Internet DRAFT - draft-ietf-pce-disco-proto-isis

draft-ietf-pce-disco-proto-isis




 


Network Working Group                              J.L. Le Roux (Editor) 
Internet Draft                                            France Telecom 
Intended Status: Standard Track          
Expires: April 2008                                J.P. Vasseur (Editor) 
                                                       Cisco System Inc. 
                                                                         
                                                          Yuichi Ikejiri  
                                                      NTT Communications 
                                                                         
                                                           Raymond Zhang 
                                                              BT Infonet 
                                                                         
                                                            October 2007 
 
 
  IS-IS Protocol Extensions for Path Computation Element (PCE) Discovery 
 
                  draft-ietf-pce-disco-proto-isis-08.txt 
 
 
Status of this Memo 
 
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Copyright Notice 
 
   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 (PCEs), 
   along with information that can be used by the PCC 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 announce PCEs 
   consists of using IGP flooding. For that purpose this document 
   defines extensions to the Intermediate System to Intermediate System 
   (IS-IS) routing protocol for the advertisement of PCE Discovery 
   information within an IS-IS area or within the entire IS-IS 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 Discovery Information...................................5 
   3.2.    Flooding Scope..............................................5 
   4.      The IS-IS PCED Sub-TLV......................................6 
   4.1.    PCE-ADDRESS Sub-TLV.........................................7 
   4.2.    The PATH-SCOPE Sub-TLV......................................7 
   4.3.    PCE-DOMAIN Sub-TLV..........................................9 
   4.4.    NEIG-PCE-DOMAIN Sub-TLV....................................10 
   4.5.    PCE-CAP-FLAGS Sub-TLV......................................10 
   5.      Elements of Procedure......................................11 
   6.      Backward Compatibility.....................................12 
   7.      IANA Considerations........................................12 
   8.      Security Considerations....................................12 
   9.      Manageability Considerations...............................12 
   9.1.    Control of Policy and Functions............................12 
   9.2.    Information and Data Model.................................13 
   9.3.    Liveness Detection and Monitoring..........................13 
   9.4.    Verify Correct Operations..................................13 
   9.5.    Requirements on Other Protocols and Functional 
             Components...............................................13 
   9.6.    Impact on Network Operations...............................13 
   10.     Acknowledgments............................................14 
   11.     References.................................................14 
   11.1.   Normative References.......................................14 
   11.2.   Informative References.....................................14 
 
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   12.     Editors' Addresses:........................................15 
   13.     Contributors' Adresses:....................................15 
   14.     Intellectual Property Statement............................15 
    
1. Terminology 
    
      ABR: IS-IS 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 (IS-IS). 
    
      Intra-area TE LSP: A TE LSP whose path does not cross an IGP area  
      boundary.  
    
      Intra-AS TE LSP: A TE LSP whose path does not cross an AS    
      boundary.  
 
      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. 
 
      IS-IS LSP: Link State PDU 
 
      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 a "domain" in 
      [RFC4655]). Examples of PCE-Domains include IGP areas and ASes. 
      This should be distinguished from an IS-IS routing domain as 
      defined by [ISO]. 
 
      PCEP: Path Computation Element communication Protocol. 
    
      TE LSP: Traffic Engineered Label Switched Path. 
    

 
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2. Introduction 
 
   [RFC4655] describes the motivations and architecture for a Path 
   Computation Element (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 (where one PCE acts as a PCC to make requests of the 
   other PCE). This relies on a communication protocol between PCC and 
   PCE, and also 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 PCEs in 
   other domains, e.g., in the case of inter-domain TE LSP computation.  
    
   A network may contain a large number of PCEs, each with potentially 
   distinct capabilities. In such a context it is highly desirable to 
   have a mechanism for automatic and dynamic PCE discovery that allows 
   PCCs to automatically discover a set of PCEs along with additional 
   information about each PCE that may be used by a PCC to perform PCE 
   selection. Additionally, it is valuable for a PCC to dynamically 
   detect new PCEs, failed PCEs, or any modification to the PCE 
   information. Detailed requirements for such a PCE discovery mechanism 
   are provided in [RFC4674]. 
    
