-type=10 (Reception
 of an invalid object) and Error-value=8 (SYMBOLIC-PATH-NAME TLV
 missing).
 The PCE MUST NOT provide a symbolic path name that conflicts with the
 symbolic path name of any existing LSP in the PCC.  (Existing LSPs
 may be either statically configured or initiated by another PCE.)  If
 there is a conflict with the symbolic path name of an existing LSP,
 the PCC MUST send a PCErr message with Error-type=23 (Bad Parameter
 value) and Error-value=1 (SYMBOLIC-PATH-NAME in use).  The only
 exception to this rule is for LSPs for which the State Timeout
 Interval timer is running (see Section 6).
 If the PCC determines that the LSP parameters proposed in the
 PCInitiate message are unacceptable, it MUST send a PCErr message
 with Error-type=24 (PCE instantiation error) and Error-value=1
 (Unacceptable instantiation parameters).  If the PCC encounters an
 internal error during the processing of the PCInitiate message, it
 MUST send a PCErr message with Error-type=24 (PCE instantiation
 error) and Error-value=2 (Internal error).
 A PCC MUST relay errors it encounters in the setup of a PCE-initiated
 LSP to the PCE by sending a PCErr message with Error-type=24 (PCE
 instantiation error) and Error-value=3 (Signaling error).  The PCErr
 message MUST echo the SRP-ID-number of the PCInitiate message.  The
 PCEP-ERROR object SHOULD include the RSVP_ERROR_SPEC TLV (if an RSVP
 ERROR_SPEC object was returned to the PCC by a downstream node).

Crabbe, et al. Standards Track [Page 11] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

 After the LSP is set up, errors in RSVP signaling are reported in
 PCRpt messages, as described in [RFC8231].
 On successful completion of the LSP instantiation, the PCC MUST send
 a PCRpt message.  The LSP object message MUST contain a non-zero
 PLSP-ID that uniquely identifies the LSP within this PCC and MUST
 have the Create flag (Section 5.3.1) and Delegate flag set.  The SRP
 object MUST contain an SRP-ID-number that echoes the value from the
 PCInitiate message that triggered the setup.  The PCRpt MUST include
 the attributes that the PCC used to instantiate the LSP.
 A PCC SHOULD be able to place a limit on either the number of LSPs or
 the percentage of resources that are allocated to honor PCE-initiated
 LSP requests.  As soon as that limit is reached, the PCC MUST send a
 PCErr message with Error-type=19 (Invalid Operation) and
 Error-value=6 (PCE-initiated LSP limit reached) and is free to drop
 any incoming PCInitiate messages without additional processing.
 Similarly, the PCE SHOULD be able to place a limit on either the
 number of PCInitiate messages pending for a particular PCC or the
 time it waits for a response (positive or negative) to a PCInitiate
 message from a PCC, and it MAY take further action (such as closing
 the session or removing all its LSPs) if this limit is reached.

5.3.1. The Create Flag

 The LSP object is defined in [RFC8231] and included here for easy
 reference with the addition of the new Create (C) flag.
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                PLSP-ID                |Flags  |C|  O  |A|R|S|D|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                        TLVs                                 //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 4: The LSP Object Format
 A new flag, the C flag, is introduced.  On a PCRpt message, the C
 flag set to 1 indicates that this LSP was created via a PCInitiate
 message.  The C flag MUST be set to 1 on each PCRpt message for the
 LSP's duration of existence.  The C flag allows PCEs to be aware of
 which LSPs were PCE initiated (a state that would otherwise only be
 known by the PCC and the PCE that initiated them).

Crabbe, et al. Standards Track [Page 12] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

5.3.2. The SPEAKER-ENTITY-ID TLV

 The optional SPEAKER-ENTITY-ID TLV defined in [RFC8232] MAY be
 included in the LSP object in a PCRpt message as an optional TLV for
 LSPs for which the C flag is 1.  The SPEAKER-ENTITY-ID TLV identifies
 the PCE that initiated the creation of the LSP on all PCEP sessions,
 a state that would otherwise only be known by the PCC and the PCE
 that initiated the LSP.  If the TLV appears in a PCRpt for an LSP for
 which the C flag is 0, the LSP MUST be ignored, and the PCE MUST send
 a PCErr message with Error-type=23 (Bad parameter value) and
 Error-value=2 (Speaker identity included for an LSP that is not PCE
 initiated).

