



PCE Working Group                                               D. Dhody
Internet-Draft                                                   S. Peng
Intended status: Experimental                                     Huawei
Expires: 3 September 2026                                         Y. Lee
                                                     Samsung Electronics
                                                           D. Ceccarelli
                                                                   Cisco
                                                                 A. Wang
                                                           China Telecom
                                                               G. Mishra
                                                            Verizon Inc.
                                                            2 March 2026


   PCEP extensions for Distribution of Link-State and TE Information
                       draft-ietf-pce-pcep-ls-05

Abstract

   In order to compute and provide optimal paths, Path Computation
   Elements (PCEs) require an accurate and timely Traffic Engineering
   Database (TED).  Traditionally, this TED has been obtained from a
   link state (LS) routing protocol supporting the traffic engineering
   extensions.

   This document extends the Path Computation Element Communication
   Protocol (PCEP) with Link-State and TE Information as an experimental
   extension to allow gathering more deployment and implementation
   feedback on the use of PCEP in this way.

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 3 September 2026.





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Copyright Notice

   Copyright (c) 2026 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
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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Scope of the Experiment . . . . . . . . . . . . . . . . .   5
       1.1.1.  Evaluation of the Experiment  . . . . . . . . . . . .   6
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   7
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Requirements for PCEP Extensions  . . . . . . . . . . . . . .   8
   5.  New Functions to distribute link-state (and TE) via PCEP  . .   9
   6.  Overview of Extensions to PCEP  . . . . . . . . . . . . . . .   9
     6.1.  New Messages  . . . . . . . . . . . . . . . . . . . . . .   9
     6.2.  Capability Advertisement  . . . . . . . . . . . . . . . .  10
     6.3.  Initial Link-State (and TE) Synchronization . . . . . . .  10
       6.3.1.  Optimizations for LS Synchronization  . . . . . . . .  12
     6.4.  LS Report . . . . . . . . . . . . . . . . . . . . . . . .  13
   7.  Transport . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  LS Report Message . . . . . . . . . . . . . . . . . . . .  13
     8.2.  The PCErr Message . . . . . . . . . . . . . . . . . . . .  14
   9.  Objects and TLV . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  TLV Format  . . . . . . . . . . . . . . . . . . . . . . .  15
     9.2.  Open Object . . . . . . . . . . . . . . . . . . . . . . .  15
       9.2.1.  LS Capability TLV . . . . . . . . . . . . . . . . . .  15
     9.3.  LS Object . . . . . . . . . . . . . . . . . . . . . . . .  16
       9.3.1.  Routing Universe TLV  . . . . . . . . . . . . . . . .  18
       9.3.2.  Route Distinguisher TLV . . . . . . . . . . . . . . .  18
       9.3.3.  Virtual Network TLV . . . . . . . . . . . . . . . . .  19
       9.3.4.  Local Node Descriptors TLV  . . . . . . . . . . . . .  19
       9.3.5.  Remote Node Descriptors TLV . . . . . . . . . . . . .  20
       9.3.6.  Node Descriptors Sub-TLVs . . . . . . . . . . . . . .  20
       9.3.7.  Link Descriptors TLV  . . . . . . . . . . . . . . . .  21
       9.3.8.  Prefix Descriptors TLV  . . . . . . . . . . . . . . .  22
       9.3.9.  PCEP-LS Attributes  . . . . . . . . . . . . . . . . .  22



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         9.3.9.1.  Node Attributes TLV . . . . . . . . . . . . . . .  22
         9.3.9.2.  Link Attributes TLV . . . . . . . . . . . . . . .  23
         9.3.9.3.  Prefix Attributes TLV . . . . . . . . . . . . . .  23
       9.3.10. Removal of an Attribute . . . . . . . . . . . . . . .  24
   10. Other Considerations  . . . . . . . . . . . . . . . . . . . .  24
     10.1.  Inter-AS Links . . . . . . . . . . . . . . . . . . . . .  24
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  24
   12. Operational Considerations  . . . . . . . . . . . . . . . . .  25
     12.1.  Control of Function and Policy . . . . . . . . . . . . .  25
     12.2.  Information and Data Models  . . . . . . . . . . . . . .  25
     12.3.  Liveness Detection and Monitoring  . . . . . . . . . . .  26
     12.4.  Verify Correct Operations  . . . . . . . . . . . . . . .  26
     12.5.  Requirements On Other Protocols  . . . . . . . . . . . .  26
     12.6.  Impact On Network Operations . . . . . . . . . . . . . .  26
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
     13.1.  PCEP Messages  . . . . . . . . . . . . . . . . . . . . .  26
     13.2.  PCEP Objects . . . . . . . . . . . . . . . . . . . . . .  27
     13.3.  LS Object  . . . . . . . . . . . . . . . . . . . . . . .  27
     13.4.  PCEP-Error Object  . . . . . . . . . . . . . . . . . . .  28
     13.5.  PCEP TLV Type Indicators . . . . . . . . . . . . . . . .  28
     13.6.  PCEP-LS Sub-TLV Type Indicators  . . . . . . . . . . . .  29
   14. TLV Code Points Summary . . . . . . . . . . . . . . . . . . .  29
   15. Implementation Status . . . . . . . . . . . . . . . . . . . .  30
     15.1.  Hierarchical Transport PCE controllers . . . . . . . . .  31
     15.2.  ONOS-based Controller (MDSC and PNC) . . . . . . . . . .  31
   16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  32
   17. References  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     17.1.  Normative References . . . . . . . . . . . . . . . . . .  32
     17.2.  Informative References . . . . . . . . . . . . . . . . .  33
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  36
     A.1.  All Nodes . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.2.  Designated Node . . . . . . . . . . . . . . . . . . . . .  37
     A.3.  Between PCEs  . . . . . . . . . . . . . . . . . . . . . .  38
   Appendix B.  Contributor Addresses  . . . . . . . . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39

1.  Introduction

   In Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS),
   a Traffic Engineering Database (TED) is used in computing paths for
   connection-oriented services.  The TED contains all the relevant
   information that a Path Computation Element (PCE) needs to perform
   its computations.  The TED must be 'complete and accurate' each time
   the PCE performs a path computation.

   In MPLS and GMPLS, Interior Gateway Protocols (IGPs) have been used
   to create and maintain a copy of the TED at each node running the
   IGP.  One of the benefits of the PCE architecture [RFC4655] is the



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   use of computationally more sophisticated path computation algorithms
   and the realization that these may need enhanced processing power
   (not necessarily available at each node).

   Section 4.3 of [RFC4655] describes the potential load of the TED on a
   network node and proposes an architecture where the TED is maintained
   by the PCE rather than the network nodes.  However, it does not
   describe how a PCE would obtain the information needed to populate
   its TED.  PCE may construct its TED by participating in the IGP
   ([RFC3630] and [RFC5305] for MPLS-TE; [RFC4203] and [RFC5307] for
   GMPLS).  An alternative mechanism is offered by BGP-LS [RFC9552] .

   [RFC8231] describes a set of extensions to PCEP to provide stateful
   control.  A stateful PCE has access to not only the information
   carried by the network's IGP, but also the set of active paths and
   their reserved resources for its computations.  Path Computation
   Client (PCC) can delegate the rights to modify the LSP parameters to
   an Active Stateful PCE.  This requires PCE to quickly be updated on
   any changes in the topology/TED, so that PCE can meet the need for
   updating LSPs effectively and in a timely manner.  The fastest way
   for a PCE to be updated on TED changes is via a direct session with
   each network node and with an incremental update from each network
   node with only the attributes that get modified.

   [RFC8281] 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.  This model requires
   timely topology and TED updates at the PCE.

   [RFC5440] describes the specifications for the Path Computation
   Element Communication Protocol (PCEP).  PCEP specifies the
   communication between a PCC and a PCE, or between two PCEs based on
   the PCE architecture [RFC4655].

   This document describes how link-state and TE information can be
   collected from networks and shared with PCE using the PCEP itself.
   This is achieved using a new PCEP message format.  The mechanism is
   applicable to physical and abstract links [RFC7926] as well as
   further subjected to various policies.  This document is designated
   as "experimental" to allow for the collection of more deployment and
   implementation information regarding the use of PCEP for learning
   link state and traffic engineering (TE) topology information before
   attempting to standardize it (see Section 1.1).

