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Network Working Group                                        Xian Zhang
Internet-Draft                                                 Gang Xie
Intended status: Standard Track                             Dhruv Dhody
                                                                 Huawei

Expires: January 04, 2014                                 July 05, 2013


      LSP Synchronization for Stateful Path Computation Element (PCE)

                  draft-zhx-pce-stateful-lsp-sync-00.txt

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-pcep] 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 for incremental LSP Database (LSP-
   DB) synchronization as well as PCE control of the LSP-DB
   synchronization process.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on January 04, 2014.



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Copyright Notice

    Copyright (c) 2013 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 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 ................................................ 2
      1.1. Motivation ............................................. 3
      1.2. Conventions used in this document .......................4
   2. PCEP Requirements and Objective ..............................4
   3. LSP Synchronization Procedure................................ 4
      3.1. New PCEP extensions .....................................4
      3.2. Procedure .............................................. 4
   4. IANA Considerations ......................................... 6
   5. Manageability Considerations .................................6
   6. Security Considerations ......................................6
   7. Contributors ................................................ 6
   8. References .................................................. 7
      8.1. Normative References.................................... 7
   Authors' Addresses ............................................. 7



1. Introduction

   [Stateful-pcep] describes a Label Switched Path (LSP) state
   synchronization mechanism between Path Computation Clients (PCCs)
   and PCEs for a stateful PCE. It includes mechanisms for LSP state
   synchronization and avoidance between a PCC and a PCE when the PCEP
   session restarts. After PCEP session set up, PCC compares the LSP
   State Database version with the PCE. If the database version is
   mismatched, state synchronization will be performed. During state
   synchronization, a PCC sends the information of all its LSPs (full
   LSP-DB) to the stateful PCE.

   This document proposes a mechanism for incremental (Delta) LSP
   Database (LSP-DB) synchronization as well as allowing PCE to control
   the timing of the LSP-DB synchronization process.
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1.1. Motivation

    If a PCE restarts and its LSP-DB survived, all PCCs with mismatched
   LSP State Database version will send all their LSPs information
   (full LSP-DB) to the stateful PCE, even if only a small number of
   LSPs underwent state change. It can take a long time and consume
   large communication channel bandwidth. Moreover, the stateful PCE
   can get overloaded with all the PCC performing full synchronization
   with it at the same time.

   Figure 1 shows an example of LSP state synchronization.

                                    +-----+
                                    | PCE |
                                    +-----+
                                   /
                                  /
                                 /
                                /
                         +------+            +------+
                         | PCC1 |------------| PCC2 |
                         +------+            +------+
                            |                   |
                            |                   |
                         +------+            +------+
                         | PCC3 |------------| PCC4 |
                         +------+            +------+

   Assuming there are 320 LSPs in the network, with each PCC having 80
   LSPs. During the time when the PCEP session is down, 20 LSPs of each
   PCC (i.e., 80 LSPs in total), are changed. Hence when PCEP session
   restarts, the stateful PCE needs to synchronize 320 LSPs with all
   PCCs. But actually, 240 LSPs stay the same. If performing full LSP
   state synchronization, it can take a long time to carry out the
   synchronization of all LSPs. It is especially true when only a low
   bandwidth communication channel is available and there is a
   substantial number of LSPs in the network. Another disadvantage of
   full LSP synchronization is that it is a waste of communication
   bandwidth to perform full LSP synchronization given the fact that
   the number of LSP changes can be small during the time when PCEP
   session is down.

   An incremental (Delta) LSP Database (LSP-DB) state synchronization
   is described in this document, where only the LSPs underwent state
   change are synchronized between the session restart. This may
   include new/modify/deleted LSPs. Furthermore, to avoid overloading
   the PCE, the proposed method enable a stateful PCE to control the
   LSP synchronization timing.
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1.2. Conventions used in this document

   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 RFC-2119 [RFC2119].

2. PCEP Requirements and Objective

    PCEP extensions for stateful PCEs to perform LSP synchronization
    SHOULD allow:

      - Incremental LSP state synchronization between session restarts.
         Note this does not exclude the need for a stateful PCE to
         request a full LSP DB synchronization.

      - A stateful PCE to control the timing of PCC synchronizing its
         LSP state with the PCE.

3. LSP Synchronization Procedure

   [Stateful-pcep] describes state synchronization as well as state
   synchronization avoidance by using LSP-DB-VERSION TLV in its OPEN
   object.  This document extends this idea to only synchronize the
   delta (changes) in case of version mismatch as well as to allow a
   stateful PCE to control the timing of this process.

3.1. New PCEP extensions

   Two new bits are added in the STATEFUL-PCE-CAPABILITY TLV defined in
   [Stateful-pcep] for incremental (delta) LSP synchronization and PCE
   control:

      D (DELTA-LSP-SYNC-CAPABILITY - 1 bit):  if set to 1 by a PCEP
   speaker, the D Flag indicates that the PCEP speaker allows delta or
   incremental state synchronization.