   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, 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 extensions to IS-IS [ISO] to allow a PCE in an 
   IS-IS 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].  
    
   Generic capability advertisement mechanisms for IS-IS are defined in 
   [IS-IS-CAP]. These allow a router to advertise its capabilities 
   within an IS-IS area or an entire IS-IS routing domain. This document 
   leverages this generic capability advertisement mechanism to fully 
   satisfy the dynamic PCE discovery requirements.  
    
   This document defines a new sub-TLV (named the PCE Discovery (PCED)) 
   to be carried within the IS-IS Router Capability TLV ([IS-IS-CAP]).  
    
   The PCE information advertised is detailed in Section 3. Protocol 
   extensions and procedures are defined in Sections 4 and 5.  
 
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   The IS-IS extensions defined in this document allow for PCE discovery 
   within an IS-IS routing domain. Solutions for PCE discovery across AS 
   boundaries are beyond the scope of this document, and for further 
   study. 
    
   This document defines a set of sub-TLVs that are nested within each 
   other. When the degree of nesting TLVs is 2 (a TLV is carried within 
   another TLV) the TLV carried within a TLV is called a sub-TLV. 
   Strictly speaking, when the degree of nesting is 3, a subsub-TLV is 
   carried within a sub-TLV that is itself carried within a TLV. For the 
   sake of terminology simplicity, a TLV carried within another TLV is 
   called a sub-TLV regardless of the degree of nesting. 
    
3. Overview 
 
3.1. PCE Discovery Information 
 
   The PCE discovery information is composed 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 if there is any connectivity to the PCE; 
    
   - The PCE path computation scope (i.e., intra-layer, inter-area,  
     inter-AS, or inter-layer); 
    
   - The set of one or more PCE-Domain(s) into which the PCE has   
     visibility and for which the PCE can compute paths; 
 
   - The set of zero, one or more neighbor PCE-Domain(s) toward which  
     the 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. Flooding Scope 
 
   The flooding scope for PCE information advertised through IS-IS can 
   be a single L1 area, an L1 area and the L2 sub-domain, or the entire 
   IS-IS routing domain.  
    
    
    

 
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4. The IS-IS PCED Sub-TLV 
    
   The IS-IS PCED sub-TLV contains a non-ordered set of sub-TLVs.  
    
   The format of the IS-IS PCED sub-TLV and its sub-TLVs is identical to 
   the TLV format used by the Traffic Engineering Extensions to IS-IS 
   [RFC3784]. That is, the TLV is comprised of 1 octet for the type, 1 
   octet specifying the TLV length, and a value field. The Length field 
   defines the length of the value portion in octets.   
 
   The IS-IS PCED sub-TLV has the following format:  
        
      TYPE: To be assigned by IANA  (suggested value = 5) 
      LENGTH: Variable 
      VALUE: set of sub-TLVs 
 
   Five sub-TLVs are defined:                   
            Sub-TLV type  Length               Name   
                1      variable     PCE-ADDRESS sub-TLV   
                2         3         PATH-SCOPE sub-TLV 
                3      variable     PCE-DOMAIN sub-TLV 
                4      variable     NEIG-PCE-DOMAIN sub-TLV  
                5      variable     PCE-CAP-FLAGS sub-TLV 
                 
    
   The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within 
   the PCED sub-TLV.  
 
   The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional. They  
   MAY be present in the PCED sub-TLV to facilitate selection of inter- 
   domain PCEs. 
  
   The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED 
   sub-TLV to facilitate the PCE selection process. 
 
   Any unrecognized sub-TLV MUST be silently ignored.   
 
   The PCED sub-TLV is carried within an IS-IS CAPABILITY TLV defined in 
   [IS-IS-CAP]. 
    
   No additional sub-TLVs will be added to the PCED TLV in the future. 
   If a future application requires the advertisement of additional PCE 
   information in IS-IS, this will not be carried in the CAPABILITY TLV. 
 