   A network node maintains one or more databases for storing link-state
   and TE information about nodes and links in any given area.  Link
   attributes stored in these databases include: local/remote IP



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   addresses, local/remote interface identifiers, link metric, and TE
   metric, link bandwidth, reservable bandwidth, per CoS class
   reservation state, preemption, and Shared Risk Link Groups (SRLG).
   The node's PCEP process can retrieve topology from these databases
   and distribute it to a PCE, either directly or via another PCEP
   Speaker, using the encoding specified in this document.

   Further [RFC6805] describes Hierarchical-PCE architecture, where a
   Parent PCE maintains a domain topology map.  To build this domain
   topology map, the Child PCE can carry the border nodes and inter-
   domain link information to the Parent PCE using the mechanism
   described in this document.  Further, as described in [RFC8637], the
   Child PCE can also transport abstract Link-State and TE information
   from a Child PCE to a Parent PCE using the mechanism described in
   this document to build an abstract topology at the Parent PCE.

   [RFC8231] describes LSP state synchronization between PCCs and PCEs
   in the case of stateful PCE.  This document does not make any changes
   to the LSP state synchronization process.  The mechanism described in
   this document is on top of the existing LSP state synchronization.

1.1.  Scope of the Experiment

   The procedures described in this document are experimental.  The
   experiment is intended to enable research on the usage of PCEP to
   populate the Link-State and TE Information from a PCC to the PCE.
   For this purpose, this document specifies a new PCEP message, a new
   PCEP object, and new TLVs.

   The new message introduced by this document will not be understood by
   legacy implementations.  On receiving the message, a legacy
   implementation will behave according to the rules for an unknown
   message as per [RFC5440].  It is assumed that this experiment will be
   conducted only when both the PCE and PCC form part of the experiment.
   It is possible that a PCC or PCE can operate with peers, some of
   which form part of the experiment and some that do not.  In this
   case, the capability exchange required before using this extension
   would take care of the mismatch.  A PCEP speaker that offers this
   feature to its peer that does not support or does not wish to support
   the feature will not receive the indication of support in the Open
   message, and so is expected not to use the feature.  Thus, this
   experimentation would not clash with or cause harm to existing
   deployments.  Further, since a PCEP speaker would use the new message
   only after capability exchange, there is no danger of this
   experimentation "escaping" to the wider Internet.  A PCEP speaker
   that receives the new message (that is part of the feature when the
   use of the feature has not been agreed upon) will send an error
   message as described in Section 6.9 of [RFC5440].  A PCEP speaker



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   that receives the new object that is part of the feature when the use
   of the feature has not been agreed, it will send an error message as
   described in Section 7.2 of [RFC5440].

1.1.1.  Evaluation of the Experiment

   For every implementation of this feature, the information as per
   [RFC7942] is collected and maintained in the Working Group (WG) wiki
   [WIKI].

   For every deployment of this feature, the following information is
   collected and maintained in the wiki[WIKI]:

   *  Network Type

   *  Network Underlying Technology

   *  Network Size (nodes and links)

   *  Number of PCEP sessions with the feature enabled

   *  Number of paths in Stateful PCE

   *  The main reason for using this feature via PCEP over others

   *  Any challenges (deployment, management, scalability...)

   The information can also be shared directly with the WG chairs who
   can anonymise the deployment information if needed.

   The experiment will end three years after the RFC is published as
   experimental.  At that point, the WG will determine how widely this
   has been implemented and deployed.  The WG will evaluate the success
   of this feature by comparing its applicability in various deployments
   in comparison to existing mechanisms.  Key considerations include
   whether the feature adversely affects the performance of the PCE and
   if it is scalable.  The Working Group will also monitor for any
   issues related to the implementation, deployment, and management of
   the feature.

   When the results of implementation and deployment are available, this
   document (or part thereof) will be updated and refined, and then it
   could be moved from Experimental to Standards Track.








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1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   The terminology is as per [RFC4655] and [RFC5440].

3.  Applicability

   The mechanism specified in this draft is applicable to deployments:

   *  Where there is no IGP or BGP-LS running in the network.

   *  Where there is no IGP or BGP-LS running at the PCE to learn link-
      state and TE information.

   *  Where there is IGP or BGP-LS running, but with a need for a faster
      and direct TE and link-state population and convergence at the
      PCE.

      -  A PCE may receive partial information (say, basic TE, link-
         state) from IGP and other information (optical and impairment)
         from PCEP.

      -  A PCE may receive an incremental update (as opposed to the full
         (entire) information of the node/link).

      -  A PCE may receive full information from both existing
         mechanisms (IGP or BGP-LS) and PCEP.

   *  Where there is a need for transporting (abstract) Link-State and
      TE information from Child PCE to a Parent PCE in H-PCE [RFC6805];
      as well as from Provisioning Network Controller (PNC) to Multi-
      Domain Service Coordinator (MDSC) in Abstraction and Control of TE
      Networks (ACTN) [RFC8453].

   *  Where there is an existing PCEP session between all the nodes and
      the PCE-based central controller (PCECC) [RFC8283], and the
      operator would like to use PCEP as a direct southbound interface
      to all the nodes in the network.  This enables the operator to use
      PCEP as a single direct protocol between the controller and all
      the nodes in the network.  In this mode, all nodes send only the
      local information.



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   Based on the local policy and deployment scenario, a PCC chooses to
   send only local information or both local and remote learned
   information.  How a PCE manages the link-state (and TE) information
   is implementation-specific and thus out of the scope of this
   document.

   The prefix information in PCEP-LS can also help in determining the
   domain of the tunnel destination in the H-PCE (and ACTN) scenario.
   Section 4.5 of [RFC6805] describes various mechanisms and procedures
   that might be used.  PCEP-LS provides a simple mechanism to exchange
   this information within PCEP.

   [RFC8453] defines three types of topology abstraction - (1) Native/
   White Topology; (2) Black Topology; and (3) Grey Topology.  Based on
   the local policy, the PNC (or Child PCE) would share the domain
   topology with the MDSC (or Parent PCE) based on the abstraction type.
   The protocol extensions defined in this document can carry any type
   of topology abstraction.

4.  Requirements for PCEP Extensions

   The following key requirements associated with link-state (and TE)
   distribution are identified for PCEP:

   1.  The PCEP speaker supporting this draft MUST have a mechanism to
       advertise the Link-State (and TE) distribution capability.

   2.  PCC supporting this draft MUST have the capability to report the
       link-state (and TE) information to the PCE.  This MUST include
       self-originated (local) information and MAY also allow remote
       information learned via routing protocols.  PCC MUST be capable
       of doing the initial bulk sync at the time of session
       initialization as well as any changes thereafter.

   3.  A PCE MAY learn link-state (and TE) from PCEP as well as from
       existing mechanisms like IGP/BGP-LS.  PCEP extensions MUST have a
       mechanism to correlate the information learned via other means.
       There MUST NOT be any changes to the existing link-state (and TE)
       population mechanism via IGP/BGP-LS.  PCEP extension SHOULD keep
       the properties in a protocol (IGP or BGP-LS) neutral way, such
       that an implementation need not know about any OSPF or IS-IS or
       BGP-LS protocol specifics.

   4.  It SHOULD be possible to encode only the changes in link-state
       (and TE) properties (after the initial sync) in the PCEP
       messages.  This leads to faster convergence.





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   5.  The same mechanism SHOULD be used for both MPLS TE as well as
       GMPLS, optical, and impairment-aware properties.

   6.  The same mechanism SHOULD be used for PCE to PCE Link-state (and
       TE) synchronization.

5.  New Functions to distribute link-state (and TE) via PCEP

   Several new functions are required in PCEP to support distribution of
   link-state (and TE) information.  A function can be initiated either
   from a PCC towards a PCE (C-E) or from a PCE towards a PCC (E-C).
   The new functions are:

   *  Capability advertisement (E-C,C-E): both the PCC and the PCE MUST
      announce during the PCEP session establishment that they support
      PCEP extensions for the distribution of link-state (and TE)
      information defined in this document.

