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Versions: (draft-kondreddy-pcep-ls-sync-optimizations) 00

PCE Working Group                                           V. Kondreddy
Internet-Draft                                                   M. Negi
Intended status: Standards Track                     Huawei Technologies
Expires: April 11, 2016                                  October 9, 2015


    Optimizations of PCEP Link-State(LS) Synchronization Procedures
           draft-kondreddy-pce-pcep-ls-sync-optimizations-00

Abstract

   For a Path Computation Element (PCE) to perform its computations, it
   is important that Link-State (and TE) information be complete and
   accurate each time.  This requires a reliable Link-State
   Synchronization mechanism between the PCE and path computation
   clients (PCCs), and between cooperating PCEs.  The basic mechanism
   for Link-State Synchronization is part of the PCEP Link-State (and
   TE) draft.  This draft presents motivations for optimizations to the
   base PCEP Link-State (and TE) procedure and specifies the required
   Path Computation Element Communication Protocol (PCEP) extensions.

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
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   This Internet-Draft will expire on April 11, 2016.

Copyright Notice

   Copyright (c) 2015 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
   (http://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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  LS Synchronization Avoidance  . . . . . . . . . . . . . . . .   4
     3.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  LS Synchronization Avoidance Procedure  . . . . . . . . .   4
   4.  Incremental LS Synchronization  . . . . . . . . . . . . . . .   8
     4.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Incremental Synchronization Procedure . . . . . . . . . .   9
   5.  PCE-triggered Initial Synchronization . . . . . . . . . . . .  11
     5.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  PCE-triggered Initial LS Synchronization Procedure  . . .  11
   6.  PCE-triggered Re-synchronization  . . . . . . . . . . . . . .  12
     6.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .  12
     6.2.  PCE-triggered LS Re-synchronization Procedure . . . . . .  12
   7.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Link-State(LS) Report Message . . . . . . . . . . . . . .  13
     7.2.  Capability Advertisement  . . . . . . . . . . . . . . . .  14
     7.3.  Advertising Support of Synchronization Optimizations  . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  PCEP-Error Object . . . . . . . . . . . . . . . . . . . .  15
     8.2.  PCEP TLV Type Indicators  . . . . . . . . . . . . . . . .  16
     8.3.  LS-CAPABILITY Flags . . . . . . . . . . . . . . . . . . .  16
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  17
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  17
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  17
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  17
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  17
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  17
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  18
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  18
   11. Ackwonoledgement  . . . . . . . . . . . . . . . . . . . . . .  18
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     12.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20







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1.  Introduction

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.

   [I-D.dhodylee-pce-pcep-ls] describes a set of extensions to PCEP to
   provide Link-State (and TE) distribution.  This draft presents
   motivations for optimizations to the base PCEP Link-State transport
   procedure and specifies the required Path Computation Element
   Communication Protocol (PCEP) extensions.  This draft specifies
   following optimizations for Link-State Synchronization and the
   corresponding PCEP procedures and extensions:

   o  Link-State Synchronization Avoidance: To skip Link-State (and TE)
      synchronization if the state has survived and not changed during
      session restart.(See Section 3)

   o  Incremental Link-State Synchronization: To do incremental (delta)
      Link-State (and TE) Synchronization when possible.(See Section 4)

   o  PCE-triggered Initial Synchronization: To let PCE control the
      timing of the initial Link-State (and TE) Synchronization.(See
      Section 5)

   o  PCE-triggered Re-synchronization: To let PCE re-synchronize the
      Link-State (and TE) information for sanity check.(See Section 6)

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Terminology

   This document uses the following terms defined in [RFC5440]: PCC,
   PCE, PCEP Peer.

   This document uses the following terms defined in
   [I-D.dhodylee-pce-pcep-ls]: LSRpt, Link-State (and TE), LS

   Link-State (and TE): "LS" is interchangably used for the keyword
   "Link-State (and TE)".

   Within this document, when describing PCE-PCE communications, the
   requesting PCE fills the role of a PCC.  This provides a saving in
   documentation without loss of function.



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   The following terms are defined in this document:

   LS-DB: Link-State (and TE) Database.

   LS Sync: LS Synchronization, an operation to send LS information
   synchronization request to PCC by LSRpt message with LS-ID 0.

   LS-Info: One LS information (i.e.  LS Node/Link/Prefix defined in I-
   D.dhodylee-pce-pcep-ls).

