Network Working Group                              J.L. Le Roux (Editor) 
Internet Draft                                            France Telecom 
Intended Status: Standard Track          
Expires: March 2008                                J.P. Vasseur (Editor) 
                                                       Cisco System Inc. 
                                                                         
                                                          Yuichi Ikejiri  
                                                      NTT Communications 
                                                                         
                                                           Raymond Zhang 
                                                              BT Infonet 
                                                                         
                                                          September 2007 
 
 
    
    
  OSPF protocol extensions for Path Computation Element (PCE) Discovery 
 
               draft-ietf-pce-disco-proto-ospf-07.txt 
 
 
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   Copyright (C) The IETF Trust (2007).  All rights reserved. 
 

 
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Abstract 
    
   There are various circumstances where it is highly desirable for a 
   Path Computation Client (PCC) to be able to dynamically and 
   automatically discover a set of Path Computation Elements (PCE), 
   along with some information that can be used for PCE selection. When 
   the PCE is a Label Switching Router (LSR) participating in the 
   Interior Gateway Protocol (IGP), or even a server participating 
   passively in the IGP, a simple and efficient way to discover PCEs 
   consists of using IGP flooding. For that purpose, this document 
   defines extensions to the Open Shortest Path First (OSPF) routing 
   protocol for the advertisement of PCE Discovery information within an 
   OSPF area or within the entire OSPF routing domain.  
 
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 [RFC2119]. 
 
Table of Contents 
    
   1.      Terminology.................................................3 
   2.      Introduction................................................4 
   3.      Overview....................................................5 
   3.1.    PCE Information.............................................5 
   3.2.    PCE Discovery Information...................................5 
   3.2.1.  PCE Overload Information....................................5 
   3.3.    Flooding Scope..............................................6 
   4.      The OSPF PCED TLV...........................................6 
   4.1.    PCE-ADDRESS Sub-TLV.........................................7 
   4.2.    PATH-SCOPE Sub-TLV..........................................8 
   4.3.    PCE-DOMAIN Sub-TLV.........................................10 
   4.4.    NEIG-PCE-DOMAIN Sub-TLV....................................11 
   4.5.    PCE-CAP-FLAGS Sub-TLV......................................12 
   4.6.    The OVERLOAD Sub-TLV.......................................13 
   5.      Elements of Procedure......................................14 
   5.1.    OVERLOAD sub-TLV Specific Procedures.......................14 
   6.      Backward Compatibility.....................................15 
   7.      IANA Considerations........................................15 
   7.1.    OSPF TLV...................................................15 
   7.2.    PCE Capability Flags registry..............................15 
   8.      Security Considerations....................................16 
   9.      Manageability Considerations...............................16 
   9.1.    Control of Policy and Functions............................16 
   9.2.    Information and Data Model.................................17 
   9.3.    Liveness Detection and Monitoring..........................17 
   9.4.    Verify Correct Operations..................................17 
   9.5.    Requirements on Other Protocols and Functional 
             Components...............................................17 
   9.6.    Impact on network operations...............................17 
   10.     Acknowledgments............................................18 
 
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   11.     References.................................................18 
   11.1.   Normative references.......................................18 
   11.2.   Informative references.....................................18 
   12.     Editor's Addresses.........................................19 
   13.     Contributors' Addresses....................................19 
   14.     Intellectual Property Statement............................19 
    
1. Terminology 
 
      ABR: OSPF Area Border Router.  
    
      AS: Autonomous System. 
       
      IGP: Interior Gateway Protocol. Either of the two routing    
      protocols Open Shortest Path First (OSPF) or Intermediate System   
      to Intermediate System (ISIS). 
    
      Intra-area TE LSP: A TE LSP whose path does not cross IGP area  
      boundaries.  
    
      Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries.  
    
      Inter-area TE LSP: A TE LSP whose path transits two or more IGP   
      areas. That is a TE-LSP that crosses at least one IGP area  
      boundary. 
        
      Inter-AS TE LSP: A TE LSP whose path transits two or more     
      ASes or sub-ASes (BGP confederations). That is a TE-LSP that  
      crosses at least one AS boundary. 
    
      LSA: Link State Advertisement 
 
      LSR: Label Switching Router. 
 
      PCC: Path Computation Client: Any client application requesting a  
      path computation to be performed by a Path Computation Element.  
 
      PCE: Path Computation Element: An entity (component, application,  
      or network node) that is capable of computing a network path or  
      route based on a network graph, and applying computational  
      constraints. 
    