   *  Link-State (and TE) synchronization (C-E): after the session
      between the PCC and a PCE is initialized, the PCE must learn Link-
      State (and TE) information before it can perform path
      computations.  In the case of stateful PCE, it is RECOMMENDED that
      this operation be done before LSP state synchronization.

   *  Link-State (and TE) Report (C-E): a PCC sends an LS (and TE)
      report to a PCE whenever the Link-State and TE information
      changes.

6.  Overview of Extensions to PCEP

6.1.  New Messages

   In this document, we define a new PCEP message called LS Report
   (LSRpt), a PCEP message sent by a PCC to a PCE to report link-state
   (and TE) information.  Each LS Report in an LSRpt message can contain
   the node or link properties.  A unique PCEP-specific LS identifier
   (LS-ID) is also carried in the message to identify a node or a link
   that remains constant for the lifetime of a PCEP session.  This
   identifier on its own is sufficient when no IGP or BGP-LS running in
   the network for PCE to learn link-state (and TE) information.  In
   case PCE learns some information from PCEP and some from the existing
   mechanism, the PCC SHOULD include the mapping of IGP or BGP-LS
   identifier to map the information populated via PCEP with IGP/BGP-LS.
   See Section 8.1 for details.







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6.2.  Capability Advertisement

   During the PCEP Initialization Phase, PCEP Speakers (PCE or PCC)
   advertise their support of LS (and TE) distribution via PCEP
   extensions.  A PCEP Speaker includes the "LS Capability" TLV,
   described in Section 9.2.1, in the OPEN Object to advertise its
   support for PCEP-LS extensions.  The presence of the LS Capability
   TLV in PCC's OPEN Object indicates that the PCC is willing to send LS
   Reports with local link-state (and TE) information.  The presence of
   the LS Capability TLV in PCE's Open message indicates that the PCE is
   interested in receiving LS Reports with local link-state (and TE)
   information.

   The PCEP extensions for LS (and TE) distribution MUST NOT be used if
   one or both PCEP Speakers have not included the LS Capability TLV in
   their respective OPEN message.  If the PCE supports the extensions
   defined in this document but does not advertise this capability, then
   upon receipt of an LSRpt message from the PCC, it SHOULD generate a
   PCErr with error-type 19 (Invalid Operation), error-value TBD1
   (Attempted LS Report if LS capability was not advertised) and it will
   terminate the PCEP session.

   The LS reports sent by PCC MAY carry the remote link-state (and TE)
   information learned via existing means like IGP and BGP-LS only if
   both PCEP Speakers set the R (remote) Flag in the "LS Capability" TLV
   to 'Remote Allowed (R Flag = 1)'.  If this is not the case, and LS
   reports carry remote link-state (and TE) information, then a PCErr
   with error-type 19 (Invalid Operation) and error-value TBD1
   (Attempted LS Report if LS remote capability was not advertised) and
   it will terminate the PCEP session.

6.3.  Initial Link-State (and TE) Synchronization

   The purpose of LS Synchronization is to provide a checkpoint-in-time
   state replica of a PCC's link-state (and TE) database in a PCE and
   the State Synchronization is performed immediately after the
   Initialization phase (see [RFC5440]).  It is RECOMMENDED that the LS
   synchronization should be done before LSP state synchronization as
   specified in [RFC8231].

   During LS Synchronization, a PCC first takes a snapshot of the state
   of its database, then sends the snapshot to a PCE in a sequence of LS
   Reports.  Each LS Report sent during LS Synchronization has the SYNC
   Flag in the LS Object set to 1.  The end of synchronization marker is
   an LSRpt message with the SYNC Flag set to 0 for an LS Object with
   LS-ID equal to the reserved value 0.  If the PCC has no link-state to
   synchronize, it will only send the end of synchronization marker.




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   Either the PCE or the PCC MAY terminate the session using the PCEP
   session termination procedures during the synchronization phase.  If
   the session is terminated, the PCE MUST clean up the state it
   received from this PCC.  The session re-establishment MUST be re-
   attempted per the procedures defined in [RFC5440], including the use
   of a back-off timer.

   If the PCC encounters a problem which prevents it from completing the
   LS synchronization, it MUST send a PCErr message with error-type TBD2
   (LS Synchronization Error) and error-value 2 (indicating an internal
   PCC error) to the PCE and terminate the session.

   The PCE does not send positive acknowledgements for properly received
   LS synchronization messages.  It MUST respond with a PCErr message
   with error-type TBD2 (LS Synchronization Error) and error-value 1
   (indicating an error in processing the LSRpt) if it encounters a
   problem with the LS Report it received from the PCC and it MUST
   terminate the session.

   The LS reports can carry local as well as remote link-state (and TE)
   information depending on the R flag in the LS capability TLV.

   The successful LS Synchronization sequence is shown in Figure 1.

         +-+-+                    +-+-+
         |PCC|                    |PCE|
         +-+-+                    +-+-+
           |                        |
           |-----LSRpt, SYNC=1----->| (Sync start)
           |                        |
           |-----LSRpt, SYNC=1----->|
           |            .           |
           |            .           |
           |            .           |
           |-----LSRpt, SYNC=1----->|
           |            .           |
           |            .           |
           |            .           |
           |                        |
           |-----LSRpt, SYNC=0----->| (End of sync marker
           |                        |  LS Report
           |                        |  for LS-ID=0)
           |                        | (Sync done)

                  Figure 1: Successful LS synchronization

   The sequence where the PCE fails during the LS Synchronization phase
   is shown in Figure 2.



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         +-+-+                    +-+-+
         |PCC|                    |PCE|
         +-+-+                    +-+-+
           |                        |
           |-----LSRpt, SYNC=1----->|
           |                        |
           |-----LSRpt, SYNC=1----->|
           |            .           |
           |            .           |
           |            .           |
           |-----LSRpt, SYNC=1----->|
           |                        |
           |---LSRpt,SYNC=1         |
           |         \    ,-PCErr---|
           |          \  /          |
           |           \/           |
           |           /\           |
           |          /   `-------->| (Ignored)
           |<--------`              |

             Figure 2: Failed LS synchronization (PCE failure)

   The sequence where the PCC fails during the LS Synchronization phase
   is shown in Figure 3.

         +-+-+                    +-+-+
         |PCC|                    |PCE|
         +-+-+                    +-+-+
           |                        |
           |-----LSRpt, SYNC=1----->|
           |                        |
           |-----LSRpt, SYNC=1----->|
           |            .           |
           |            .           |
           |            .           |
           |-------- PCErr--------->|
           |                        |


             Figure 3: Failed LS synchronization (PCC failure)

6.3.1.  Optimizations for LS Synchronization

   These optimizations are described in
   [I-D.kondreddy-pce-pcep-ls-sync-optimizations].






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6.4.  LS Report

   The PCC MUST report any changes in the link-state (and TE)
   information to the PCE by sending an LS Report carried on an LSRpt
   message to the PCE.  Each node and Link would be uniquely identified
   by a PCEP LS identifier (LS-ID).  The LS reports may carry local as
   well as remote link-state (and TE) information depending on the R
   flag in LS capability TLV.  It MAY also include the mapping of IGP or
   BGP-LS identifier to map the information populated via PCEP with IGP/
   BGP-LS identifiers.

   More details about the LSRpt message are in Section 8.1.

7.  Transport

   A permanent PCEP session (section 4.2.8 of [RFC5440]) MUST be
   established between a PCE and PCC supporting link-state (and TE)
   distribution via PCEP.  In the case of session failure, session re-
   establishment is re-attempted as per the procedures defined in
   [RFC5440].

8.  PCEP Messages

   As defined in [RFC5440], a PCEP message consists of a common header
   followed by a variable-length body made of a set of objects that can
   be either mandatory or optional.  An object is said to be mandatory
   in a PCEP message, when the object must be included for the message
   to be considered valid.  For each PCEP message type, a set of rules
   is defined that specifies the set of objects that the message can
   carry.  An implementation MUST form the PCEP messages using the
   object ordering specified in this document.