3.  LS Synchronization Avoidance

3.1.  Motivation

   The purpose of LS Synchronization is to provide a checkpoint-in-time
   state replica of a PCC's Link-State (and TE) information in a PCE.
   LS Synchronization is performed immediately after the initialization
   phase ([RFC5440]).  [I-D.dhodylee-pce-pcep-ls] describes the basic
   mechanism for LS synchronization.

   LS Synchronization is not always necessary following a PCEP session
   restart.  If the Link-State (and TE) information of both PCEP peers
   did not change, the synchronization phase may be skipped.  This can
   result in significant savings in both control-plane data exchanges
   and the time it takes for the PCE to become fully operational.

3.2.  LS Synchronization Avoidance Procedure

   LS Synchronization MAY be skipped following a PCEP session restart if
   the Link-State (and TE) information of both PCEP peers did not change
   during the period prior to session re-initialization.  To be able to
   make this determination, LS-DB must be exchanged and maintained by
   both PCE and PCC during normal operation.  This is accomplished by
   keeping track of the changes to the Link-State (and TE) Database (LS-
   DB), using a version tracking field called the LS-DB Version Number.

   The LS-DB Version Number, carried in LS-DB-VERSION TLV (see
   Section 7.2), is owned by a PCC and it MUST be incremented by 1 for
   each successive change in the PCC's LS-DB.  The LS-DB Version Number
   MUST start at 1 and may wrap around.  Values 0 and 0xFFFFFFFFFFFFFFFF
   are reserved.  If either of the two values are used during LS re-
   synchronization, the PCE speaker receiving this node should send back
   a PCErr with Error-type TBD1 Error-value 1 'Received an invalid LS-DB
   Version Number', and close the PCEP session.  Operations that trigger
   a change to the local LS-DB include but not limited to -

   - a change in the link status or attributes(i.e. bandwidth, metric
   etc), addition or deletion of link.



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   - a change in the node attributes, addition or deletion of node.

   - a change in the prefix attributes, addition or deletion of prefix.

   LS Synchronization avoidance is advertised on a PCEP session during
   session startup using the LS-INCLUDE-DB-VERSION (S) bit in the LS-
   CAPABILITY TLV (see Section 7.3).  The peer may move in the network,
   either physically or logically, which may cause its connectivity
   details and transport-level identity (such as IP address) to change.
   To ensure that a PCEP peer can recognize a previously connected peer
   even in case of such mobility, each PCEP peer includes the SPEAKER-
   ENTITY-ID TLV in the OPEN message.  SPEAKER-ENTITY-ID TLV is
   described in [I-D.ietf-pce-stateful-sync-optimizations]

   If both PCEP speakers set the S flag in the OPEN object's LS-
   CAPABILITY TLV to 1, the PCC MUST include the LS-DB-VERSION TLV in
   each LS object of the LSRpt message.  If the LS-DB-VERSION TLV is
   missing in a LSRpt message, the PCE will generate an error with
   Error-Type 6 (mandatory object missing) and Error-Value TBD2 'LS-DB-
   VERSION TLV missing' and close the session.  If LS Synchronization
   avoidance has not been enabled on a PCEP session, the PCC SHOULD NOT
   include the LS-DB-VERSION TLV in the LS object and the PCE SHOULD
   ignore it, if it were to receive one.

   If a PCE's LS-DB survived the restart of a PCEP session, the PCE will
   include the LS-DB-VERSION TLV in its OPEN object, and the TLV will
   contain the last LS-DB Version Number received on an LS Report from
   the PCC in the previous PCEP session.  If a PCC's LS-DB survived the
   restart of a PCEP session, the PCC will include the LS-DB-VERSION TLV
   in its OPEN object and the TLV will contain the latest LS-DB Version
   Number.  If a PCEP speaker's LS-DB did not survive the restart of a
   PCEP session, the PCEP speaker MUST NOT include the LS-DB-VERSION TLV
   in the OPEN object.

   If both PCEP speakers include the LS-DB-VERSION TLV in the OPEN
   Object and the TLV values match, the PCC MAY skip LS Synchronization.
   Otherwise, the PCC MUST perform complete LS Synchronization.  If the
   PCC attempts to skip LS Synchronization (i.e., the SYNC Flag = 0 on
   the first LS Report from the PCC, the PCE MUST send back a PCErr with
   Error-Type TBD1 Error-Value 2 'LS-DB version mismatch', and close the
   PCEP session.