      PCE-Domain: In a PCE context this refers to any collection of 
      network elements within a common sphere of address management or 
      path computational responsibility (referred to as "domain" in 
      [RFC4655]). Examples of PCE-Domains include IGP areas and ASes. 
      This should be distinguished from an OSPF routing domain. 
 
      PCEP: Path Computation Element Protocol. 
    
      TE LSP: Traffic Engineered Label Switched Path. 
    
 
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2. Introduction 
 
   [RFC4655] describes the motivations and architecture for a PCE-based  
   path computation model for Multi Protocol Label Switching (MPLS) and 
   Generalized MPLS (GMPLS) Traffic Engineered Label Switched Paths (TE-
   LSPs). The model allows for the separation of the PCE from a Path 
   Computation Client (PCC) (also referred to as a non co-located PCE) 
   and allows for cooperation between PCEs. This relies on a 
   communication protocol between PCC and PCE, and between PCEs. The 
   requirements for such a communication protocol can be found in 
   [RFC4657] and the communication protocol is defined in [PCEP]. 
          
   The PCE architecture requires that a PCC be aware of the location of 
   one or more PCEs in its domain, and also potentially of some PCEs in 
   other domains, e.g. in case of inter-domain TE LSP computation.  
    
   A network may contain a large number of PCEs with potentially 
   distinct capabilities. In such a context it is highly desirable to 
   have a mechanism for automatic and dynamic PCE discovery, which 
   allows PCCs to automatically discover a set of PCEs, along with 
   additional information about each PCE that may be required for the 
   PCC to perform PCE selection. Additionally, it is valuable for a PCC 
   to dynamically detect new PCEs or any modification of the PCE 
   information. Detailed requirements for such a PCE discovery mechanism 
   are provided in [RFC4674]. 
    
   Moreover, it may also be useful to discover when a PCE experiences 
   processing overload and when it exits such a state, in order for the 
   PCCs to take some appropriate actions (e.g. to redirect their 
   requests to another PCE). Note that the PCE selection algorithm 
   applied by a PCC is out of the scope of this document. 
    
   When PCCs are LSRs participating in the IGP (OSPF or IS-IS), and PCEs 
   are either LSRs or servers also participating in the IGP, an 
   effective mechanism for PCE discovery within an IGP routing domain 
   consists of utilizing IGP advertisements. 
    
   This document defines OSPF extensions to allow a PCE in an OSPF 
   routing domain to advertise its location along with some information 
   useful to a PCC for PCE selection so as to satisfy dynamic PCE 
   discovery requirements set forth in [RFC4674]. This document also 
   defines extensions allowing a PCE in an OSPF routing domain to 
   advertise its overload state. 
    
   Generic capability advertisement mechanisms for OSPF are defined in 
   [OSPF-CAP]. These allow a router to advertise its capabilities within 
   an OSPF area or an entire OSPF routing domain. This document 
   leverages this generic capability advertisement mechanism to fully 
   satisfy the aforementioned dynamic PCE discovery requirements.  
    
   This document defines a new TLV (named the PCE Discovery (PCED) TLV) 
   to be carried within the OSPF Router Information LSA ([OSPF-CAP]). 
 
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   The PCE information advertised is detailed in section 3. Protocol 
   extensions and procedures are defined in section 4 and 5. 
    
   The OSPF extensions defined in this document allow for PCE discovery 
   within an OSPF Routing domain. Solutions for PCE discovery across AS 
   boundaries are beyond the scope of this document, and for further 
   study. 
 
3. Overview 
 
3.1. PCE Information  
 
   The PCE information advertised via OSPF falls into two categories: 
   PCE Discovery information and PCE Overload information.  
 
3.2. PCE Discovery Information 
    
   The PCE Discovery information is comprised of: 
 
   - The PCE location: an IPv4 and/or IPv6 address that is used to reach    
     the PCE. It is RECOMMENDED to use an address that is always     
     reachable; 
    
   - The PCE path computation scope (i.e. inter-area, inter-AS, inter- 
     layer); 
    
   - The set of one or more PCE-Domain(s) into which the PCE has   
     visibility and can compute paths; 
 
   - The set of one or more neighbor PCE-Domain(s) towards which a PCE  
     can compute paths; 
 
   - A set of communication capabilities (e.g. support for request  
     prioritization) and path computation specific capabilities    
     (e.g. supported constraints).  
    