8.1.  LS Report Message

   A PCEP LS Report message (also referred to as LSRpt message) is a
   PCEP message sent by a PCC to a PCE to report the link-state (and TE)
   information.  An LSRpt message can carry more than one LS Reports (LS
   object).  The Message-Type field of the PCEP common header for the
   LSRpt message is set to [TBD3].

   The format of the LSRpt message is as follows:

   <LSRpt Message> ::= <Common Header>
                       <ls-report-list>
   Where:

   <ls-report-list> ::= <LS>[<ls-report-list>]




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   The LS object is a mandatory object that carries LS information of a
   node/prefix or a link.  Each LS object has a unique LS-ID as
   described in Section 9.3.  If the LS object is missing, the receiving
   PCE MUST send a PCErr message with Error-type=6 (Mandatory Object
   missing) and Error-value=[TBD4] (LS object missing).

   A PCE may choose to implement a limit on the LS information of a
   single PCC can populate.  If an LSRpt is received that causes the PCE
   to exceed this limit, it MUST send a PCErr message with error-type 19
   (invalid operation) and error-value 4 (indicating resource limit
   exceeded) in response to the LSRpt message triggering this condition
   and SHOULD terminate the session.

8.2.  The PCErr Message

   If a PCEP speaker has advertised the LS capability on the PCEP
   session, the PCErr message MAY include the LS object.  If the error
   reported is the result of an LS report, then the LS-ID number MUST be
   the one from the LSRpt that triggered the error.

   The format of a PCErr message from [RFC5440] is extended as follows:

   <PCErr Message> ::= <Common Header>
                     ( <error-obj-list> [<Open>] ) | <error>
                     [<error-list>]

   <error-obj-list>::=<PCEP-ERROR>[<error-obj-list>]

   <error>::=[<request-id-list> | <ls-id-list>]
              <error-obj-list>

   <request-id-list>::=<RP>[<request-id-list>]

   <ls-id-list>::=<LS>[<ls-id-list>]

   <error-list>::=<error>[<error-list>]

9.  Objects and TLV

   The PCEP objects defined in this document are compliant with the PCEP
   object format defined in [RFC5440].  The P flag and the I flag of the
   PCEP objects defined in this document MUST always be set to 0 on
   transmission and MUST be ignored on receipt since these flags are
   exclusively related to path computation requests.







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9.1.  TLV Format

   The TLV and the sub-TLV format (and padding) in this document are as
   per section 7.1 of [RFC5440].

9.2.  Open Object

   This document defines a new optional TLV for use in the OPEN Object.

9.2.1.  LS Capability TLV

   The LS-CAPABILITY TLV is an optional TLV for use in the OPEN Object
   for link-state (and TE) distribution via PCEP capability
   advertisement.  Its format is shown in the following figure:

    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=[TBD5]     |            Length=4           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Flags                           |R|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The type of the TLV is [TBD5] and it has a fixed length of 4 octets.

   The value comprises a single field for Flags (32 bits) with 1 flag
   defined:

   *  R (remote allowed - 1 bit): if set to 1 by a PCC, the R Flag
      indicates that the PCC allows the reporting of remote LS
      information learned via other means like IGP and BGP-LS; if set to
      1 by a PCE, the R Flag indicates that the PCE is capable of
      receiving remote LS information (from the PCC point of view).  The
      R Flag must be advertised by both PCC and PCE for LSRpt messages
      to report remote as well as local LS information on a PCEP
      session.  The TLVs related to the IGP/BGP-LS identifier MUST be
      encoded when both PCEP speakers have the R Flag set.

   Unassigned bits are considered reserved.  They MUST be set to 0 on
   transmission and MUST be ignored on receipt.

   Advertisement of the LS capability implies support of local link-
   state (and TE) distribution, as well as the objects, TLVs and
   procedures defined in this document.







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9.3.  LS Object

   The LS (link-state) object MUST be carried within LSRpt messages and
   MAY be carried within PCErr messages.  The LS object contains a set
   of fields used to specify the target node or link.  It also contains
   a flag indicating to a PCE that the LS synchronization is in
   progress.  The TLVs used with the LS object correlate with the IGP/
   BGP-LS encodings.

   LS Object-Class is TBD6.

   Four Object-Type values are defined for the LS object so far:

   *  LS Node: LS Object-Type is 1.

   *  LS Link: LS Object-Type is 2.

   *  LS IPv4 Topology Prefix: LS Object-Type is 3.

   *  LS IPv6 Topology Prefix: LS Object-Type is 4.

   The format of all types of LS objects are as follows:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Protocol-ID  |          Flag                             |R|S|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          LS-ID                                |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                         TLVs                                //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Protocol-ID (8-bit): The field provides the source information.  The
   protocol could be an IGP, BGP-LS, or an abstraction algorithm.  In
   case the PCC only provides local information of the PCC, it MUST use
   Protocol-ID as Direct.  The following values are defined (1-6 are
   same as [RFC9552]):











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            +-------------+----------------------------------+
            | Protocol-ID | Source protocol                  |
            +-------------+----------------------------------+
            |      1      | IS-IS Level 1                    |
            |      2      | IS-IS Level 2                    |
            |      3      | OSPFv2                           |
            |      4      | Direct                           |
            |      5      | Static configuration             |
            |      6      | OSPFv3                           |
            |      7      | BGP                              |
            |      8      | RSVP-TE                          |
            |      9      | Unassigned                       |
            |      10     | PCEP                             |
            |      11     | Abstraction                      |
            +-------------+----------------------------------+

   Flags (24-bit):

   *  S (SYNC - 1 bit): the S Flag MUST be set to 1 on each LSRpt sent
      from a PCC during LS Synchronization.  The S Flag MUST be set to 0
      in other LSRpt messages sent from the PCC.

   *  R (Remove - 1 bit): On LSRpt messages, the R Flag indicates that
      the node/link/prefix has been removed from the PCC and the PCE
      SHOULD remove from its database.  Upon receiving an LS Report with
      the R Flag set to 1, the PCE SHOULD remove all state for the
      node/link/prefix identified by the LS Identifiers from its
      database.

   LS-ID(64-bit): A PCEP-specific identifier for the node, link, or
   prefix information.  A PCC creates a unique LS-ID for each node/link/
   prefix that is constant for the lifetime of a PCEP session.  The PCC
   will advertise the same LS-ID on all PCEP sessions it maintains at a
   given time.  All subsequent PCEP messages then address the node/link/
   prefix by the LS-ID.  The values of 0 and 0xFFFFFFFFFFFFFFFF are
   reserved.

   Unassigned bits are considered reserved.  They MUST be set to 0 on
   transmission and MUST be ignored on receipt.

   TLVs that may be included in the LS Object are described in the
   following sections.









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9.3.1.  Routing Universe TLV

   In the case of remote link-state (and TE) population when existing
   IGP/BGP-LS are also used, OSPF and IS-IS may run multiple routing
   protocol instances over the same link as described in [RFC9552].  See
   [RFC8202] and [RFC6549] for more information.  These instances define
   an independent "routing universe".  The 64-bit 'Identifier' field is
   used to identify the "routing universe" of the LS object (same as
   Instance-ID in [RFC9552].)  The LS objects representing IGP objects
   (nodes, links, or prefixes) from the same routing universe MUST have
   the same 'Identifier' value; LS objects with different 'Identifier'
   values MUST be considered to be from different routing universes.

   The format of the optional ROUTING-UNIVERSE TLV is shown in the
   following figure:

      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=[TBD7]         |           Length=8            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Identifier                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The below table lists the 'Identifier' values that are defined as
   well-known in this draft (same as [RFC9552]).

            +------------+-----------------------------------+
            | Identifier | Routing Universe                  |
            +------------+-----------------------------------+
            |     0      | Default Layer 3 Routing topology  |
            +------------+-----------------------------------+

   If this TLV is not present the default value 0 is assumed.

9.3.2.  Route Distinguisher TLV

   To allow identification of VPN link, node, and prefix information in
   PCEP-LS, a Route Distinguisher (RD) [RFC4364] is used.  The LS
   objects from the same VPN MUST have the same RD; LS objects with
   different RD values MUST be considered to be from different VPNs.