5.4. LSP Deletion

 A PCE can initiate the removal of a PCE-initiated LSP by sending a
 PCInitiate message with an LSP object carrying the PLSP-ID of the LSP
 to be removed and an SRP object with the R flag set (see
 Section 5.2).  A PLSP-ID of zero removes all LSPs with the C flag set
 to 1 (in their LSP object) that are delegated to the PCE.
 If the PLSP-ID is unknown, the PCC MUST send a PCErr message with
 Error-type=19 (Invalid Operation) and Error-value=3 (Unknown PLSP-ID)
 [RFC8231].
 If the PLSP-ID specified in the PCInitiate message is not delegated
 to the PCE, the PCC MUST send a PCErr message with Error-type=19
 (Invalid operation) and Error-value=1 (LSP is not delegated)
 [RFC8231].
 If the PLSP-ID specified in the PCInitiate message was not created by
 a PCE, the PCC MUST send a PCErr message with Error-type=19 (Invalid
 operation) and Error-value=9 (LSP is not PCE initiated).
 Following the removal of the LSP, the PCC MUST send a PCRpt as
 described in [RFC8231].  The SRP object in the PCRpt MUST include the
 SRP-ID-number from the PCInitiate message that triggered the removal.
 The R flag in the SRP object MUST be set.

Crabbe, et al. Standards Track [Page 13] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

6. LSP Delegation and Cleanup

 The PCC MUST delegate PCE-initiated LSPs to the PCE upon
 instantiation.  The PCC MUST set the delegation bit to 1 in the PCRpt
 that includes the assigned PLSP-ID.
 The PCC MUST NOT revoke the delegation for a PCE-initiated LSP on an
 active PCEP session.  Therefore, all PCRpt messages from the PCC to
 the PCE that owns the delegation MUST have the delegation bit set to
 1.  If the PCE that owns the delegation receives a PCRpt message with
 the delegation bit set to 0, then it MUST send a PCErr message with
 Error-type=19 (Invalid Operation) and Error-value=7 (Delegation for
 PCE-initiated LSP cannot be revoked).  The PCE MAY further react by
 closing the session.
 Control over a PCE-initiated LSP can revert to the PCC in two ways.
 A PCE MAY return a delegation to the PCC to allow for LSP transfer
 between PCEs.  Alternatively, the PCC gains control of an LSP if the
 PCEP session that it was delegated on fails and the Redelegation
 Timeout Interval timer expires.  In both cases, the LSP becomes an
 orphan until the expiration of the State Timeout Interval timer
 [RFC8231].
 The PCC MAY attempt to redelegate an orphaned LSP by following the
 procedures of [RFC8231].  Alternatively, if the orphaned LSP was
 PCE-initiated, then a PCE MAY obtain control over it, as follows.
 A PCE (either the original or one of its backups) sends a PCInitiate
 message that includes just the SRP and LSP objects and carries the
 PLSP-ID of the LSP it wants to take control of.  If the PCC receives
 a PCInitiate message with a PLSP-ID pointing to an orphaned
 PCE-initiated LSP, then it MUST redelegate that LSP to the PCE.  Any
 other non-zero PLSP-ID MUST result in the generation of a PCErr
 message using the rules described in Section 5.4.  The State Timeout
 Interval timer for the LSP is stopped upon the redelegation.  After
 obtaining control of the LSP, the PCE may remove it using the
 procedures described in this document.
 The State Timeout Interval timer ensures that a PCE crash does not
 result in automatic and immediate disruption for the services using
 PCE-initiated LSPs.  PCE-initiated LSPs are not removed immediately
 upon PCE failure.  Instead, they are cleaned up on the expiration of
 this timer.  This allows for network cleanup without manual
 intervention.  The PCC MUST support removal of PCE-initiated LSPs as
 one of the behaviors applied on expiration of the State Timeout
 Interval timer.  The behavior MUST be picked based on local policy
 and can result in either LSP removal or reverting to operator-defined
 default parameters.