   PCE Discovery information is by nature fairly static and does not 
   change with PCE activity. Changes in PCE Discovery information may 
   occur as a result of PCE configuration updates, PCE 
   deployment/activation, PCE deactivation/suppression, or PCE failure. 
   Hence, this information is not expected to change frequently. 
 
3.2.1. PCE Overload Information  
 
   The PCE Overload information is optional and can be used to report a 
   PCE's overload state in order to discourage the PCCs to send new path 
   computation requests. 
    
   A PCE may decide to clear the overload state according to local 
   implementation triggers (e.g. CPU utilization, average queue length 
   below some predefined thresholds). The rate at which a PCE Status 
 
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   change is advertised MUST NOT impact by any means the IGP 
   scalability. Particular attention MUST be given on procedures to 
   avoid state oscillations.  
    
3.3. Flooding Scope 
 
   The flooding scope for PCE information advertised through OSPF can be 
   limited to one or more OSPF areas the PCE belongs to, or can be 
   extended across the entire OSPF routing domain.  
    
   Note that some PCEs may belong to multiple areas, in which case the 
   flooding scope may comprise these areas. This could be the case for 
   an ABR for instance advertising its PCE information within the 
   backbone area and/or a subset of its attached IGP area(s). 
 
4. The OSPF PCED TLV  
    
   The OSPF PCE Discovery TLV (PCED TLV) is made of a set of non-ordered 
   sub-TLVs.  
    
   The format of the OSPF PCED TLV and its sub-TLVs is identical to the 
   TLV format used by the Traffic Engineering Extensions to OSPF 
   [RFC3630]. That is, the TLV is comprised of 2 octets for the type, 2 
   octets specifying the TLV length, and a value field. The Length field 
   defines the length of the value portion in octets.  
    
   The TLV is padded to four-octet alignment; padding is not included in 
   the Length field (so a three octet value would have a length of 
   three, but the total size of the TLV would be eight octets). Nested 
   TLVs are also four-octet aligned. Unrecognized types are ignored.   
 
   The OSPF PCED TLV has the following format:  
    
                        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            | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
   |                                                               |  
   //                            sub-TLVs                          //          
   |                                                               |  
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
    
              
         Type     To be defined by IANA (suggested value=5) 
         Length   Variable 
         Value    This comprises one or more sub-TLVs  
 
 
 
 
 
 
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   Six sub-TLVs are defined:                   
         Sub-TLV type  Length               Name   
               1      variable     PCE-ADDRESS sub-TLV   
               2         4         PATH-SCOPE sub-TLV 
               3      variable     PCE-DOMAIN sub-TLV 
               4      variable     NEIG-PCE-DOMAIN sub-TLV 
               5      variable     PCE-CAP-FLAGS sub-TLV 
               6         4         OVERLOAD sub-TLV 
               
   The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within 
   the PCED TLV. 
    
   The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional. They MAY be 
   present in the PCED TLV to facilitate selection of inter-domain PCEs. 
    
   The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED 
   TLV to facilitate the PCE selection process. 
    
   The OVERLOAD sub-TLV is optional and MAY be present in the PCED TLV, 
   to indicate a PCE's overload state. 
    
   Any non recognized sub-TLV MUST be silently ignored. 
 
   The PCED TLV is carried within an OSPF Router Information LSA  
   defined in [OSPF-CAP]. 
    
   No additional sub-TLVs will be added to the PCED TLV in the future. 
   If a future application requires advertising additional PCE 
   information in OSPF, this will not be carried in the Router 
   Information LSA. 
 
   The following sub-sections describe the sub-TLVs which may be carried 
   within the PCED sub-TLV. 
 
4.1. PCE-ADDRESS Sub-TLV  
    
   The PCE-ADDRESS sub-TLV specifies the IP address(es) that can be  
   used to reach the PCE. It is RECOMMENDED to make use of an address      
   that is always reachable, provided that the PCE is alive. 
 
   The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the 
   PCED TLV. It MAY appear twice, when the PCE has both an IPv4 and IPv6 
   address. It MUST NOT appear more than once for the same address type. 
   If it appears more than once, only the first occurrence MUST be 
   processed and other MUST be ignored. 
    