   The ROUTE-DISTINGUISHER TLV is defined in [RFC9168] as a Flow
   Specification TLVs with a separate registry.  This document also adds
   the ROUTE-DISTINGUISHER TLV with TBD15 in the PCEP TLV registry to be
   used inside the LS object.




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9.3.3.  Virtual Network TLV

   Following the requirements specified in [RFC8453] and [RFC8454],
   there is a need to associate abstracted link-state and TE topology
   information with a Virtual Network (VN) construct in order to
   facilitate VN operations within the PCE architecture.

   The VIRTUAL-NETWORK-TLV, as defined in [RFC9358], can be included in
   the LS object to identify the link, node, and prefix information
   belongs to a particular VN.

9.3.4.  Local Node Descriptors TLV

   As described in [RFC9552], each link is anchored by a pair of Router-
   IDs that are used by the underlying IGP, namely, 48-bit ISO System-ID
   for IS-IS and 32-bit Router-ID for OSPFv2 and OSPFv3.  In case of
   additional auxiliary Router-IDs used for TE, these MUST also be
   included in the link attribute TLV (see Section 9.3.9.2).

   It is desirable that the Router-ID assignments inside the Node
   Descriptors TLV are globally unique.  Some considerations for
   globally unique Node/Link/Prefix identifiers are described in
   [RFC9552].

   The Local Node Descriptors TLV contains Node Descriptors for the node
   anchoring the local end of the link.  This TLV MUST be included in
   the LS Report when during a given PCEP session a node/link/prefix is
   first reported to a PCE.  A PCC sends to a PCE the first LS Report
   either during the State Synchronization, or when a new node/link/
   prefix is learned at the PCC.  The value contains one or more Node
   Descriptor Sub-TLVs, which allows the specification of a flexible key
   for any given node/link/prefix information such that the global
   uniqueness of the node/link/prefix is ensured.

   This TLV is applicable for all LS Object-Type.

      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=[TBD8]         |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //              Node Descriptor Sub-TLVs (variable)            //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The value contains one or more Node Descriptor Sub-TLVs defined in
   Section 9.3.6.



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9.3.5.  Remote Node Descriptors TLV

   The Remote Node Descriptors contain Node Descriptors for the node
   anchoring the remote end of the link.  This TLV MUST be included in
   the LS Report when during a given PCEP session, a link is first
   reported to a PCE.  A PCC sends to a PCE the first LS Report either
   during the State Synchronization, or when a new link is learned at
   the PCC.  The length of this TLV is variable.  The value contains one
   or more Node Descriptor Sub-TLVs defined in Section 9.3.6.

   This TLV is applicable for LS Link Object-Type.

      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=[TBD9]         |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //              Node Descriptor Sub-TLVs (variable)            //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

9.3.6.  Node Descriptors Sub-TLVs

   The Node Descriptors TLV (Local and Remote) carries one or more Node
   Descriptor Sub-TLV following the format of all PCEP TLVs as defined
   in [RFC5440], however, the Type values are selected from a new PCEP-
   LS sub-TLV IANA registry (see Section 13.6).

   Type values are chosen so that there can be commonality with BGP-LS
   [RFC9552].  This is possible because the "BGP-LS Node Descriptor,
   Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry
   marks 0-255 as reserved.  Thus the space of the sub-TLV values for
   the Type field can be partitioned as shown below -

   Range          |
   ---------------+---------------------------------------------
   0              | Reserved - must not be allocated.
                  |
   1 .. 255       | New PCEP sub-TLV allocated according to the
                  | registry defined in this document.
                  |
   256 ..   65535 | Per BGP registry defined by
                  | [RFC9552].
                  | Not to be allocated in this registry.






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   All Node Descriptors TLVs defined for BGP-LS can then be used with
   PCEP-LS as well.  One new PCEP sub-TLVs for Node Descriptor are
   defined in this document.

       +----------+-------------------+---------------------------+
       | Sub-TLV  | Description       |  Length & Value defined in|
       +----------+-------------------+---------------------------+
       |      24  | SPEAKER-ENTITY-ID |      [RFC8232]            |
       +----------+-------------------+---------------------------+

   A new sub-TLV type (24) is allocated for SPEAKER-ENTITY-ID sub-TLV.
   The length and value fields are as per [RFC8232].

9.3.7.  Link Descriptors TLV

   The Link Descriptors TLV contains Link Descriptors for each link.
   This TLV MUST be included in the LS Report when during a given PCEP
   session, a link is first reported to a PCE.  A PCC sends to a PCE the
   first LS Report either during State Synchronization, or when a new
   link is learned at the PCC.  The length of this TLV is variable.  The
   value contains one or more Link Descriptor Sub-TLVs.

   The 'Link descriptor' TLVs uniquely identify a link among multiple
   parallel links between a pair of anchor routers, similar to
   [RFC9552].

   This TLV is applicable for LS Link Object-Type.

      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=[TBD10]        |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //              Link Descriptor Sub-TLVs (variable)            //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All Link Descriptors TLVs defined for BGP-LS can then be used with
   PCEP-LS as well.  No new PCEP sub-TLVs for Link Descriptor are
   defined in this document.

   The format and semantics of the 'value' fields in most 'Link
   Descriptor' sub-TLVs correspond to the format and semantics of the
   value fields in IS-IS Extended IS Reachability sub-TLVs, defined in
   [RFC5305], [RFC5307] and [RFC6119].  Although the encodings for 'Link
   Descriptor' TLVs were originally defined for IS-IS, the TLVs can
   carry data sourced by IS-IS, OSPF, or direct.



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   The information about a link present in the LSA/LSP originated by the
   local node of the link determines the set of sub-TLVs in the Link
   Descriptor of the link as described in [RFC9552].

9.3.8.  Prefix Descriptors TLV

   The Prefix Descriptors TLV contains Prefix Descriptors that uniquely
   identify an IPv4 or IPv6 Prefix originated by a Node.  This TLV MUST
   be included in the LS Report when during a given PCEP session a
   prefix is first reported to a PCE.  A PCC sends to a PCE the first LS
   Report either during the State Synchronization, or when a new prefix
   is learned at the PCC.  The length of this TLV is variable.

   This TLV is applicable for LS Prefix Object-Types for both IPv4 and
   IPv6.

      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=[TBD11]        |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //             Prefix Descriptor Sub-TLVs (variable)           //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All Prefix Descriptors TLVs defined for BGP-LS can then be used with
   PCEP-LS as well.  No new PCEP sub-TLVs for Prefix Descriptor are
   defined in this document.

9.3.9.  PCEP-LS Attributes

9.3.9.1.  Node Attributes TLV

   This is an optional TLV that is used to carry node attributes.  This
   TLV is applicable for LS Node Object-Type.

      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=[TBD12]        |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //              Node Attributes Sub-TLVs (variable)            //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   All Node Attributes TLVs defined for BGP-LS can then be used with
   PCEP-LS as well.  No new PCEP sub-TLVs for Node Attributes are
   defined in this document.

9.3.9.2.  Link Attributes TLV

   This TLV is applicable for LS Link Object-Type.  The format and
   semantics of the 'value' fields in some 'Link Attribute' sub-TLVs
   correspond to the format and semantics of the 'value' fields in IS-IS
   Extended IS Reachability sub-TLVs, defined in [RFC5305], [RFC5307]
   and [RFC9552].  Although the encodings for 'Link Attribute' TLVs were
   originally defined for IS-IS, the TLVs can carry data sourced by IS-
   IS, OSPF, or direct.

      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=[TBD13]        |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //              Link Attributes Sub-TLVs (variable)            //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All Link Attributes TLVs defined for BGP-LS can then be used with
   PCEP-LS as well.  No new PCEP sub-TLVs for Link Attributes are
   defined in this document.

9.3.9.3.  Prefix Attributes TLV

   This TLV is applicable for LS Prefix Object-Types for both IPv4 and
   IPv6.  Prefixes are learned from the IGP (IS-IS or OSPF) or BGP
   topology with a set of IGP attributes (such as metrics, route tags,
   etc.).  This section describes the different attributes related to
   the IPv4/IPv6 prefixes.  Prefix Attributes TLVs SHOULD be encoded in
   the LS Prefix Object.