   The following sub-sections describe the sub-TLVs which may be carried 
   within the PCED sub-TLV. 
    
    
    
 

 
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4.1. PCE-ADDRESS Sub-TLV  
    
   The PCE-ADDRESS sub-TLV specifies an IP address that can be  
   used to reach the PCE. It is RECOMMENDED to make use of an address     
   that is always reachable, provided the PCE is alive and reachable. 
 
   The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the  
   PCED sub-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 is 
   processed and any others MUST be ignored. 
 
   The PCE-ADDRESS sub-TLV has the following format:  
        
      TYPE: 1   
      LENGTH: 5 for an IPv4 address or 17 for an IPv6 address 
      VALUE: This comprises one octet indicating the address-type and 4  
             or 16 octets encoding the IPv4 or IPv6 address to be used  
             to reach the PCE. 
 
   Address-type:  
                  1   IPv4  
                  2   IPv6  
     
4.2. The 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 paths for intra-area, inter-area, inter-AS, or inter-
   layer_TE LSPs.  
    
   The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the 
   PCED sub-TLV. There MUST be exactly one instance of the PATH-SCOPE 
   sub-TLV within each PCED sub-TLV. If it appears more than once only 
   the first occurrence is processed and any others 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:  
    
   TYPE: 2   
   LENGTH: 3 
   VALUE: This comprises a one-octet flags field where each flag  
          represents a supported path scope, followed by a 2-octets  
          preferences field indicating PCE preferences.  
           
   Here is the structure of the flags field: 
    
      +-+-+-+-+-+-+-+-+  
      |0|1|2|3|4|5|Res|              
      +-+-+-+-+-+-+-+-+ 
 
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   Bit      Path Scope 
 
   0      L bit:  Can compute intra-area path 
   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 LSPs   
                  computation       
   5      Y bit:  Can compute or take part into the computation of  
                  paths across layers 
   6-7   Reserved for future use. 
    
    
   Here is the structure of the preferences field 
    
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |PrefL|PrefR|PrefS|PrefY| Res   |              
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
   Res: Reserved for future usage. 
    
   PrefL field: PCE's preference for intra-area TE LSPs computation. 
    
   PrefR field: PCE's preference for inter-area TE LSPs computation. 
         
   PrefS 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 use. 
 
   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 LSP computation (that is, the PCE can compute a 
   path toward 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 toward any neighbor AS).  
    
   When the Rd and Sd bit are set, the PCED sub-TLV MUST NOT contain a 
   NEIG-PCE-DOMAIN sub-TLV (see Section 4.4). 
     
   When the R bit is clear, the Rd bit SHOULD be clear on transmission 
   and MUST be ignored on receipt. When the S bit is clear, the Sd bit 
   SHOULD be clear on transmission and MUST be ignored on receipt. 
    

 
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   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 preferences can be used 
   for weighted load balancing of path computation requests. An operator 
   may decide to configure a preference for each computation scope at 
   each PCE so as to balance the path computation load among them. The 
   algorithms used by a PCC to balance its path computation requests 
   according to such PCE preferences are out of the scope of this 
   document and are a matter for local or network-wide policy. The same 
   or different 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 preferred for use for inter-AS computations may 
   configure PrefS higher than PrefR. 
    
   When the L, R, S, or Y bits are clear, the PrefL, PrefR, PrefS, PrefY 
   fields SHOULD respectively be set to 0 on transmission and MUST be 
   ignored on receipt. 
    
   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 SHOULD be present when PCE-Domains for which 
   the PCE can operate 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 sub-TLV may include multiple PCE-DOMAIN sub-TLVs when the PCE 
   has visibility into multiple PCE-Domains. 
 
   The PCE-DOMAIN sub-TLV has the following format: 
    
   TYPE: 3   
   LENGTH: Variable 
   VALUE: This is composed of one octet indicating the domain-type (area 
   ID or AS Number) and a variable length IS-IS area ID or a 32 bits AS 
   number, identifying a PCE-domain where the PCE has visibility and can 
   compute paths.   
 