    
    
    
    
    
 
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   The format of the PCE-ADDRESS sub-TLV is as follows: 
        
                            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 = 1         |             Length            | 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
       |     address-type              |          Reserved             |  
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
       |                                                               |  
       //                       PCE IP Address                        // 
       |                                                               |  
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
                             
                            PCE-ADDRESS sub-TLV format  
        
         Type     1 
         Length   8 (IPv4) or 20 (IPv6) 
    
         Address-type:  
                       1   IPv4  
                       2   IPv6  
    
         PCE IP Address: The IP address to be used to reach the PCE.  
                          
       
4.2. PATH-SCOPE Sub-TLV 
 
   The PATH-SCOPE sub-TLV indicates the PCE path computation scope, 
   which refers to the PCE's ability to compute or take part in the 
   computation of intra-area, inter-area, inter-AS, or inter-layer_TE 
   LSP(s).  
    
   The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the 
   PCED TLV. There MUST be exactly one instance of the PATH-SCOPE sub-
   TLV within each PCED TLV. If it appears more than once, only the 
   first occurrence MUST be processed and other MUST be ignored. 
 
   The PATH-SCOPE sub-TLV contains a set of bit flags indicating the 
   supported path scopes and four fields indicating PCE preferences. 
    
   The PATH-SCOPE sub-TLV has the following format:  
      
                        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 = 2         |             Length            | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
   |0|1|2|3|4|5|   Reserved        |PrefL|PrefR|PrefS|PrefY| Res   |              
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
    
 
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         Type     2 
         Length   4 
         Value    This comprises a 2-octet flag field where each bit  
                  represents a supported path scope, as well as four  
                  preference fields used to specify PCE preferences.    
          
         The following bits are defined: 
 
         Bit      Path Scope 
 
          0      L bit:  Can compute intra-area paths 
          1      R bit:  Can act as PCE for inter-area TE LSP  
                         computation 
          2      Rd bit: Can act as a default PCE for inter-area TE LSP  
                         computation        
          3      S bit:  Can act as PCE for inter-AS TE LSP computation 
          4      Sd bit: Can act as a default PCE for inter-AS TE LSP   
                         computation       
          5      Y bit:  Can compute or take part into the computation    
                         of paths across layers. 
 
   Pref-L field: PCE's preference for intra-area TE LSPs computation. 
    
   Pref-R field: PCE's preference for inter-area TE LSPs computation. 
    
   Pref-S field: PCE's preference for inter-AS TE LSPs computation. 
    
   Pref-Y field: PCE's preference for inter-layer TE LSPs computation. 
    
   Res: Reserved for future usage. 
 
   The L, R, S, and Y bits are set when the PCE can act as a PCE for 
   intra-area, inter-area, inter-AS, or inter-layer TE LSPs computation 
   respectively. These bits are non-exclusive. 
    
   When set the Rd bit indicates that the PCE can act as a default PCE 
   for inter-area TE LSPs computation (that is the PCE can compute a 
   path towards any neighbor area). Similarly, when set, the Sd bit 
   indicates that the PCE can act as a default PCE for inter-AS TE LSP 
   computation (the PCE can compute a path towards any neighbor AS).  
    
   When the Rd and Sd bit are set the PCED TLV MUST NOT contain any 
   NEIG-PCE-DOMAIN sub-TLV (see 4.1.4). 
    
   When the R/S bit is cleared, the Rd/Sd bit SHOULD be cleared and MUST 
   be ignored. 
    
   The PrefL, PrefR, PrefS and PrefY fields are each three bits long and 
   allow the PCE to specify a preference for each computation scope, 
   where 7 reflects the highest preference. Such preference can be used 
   for weighted load balancing of requests. An operator may decide to 
 
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   configure a preference for each computation scope to each PCE so as 
   to balance the path computation load among them. The algorithms used 
   by a PCC to load balance its path computation requests according to 
   such PCE preference is out of the scope of this document and is a 
   matter for local or network wide policy. The same or distinct 
   preferences may be used for each scope. For instance an operator that 
   wants a PCE capable of both inter-area and inter-AS computation to be 
   used preferably for inter-AS computation may configure a PrefS higher 
   than the PrefR.  
    
   When the L bit, R bit, S bit or Y bit are cleared, the PrefL, PrefR, 
   PrefS, PrefY fields SHOULD respectively be set to 0 and MUST be 
   ignored. 
    
   Both reserved fields SHOULD be set to zero on transmission and MUST  
   be ignored on receipt. 
 
4.3. PCE-DOMAIN Sub-TLV 
    
   The PCE-DOMAIN sub-TLV specifies a PCE-Domain (areas and/or ASes) 
   where the PCE has topology visibility and through which the PCE can 
   compute paths.  
 