      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=[TBD14]        |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //            Prefix Attributes Sub-TLVs (variable)            //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   All Prefix Attributes TLVs defined for BGP-LS can then be used with
   PCEP-LS as well.  No new PCEP sub-TLVs for Prefix Attributes are
   defined in this document.

9.3.10.  Removal of an Attribute

   One of the key objectives of PCEP-LS is to encode and carry only the
   impacted attributes of a Node, a Link, or a Prefix.  To accommodate
   this requirement, in case of a removal of an attribute, the sub-TLV
   MUST be included with no 'value' field and length=0 to indicate that
   the attribute is removed.  On receiving a sub-TLV with zero length,
   the receiver removes the attribute from the database.  An absence of
   a sub-TLV that was included earlier MUST be interpreted as no change.
   A sub-TLV with a non-zero length indicates that the attribute is
   being added or updated with the new value.

10.  Other Considerations

10.1.  Inter-AS Links

   The main source of LS (and TE) information is the IGP, which is not
   active on inter-AS links.  In some cases, the IGP may have
   information of inter-AS links ([RFC5392], [RFC9346]).  In other
   cases, an implementation SHOULD provide a means to inject inter-AS
   links into PCEP.  The exact mechanism used to provision the inter-AS
   links is outside the scope of this document.

11.  Security Considerations

   This document extends PCEP for LS (and TE) distribution including a
   new LSRpt message with a new object and TLVs.  Procedures and
   protocol extensions defined in this document do not affect the
   overall PCEP security model.  See [RFC5440], [RFC8253].  Tampering
   with the LSRpt message may have an effect on path computations at
   PCE.  It also provides adversaries an opportunity to eavesdrop and
   learn sensitive information and plan sophisticated attacks on the
   network infrastructure.  The PCE implementation SHOULD provide
   mechanisms to prevent strains created by network flaps and amount of
   LS (and TE) information.  Thus it is suggested that any mechanism
   used for securing the transmission of other PCEP message be applied
   here as well.  As a general precaution, it is RECOMMENDED that these
   PCEP extensions only are activated on authenticated and encrypted
   sessions belonging to the same administrative authority.








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   Further, as stated in [RFC6952], PCEP implementations SHOULD support
   the TCP-AO [RFC5925] and not use TCP MD5 because of TCP MD5's known
   vulnerabilities and weaknesses.  PCEP also support Transport Layer
   Security (TLS) [RFC8253] as per the recommendations and best current
   practices in [RFC9325].

12.  Operational Considerations

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

12.1.  Control of Function and Policy

   A PCE or PCC implementation MUST allow configuring the PCEP-LS
   capabilities as described in this document.

   A PCC implementation SHOULD allow configuration to suggest if remote
   information learned via routing protocols should be reported or not.

   An implementation SHOULD allow the operator to specify the maximum
   number of LS data to be reported.

   An implementation MAY also allow the operator to create abstracted
   topologies that are reported to the peers and create different
   abstractions for different peers.  This implies that the PCEP-LS
   speaker may advertise distinct abstracted topology views per peer,
   and the PCEP mechanisms defined in this document (including the
   association of LS information with a specific Virtual Network
   construct) enable correct identification and separation of such
   views.

   An implementation SHOULD allow the operator to configure a 64-bit
   identifier for Routing Universe TLV.

12.2.  Information and Data Models

   An implementation SHOULD allow the operator to view the LS
   capabilities advertised by each peer.  To serve this purpose, the
   PCEP YANG module [I-D.ietf-pce-pcep-yang] can be extended to include
   advertised capabilities.

   An implementation SHOULD also provide the following statistics:

   *  Total number of LSRpt sent/received, as well as per neighbour

   *  Number of errors received for LSRpt, per neighbour




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   *  Total number of locally originated Link-State Information

   These statistics should be recorded as absolute counts since the
   system or session start time.  An implementation MAY also enhance
   this information by recording peak per-second counts in each case.

   In addition, a mechanism to limit inbound LSRpt, including the
   ability to drop all LSRpt messages from a particular peer, is needed
   to protect against excessive inbound LSRpt messages.

12.3.  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]".

12.4.  Verify Correct Operations

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

12.5.  Requirements On Other Protocols

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

12.6.  Impact On Network Operations

   Mechanisms defined in this document do not have any impact on the
   network operations in addition to those already listed in [RFC5440].

13.  IANA Considerations

   This document requests IANA actions to allocate code points for the
   protocol elements defined in this document.

13.1.  PCEP Messages

   IANA created a registry for "PCEP Messages".  Each PCEP message has a
   message type value.  This document defines a new PCEP message value.

           Value     Meaning                          Reference
            TBD3     LSRpt                            [This I-D]







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13.2.  PCEP Objects

   This document defines the following new PCEP Object-classes and
   Object-values:

          Object-Class Value  Name                    Reference
               TBD6           LS Object               [This I-D]
                              Object-Type=1
                              (LS Node)
                              Object-Type=2
                              (LS Link)
                              Object-Type=3
                              (LS IPv4 Prefix)
                              Object-Type=4
                              (LS IPv6 Prefix)

13.3.  LS Object

   This document requests that a new sub-registry, named "LS Object
   Protocol-ID Field", is created within the "Path Computation Element
   Protocol (PCEP) Numbers" registry to manage the Protocol-ID field of
   the LS object.  New values are to be assigned by "IETF Review"
   [RFC8126].

           Value       Meaning                        Reference
           0           Reserved                       [This I-D]
           1           IS-IS Level 1                  [This I-D]
           2           IS-IS Level 2                  [This I-D]
           3           OSPFv2                         [This I-D]
           4           Direct                         [This I-D]
           5           Static configuration           [This I-D]
           6           OSPFv3                         [This I-D]
           7           BGP                            [This I-D]
           8           RSVP-TE                        [This I-D]
           9           Unassigned                     [This I-D]
           10          PCEP                           [This I-D]
           11          Abstraction                    [This I-D]
           12-255      Unassigned

   Further, this document also requests that a new sub-registry, named
   "LS Object Flag Field", is created within the "Path Computation
   Element Protocol (PCEP) Numbers" registry to manage the Flag field of
   the LSP object.  New values are to be assigned by "IETF Review"
   [RFC8126].  Each bit should be tracked with the following qualities:

   *  Bit number (counting from bit 0 as the most significant bit)

   *  Capability description



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   *  Defining RFC

   The following values are defined in this document:

                 Bit     Description           Reference
                 0-21    Unassigned
                 22      R (Remove bit)        [This I-D]
                 23      S (Sync bit)          [This I-D]

13.4.  PCEP-Error Object

   IANA is requested to make the following allocation in the "PCEP-ERROR
   Object Error Types and Values" registry.

           Error-Type Meaning                        Reference
           6          Mandatory Object missing       [RFC5440]
                      Error-Value=TBD4               [This I-D]
                      (LS object missing)

           19         Invalid Operation              [RFC8231]
                      Error-Value=TBD1               [This I-D]
                      (Attempted LS Report if LS
                      remote capability was not
                      advertised)

           TBD2       LS Synchronization Error       [This I-D]
                      Error-Value=1
                      (An error in processing the
                      LSRpt)
                      Error-Value=2
                      (An internal PCC error)

13.5.  PCEP TLV Type Indicators

   IANA is requested to make the following allocation in the "PCEP TLV
   Type Indicators" registry.

            Value     Meaning                        Reference
             TBD5     LS-CAPABILITY TLV              [This I-D]
             TBD7     ROUTING-UNIVERSE TLV           [This I-D]
             TBD15    ROUTE-DISTINGUISHER TLV        [This I-D]
             TBD8     Local Node Descriptors TLV     [This I-D]
             TBD9     Remote Node Descriptors TLV    [This I-D]
             TBD10    Link Descriptors TLV           [This I-D]
             TBD11    Prefix Descriptors TLV         [This I-D]
             TBD12    Node Attributes TLV            [This I-D]
             TBD13    Link Attributes TLV            [This I-D]
             TBD14    Prefix Attributes TLV          [This I-D]



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13.6.  PCEP-LS Sub-TLV Type Indicators

   This document specifies the PCEP-LS Sub-TLVs.  IANA is requested to
   create a "PCEP-LS Sub-TLV Types" sub-registry for the sub-TLVs
   carried in the PCEP-LS TLV (Local and Remote Node Descriptors TLV,
   Link Descriptors TLV, Prefix Descriptors TLV, Node Attributes TLV,
   Link Attributes TLV and Prefix Attributes TLV.