   Two domain types are defined:  
                  1   Area ID  
                  2   AS Number 
    
   The Area ID is the area address as defined in [ISO].  
    
 
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    When the AS number is coded in two octets, 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 neighbor PCE-domain (area or 
   AS) toward which a PCE can compute paths. It means that the PCE can 
   take part in the computation of inter-domain TE LSPs with paths that 
   transit this neighbor 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: 
 
   TYPE: 4   
   LENGTH: Variable 
   VALUE: This comprises one octet indicating the domain-type (area ID 
   or AS Number) and a variable length IS-IS area ID or a 32 bits AS 
   number, identifying a PCE-domain toward which the PCE can compute 
   paths.   
 
   Two domain types are defined:  
                  1   Area ID  
                  2   AS Number 
    
   The Area ID is the area address as defined in [ISO].  
 
   When the AS number is coded in two octets, the AS Number field MUST  
   have its first two octets set to 0. 
    
   The NEIG-PCE-DOMAIN sub-TLV MUST be present at least once with domain 
   type 1 if the R bit is set and the Rd bit is clear, and MUST be 
   present at least once with domain type 2 if the S bit is set and the 
   Sd bit is clear. 
 
4.5. PCE-CAP-FLAGS Sub-TLV  
           
   The PCE-CAP-FLAGs sub-TLV is an optional sub-TLV used to indicate 
   PCEP related capabilities. It MAY be present within the PCED sub-TLV. 
   It MUST NOT be present more than once. If it appears more than once 
   only the first occurrence is processed and any others MUST be ignored. 
    
    
   The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array 
   of units of 32 bit-flags numbered from the most significant as bit 
   zero, where each bit represents one PCE capability.  
 
   The PCE-CAP-FLAGS sub-TLV has the following format:  
        
 
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      TYPE: 5   
      LENGTH: Multiple of 4 
      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.  
    
   The PCE capability registry is managed by IANA, it is common    
   with OSPF and defined in [PCED-OSPF]. 
    
   Reserved bits SHOULD be set to zero on transmission and MUST be 
   ignored on receipt. 
 
 
5. Elements of Procedure 
     
   The PCED sub-TLV is advertised within an IS-IS Router Capability TLV  
   defined in [IS-IS-CAP]. As such, elements of procedures are inherited  
   from those defined in [IS-IS-CAP]. 
    
   The flooding scope is controlled by the S flag in the IS-IS Router 
   Capability TLV (see [IS-IS-CAP]). When the scope of the PCED sub-TLV 
   is area local it MUST be carried within an IS-IS Router Capability 
   TLV having the S bit cleared. When the scope of the PCED sub-TLV is 
   the entire IS-IS routing domain, it MUST be carried within an IS-IS 
   Router Capability TLV having the S bit set. Note that when only the L 
   bit of the PATH-SCOPE sub-TLV is set, the flooding scope MUST be area 
   local. 
    
   Note that a L1L2 node may include a PCED TLV in a Router Capability 
   TLV with the S bit cleared in both in its L1 and L2 LSPs. This allows 
   the flooding scope to be restricted to the L1 area and the L2 sub-
   domain. 
    
   When the PCE function is deactivated, the IS-IS speaker advertising 
   this PCE MUST originate a new IS-IS LSP that no longer includes the 
   corresponding PCED TLV. 
 
   The PCE address (i.e., the address indicated within the PCE ADDRESS 
   sub-TLV) SHOULD be reachable via some prefixes advertised by IS-IS. 
   This allows the detection of a PCE failure to be sped up. When the 
   PCE address is no longer reachable, the PCE node has failed, has been 
   torn down, or there is no longer IP connectivity to the PCE node. 
    
   A change in information in the PCED sub-TLV 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 (e.g., 
   address, preferences, scope) and other information may be 
   automatically determined by the PCE (e.g. areas of visibility). 
    
