LSP-DB Synchronization between Stateful PCEs
draft-palle-pce-stateful-pce-lspdb-sync-02

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PCE Working Group                                               U. Palle
Internet-Draft                                                  D. Dhody
Intended status: Standards Track                                X. Zhang
Expires: July 26, 2014                               Huawei Technologies
                                                        January 22, 2014

              LSP-DB Synchronization between Stateful PCEs
               draft-palle-pce-stateful-pce-lspdb-sync-02

Abstract

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

   [STATEFUL-PCE] specifies a set of extensions to PCEP to enable
   stateful control of MPLS-TE and GMPLS Label Switched Paths (LSPs) via
   PCEP and maintaining of these LSPs at the stateful PCE.  This
   document describes the mechanisms of LSP Database (LSP-DB)
   synchronization between stateful PCEs.

Status of This Memo

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation and Use  . . . . . . . . . . . . . . . . . . . . .   3
   4.  Functions to Support LSP-DB Synchronization . . . . . . . . .   4
   5.  Architectural Overview  . . . . . . . . . . . . . . . . . . .   5
     5.1.  LSP-DB Synchronization between Primary and Backup
           Stateful PCEs . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  LSP-DB Synchronization between Load-Balanced Stateful
           PCEs  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Other Considerations  . . . . . . . . . . . . . . . . . .   8
   6.  PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  The PCRpt Message . . . . . . . . . . . . . . . . . . . .   8
     6.2.  The PCUpd Message . . . . . . . . . . . . . . . . . . . .   9
   7.  TLVs  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Stateful PCE Capability TLV . . . . . . . . . . . . . . .   9
     7.2.  PCE Redundancy Group Identifier TLV . . . . . . . . . . .   9
     7.3.  PCE-CAP-FLAGS sub-TLV . . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  10
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  10
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  10
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  10
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  10
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  11
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  11
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  STATEFUL-PCE-CAPABILITY TLV  . . . . . . . . . . . . . .  11
     10.2.  PCE-CAP-FLAGS sub-TLV  . . . . . . . . . . . . . . . . .  11
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     12.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  13

1.  Introduction

   [RFC5440] describes the Path Computation Element Protocol (PCEP) as
   the communication between a Path Computation Client (PCC) and a Path
   Computation Element (PCE), or between PCEs, enabling computation of

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   Multiprotocol Label Switching (MPLS) for Traffic Engineering Label
   Switched Paths (TE LSPs).

   [STATEFUL-PCE] specifies a set of extensions to PCEP to enable
   stateful control of LSPs in compliance with [RFC4655].  It includes
   mechanisms for LSP state synchronization between a PCC and a PCE,
   i.e., all stateful PCEs synchronize their LSP states from the
   network.

   When multiple stateful PCEs are operating in the network, they could
   be either Primary/Backup or Loadbalanced.  In a scenario where the
   network operator has deployed backup stateful PCE(s) with only
   purpose to be used in the event of failure of the primary PCE, it
   makes sense that in such a deployment, PCE should have as latest LSP
   states as possible.  Further as stateful PCE make changes to the
   delegated LSPs, these changes (pending LSPs and sticky resources)
   needs to be synchronized to other PCEs as soon as possible.
   [PCE-QUESTIONS] describes the synchronization issues when PCEs are
   synchronized from the network (PCC) only.

   This document specifies the mechanisms of LSP-DB synchronization
   between stateful PCEs (in the same domain) to be able to get the
   latest LSP state.

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

   The terminology is as per [RFC5440] and [STATEFUL-PCE].

   LSP-DB:  A database of LSPs that are active in the network as
      maintained by a stateful PCE.

   Sticky Resources:  The temporarily assigned resources that are
      allocated to a pending LSP and are provisionally blocked.

3.  Motivation and Use

   Distributed computation model ([RFC4655]) refers to a domain or
   network that may include multiple PCEs where computation of paths is
   shared among the PCEs, this is further clarified in [PCE-QUESTIONS].