Crabbe, et al. Standards Track [Page 14] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

7. LSP State Synchronization

 LSP State Synchronization procedures are described in Section 5.6 of
 [RFC8231].  During State Synchronization, a PCC reports the state of
 its LSPs to the PCE using PCRpt messages, setting the SYNC flag in
 the LSP object.  For PCE-initiated LSPs, the PCC MUST also set the
 Create flag in the LSP object and MAY include the SPEAKER-ENTITY-ID
 TLV identifying the PCE that requested the LSP creation.  At the end
 of State Synchronization, the PCE SHOULD send a PCInitiate message to
 initiate any missing LSPs and/or remove any LSPs that are not wanted.
 Under some circumstances, depending on the deployment, it might be
 preferable for a PCE not to send this PCInitiate immediately, or at
 all.  For example, the PCC may be a slow device, or the operator
 might prefer not to disrupt active flows.

8. IANA Considerations

 As detailed below, IANA has allocated code points for the protocol
 elements defined in this document.

8.1. PCEP Messages

 IANA has registered the following message type within the "PCEP
 Messages" subregistry of the PCEP Numbers registry.  (Note that the
 early allocation for this message type was called "Initiate"; it has
 been changed as follows.)
             Value     Meaning                  Reference
             -----     --------------------     -------------
               12      LSP Initiate Request     RFC 8281

8.2. LSP Object

 [RFC8231] defines the LSP object; per that RFC, IANA created a
 registry to manage the value of the LSP object's Flag field.  IANA
 has allocated a new bit in the "LSP Object Flag Field" subregistry,
 as follows:
                  Bit     Description       Reference
                  ---     -----------       -------------
                   4      Create            RFC 8281

Crabbe, et al. Standards Track [Page 15] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

8.3. SRP object

 IANA has created a new subregistry, named "SRP Object Flag Field",
 within the "Path Computation Element Protocol (PCEP) Numbers"
 registry, to manage the Flag field of the SRP object.  New values are
 to be assigned by Standards Action [RFC8126].  Each bit is tracked
 with the following qualities: bit number (counting from bit 0 as the
 most significant bit), description, and defining RFC.
 The following values are defined in this document:
                  Bit     Description       Reference
                  ---     -----------       -------------
                   31     LSP-Remove        RFC 8281

8.4. STATEFUL-PCE-CAPABILITY TLV

 [RFC8231] defines the STATEFUL-PCE-CAPABILITY TLV; per that RFC, IANA
 created a registry to manage the value of the STATEFUL-PCE-CAPABILITY
 TLV's Flag field.  IANA has allocated a new bit in the STATEFUL-PCE-
 CAPABILITY TLV Flag Field registry, as follows:
          Bit  Description                      Reference
          ---  -------------------------------- -------------
           29  LSP-INSTANTIATION-CAPABILITY (I) RFC 8281

Crabbe, et al. Standards Track [Page 16] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

8.5. PCEP-Error Object

 IANA has registered the following error types and error values within
 the "PCEP-ERROR Object Error Types and Values" subregistry of the
 PCEP Numbers registry.
 Error-Type  Meaning
 ----------  --------------
    10       Reception of an invalid object
              Error-value=8:  SYMBOLIC-PATH-NAME TLV missing
    19       Invalid Operation
              Error-value=6:  PCE-initiated LSP limit reached
              Error-value=7:  Delegation for PCE-initiated LSP cannot
                               be revoked
              Error-value=8:  Non-zero PLSP-ID in LSP Initiate Request
              Error-value=9:  LSP is not PCE initiated
              Error-value=10: PCE-initiated operation-frequency limit
                               reached
    23       Bad parameter value
              Error-value=1:  SYMBOLIC-PATH-NAME in use
              Error-value=2:  Speaker identity included for an LSP
                               that is not PCE initiated
    24       LSP instantiation error
              Error-value=1:  Unacceptable instantiation parameters
              Error-value=2:  Internal error
              Error-value=3:  Signaling error

Crabbe, et al. Standards Track [Page 17] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

9. Security Considerations

 The security considerations described in [RFC8231] apply to the
 extensions described in this document.  Additional considerations
 related to a malicious PCE are introduced.