   The PCE-DOMAIN sub-TLV MAY be present when PCE-Domains cannot be 
   inferred by other IGP information, for instance when the PCE is 
   inter-domain capable (i.e. when the R bit or S bit is set) and the 
   flooding scope is the entire routing domain (see section 5 for a 
   discussion of how the flooding scope is set and interpreted). 
    
   A PCED TLV MAY include multiple PCE-DOMAIN sub-TLVs when the PCE has 
   visibility in multiple PCE-Domains. 
 
   The PCE-DOMAIN sub-TLV has the following format:  
    
                            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=3           |             Length            | 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
       |     Domain-type               |          Reserved             |  
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
       |                                                               |  
       //                       Domain ID                             // 
       |                                                               |  
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
                             
                            PCE-DOMAIN sub-TLV format  
        
         Type     3 
         Length   Variable 
    
 
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         3 domain-type values are defined:  
                       1   IPv4 Area Address 
                       2   IPv6 Area Address 
                       3   AS Number 
    
         Domain ID: With the address type 1/2 this indicates the IPv4/v6  
         address of an area where the PCE has visibility. With address- 
         type 3 this indicates an AS number where the PCE has  
         visibility. When coded in two octets (which is the current   
         defined format as the time of writing this document), the AS  
         Number field MUST have its first two octets set to 0. 
.                       
4.4. NEIG-PCE-DOMAIN Sub-TLV 
    
   The NEIG-PCE-DOMAIN sub-TLV specifies a neighbour PCE-domain (area, 
   AS) toward which a PCE can compute paths. It means that the PCE can 
   take part in the computation of inter-domain TE LSPs whose path 
   transits this neighbour PCE-domain.  
 
   A PCED sub-TLV MAY include several NEIG-PCE-DOMAIN sub-TLVs when the 
   PCE can compute paths towards several neighbour PCE-domains.  
 
   The NEIG-PCE-DOMAIN sub-TLV has the same format as the PCE-DOMAIN 
   sub-TLV: 
 
                            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 = 4         |             Length            | 
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
       |     Domain-type               |          Reserved             |  
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
       |                                                               |  
       //                       Domain ID                             // 
       |                                                               |  
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  
                             
                            NEIG-PCE-DOMAIN sub-TLV format  
        
         Type     4 
         Length   Variable 
    
         3 domain-type values are defined:  
                       1   IPv4 Area Address 
                       2   IPv6 Area Address 
                       3   AS Number 
    
         Domain ID: With the address type 1/2 this indicates the  
         IPv4/v6 address of a neighbour area towards which the PCE can  
         compute paths. With address-type 3 this indicates the AS number  
         of a neighbour AS towards which the PCE can compute paths. When  
 
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         coded in two octets (which is the current defined format as the  
         time of writing this document), the AS Number field MUST have  
         its first two octets set to 0. 
 
   The NEIG-PCE-DOMAIN sub-TLV MUST be present if the R bit is set and 
   the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is 
   cleared. 
 
4.5. PCE-CAP-FLAGS Sub-TLV  
           
   The PCE-CAP-FLAGS sub-TLV is an optional sub-TLV used to indicate PCE 
   capabilities. It MAY be present within the PCED TLV. It MUST NOT be 
   present more than once. If it appears more than once, only the first 
   occurrence MUST be processed and other MUST be ignored. 
    
   The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array 
   of units of 32 flags numbered from the most significant as bit zero, 
   where each bit represents one PCE capability.  
        
   The format of the PCE-CAP-FLAGS sub-TLV is as follows: 
 
       0                   1                   2                   3 
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |              Type = 5         |             Length            | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |                                                               | 
     //                 PCE Capability Flags                          // 
      |                                                               | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
 
         Type     5 
         Length   Multiple of 4 octets 
         Value    This contains an array of units of 32 bit flags  
                  numbered from the most significant as bit zero, where  
                  each bit represents one PCE capability.  
 
   IANA is requested to manage the space of the PCE Capability Flags 
    
    
    
    
    
    
    
    
    
    
    
 
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   The following bits are to be assigned by IANA: 
 
 
     Bit       Capabilities 
 
      0        Path computation with GMPLS link constraints  
      1        Bidirectional path computation  
      2        Diverse path computation  
      3        Load-balanced path computation  
      4        Synchronized paths computation  
      5        Support for multiple objective functions  
      6        Support for additive path constraints                           
               (max hop count, etc.) 
      7        Support for request prioritization 
      8        Support for multiple requests per message   
    
     9-31    Reserved for future assignments by IANA. 
    