   Allocations from this registry are to be made according to the
   following assignment policies [RFC8126]:

   Range          | Assignment policy
   ---------------+---------------------------------------------------
   0              | Reserved - must not be allocated.
                  |
   1 .. 251       | IETF Review
                  |
   252 .. 255     | Experimental Use
                  |
   256 ..   65535 | Reserved - must not be allocated.
                  | Usage mirrors the BGP-LS TLV registry
                  | [RFC9552]
                  |


   IANA is requested to pre-populate this registry with values defined
   in this document as follows, taking the new values from the range 1
   to 251:

    Value | Meaning
   -------+------------------------
    24    | SPEAKER-ENTITY-ID


14.  TLV Code Points Summary

   This section contains the global table of all TLVs in the LS object,
   defined in this document.













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   +-----------+---------------------+---------------+-----------------+
   |    TLV    | Description         |     Ref TLV   | Value defined   |
   |           |                     |               | in:             |
   +-----------+---------------------+---------------+-----------------+
   |    TBD7   | Routing Universe    |      --       | Sec 9.2.1       |
   |    TBD15  | Route               |      --       | Sec 9.2.2       |
   |           | Distinguisher       |               |                 |
   |     *     | Virtual Network     |      --       | [RFC9358]       |
   |    TBD8   | Local Node          |      256      | [RFC9552]       |
   |           | Descriptors         |               | /5.2.1.2        |
   |    TBD9   | Remote Node         |      257      | [RFC9552]       |
   |           | Descriptors         |               | /5.2.1.3        |
   |    TBD10  | Link Descriptors    |      --       | Sec 9.2.8       |
   |    TBD11  | Prefix Descriptors  |      --       | Sec 9.2.9       |
   |    TBD12  | Node Attributes     |      --       | Sec 9.2.10.1    |
   |    TBD13  | Link Attributes     |      --       | Sec 9.2.10.2    |
   |    TBD14  | Prefix Attributes   |      --       | Sec 9.2.10.3    |
   +-----------+---------------------+---------------+-----------------+

   * this TLV is defined in a different PCEP document

                            Figure 4: TLV Table

15.  Implementation Status

   [Note to RFC Editor: Please remove this section.]

   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 RFC 7942.
   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 RFC 7942, "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".





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   The PCEP-LS protocol extensions as described in this I-D were
   implemented and tested for a variety of applications.  Apart from the
   below implementation, there exist other experimental implementations
   done for optical networks.

15.1.  Hierarchical Transport PCE controllers

   The PCEP-LS has been implemented as part of the IETF97 Hackathon and
   Bits-N-Bites demonstration.  The use-case demonstrated was the DCI
   use case of ACTN architecture in which to show the following
   scenarios:

      - connectivity services on the ACTN-based recursive hierarchical
      SDN/PCE platform that has the three-tier level SDN controllers
      (two-tier level MDSC and PNC) on the top of the PTN systems
      managed by EMS.

      - Integration test of two tier-level MDSC: The SBI of the low-
      level MDSC is the YANG-based Korean national standards and one of
      the high-level MDSC is the PCEP-LS based ACTN protocols.

      - Performance test of three types of SDN controller based recovery
      schemes including protection, reactive, and proactive restoration.
      PCEP-LS protocol was used to demonstrate a quick report of failed
      network components.

15.2.  ONOS-based Controller (MDSC and PNC)

   Huawei (PNC, MDSC) and SKT (MDSC) implemented PCEP-LS during the
   Hackathon and IETF97 Bits-N-Bites demonstration.  The demonstration
   was ONOS-based ACTN architecture in which to show the following
   capabilities:

      Both packet PNC and optical PNC (with optical PCEP-LS extensions)
      implemented PCEP-LS on its SBI as well as its NBI (towards MDSC).

      SKT orchestrator (acting as MDSC) also supported PCEP-LS (as well
      as RestConf) towards packet and optical PNCs on its SBI.

   Further description can be found at ONOS-PCEP
   (https://wiki.onosproject.org/display/ONOS/PCEP+Protocol) and the
   code at ONOS-PCEP-GITHUB
   (https://github.com/opennetworkinglab/onos/tree/master/protocols/
   pcep).







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16.  Acknowledgments

   This document borrows some of the structure and text from the
   [RFC9552].

   Thanks to Eric Wu, Venugopal Kondreddy, Mahendra Singh Negi,
   Avantika, Zhengbin Li, Daniel King, and Adrian Farrel for the
   reviews.

   Thanks to Ramon Casellas for his comments and suggestions based on
   his implementation experience.

17.  References

17.1.  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>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC5307]  Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
              in Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
              <https://www.rfc-editor.org/info/rfc5307>.

   [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>.

   [RFC6119]  Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
              Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
              February 2011, <https://www.rfc-editor.org/info/rfc6119>.

   [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>.

   [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>.



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   [RFC9552]  Talaulikar, K., Ed., "Distribution of Link-State and
              Traffic Engineering Information Using BGP", RFC 9552,
              DOI 10.17487/RFC9552, December 2023,
              <https://www.rfc-editor.org/info/rfc9552>.

17.2.  Informative References

   [I-D.ietf-pce-pcep-yang]
              Dhody, D., Beeram, V. P., Hardwick, J., and J. Tantsura,
              "A YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-yang-30, 26 January
              2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pce-pcep-yang-30>.

   [I-D.kondreddy-pce-pcep-ls-sync-optimizations]
              Kondreddy, V. R. and M. S. Negi, "Optimizations of PCEP
              Link-State(LS) Synchronization Procedures", Work in
              Progress, Internet-Draft, draft-kondreddy-pce-pcep-ls-
              sync-optimizations-01, 5 April 2024,
              <https://datatracker.ietf.org/doc/html/draft-kondreddy-
              pce-pcep-ls-sync-optimizations-01>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
              <https://www.rfc-editor.org/info/rfc4203>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC5392]  Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392,
              January 2009, <https://www.rfc-editor.org/info/rfc5392>.





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   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC6549]  Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
              Instance Extensions", RFC 6549, DOI 10.17487/RFC6549,
              March 2012, <https://www.rfc-editor.org/info/rfc6549>.

   [RFC6805]  King, D., Ed. and A. Farrel, Ed., "The Application of the
              Path Computation Element Architecture to the Determination
              of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
              DOI 10.17487/RFC6805, November 2012,
              <https://www.rfc-editor.org/info/rfc6805>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.

   [RFC7926]  Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
              Ceccarelli, D., and X. Zhang, "Problem Statement and
              Architecture for Information Exchange between
              Interconnected Traffic-Engineered Networks", BCP 206,
              RFC 7926, DOI 10.17487/RFC7926, July 2016,
              <https://www.rfc-editor.org/info/rfc7926>.

   [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>.

   [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>.

   [RFC8202]  Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS
              Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June
              2017, <https://www.rfc-editor.org/info/rfc8202>.

   [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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   [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>.

   [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>.

   [RFC8283]  Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
              Architecture for Use of PCE and the PCE Communication
              Protocol (PCEP) in a Network with Central Control",
              RFC 8283, DOI 10.17487/RFC8283, December 2017,
              <https://www.rfc-editor.org/info/rfc8283>.

   [RFC8453]  Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
              Abstraction and Control of TE Networks (ACTN)", RFC 8453,
              DOI 10.17487/RFC8453, August 2018,
              <https://www.rfc-editor.org/info/rfc8453>.

   [RFC8454]  Lee, Y., Belotti, S., Dhody, D., Ceccarelli, D., and B.
              Yoon, "Information Model for Abstraction and Control of TE
              Networks (ACTN)", RFC 8454, DOI 10.17487/RFC8454,
              September 2018, <https://www.rfc-editor.org/info/rfc8454>.

   [RFC8637]  Dhody, D., Lee, Y., and D. Ceccarelli, "Applicability of
              the Path Computation Element (PCE) to the Abstraction and
              Control of TE Networks (ACTN)", RFC 8637,
              DOI 10.17487/RFC8637, July 2019,
              <https://www.rfc-editor.org/info/rfc8637>.