9.1. Malicious PCE

 The LSP instantiation mechanism described in this document allows a
 PCE to generate state on the PCC and throughout the network.  As a
 result, it introduces a new attack vector: an attacker may flood the
 PCC with LSP instantiation requests and consume network and LSR
 resources by either spoofing messages or compromising the PCE itself.
 A PCC can protect itself from such an attack by imposing a limit on
 either the number of LSPs or the percentage of resources that are
 allocated to honor PCE-initiated LSP requests.  As soon as that limit
 is reached, the PCC MUST send a PCErr message with Error-type=19
 (Invalid Operation) and Error-value=6 (PCE-initiated LSP limit
 reached) and is free to drop any incoming PCInitiate messages for LSP
 initiation without additional processing.
 Rapid flaps triggered by the PCE can also be an attack vector.  A PCC
 can protect itself from such an attack by imposing a limit on the
 number of flaps per unit of time that it allows a PCE to generate.
 As soon as that limit is reached, a PCC MUST send a PCErr message
 with Error-type=19 (Invalid Operation) and Error-value=10
 (PCE-initiated operation-frequency limit reached) and is free to
 treat the session as having reached the limit in terms of resources
 allocated to honor PCE-initiated LSP requests, either permanently or
 for a locally-defined cool-off period.

9.2. Malicious PCC

 The LSP instantiation mechanism described in this document requires
 the PCE to keep state for LSPs that it instantiates and relies on the
 PCC responding (with either a state report or an error message) to
 requests for LSP instantiation.  A malicious PCC or one that reached
 the limit of the number of PCE-initiated LSPs can ignore PCE requests
 and consume PCE resources.  A PCE can protect itself by imposing a
 limit on the number of requests pending or by setting a timeout, and
 it MAY take further action such as closing the session or removing
 all the LSPs it initiated.

Crabbe, et al. Standards Track [Page 18] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

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>.
 [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>.
 [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
            Used to Form Encoding Rules in Various Routing Protocol
            Specifications", RFC 5511, DOI 10.17487/RFC5511, April
            2009, <https://www.rfc-editor.org/info/rfc5511>.
 [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>.
 [RFC8232]  Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
            and D. Dhody, "Optimizations of Label Switched Path State
            Synchronization Procedures for a Stateful PCE", RFC 8232,
            DOI 10.17487/RFC8232, September 2017,
            <https://www.rfc-editor.org/info/rfc8232>.

10.2. Informative References

 [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
            Element (PCE) Communication Protocol Generic
            Requirements", RFC 4657, DOI 10.17487/RFC4657, September
            2006, <https://www.rfc-editor.org/info/rfc4657>.
 [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>.

Crabbe, et al. Standards Track [Page 19] RFC 8281 PCE-Initiated LSPs in Stateful PCE December 2017

 [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>.

Acknowledgments

 We would like to thank Jan Medved, Ambrose Kwong, Ramon Casellas,
 Cyril Margaria, Dhruv Dhody, Raveendra Trovi, and Jon Hardwick for
 their contributions to this document.

Authors' Addresses

 Edward Crabbe
 Individual Contributor
 Email: edward.crabbe@gmail.com
 Ina Minei
 Google, Inc.
 1600 Amphitheatre Parkway
 Mountain View, CA  94043
 United States of America
 Email: inaminei@google.com
 Siva Sivabalan
 Cisco Systems, Inc.
 170 West Tasman Dr.
 San Jose, CA  95134
 United States of America
 Email: msiva@cisco.com
 Robert Varga
 Pantheon Technologies SRO
 Mlynske Nivy 56
 Bratislava  821 05
 Slovakia
 Email: robert.varga@pantheon.tech

Crabbe, et al. Standards Track [Page 20]

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