   These capabilities are defined in [RFC4657]. 
    
   Reserved bits SHOULD be set to zero on transmission and MUST be 
   ignored on receipt. 
    
4.6. The OVERLOAD Sub-TLV 
           
   The OVERLOAD sub-TLV is used to indicate that a PCE is experiencing  
   a processing overload state. 
    
   The OVERLOAD sub-TLV is optional, it MAY be carried within the PCED 
   TLV. It MUST NOT be present more than once. If it appears more than 
   once, only the first occurrence MUST be processed and other MUST be 
   ignored. 
 
   The format of the OVERLOAD sub-TLV is as follows: 
 
       0                   1                   2                   3 
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |              Type = 6         |             Length            | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |C|                   Reserved                                  |               
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       
 
         Type     6 
         Length   4  
         Value  
           -C bit: When set this indicates that the PCE is overloaded   
                   and cannot accept any new request. When cleared this   

 
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                   indicates that the PCE is not overloaded and  can  
                   accept new requests. 
 
5. Elements of Procedure 
     
   The PCED TLV is advertised within OSPFv2 Router Information LSAs 
   (Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router information 
   LSAs (function code of 12) which are defined in [OSPF-CAP].  As such, 
   elements of procedure are inherited from those defined in [OSPF-CAP]. 
    
   In OSPFv2 the flooding scope is controlled by the opaque LSA type (as  
   defined in [RFC2370]) and in OSPFv3 by the S1/S2 bits (as defined in  
   [RFC2740]). If the flooding scope is local to an area then the PCED 
   TLV MUST be carried within an OSPFv2 type 10 router information LSA 
   or an OSPFV3 Router Information LSA with the S1 bit set and the S2 
   bit cleared. If the flooding scope is the entire domain then the PCED 
   TLV MUST be carried within an OSPFv2 type 11 Router Information LSA 
   or OSPFv3 Router Information LSA with the S1 bit cleared and the S2 
   bit set. When only the L bit of the PATH-SCOPE sub-TLV is set, the 
   flooding scope MUST be area local. 
    
   An OSPF router MUST originate a new Router Information LSA whenever 
   there is a change in a PCED TLV associated with a PCE it advertises. 
    
   When a PCE is deactivated, the OSPF router advertising this PCE MUST 
   originate a new Router Information LSA that no longer includes the 
   corresponding PCED TLV. 
 
   The PCE address, i.e. the address indicated within the PCE ADDRESS 
   TLV, SHOULD be reachable via some prefixes advertised by OSPF; this 
   allows speeding up the detection of a PCE failure. Note that when the 
   PCE address is no longer reachable, this means that the PCE node has 
   failed or has been torn down, or that there is no longer IP 
   connectivity to the PCE node.  
 
   A change in PCED information MUST NOT trigger any SPF computation at  
   a receiving router. 
    
   The way PCEs determine the information they advertise is out of the  
   scope of this document. Some information may be configured on the PCE    
   (e.g., address, preferences, scope) and other information may be  
   automatically determined by the PCE (e.g., areas of visibility). 
 
5.1. OVERLOAD sub-TLV Specific Procedures 
 
   When a PCE enters into an overload state, the conditions of which are 
   implementation dependent, a Router Information LSA with an OVERLOAD 
   sub-TLV with the C bit set MAY be generated. 
 
   When a PCE exits from an overload state, the conditions of which are 
   implementation dependent (e.g. CPU utilization, average queue length 
   below some pre-defined threshold), a new Router Information LSA with 
 
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   an OVERLOAD sub-TLV with the C bit cleared SHOULD be generated, if 
   the overload information had been previously advertised. 
 
   A PCE implementation supporting the OSPF extensions defined in this 
   document SHOULD support an appropriate dampening algorithm so as to 
   dampen OSPF flooding of PCE Overload information in order to not 
   impact the OSPF scalability. It is RECOMMENDED to introduce some 
   hysteresis for overload state transition, so as to avoid state 
   oscillations that may impact OSPF performance. For instance two 
   thresholds MAY be configured: An upper-threshold and a lower-
   threshold; an LSR enters the overload state when the CPU load reaches 
   the upper threshold and leaves the overload state when the CPU load 
   goes under the lower threshold.  
    