   When multiple stateful PCEs are operating in the network, they could
   be either -

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   Primary or Backup PCE:  A backup PCE exists to perform functions in
      the network, only in the event of a failure of the primary PCE.
      In this case, all LSPs to be delegated are under primary stateful
      PCE control while other PCEs in the domain act as backup.  The
      backup PCE should have the same view of LSP-DB as primary stateful
      PCE.  The LSP-DB of a backup PCE can be synchronized via the
      primary stateful PCE or collected from multiple network nodes
      (PCC).  In case of latter only, the backup PCE may face
      synchronization issues as described in [PCE-QUESTIONS].  Thus it
      is suggested that backup PCE can be synchronized via the primary
      stateful PCE, this mechanism is described in Section 5.1.  Note
      that backup PCE MAY use synchronization from network as a
      mechanism to cross-check the LSP-DB.

   Load-Balanced 'Backup' PCE:  Load-Balanced PCEs share the computation
      load all the time as well as act backup to each other.  One PCE
      MAY serve a set of PCCs as the primary computation server, and
      only addresses requests from other PCCs in the event of the
      failure of some other PCE.  Delegated LSPs are thus distributed
      among stateful PCEs.  It is suggested that in this case each load-
      balanced stateful PCE should build their LSP-DB independently from
      the network (PCCs) (via mechanism described in [STATEFUL-PCE])
      during initial LSP state synchronization and not from other
      stateful PCEs.  But it is important that these load-balanced
      stateful PCEs needs to be synchronized to have a similar view of
      pending LSPs and sticky resources, this mechanism is described in
      Section 5.2.

4.  Functions to Support LSP-DB Synchronization

   [STATEFUL-PCE] specifies new functions to support a stateful PCE.  It
   also specifies that a function can be initiated either from a PCC
   towards a PCE (C-E) or from a PCE towards a PCC (E-C).

   o  Capability negotiation (E-C,C-E)

   o  LSP state synchronization (C-E)

   o  LSP update request (E-C)

   o  LSP state report (C-E)

   o  LSP control delegation (C-E,E-C)

   o  Stateful PCE discovery via [STATEFUL-PCE-DISC]

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   This document extends some of these functions to support LSP-DB
   synchronization.  Some are initiated either from a PCE towards
   another PCE (E-E) or specifically from primary to backup PCE (PE-BE).

   Capability negotiation (E-E):  both the PCEs must announce during
      PCEP session establishment that they support PCEP Stateful PCE
      extensions defined in [STATEFUL-PCE].  It should also declare
      whether it has primary or backup stateful PCE capability.  This is
      done via Open message.

   LSP state synchronization (PE-BE):  after the session between the
      stateful PCEs is initialized, the backup PCE must learn the state
      of LSPs from the primary PCE.  This is done via PCRpt message.

   LSP update request (E-E):  When a PCE requests modification of
      attributes of a delegated LSP, this information should also be
      sent to other PCEs.  This is done via PCUpd message.  This is
      needed to synchronize the pending LSPs and sticky resources.

   Stateful PCE discovery:  PCE can advertise its primary or backup
      capability via IGP.

5.  Architectural Overview

   LSP-DB synchronization function is defined in section 5.4 of
   [STATEFUL-PCE] between PCC and PCEs.  This document extends the LSP
   state synchronization between stateful PCEs.

5.1.  LSP-DB Synchronization between Primary and Backup Stateful PCEs

   As shown in Figure 1, PCE1 is the primary stateful PCE and PCE2 is
   the backup stateful PCE.  PCC1 and PCC2 synchronize the LSP-DB with
   the primary stateful PCE1 after session initialization phase.  And
   primary stateful PCE1 synchronizes LSP-DB with its backup stateful
   PCE2 after session initialization phase.  This is LSP state
   synchronization as described in Section 4 and uses PCRpt message.

   PCC1 and PCC2 delegates LSP1 and LSP2 to the primary PCE1.  Whenever
   there is an update in LSP, PCE1 sends a PCUpd message to
   corresponding PCC and also to backup PCE2.  This is LSP update
   request as described in Section 4 and uses PCUpd message.  This makes
   sure that the pending LSP changes and sticky resources are backed up.
   The PCC sends a PCRpt message to the primary PCE, indicating the
   LSP's status, the primary PCE further synchronizes the state with
   backup PCEs via PCRpt message.

