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Network Working Group                                  J.L. Le Roux, Ed.Request for Comments: 4674                                France TelecomCategory: Informational                                     October 2006Requirements for Path Computation Element (PCE) DiscoveryStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   This document presents a set of requirements for a Path Computation   Element (PCE) discovery mechanism that would allow a Path Computation   Client (PCC) to discover dynamically and automatically a set of PCEs   along with certain information relevant for PCE selection.  It is   intended that solutions that specify procedures and protocols or   extensions to existing protocols for such PCE discovery satisfy these   requirements.Table of Contents1. Introduction ....................................................21.1. Conventions Used in This Document ..........................31.2. Terminology ................................................32. Problem Statement and Requirements Overview .....................42.1. Problem Statement ..........................................42.2. Requirements Overview ......................................53. Example of Application Scenario .................................64. Detailed Requirements ...........................................74.1. PCE Information to Be Disclosed ............................74.1.1. General PCE Information (Mandatory Support) .........84.1.1.1. Discovery of PCE Location ..................8                  4.1.1.2. Discovery of PCE Domains and                           Inter-domain Functions .....................84.1.2. Detailed PCE Information (Optional Support) .........94.1.2.1. Discovery of PCE Capabilities ..............94.1.2.2. Discovery of Alternate PCEs ...............104.2. Scope of PCE Discovery ....................................104.2.1. Inter-AS Specific Requirements .....................10Le Roux                      Informational                      [Page 1]

RFC 4674             Requirements for PCE Discovery         October 20064.3. PCE Information Synchronization ...........................114.4. Discovery of PCE Deactivation .............................114.5. Policy Support ............................................124.6. Security Requirements .....................................124.7. Extensibility .............................................134.8. Scalability ...............................................134.9. Operational Orders of Magnitudes ..........................134.10. Manageability Considerations .............................144.10.1. Configuration of PCE Discovery Parameters .........144.10.2. PCE Discovery MIB Modules .........................144.10.2.1. PCC MIB Module ...........................144.10.2.2. PCE MIB module ...........................154.10.3. Monitoring Protocol Operations ....................154.10.4. Impact on Network Operations ......................165. Security Considerations ........................................166. Acknowledgements ...............................................167. Contributors ...................................................178. References .....................................................178.1. Normative References ......................................178.2. Informative References ....................................171.  Introduction   The PCE-based network architecture [RFC4655] defines a Path   Computation Element (PCE) as an entity capable of computing TE-LSP   paths based on a network graph, and applying computational   constraints.  A PCE serves path computation requests sent by Path   Computation Clients (PCC).   A PCC is a client application requesting a path computation to be   performed by a PCE.  This can be, for instance, an LSR requesting a   path for a TE-LSP for which it is the head-end, or a PCE requesting a   path computation of another PCE (inter-PCE communication).  The   communication between a PCC and a PCE requires a client-server   protocol whose generic requirements are listed in [RFC4657].   The PCE based 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 path   computation.Le Roux                      Informational                      [Page 2]

RFC 4674             Requirements for PCE Discovery         October 2006   In that context, it would be highly desirable to define a mechanism   for automatic and dynamic PCE discovery, which would allow PCCs to   automatically discover a set of PCEs, to determine additional   information required for PCE selection, and to dynamically detect new   PCEs or any modification of the PCEs' information.  This includes the   discovery by a PCC of a set of one or more PCEs in its domain, and   potentially in some other domains.  The latter is a desirable   function in the case of inter-domain path computation, for example.   This document lists a set of functional requirements for such an   automatic and dynamic PCE discovery mechanism.Section 2 points out   the problem statement.Section 3 illustrates an application   scenario.  Finally,Section 4 addresses detailed requirements.   It is intended that solutions that specify procedures and protocols   or protocol extensions for PCE discovery satisfy these requirements.   There is no intent either to specify solution-specific requirements   or to make any assumption on the protocols that could be used for the   discovery.   Note that requirements listed in this document apply equally to PCEs   that are capable of computing paths in MPLS-TE-enabled networks and   PCEs that are capable of computing paths in GMPLS-enabled networks   (and PCEs capable of both).   It is also important to note that the notion of a PCC encompasses a   PCE acting as PCC when requesting a path computation of another PCE   (inter-PCE communication).  Hence, this document does not make the   distinction between PCE discovery by PCCs and PCE discovery by PCEs.1.1.  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 inRFC 2119.1.2.  Terminology   Terminology used in this document:   LSR: Label Switch Router.   TE-LSP: Traffic Engineered Label Switched Path.   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.Le Roux                      Informational                      [Page 3]