 
 
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6. Backward Compatibility 
    
   The PCED sub-TLV defined in this document does not introduce any 
   interoperability issues. 
     
   An IS-IS router not supporting the PCED sub-TLV will just silently 
   ignore the sub-TLV as specified in [IS-IS-CAP]. 
 
7. IANA Considerations  
 
   IANA has defined a registry for the sub-TLVs carried in the IS-IS 
   Router Capability sub-TLVs defined in [IS-IS-CAP]. IANA is requested 
   to assign a new sub-TLV code-point for the PCED sub-TLV carried 
   within the Router Capability sub-TLV. 
 
   Value      Sub-TLV                   References 
   -----     --------                   ---------- 
     5       PCED sub-TLV              (this document)       
        
8. Security Considerations 
 
   This document defines IS-IS extensions for PCE discovery within an 
   administrative domain. Hence the security of the PCE discovery relies 
   on the security of IS-IS. 
 
   Mechanisms defined to ensure authenticity and integrity of IS-IS LSPs 
   [RFC3567], and their TLVs, can be used to secure the PCED sub-TLV as 
   well. 
    
   IS-IS provides no encryption mechanism for protecting the privacy of  
   LSPs, 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 for the configuration of PCE discovery parameters on 
   PCCs and PCEs are discussed in Section 4.10.1 of [RFC4674]. 
    
   In particular, a PCE implementation SHOULD allow the following 
   parameters to be configured on the PCE: 
        -The PCE IPv4/IPv6 address(es) (see Section 4.1) 
        -The PCE Scope, including the inter-domain functions (inter- 
         area, inter-AS, inter-layer), the preferences, and whether the  
         PCE can act as default PCE (see Section 4.2) 
        -The PCE domains (see Section 4.3) 
        -The neighbour PCE domains (see Section 4.4) 
        -The PCE capabilities (see Section 4.5) 
 
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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 IS-IS liveness 
   detection. IS-IS already includes a liveness detection mechanism 
   (Hello PDUs), and PCE discovery does not require additional 
   capabilities. 
    
   Procedures defined in Section 5 allow a PCC to detect 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 information in the PCED 
   sub-TLV received by the PCC with that stored at the PCE  using the 
   PCED MIB [PCED-MIB].  The number of dropped, corrupt, and rejected 
   information elements are available through the PCED MIB. 
    
9.5. Requirements on Other Protocols and Functional Components 
 
   The IS-IS extensions defined in this document do not imply any  
   requirement on other protocols. 
 
9.6. Impact on Network Operations 
 
   Frequent changes in PCE information advertised in the PCED sub-TLV 
   may have a significant impact on IS-IS and might destabilize the 
   operation of the network by causing the PCCs to swap between PCEs.  
 
   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 rate-limiting the  
        processing of PCED sub-TLVs. 
      - 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, Lou Berger, and David Ward, for their useful comments and 
   suggestions. 
 
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. 
    
   [ISO] "Intermediate System to Intermediate System Intra-Domain 
   Routeing Exchange Protocol for use in Conjunction with the 
   Protocol for Providing the Connectionless-mode Network Service 
   ISO/IEC 10589:2002 Second Edition. 
 
   [RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic 
   Engineering", RFC 3784, June 2004. 
 
   [IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising 
   router information", draft-ietf-isis-caps, work in progress. 
 
   [RFC3567] Li, T. and R. Atkinson, "Intermediate System to 
   Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, 
   July 2003. 
 
   [PCED-OSPF] Le Roux, Vasseur, et al. "OSPF protocol extensions for  
   Path Computation Element (PCE) Discovery", draft-ietf-pce-disco- 
   proto-ospf, work in progress. 
 
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. 
    
   [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation 
   Element (PCE)-based Architecture", RFC4655, august 2006. 
    
   [RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery", 
   RFC4674, October 2006. 
   

 
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12. Editors' 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' Adresses: 
    
   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 
    
  
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   The IETF invites any interested party to bring to its attention any 
 
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