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   +----+            +----+             +----+              +----+
   |PCC1|            |PCC2|             |PCE1|              |PCE2|
   +-+--+            +-+--+             +-+--+              +-+--+
     |                 |                  |                   |
     |---- LSP SYNC ---+----------------->|                   |
     |                 |---- LSP SYNC --->|                   |
     |                 |                  |---- LSP SYNC----->|
     |                 |---- LSP SYNC ----+------------------>|
     |---- LSP SYNC ---+------------------+------------------>|
     |                 |                  |                   |
     |-- PCRpt,lsp1,D -+----------------->|                   |
     |<----------------+----PCUpd,lsp1 ---|                   |
     |                 |                  |--- PCUpd,lsp1 --->|
     |-- PCRpt,lsp1,up-+----------------->|                   |
     |-- PCRpt,lsp1,up-+------------------+------------------>|
     |                 |                  |----PCRpt,lsp1,up->|
     |                 |                  |                   |
     |                 |-- PCRpt,lsp2,D ->|                   |
     |                 |<---PCUpd,lsp2 ---|                   |
     |                 |                  |--- PCUpd,lsp2---->|
     |                 |-- PCRpt,lsp2,up->|                   |
     |                 |-- PCRpt,lsp2,up--+------------------>|
     |                 |                  |----PCRpt,lsp2,up->|
     |                 |                  |                   |

   Figure 1: LSP-DB synchronization between primary and backup stateful
                                   PCEs

   In this case LSP state synchronization is done via primary stateful
   PCE.  The backup PCE MAY choose to cross-check the LSP-DB with the
   state learned from the network (PCCs).

   The backup PCE is used only in case the primary PCE fails.  At the
   time of failure of primary PCE (PCE1), the backup PCE (PCE2) act as a
   primary.  In case of multiple backup PCEs, a selection mechanism
   (e.g.  least IP address among backup PCEs) may be used.  When PCE1
   recovers from failure, the acting primary PCE (PCE2) should backup
   using the mechanism as described in this section and restart all its
   PCEP sessions, thus making sure all PCEP speakers now considers PCE1
   as primary.

   [STATEFUL-LSPSYNC-OPT] describes LSP state synchronization
   optimizations - PCE triggered synchronization, state synchronization
   avoidance, and incremental state synchronization.  A Backup PCE
   should trigger the state synchronization with primary PCE first in
   order to get the full LSP-DB, likewise when the original primary PCE
   gets up, it can trigger the state synchronization with the current

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   stateful PCE first.  Further state synchronization avoidance and
   incremental state synchronization can optimize the state
   synchronization process making sure that the PCEs have the latest
   LSP-DB as quickly as possible.

5.2.  LSP-DB Synchronization between Load-Balanced Stateful PCEs

   As shown in Figure 2, PCE1 and PCE2 are load-balanced stateful PCEs
   and share the computation load as well as act as backup to each
   other.  PCC1 and PCC2 synchronize their LSP-DB with both PCEs after
   session initialization phase as per [STATEFUL-PCE].  In this case,
   state synchronization does not happen between PCE1 and PCE2 as they
   synchronize the LSP-DB with the network (PCCs).

   PCC1 delegates LSP1 to PCE1.  Whenever there is an update in LSP1,
   PCE1 sends the PCUpd message to PCC1 and other stateful PCEs (PCE2).
   Similarly, PCC2 delegates LSP2 to PCE2.  Whenever there is an update
   in LSP2, PCE2 sends the PCUpd message to PCC2 and other stateful PCEs
   (PCE1).  This is LSP update request as described in Section 4 and it
   makes sure that the pending LSP changes and sticky resources are
   synchronized.  The PCC sends an PCRpt message to the all load-
   balanced PCEs as per [STATEFUL-PCE], indicating the LSP's status.

   Note that the PCUpd message are exchanged between load-balanced PCEs
   for pending LSP changes and sticky resources.  And the status of the
   LSPs are received from the network (PCC) via PCRpt message as
   described in [STATEFUL-PCE] as well as from the PCE.

