Internet DRAFT - draft-zhx-pce-stateful-lsp-sync

draft-zhx-pce-stateful-lsp-sync



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-   
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   Internet-Drafts are draft documents valid for a maximum of six 
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   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    
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    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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