   Upon receipt of an updated OVERLOAD sub-TLV a PCC SHOULD take  
   appropriate actions. In particular, the PCC SHOULD stop sending  
   requests to an overloaded PCE, and SHOULD gradually start sending  
   again requests to a PCE that is no longer overloaded.  
            
6. Backward Compatibility 
    
   The PCED TLV defined in this document does not introduce any 
   interoperability issues.  
    
   A router not supporting the PCED TLV will just silently ignore the 
   TLV as specified in [OSPF-CAP].  
 
 
7. IANA Considerations 
 
7.1. OSPF TLV 
    
   Once the OSPF RI TLVs registry defined in [OSPF-CAP] will have been 
   assigned, IANA will assign a new TLV code-point for the PCED TLV 
   carried within the Router Information LSA. 
 
   Value      TLV Name                      Reference 
   -----     --------                       ---------- 
     5         PCED                       (this document)               
     
 
7.2. PCE Capability Flags registry 
    
   This document provides new capability bit flags, which are present  
   in the PCE-CAP-FLAGS TLV referenced in section 4.1.5. 
    
   The IANA is requested to create a new top-level OSPF registry, the 
   "PCE Capability Flags" registry, and to manage the space of PCE 
   capability bit flags numbering them in the usual IETF notation 
   starting at zero and continuing at least through 31, with the most 
   significant bit as bit zero. 
 
 
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   New bit numbers may be allocated only by an IETF Consensus action. 
    
   Each bit should be tracked with the following qualities: 
    
   - Bit number      
   - Capability Description 
   - Defining RFC     
       
   Several bits are defined in this document. Here are the suggested 
   values: 
 
     Bit       Capability Description     
 
      0        Path computation with GMPLS link constraints 
      1        Bidirectional path computation  
      2        Diverse path computation 
      3        Load-balanced path computation 
      4        Synchronized paths computation 
      5        Support for multiple objective functions 
      6        Support for additive path constraints                            
               (max hop count, etc.) 
      7        Support for request prioritization 
      8        Support for multiple requests per message       
 
8. Security Considerations 
 
   This document defines OSPF extensions for PCE discovery within an 
   administrative domain. Hence the security of the PCE discovery relies 
   on the security of OSPF. 
 
   Mechanisms defined to ensure authenticity and integrity of OSPF LSAs 
   [RFC2154], and their TLVs, can be used to secure the PCE Discovery 
   information as well. 
    
   OSPF provides no encryption mechanism for protecting the privacy of 
   LSAs, and in particular the privacy of the PCE discovery information.  
 
9. Manageability Considerations 
    
   Manageability considerations for PCE Discovery are addressed in 
   section 4.10 of [RFC4674]. 
    
9.1. Control of Policy and Functions 
    
   Requirements on the configuration of PCE discovery parameters on PCCs 
   and PCEs are discussed in section 4.10.1 of [RFC4674]. 
    
   Particularly, a PCE implementation SHOULD allow configuring the 
   following parameters on the PCE: 
        -The PCE IPv4/IPv6 address(es) (see section 4.1.1) 
        -The PCE Scope, including the inter-domain functions (inter- 
         area, inter-AS, inter-layer), the preferences, and whether the  
 
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         PCE can act as default PCE (see section 4.1.2) 
        -The PCE domains (see section 4.1.3) 
        -The neighbour PCE domains (see section 4.1.4) 
        -The PCE capabilities (see section 4.1.5) 
    
9.2. Information and Data Model 
    
   A MIB module for PCE Discovery is defined in [PCED-MIB]. 
    
9.3. Liveness Detection and Monitoring 
    
   PCE Discovery Protocol liveness detection relies upon OSPF liveness 
   detection. OSPF already includes a liveness detection mechanism 
   (Hello protocol), and PCE discovery does not require additional 
   capabilities. 
    
   Procedures defined in section 5.1 allow a PCC detecting when a PCE 
   has been deactivated, or is no longer reachable. 
 
9.4. Verify Correct Operations  
    
   The correlation of information advertised against information 
   received can be achieved by comparing the PCED information in the PCC 
   and in the PCE, which is stored in the PCED MIB [PCED-MIB].  The 
   number of dropped, corrupt, and rejected information elements are 
   stored in the PCED MIB. 
    
9.5. Requirements on Other Protocols and Functional Components 
 
   The OSPF extensions defined in this document do not imply any  
   requirement on other protocols. 
 