   If LS Synchronization is required, then prior to completing the
   initialization phase, the PCE MUST mark any LS-Infos in the LS-DB
   that were previously reported by the PCC as stale.  When the PCC
   reports a LS-Info during LS Synchronization, if the LS-Info already
   exists in the LS-DB, the PCE MUST update the LS-DB and clear the
   stale marker from the LS-Info.  When it has finished LS



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   Synchronization, the PCC MUST immediately send an end of LS
   Synchronization marker.  The end of synchronization marker is a LS
   Report (LSRpt) message with an LS object containing a LS-ID of 0 and
   with the SYNC flag set to 0.  The LS-DB-VERSION TLV MUST be included
   in this LSRpt message.  On receiving this LS Report, the PCE MUST
   purge any LS-Infos from the LS-DB that are still marked as stale.  It
   should be noted that PCE may receive the same Link-state and TE
   information from multiple PCCs and the purging should take that into
   account.

   Note that a PCE/PCC MAY force LS Synchronization by not including the
   LS-DB-VERSION TLV in its OPEN object.

   Since a PCE does not make changes to the LS-DB Version Number, a PCC
   should never encounter this TLV in a message from the PCE (other than
   the OPEN message).  A PCC SHOULD ignore the LS-DB-VERSION TLV, were
   it to receive one from a PCE.

   Figure 1 shows an example sequence where the LS synchronization is
   skipped.


                  +-+-+                        +-+-+
                  |PCC|                        |PCE|
                  +-+-+                        +-+-+
                    |                            |
                    |---Open--,                  |
                    |LS-DBv=82 \    ,---Open-----|
                    |     S=1   \  /LS-DBv=82    |
                    |            \/      S=1     |
                    |            /\              |
                    |           /   `----------->| (OK to skip
            (Skip   |<---------`                 |  LS sync)
            LS sync)|             .              |
                    |             .              |
                    |             .              |
                    |                            |
                    |---LSRpt,LS-DBv=83,SYNC=0-->| (Regular
                    |                            |  LS Report)
                    |---LSRpt,LS-DBv=84,SYNC=0-->| (Regular
                    |                            |  LS Report)
                    |---LSRpt,LS-DBv=85,SYNC=0-->|
                    |                            |


                   Figure 1: LS Synchronization Skipped





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   Figure 2 shows an example sequence where the LS Synchronization is
   performed due to LS-DB Version mismatch during the PCEP session
   setup.  Note that the same LS Synchronization sequence would happen
   if either the PCC or the PCE would not include the LS-DB-VERSION TLV
   in their respective Open messages.


                 +-+-+                        +-+-+
                 |PCC|                        |PCE|
                 +-+-+                        +-+-+
                   |                            |
                   |---Open--,                  |
                   |LS-DBv=86 \    ,---Open-----|
                   |     S=1   \  /LS-DBv=82    |
                   |            \/      S=1     |
                   |            /\              |
                   |           /   `----------->| (Expect sync)
               (Do |<---------`                 |
             sync) |                            |
                   |                            |
                   |---LSRpt,LS-DBv=86,SYNC=1-->| (Sync start)
                   |                .           |
                   |                .           |
                   |                .           |
                   |---LSRpt,LS-DBv=86,SYNC=0-->| (Sync done)
                   |                .           |(Purge LS-Info
                   |                .           | if applicable)
                   |                .           |
                   |---LSRpt,LS-DBv=87,SYNC=0-->| (Regular
                   |                            |  LS Report)
                   |---LSRpt,LS-DBv=88,SYNC=0-->| (Regular
                   |                            |  LS Report)
                   |---LSRpt,LS-DBv=89,SYNC=0-->|
                   |                            |




                  Figure 2: LS Synchronization Performed

   Figure 3 shows an example sequence where the LS Synchronization is
   skipped, but because one or both PCEP speakers set the S Flag to 0,
   the PCC does not send LS-DB-VERSION TLVs in subsequent LSRpt messages
   to the PCE.  If the current PCEP session restarts, the PCEP speakers
   will have to perform LS Synchronization, since the PCE does not know
   the PCC's latest LS-DB Version Number information.