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   +----+            +----+             +----+              +----+
   |PCC1|            |PCC2|             |PCE1|              |PCE2|
   +-+--+            +-+--+             +-+--+              +-+--+
     |                 |                  |                   |
     |---- LSP SYNC ---+----------------->|                   |
     |---- LSP SYNC ---+------------------+------------------>|
     |                 |---- LSP SYNC --->|                   |
     |                 |---- LSP SYNC ----+------------------>|
     |                 |                  |                   |
     |-- PCRpt,lsp1,D -+----------------->|                   |
     |<----------------+----PCUpd, lsp1---|                   |
     |                 |                  |--- PCUpd, lsp1--->|
     |-- PCRpt,lsp1,up-+----------------->|                   |
     |-- PCRpt,lsp1,up-+------------------+------------------>|
     |                 |                  |----PCRpt,lsp1,up->|
     |                 |                  |                   |
     |                 |                  |                   |
     |                 |-- PCRpt,lsp2,D --+------------------>|
     |                 |<---PCUpd, lsp2---|-------------------|
     |                 |                  |<--- PCUpd, lsp2 --|
     |                 |-- PCRpt,lsp2,up->|                   |
     |                 |-- PCRpt,lsp2,up--+------------------>|
     |                 |                  |<---PCRpt,lsp1,up--|
     |                 |                  |                   |

   Figure 2: LSP-DB synchronization between load-balanced stateful PCEs

   At the time of failure of one of the PCEs (say PCE1), the other PCE
   (PCE2) may take up the load.  When PCE1 recovers from failure, the
   load can be redistributed again among the PCEs.

5.3.  Other Considerations

   o  This document does not tackle the issue about TED synchronization
      which is described in detail in [PCE-QUESTIONS].

   o  The computation mechanism and how PCE chooses to handle the sticky
      resources during computation is out of scope of this document.

6.  PCEP Messages

6.1.  The PCRpt Message

   The format of PCRpt message is defined in [STATEFUL-PCE].  It
   specifies the PCRpt message is sent from PCC to PCE in reporting the
   LSP state.  This document extends the usage of PCRpt message between

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   primary and backup stateful PCEs for LSP synchronization as described
   in Section 5.1.

6.2.  The PCUpd Message

   The format of PCUpd Message is defined in [STATEFUL-PCE].  It
   specifies the PCUpd message is sent from PCE to PCC to request
   changes in LSP attributes.  This document extends the usage of PCUpd
   message between stateful PCEs for LSP synchronization of pending LSPs
   and sticky resources as described in Section 5.2.  Whenever there is
   a PCUpd message sent from PCE to PCC, PCE should also send it to
   other PCEs (backup or load-balanced).

7.  TLVs

7.1.  Stateful PCE Capability TLV

   As per [STATEFUL-PCE], STATEFUL-PCE-CAPABILITY TLV can be used in the
   OPEN object for stateful PCE capability negotiation.  A stateful PCE
   must announce during PCEP session establishment that they support
   PCEP stateful PCE extensions defined in [STATEFUL-PCE].  A new flag
   is added -

   B (BACKUP - 1 bit):  if set to 1 by PCE, the PCE should act as a
      backup.  It MAY become an 'acting primary PCE' only in case of
      failure or unavailability of primary PCE.  In case of PCC, this
      bit has no meaning and is simply ignored.

7.2.  PCE Redundancy Group Identifier TLV

   [STATEFUL-PCE] defines a PREDUNDANCY-GROUP-ID TLV which is an unique
   identifier of a PCC and carried in OPEN object, [STATEFUL-PCE] also
   specifies PLSP-ID in LSP object and SYMBOLIC-PATH-NAME TLV which is
   used to identify the originating PCC.

   To uniquely identify LSP across stateful PCEs, PREDUNDANCY-GROUP-ID
   TLV MUST be encoded along with LSP object when PCRpt message is sent
   from primary to backup stateful PCE.  This way the backup stateful
   PCE will also learn the unique identifier for the PCC that does not
   change.

   The existing PREDUNDANCY-GROUP-ID TLV MAYBE encoded in LSP object's
   optional TLV to identify the originating PCC.