   [RFC9168]  Dhody, D., Farrel, A., and Z. Li, "Path Computation
              Element Communication Protocol (PCEP) Extension for Flow
              Specification", RFC 9168, DOI 10.17487/RFC9168, January
              2022, <https://www.rfc-editor.org/info/rfc9168>.

   [RFC9325]  Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/info/rfc9325>.







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   [RFC9346]  Chen, M., Ginsberg, L., Previdi, S., and D. Xiaodong, "IS-
              IS Extensions in Support of Inter-Autonomous System (AS)
              MPLS and GMPLS Traffic Engineering", RFC 9346,
              DOI 10.17487/RFC9346, February 2023,
              <https://www.rfc-editor.org/info/rfc9346>.

   [RFC9358]  Lee, Y., Zheng, H., and D. Ceccarelli, "Path Computation
              Element Communication Protocol (PCEP) Extensions for
              Establishing Relationships between Sets of Label Switched
              Paths and Virtual Networks", RFC 9358,
              DOI 10.17487/RFC9358, February 2023,
              <https://www.rfc-editor.org/info/rfc9358>.

   [WIKI]     "PCE WG Wiki - Path Computation Element",
              <https://wiki.ietf.org/group/pce/>.

Appendix A.  Examples

   These examples are for illustration purposes only to show how the new
   PCEP-LS message could be encoded.  They are not meant to be an
   exhaustive list of all possible use cases and combinations.

A.1.  All Nodes

   Each node (PCC) in the network chooses to provide its own local node
   and link information, and in this way PCE can build the full link-
   state and TE information.

   +--------------------+                    +--------------------+
   |                    |                    |                    |
   |     RTA            |192.0.2.0/24        |     RTB            |
   |     11.11.11.11    |--------------------|     22.22.22.22    |
   |     Area 0         |       192.0.2.0/24 |     Area 0         |
   |                    |                    |                    |
   +--------------------+                    +--------------------+
   RTA
   ---
   LS Node
      TLV - Local Node Descriptors
          Sub-TLV - 514: OSPF Area-ID: 0.0.0.0
          Sub-TLV - 515: IGP Router-ID: 11.11.11.11
      TLV - Node Attributes TLV
          Sub-TLV(s)


   LS Link
      TLV - Local Node Descriptors
          Sub-TLV - 514: OSPF Area-ID: 0.0.0.0



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          Sub-TLV - 515: IGP Router-ID: 11.11.11.11
      TLV - Remote Node Descriptors
          Sub-TLV - 514: OSPF Area-ID: 0.0.0.0
          Sub-TLV - 515: IGP Router-ID: 22.22.22.22
      TLV - Link Descriptors
          Sub-TLV - 259: IPv4 interface:  192.0.2.1
          Sub-TLV - 260: IPv4 neighbor:  192.0.2.2
      TLV - Link Attributes TLV
          Sub-TLV(s)

   RTB
   ---
   LS Node
      TLV - Local Node Descriptors
          Sub-TLV - 514: OSPF Area-ID: 0.0.0.0
          Sub-TLV - 515: IGP Router-ID: 22.22.22.22
      TLV - Node Attributes TLV
          Sub-TLV(s)

   LS Link
      TLV - Local Node Descriptors
          Sub-TLV - 514: OSPF Area-ID: 0.0.0.0
          Sub-TLV - 515: IGP Router-ID: 22.22.22.22
      TLV - Remote Node Descriptors
          Sub-TLV - 514: OSPF Area-ID: 0.0.0.0
          Sub-TLV - 515: IGP Router-ID: 11.11.11.11
      TLV - Link Descriptors
          Sub-TLV - 259: IPv4 interface: 192.0.2.2
          Sub-TLV - 260: IPv4 neighbor: 192.0.2.1
      TLV - Link Attributes TLV
          Sub-TLV(s)

   A similar example with IPv6 address (say 2001:db8::1 and 2001:db8::2)
   for the links could be imagined with all other information as same
   and just IPv6 interface and neighbour TLVs.

A.2.  Designated Node

   A designated node(s) in the network will provide its own local node
   as well as all learned remote information, and in this way, PCE can
   build the full link-state and TE information.

   As described in Appendix A.1, the same LS Node and Link objects will
   be generated with a difference that it would be a designated router
   say RTA that generates all this information.






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A.3.  Between PCEs

   As per Hierarchical-PCE [RFC6805], Parent PCE builds an abstract
   domain topology map with each domain as an abstract node and inter-
   domain links as an abstract link.  Each Child PCE may provide this
   information to the Parent PCE.  Considering the example in figure 1
   of [RFC6805], following LS object will be generated:

   PCE1
   ----
   LS Node
      TLV - Local Node Descriptors
          Sub-TLV - 512: Autonomous System: 100 (Domain 1)
          Sub-TLV - 515: IGP Router-ID: 11.11.11.11 (abstract)

   LS Link
      TLV - Local Node Descriptors
          Sub-TLV - 512: Autonomous System: 100
          Sub-TLV - 515: IGP Router-ID: 11.11.11.11 (abstract)
      TLV - Remote Node Descriptors
          Sub-TLV - 512: Autonomous System: 200 (Domain 2)
          Sub-TLV - 515: IGP Router-ID: 22.22.22.22 (abstract)
      TLV - Link Descriptors
          Sub-TLV - 259: IPv4 interface:  192.0.2.1
          Sub-TLV - 260: IPv4 neighbor:  192.0.2.2
      TLV - Link Attributes TLV
          Sub-TLV(s)

   LS Link
      TLV - Local Node Descriptors
          Sub-TLV - 512: Autonomous System: 100
          Sub-TLV - 515: IGP Router-ID: 11.11.11.11 (abstract)
      TLV - Remote Node Descriptors
          Sub-TLV - 512: Autonomous System: 200
          Sub-TLV - 515: IGP Router-ID: 22.22.22.22 (abstract)
      TLV - Link Descriptors
          Sub-TLV - 259: IPv4 interface: 198.51.100.1
          Sub-TLV - 260: IPv4 neighbor: 198.51.100.2
      TLV - Link Attributes TLV
          Sub-TLV(s)

   LS Link
      TLV - Local Node Descriptors
          Sub-TLV - 512: Autonomous System: 100
          Sub-TLV - 515: IGP Router-ID: 11.11.11.11 (abstract)
      TLV - Remote Node Descriptors
          Sub-TLV - 512: Autonomous System: 400 (Domain 4)
          Sub-TLV - 515: IGP Router-ID: 44.44.44.44 (abstract)



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      TLV - Link Descriptors
          Sub-TLV - 259: IPv4 interface: 203.0.113.1
          Sub-TLV - 260: IPv4 neighbor: 203.0.113.2
      TLV - Link Attributes TLV
          Sub-TLV(s)

   * similar information will be generated by other PCE
     to help form the abstract domain topology.

   Further the exact border nodes and the abstract internal path between
   the border nodes may also be transported to the Parent PCE to enable
   ACTN as described in [RFC8637] using the similar LS node and link
   objects encodings.

Appendix B.  Contributor Addresses

   Siva Sivabalan
   Ciena Corporation

   Email: ssivabal@ciena.com

   Udayasree Palle

   EMail: udayasreereddy@gmail.com

   Sergio Belotti
   Nokia

   EMail: sergio.belotti@nokia.com

   Satish Karunanithi
   India

   Email: satish.karunanithi@gmail.com

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

   Email: c.l@huawei.com

Authors' Addresses

   Dhruv Dhody
   Huawei
   India



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   Email: dhruv.ietf@gmail.com


   Shuping Peng
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China
   Email: pengshuping@huawei.com


   Young Lee
   Samsung Electronics
   Seoul
   South Korea
   Email: younglee.tx@gmail.com


   Daniele Ceccarelli
   Cisco
   Email: daniele.ietf@gmail.com


   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing
   102209
   China
   Email: wangaijun@tsinghua.org.cn


   Gyan Mishra
   Verizon Inc.
   Email: gyan.s.mishra@verizon.com















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