9.6. Impact on network operations 
 
   Frequent changes in PCE information, and particularly in PCE overload 
   information, may have a significant impact on OSPF and might 
   destabilize the operation of the network by causing the PCCs to swap 
   between PCEs.  
    
   As discussed in section 5.1, a PCE implementation SHOULD support an 
   appropriate dampening algorithm so as to dampen OSPF flooding in 
   order to not impact the OSPF scalability. 
    
   Also, as discussed in section 4.10.4 of [RFC4674], it MUST be 
   possible to apply at least the following controls: 
    
      - Configurable limit on the rate of announcement of changed 
        parameters at a PCE. 
      - Control of the impact on PCCs such as through discovery messages 
        rate-limiting. 
      - Configurable control of triggers that cause a PCC to swap to 
        another PCE. 
 
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10. Acknowledgments 
 
   We would like to thank Lucy Wong, Adrian Farrel, Les Ginsberg, Mike 
   Shand and Lou Berger for their useful comments and suggestions. 
    
   We would also like to thank Dave Ward, Lars Eggert, Sam Hartman, and 
   Tim Polk for their comments during the final stages of publication. 
 
11. References 
    
11.1. Normative references 
    
   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate 
   Requirement Levels", BCP 14, RFC 2119, March 1997. 
 
   [RFC2740] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6", 
   RFC 2740, December 1999. 
 
   [RFC2370] Coltun, R., "The OSPF Opaque LSA Option", RFC 2370, July 
   1998. 
    
   [RFC3630] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering 
   Extensions to OSPF Version 2", RFC 3630, September 2003. 
    
   [OSPF-CAP] Lindem, A., Shen, N., Aggarwal, R., Shaffer, S., Vasseur, 
   J.P., "Extensions to OSPF for advertising Optional Router 
   Capabilities", draft-ietf-ospf-cap, work in progress. 
    
   [RFC2154] Murphy, S., Badger, M., and B. Wellington, "OSPF with 
   Digital Signatures", RFC 2154, June 1997. 
 
11.2. Informative references 
 
   [RFC4657] Ash, J., Le Roux, J.L., "PCE Communication Protocol Generic 
   Requirements", RFC4657, September 2006. 
    
   [PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE) 
   communication Protocol (PCEP) - Version 1", draft-ietf-pce-pcep, work 
   in progress. 
    
   [PCED-MIB] Stephan, E., "Definitions of Managed Objects for Path 
   Computation Element Discovery", draft-ietf-pce-disc-mib, work in 
   progress. 
    
   [PCED-ISIS] Le Roux, Vasseur, et al. "IS-IS protocol extensions for  
   Path Computation Element (PCE) Discovery", draft-ietf-pce-disco- 
   proto-isis, work in progress. 
    
   [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation 
   Element (PCE)-based Architecture", RFC4655, August 2006. 
    
 
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   [RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery", 
   RFC4674, October 2006. 
 
12. Editor's Addresses 
     
   Jean-Louis Le Roux (Editor) 
   France Telecom  
   2, avenue Pierre-Marzin  
   22307 Lannion Cedex  
   FRANCE 
   Email: jeanlouis.leroux@orange-ftgroup.com 
     
   Jean-Philippe Vasseur (Editor) 
   Cisco Systems, Inc.  
   1414 Massachusetts avenue  
   Boxborough , MA - 01719  
   USA  
   Email: jpv@cisco.com  
 
13. Contributors' Addresses 
    
   Yuichi Ikejiri                                       
   NTT Communications Corporation                      
   1-1-6, Uchisaiwai-cho, Chiyoda-ku                  
   Tokyo 100-8019    
   JAPAN    
   Email: y.ikejiri@ntt.com   
    
    
   Raymond Zhang 
   BT Infonet 
   2160 E. Grand Ave. 
   El Segundo, CA 90025 
   USA 
   Email: raymond_zhang@bt.infonet.com 
    
  
14. Intellectual Property Statement 
 
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   attempt made to obtain a general license or permission for the use of 
   such proprietary rights by implementers or users of this 
 
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   specification can be obtained from the IETF on-line IPR repository at 
   http://www.ietf.org/ipr. 
    
   The IETF invites any interested party to bring to its attention any 
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   Disclaimer of Validity 
    
   This document and the information contained herein are provided 
   on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 
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   Copyright Statement 
    
   Copyright (C) The IETF Trust (2007). This document is subject to the 
   rights, licenses and restrictions contained in BCP 78, and except as 
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