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7.3.  PCE-CAP-FLAGS sub-TLV

   [RFC5088] and [RFC5089] describe the mechanism to advertise the PCE
   Discovery information via OSPF and IS-IS respectively along with
   processing rules for the sub-TLVs.  [STATEFUL-PCE-DISC] further
   enhances the optional PCE-CAP-FLAGS sub-TLV used to advertise PCE
   stateful capabilities.

   Further a new bit is added -

         Bit       Capabilities

         TBD       Backup Stateful PCE

   If this bit is set to 1, the PCE should act as a backup.  It MAY
   become an 'acting primary PCE' only in case of failure or
   unavailability of primary PCE.

8.  Security Considerations

   This document does not introduce any new security concerns besides
   those in [STATEFUL-PCE].

9.  Manageability Considerations

9.1.  Control of Function and Policy

   A PCE may be deployed to act only as a backup (Section 5.1), an
   operator SHOULD be able to configure a PCE as backup.

9.2.  Information and Data Models

   [PCEP-MIB] describes the PCEP MIB, there are no new MIB Objects for
   this document.

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

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9.5.  Requirements On Other Protocols

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

9.6.  Impact On Network Operations

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

10.  IANA Considerations

10.1.  STATEFUL-PCE-CAPABILITY TLV

   As discussed in Section 7.1, a new STATEFUL-PCE-CAPABILITY TLV Flag
   Field has been defined.  IANA has made the following allocation from
   the PCEP "STATEFUL-PCE-CAPABILITY TLV Flag Field" sub-registry:

         Bit    Description                               Reference

         TBD    BACKUP                                    [This I.D.]

10.2.  PCE-CAP-FLAGS sub-TLV

   As discussed in Section 7.1, a new bit is added, IANA is requested to
   allocate a new bit in "PCE Capability Flags" registry for backup
   stateful PCE capability as follows:

         Bit    Description                               Reference

         TBD    BACKUP                                    [This I.D.]

11.  Acknowledgments

   Thanks to Adrian Farrel and Daniel King for writing [PCE-QUESTIONS].

   We would like to thank Avantika Kumar for her useful comments and
   suggestions.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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12.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, August 2006.

   [RFC5088]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "OSPF Protocol Extensions for Path Computation Element
              (PCE) Discovery", RFC 5088, January 2008.

   [RFC5089]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "IS-IS Protocol Extensions for Path Computation Element
              (PCE) Discovery", RFC 5089, January 2008.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440, March
              2009.

   [STATEFUL-PCE]
              Crabbe, E., Medved, J., Minei, I., and R. Varga,, "PCEP
              Extensions for Stateful PCE (draft-ietf-pce-stateful-
              pce)", October 2013.

   [PCE-QUESTIONS]
              Farrel, A. and D. King, "Unanswered Questions in the Path
              Computation Element Architecture (draft-ietf-pce-
              questions)", October 2013.

   [STATEFUL-PCE-DISC]
              Sivabalan, S., Medved, J., and X. Zhang, "IGP Extensions
              for Stateful PCE Discovery (draft-sivabalan-pce-disco-
              stateful-01)", January 2014.

   [STATEFUL-LSPSYNC-OPT]
              Crabbe, E., Medved, J., Minei, I., Varga,, R., Zhang, X.,
              and D. Dhody, "Optimizations of Label Switched Path State
              Synchronization Procedures for a Stateful PCE (draft-
              minei-pce-stateful-sync-optimizations)", December 2013.

   [PCEP-MIB]
              Kiran Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "PCE communication protocol(PCEP) Management
              Information Base [draft-ietf-pce-pcep-mib]", January 2014.

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Internet-Draft                 LSPDB-SYNC                   January 2014

Appendix A.  Contributor Addresses

   Young Lee
   Huawei
   1700 Alma Drive, Suite 100
   Plano, TX  75075
   US

   Phone: +1 972 509 5599 x2240
   Fax:   +1 469 229 5397
   EMail: leeyoung@huawei.com

Authors' Addresses

   Udayasree Palle
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: udayasree.palle@huawei.com

   Dhruv Dhody
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: dhruv.ietf@gmail.com

   Xian Zhang
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R.China

   EMail: zhang.xian@huawei.com

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