      C (PCE-CONTROL-SYNC - 1 bit):  if set to 1 by a stateful PCE, the
   C Flag indicates that the PCE will control the triggering of LSP
   state synchronization. This bit is not used by a PCC and MUST be set
   to 0 and ignored by the PCE upon receipt.

3.2. Procedure

   If both PCEP speakers include the LSP-DB-VERSION TLV in the OPEN
   Object and the TLV values match, the PCC MAY skip state
   synchronization.  Otherwise, the PCC MUST perform state
   synchronization.  Instead of dumping full LSP-DB to PCE again, the
   PCC synchronizes the delta (changes) as described in figure 1 when D
   flag is set to 1 by both PCC and PCE. Other combinations of D flag
   setting by PCC and PCE result in full LSP-DB synchronization
   procedure as described in [Stateful-pcep].
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                     +-+-+                    +-+-+
                     |PCC|                    |PCE|
                     +-+-+                    +-+-+
                       |                        |
                       |--Open--,               |
                       |  DBv=46 \    ,---Open--|
                       |   IDB=1  \  /   DBv=42 |
                       |   D=1     \/     IDB=1 |
                       |           /\      C=1  |
                       |          /  \     D=1  |
                       |         /    `-------->| (Expect Delta sync)
             (Do sync) |<--------`              | (Do not Purge LSP State)
             (Delta)   |                        |
  (Wait for PCE to     |                        |
   trigger LSP state   |                        |
   sync)               |                        |
                       |<-----PCUpd, S=1--------| (ask for LSP Sync, PLSP-ID =0)
                       |                        |
  (Delta Sync starts)  |--PCRpt,DBv=43,SYNC=1-->|
                       |            .           |
                       |            .           |
                       |            .           |
                       |            .           |
                       |--PCRpt,DBv=46,SYNC=0-->| (Sync done, PLSP-ID=0)
                       |                        |
                       |                        |
                       |--PCRpt,DBv=47,SYNC=0-->| (Regular
                       |                        |  LSP State Report)
                       |--PCRpt,DBv=48,SYNC=0-->| (Regular
                       |                        |  LSP State Report)
                       |--PCRpt,DBv=49,SYNC=0-->|
                       |                        |


   A stateful PCE MAY choose to control the LSP-DB synchronization
   process. To allow PCE to do so, it MUST set C bit to 1 to indicate
   this. If the LSP DB version is mis-matched, it can send a PCUpd
   message with PLSP-ID = 0 and S =1 in order to trigger the LSP-DB
   synchronization process. In this way, the PCE can control the
   sequence of LSP synchronization among all the PCCs that re-
   establishing PCEP sessions with it. When the capability of PCE
   control is enable, only after a PCC receives this message, it will
   then start sending information that PCE does not possess, which is

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   inferred from the LSP DB Version information exchange in the OPEN
   message.

   As per [Stateful-pcep], the LSP State Database version is
   incremented each time a change is made to the PCC's local LSP State
   Database. Each LSP is associated with the DB version at the time of
   its state change. This is needed to determine which LSP and what
   information needs to be synchronized in incremental state
   synchronization.

   In the example shown in Figure 1, PCC synchronizes all LSPs that are
   updated between DB Version 43 to 46. A PCC SHOULD remember the
   deleted LSP as well, so that PCRpt message with deleted status can
   be sent to the stateful PCE.

4. IANA Considerations

   4.1. STATEFUL-PCE-CAPABILITY TLV

      As discussed in Section 3.1, two 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    DELTA-LSP-SYNC-CAPABILITY                [This I.D.]

            TBD    PCE-CONTROL-SYNC-CAPABILITY              [This I.D.]

5. Manageability Considerations

   The procedure defined in this document does not incur new
   manageability issues and the issues described in [Stateful-pcep]
   should be followed.

6. Security Considerations

   NONE

7. Contributors

   Young Lee

   Huawei Technologies
   5360 Legacy Dr. Building 3
   Plano, TX 75024
   USA

   Phone: (469) 277-5838
   Email: leeyoung@huawei.com

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8. References

8.1. Normative References

   [Stateful-pcep] Crabbe, E., Medved, J., Varga, R., Minei, I., "PCEP
             Extensions for Stateful PCE", draft-ietf-pce-stateful-pce,
             work in progress.

Authors' Addresses

   Xian Zhang

   Huawei Technologies
   Research Area F3-1B,
   Huawei Industrial Base,
   Shenzhen, 518129, China

   Phone: +86-755-28972645
   Email: zhang.xian@huawei.com


   Gang Xie
   Huawei Technologies

   Research Area F3
   Huawei Industrial Base,
   Shenzhen, 518129, China

   Email xiegang09@huawei.com


   Dhruv Dhody
   Huawei Technologies

   Leela Palace
   Bangalore, Karnataka 560008
   INDIA
   Email: dhruv.dhody@huawei.com













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