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                  +-+-+                        +-+-+
                  |PCC|                        |PCE|
                  +-+-+                        +-+-+
                    |                            |
                    |---Open--,                  |
                    |LS-DBv=82 \    ,---Open-----|
                    |     S=0   \  /LS-DBv=82    |
                    |            \/      S=0     |
                    |            /\              |
                    |           /   `----------->| (OK to skip
            (Skip   |<---------`                 |  LS sync)
            LS sync)|             .              |
                    |             .              |
                    |             .              |
                    |                            |
                    |--------LSRpt,SYNC=0------->| (Regular
                    |                            |  LS Report)
                    |--------LSRpt,SYNC=0------->| (Regular
                    |                            |  LS Report)
                    |--------LSRpt,SYNC=0------->|
                    |                            |



   Figure 3: LS Synchronization Skipped, no LS-DB-VERSION TLVs sent from
                                    PCC

4.  Incremental LS Synchronization

   [I-D.dhodylee-pce-pcep-ls] describes the LS synchronization mechanism
   during session initialization between PCCs and PCEs.  During the LS
   synchronization, a PCC sends the information of its LS-DB to the PCE
   based on the local policy.  In order to reduce the LS Synchronization
   overhead when there is a small number of LS-DB change in the network
   between PCEP session restart, this section defines a mechanism for
   incremental (Delta) LS synchronization.

4.1.  Motivation

   According to [I-D.dhodylee-pce-pcep-ls], if a PCEP session restarts,
   PCCs send snapshot of LS-DB information to the PCE, though LS-DB did
   not change.  And as per Section 3 (LS Synchronization Avoidance
   Procedure), if there is a change in a small number of LS-Infos.  PCC
   yet sends complete snapshot of LS-DB information to the PCE, which
   takes a long time and consume large communication channel bandwidth.






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4.2.  Incremental Synchronization Procedure

   Section 3 describes LS Synchronization avoidance by using LS-DB-
   VERSION TLV in its OPEN object.  This section extends this idea to
   only synchronize the delta (changes) in case of version mismatch.

   If both PCEP speakers include the LS-DB-VERSION TLV in the OPEN
   object and the LS-DB-VERSION TLV values match, the PCC MAY skip LS
   Synchronization.  Otherwise, the PCC MUST perform LS Synchronization.
   Incremental LS Synchronization capability is advertised on a PCEP
   session during session startup using the LS-DELTA-SYNC-CAPABILITY (D)
   bit in the capabilities TLV (see Section 7.3).  Instead of dumping
   full LS-DB to the PCE again, PCC synchronizes the delta (changes) as
   described in Figure 4 when D flag and S flag is set to 1 by both PCC
   and PCE.  Other combinations of D and S flags setting by PCC and PCE
   result in complete LS Synchronization procedure as described in
   [I-D.dhodylee-pce-pcep-ls].  If a PCC has to force complete LS
   Synchronization due to reasons including but not limited: (1) local
   policy configured at the PCC; (2) no sufficient LS-DB caches for
   incremental update, the PCC can set the D flag to 0.  Note a PCC may
   have to bring down the current session and force a complete LS
   Synchronization with D flag set to 0 in the subsequent open message.





























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              +-+-+                        +-+-+
              |PCC|                        |PCE|
              +-+-+                        +-+-+
                |                            |
                |---Open--,                  |
                |LS-DBv=86 \    ,---Open-----|
                |     S=1   \  /LS-DBv=82    |
                |     D=1    \/      S=1     |
                |            /\      D=1     |
                |           /   `----------->| (Expect Delta sync)
          (Do   |<---------`                 | (Donot purge
          Delta |                            |  LS-Infos)
          sync) |                            |
                |---LSRpt,LS-DBv=86,SYNC=1-->| (Delta Sync start)
                |                .           |
                |                .           |
                |                .           |
                |---LSRpt,LS-DBv=86,SYNC=0-->| (Sync done)
                |                            | LS-ID=0)
                |                            |
                |---LSRpt,LS-DBv=87,SYNC=0-->| (Regular
                |                            |  LS Report)
                |---LSRpt,LS-DBv=88,SYNC=0-->| (Regular
                |                            |  LS Report)
                |---LSRpt,LS-DBv=89,SYNC=0-->|
                |                            |




              Figure 4: Incremental Synchronization Procedure

   As per Section 3, the LS-DB Version Number is incremented each time a
   change is made to the PCC's local LS-DB.  Each LS-Info is associated
   with the DB version at the time of change.  This is needed to
   determine which LS-Info needs to be synchronized in incremental LS
   Synchronization.

   PCC MAY store a then history of LS-DB change that happened between
   the PCEP session(s) restart in order to carry out incremental LS
   Synchronization.  After the synchronization procedure finishes, the
   PCC can dump this history information.  In the example shown in
   Figure 4, the PCC needs to store the LS-DB changes that happened
   between DB Version 83 to 86 and synchronizes these changes only when
   performing incremental LS-DB update.  So a PCC needs to remember the
   LS-DB changes that happened when an existing PCEP session to a PCE
   goes down in the hope of doing incremental synchronization when the
   session is re-established.



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   If a PCC finds out it does not have sufficient information to
   complete incremental synchronization after advertising incremental LS
   Synchronization capability, it MUST send a PCErr with Error-Type TBD1
   and Error-Value 3 'A PCC indicates to a PCE that it can not complete
   the LS synchronization' and terminate the session.

5.  PCE-triggered Initial Synchronization

5.1.  Motivation

   In networks such as optical transport networks, the control channel
   between network nodes can be realized through in-band overhead thus
   has limited bandwidth.  With a PCE connected to the network via one
   network node, it is desirable to control the timing of PCC LS
   Synchronization so as not to overload the low communication channel
   available in the network during the initial synchronization (be it
   incremental or full) when the session restarts, when there is
   comparatively large amount of control information needing to be
   synchronized between the PCE and the network.  The method proposed,
   i.e., allowing PCE to trigger the LS synchronization, is similar to
   the function proposed in Section 6 but is used in different scenarios
   and for different purposes.

5.2.  PCE-triggered Initial LS Synchronization Procedure

   Support of PCE-triggered LS Synchronization is advertised during
   session startup using the LS-TRIGGERED-INITIAL-SYNC (F) bit in the
   LS-CAPABILITY TLV (see Section 7.3).

   As per [I-D.dhodylee-pce-pcep-ls], LSRpt is sent from PCC to PCE,
   this document extends the usage of LSRpt to trigger syncronization.
   Where a PCC can send a LSRpt (for LS Sync) with an LS object
   containing a LS-ID of 0 and with the SYNC flag set to 1.  This LSRpt
   message is the trigger for the PCC to enter the synchronization phase
   and start sending LSRpt messages.

   If the LS-TRIGGERED-INITIAL-SYNC capability is not advertised and the
   PCC receives a LSRpt with the SYNC flag set to 1, it MUST send a
   PCErr for LSRpt(LS Sync from PCE) with Error-Type TBD1 and Error-
   Value 4 'Attempt to trigger synchronization when the PCE triggered
   synchronization capability has not been advertised'.

   A PCE MAY choose to control the LS Synchronization process.  To allow
   PCE to do so, PCEP speakers MUST set T bit to 1 to indicate this (as
   described in Section 7.3).  If the LS-DB version is mis-matched, it
   can send a LSRpt message with LS-ID = 0 and SYNC = 1 in order to
   trigger the LS Synchronization process.  In this way, the PCE can
   control the sequence of LS Synchronization among all the PCCs that



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   are re-establishing PCEP sessions with it.  When the capability of
   PCE control is enabled, only after a PCC receives this message, it
   will start sending information to the PCE.  The PCC SHOULD NOT send
   LSRpt messages to the PCE before it triggers the LS Synchronization.
   This PCE-triggering capability can be applied to both full and
   incremental LS Synchronization.  If applied to the later, the PCCs
   only send information that PCE does not possess, which is inferred
   from the LS-DB version information exchanged in the OPEN message (see
   Section 3.2) for detailed procedure).

6.  PCE-triggered Re-synchronization

6.1.  Motivation

   The accuracy of the computations performed by the PCE is tied to the
   accuracy of the view the PCE has on the LS-DB.  Therefore, it can be
   beneficial to be able to re-synchronize LS-DB even after the session
   has been established.  The PCE may use this approach to continuously
   sanity check its LS-DB against the network, or to recover from error
   conditions without having to tear down sessions.

6.2.  PCE-triggered LS Re-synchronization Procedure

   Support of PCE-triggered LS Synchronization is advertised during
   session startup using the LS-TRIGGERED-RESYNC (T) bit in the LS-
   CAPABILITY TLV (see Section 7.3).

   The PCE triggers re-synchronization of the entire LS-DB.  The PCE
   MUST first mark all LS-Infos in the LS-DB that were previously
   reported by the PCC as stale and then send a LSRpt (for LS Sync) with
   an LS object containing a LS-ID of 0 and with the SYNC flag set to 1.
   This LSRpt message is the trigger for the PCC to enter the
   synchronization phase and start sending LSRpt messages.  After the
   receipt of the end-of-synchronization marker, the PCE will purge LS-
   Infos which were not refreshed.

   If the LS-TRIGGERED-RESYNC capability is not advertised and the PCC
   receives a LSRpt with the SYNC flag set to 1, it MUST send a PCErr
   with Error-Type TBD1 and Error-Value 4 'Attempt to trigger
   synchronization when the TRIGGERED-SYNC capability has not been
   advertised'.

   Once the state re-synchronization is triggered by the PCE, the
   procedures and error checks remain unchanged from the full state
   synchronization ([I-D.dhodylee-pce-pcep-ls]).  This would also
   include PCE triggering multiple state re-synchronization requests
   while synchronization is in progress.




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


          Figure 5: PCE Triggered Complete LS re-synchronization

7.  PCEP Extensions

7.1.  Link-State(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 LS information.
   The definition of the LSRpt message from [I-D.dhodylee-pce-pcep-ls]
   is extended to use LSRpt message with LS-ID = 0 to request LS
   Synchronization from PCE to PCC.

   If a PCC that does not support extention defined in this document
   receives a LSRpt message, it will act according to existing behavior
   of receiving invalid message.  If a PCC supports the extention, but
   did not set the flag T or F, and receives the LSRpt message, it sends
   PCErr message as described earlier in section [x] and [y].  If a PCC
   supports the extention and set the flag T or F, and receives the
   LSRpt message without LS-ID as 0 and SYNC flag set, PCC will send an
   error message with Error-Type TBD1 Error-Value 6 'Invalid LSRpt
   message'.








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7.2.  Capability Advertisement

   The LS-DB Version Number is an carried in optional LS-DB-VERSION TLV
   that MAY be included in the OPEN object and the LS object.  This TLV
   MUST NOT be included if LS-INCLUDE-DB-VERSION bit in LS-CAPABILITY
   TLV is not set.

   The format of the LS-DB-VERSION 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=[TBD]          |            Length=8           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 LS-DB Version Number                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                    Figure 6: LS-DB-VERSION TLV format

   The type of the TLV is [TBD] and it has a fixed length of 8 octets.
   The value contains a 64-bit unsigned integer, representing the LS-DB
   Version Number.

7.3.  Advertising Support of Synchronization Optimizations

   Support for each of the optimizations described in this document
   requires advertising the corresponding capabilities during session
   establishment.

   New flags are defined for the LS-CAPABILITY TLV defined in
   [I-D.dhodylee-pce-pcep-ls].


      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                   |F|D|T|S|R|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



                    Figure 7: LS-CAPABILITY TLV Format




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   The value comprises a single field - Flags (32 bits):

   R (LS-REMOTE-BIT - 1 bit): Defined in [I-D.dhodylee-pce-pcep-ls]

   S (LS-INCLUDE-DB-VERSION - 1 bit): If set to 1 by both PCEP speakers,
   the PCC will include the LS-DB-VERSION TLV in each LS object.  See
   Section 3 for details.

   T (LS-TRIGGERED-RESYNC - 1 bit): If set to 1 by both PCEP speakers,
   the PCE can trigger re-synchronization of LS-Infos at any point in
   the life of the session.  See Section 6 for details.

   D (LS-DELTA-SYNC-CAPABILITY - 1 bit): If set to 1 by a PCEP speaker,
   it indicates that the PCEP speaker allows incremental (delta) state
   synchronization.  See Section 4 for details.

   F (LS-TRIGGERED-INITIAL-SYNC - 1 bit): If set to 1 by both PCEP
   speakers, the PCE SHOULD trigger initial (first) LS synchronization.
   See Section 5 for details.

8.  IANA Considerations

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

8.1.  PCEP-Error Object

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






















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           Error-Type Meaning                        Reference
               6      Mandatory Object missing       [RFC5440]
                      Error-Value= TBD2              This document
                      LS-DB-VERSION TLV missing
               TBD1   LS synchronization             This document
                      error
                      Error-Value= TBD(suggested     This document
                      value 1):Received an invalid
                      LSDB Version Number
                      Error-Value= TBD(suggested     This document
                      value 2): LS-DB
                      version mismatch.
                      Error-Value=TBD(suggested      This document
                      value 3): PCC indicates to a
                      PCE that it cannot complete
                      the LS Synchronization
                      Error-Value=TBD(suggested      This document
                      value 4): Attempt to trigger a
                      synchronization when the
                      PCE triggered synchronization
                      capability has not been
                      advertised.
                      Error-Value=TBD(suggested      This document
                      value 5): LS-DB-VERSION
                      TLV Missing when LS
                      synchronization avoidance is
                      enabled.
                      Error-Value=TBD(suggested      This document
                      value 6): Invalid LSRpt
                      message.


8.2.  PCEP TLV Type Indicators

   This document defines the following new PCEP TLVs:

               Value                   Meaning        Reference
               TBD                     LS-DB-VERSION   This document

8.3.  LS-CAPABILITY Flags

   The following values are defined in this document for the Flags field
   in the LS-CAPABILITY TLV in the OPEN object:








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       Bit                     Description            Reference
       TBD
       (Suggested value 30) LS-INCLUDE-DB-VERSION     This document
       (Suggested value 29) LS-TRIGGERED-RESYNC       This document
       (Suggested value 28) LS-DELTA-SYNC-CAPABILITY  This document
       (Suggested value 27) LS-TRIGGERED-INITIAL-SYNC This document

9.  Manageability Considerations

   All manageability requirements and considerations listed in [RFC5440]
   and [I-D.dhodylee-pce-pcep-ls] apply to PCEP protocol extensions
   defined in this document.  In addition, requirements and
   considerations listed in this section apply.

9.1.  Control of Function and Policy

   A PCE or PCC implementation MUST allow configuring the state
   synchronization optimization capabilities as described in this
   document.

9.2.  Information and Data Models

   PCEP session configuration and information in the PCEP MIB module
   SHOULD be extended to include advertised LS Capabilities, LS-DB
   Version Number and LS synchronization status, Message statistics.

9.3.  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].

9.4.  Verify Correct Operations

   Mechanisms defined in section 8.4 of [RFC5440] also apply to PCEP
   protocol extensions defined in this document.  In addition to
   monitoring parameters defined in [RFC5440], a PCEP implementation
   with LS-DB SHOULD provide the following parameters:

   o  Total number of LSRpt(Synchronization request) requests

   o  LS-DB Version Number and synchronization status

9.5.  Requirements On Other Protocols

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




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9.6.  Impact On Network Operations

   Mechanisms defined in section 8.6 of [RFC5440] also apply to PCEP
   protocol extensions defined in this document.

   Additionally, a PCEP implementation SHOULD allow a limit to be placed
   on the amount and rate of LSRpt messages sent by a PCEP speaker and
   processed by the peer.  It SHOULD also allow sending a notification
   when a rate threshold is reached.

10.  Security Considerations

   The security considerations listed in [I-D.dhodylee-pce-pcep-ls]
   apply to this document as well.  However, because the protocol
   modifications outlined in this document allow the PCE to control LS
   Re-synchronization timing and sequence, it also introduces a new
   attack vector: an attacker may flood the PCC with triggered re-
   synchronization request at a rate which exceeds the PCC's ability to
   process them, either by spoofing messages or by compromising the PCE
   itself.  The PCC is free to drop any trigger re-synchronization
   request without additional processing.

11.  Ackwonoledgement

   The document borrows some of the text and structure from
   [I-D.ietf-pce-stateful-sync-optimizations].

12.  References

12.1.  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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc5440>.

   [I-D.dhodylee-pce-pcep-ls]
              Dhody, D., Lee, Y., and D. Ceccarelli, "PCEP Extension for
              Distribution of Link-State and TE Information.", draft-
              dhodylee-pce-pcep-ls-00 (work in progress), September
              2015.





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12.2.  Informative References

   [I-D.ietf-pce-stateful-sync-optimizations]
              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", draft-
              ietf-pce-stateful-sync-optimizations-03 (work in
              progress), October 2015.











































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Appendix A.  Contributor Addresses

                    Dhruv Dhody
                    Huawei Technologies
                    Divyashree Techno Park, Whitefield
                    Bangalore, Karnataka  560037
                    India

                    EMail: dhruv.ietf@gmail.com


Authors' Addresses

   Venugopal Reddy Kondreddy
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560037
   India

   EMail: venugopalreddyk@huawei.com


   Mahendra Singh Negi
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560037
   India

   EMail: mahendrasingh@huawei.com






















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