RFC 4674             Requirements for PCE Discovery         October 2006   PCC: Path Computation Client.  Any client application requesting a   path computation to be performed by a Path Computation Element.   Interior Gateway Protocol (IGP) Area: OSPF Area or ISIS level/area.   ABR: IGP Area Border Router (OSPF ABR or ISIS L1L2 router).   AS: Autonomous System.   ASBR: AS Border Router.   Intra-area TE LSP: A TE LSP whose path does not cross IGP area   boundaries.   Inter-area TE LSP: A TE LSP whose path transits through two or more   IGP areas.   Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or   more ASs or sub-ASs (BGP confederations).   Domain: Any collection of network elements within a common sphere of   address management or path computational responsibility.  Examples of   domains include IGP areas and Autonomous Systems.2.  Problem Statement and Requirements Overview2.1.  Problem Statement   A routing domain may, in practice, contain multiple PCEs:   - The path computation load may be balanced among a set of PCEs to     improve scalability.   - For the purpose of redundancy, primary and backup PCEs may be used.   - PCEs may have distinct path computation capabilities (multi-     constrained path computation, backup path computation, etc.).   - In an inter-domain context, there can be several PCEs with distinct     inter-domain functions (inter-area, inter-AS, inter-layer), each     PCE being responsible for path computation in one or more domains.   In order to allow for effective PCE selection by PCCs, that is, to   select the appropriate PCE based on its capabilities and perform   efficient load balancing of requests, a PCC needs to know the   location of PCEs in its domain, along with some information relevant   to PCE selection, and also potentially needs to know the location of   some PCEs in other domains, for inter-domain path computation   purpose.Le Roux                      Informational                      [Page 4]

RFC 4674             Requirements for PCE Discovery         October 2006   Such PCE information could be learned through manual configuration,   on each PCC, of the set of PCEs along with their capabilities.  Such   a manual configuration approach may be sufficient, and even desired   in some particular situations (e.g., inter-AS PCE discovery, where   manual configuration of neighbor PCEs may be preferred for security   reasons), but it obviously faces several limitations:   - This may imply a substantial configuration overhead.   - This would not allow a PCC to dynamically detect that a new PCE is     available, that an existing PCE is no longer available, or that     there is a change in the PCE's information.   Furthermore, as with any manual configuration approach, there is a   risk of configuration errors.   As an example, in a multi-area network made up of one backbone area   and N peripheral areas, and where inter-area MPLS-TE path computation   relies on multiple-PCE path computation with ABRs acting as PCEs, the   backbone area would comprise at least N PCEs, and the configuration   of PCC would be too cumbersome (e.g., in existing multi-area   networks, N can be beyond fifty).   Hence, an automated PCE discovery mechanism allowing a PCC to   dynamically discover a set of PCEs is highly desirable.2.2.  Requirements Overview   A PCE discovery mechanism that satisfies the requirements set forth   in this document MUST allow a PCC to automatically discover the   location of one or more of the PCEs in its domain.   Where inter-domain path computation is required and policy permits,   the PCE discovery method MUST allow a PCC to automatically discover   the location of PCEs in other domains that can assist with inter-   domain path computation.   A PCE discovery mechanism MUST allow a PCC to discover the set of one   or more domains where a PCE has TE topology visibility and can   compute paths.  It MUST also allow the discovery of the potential   inter-domain path computation functions of a PCE (inter-area, inter-   AS, inter-layer, etc.).   A PCE discovery mechanism MUST allow the control of the discovery   scope, that is the set of one or more domains (areas, ASs) where   information related to a given PCE has to be disclosed.Le Roux                      Informational                      [Page 5]

RFC 4674             Requirements for PCE Discovery         October 2006   A PCE discovery mechanism MUST allow PCCs in a given discovery scope   to dynamically discover that a new PCE has appeared or that there is   a change in a PCE's information.   A PCE discovery mechanism MUST allow PCCs to dynamically discover   that a PCE is no longer available.   A PCE discovery mechanism MUST support security procedures.  In   particular, key consideration MUST be given in terms of how to   establish a trust model for PCE discovery.   OPTIONALLY, a PCE discovery mechanism MAY be used so as to disclose a   set of detailed PCE capabilities so that the PCC may make advanced   and informed choices about which PCE to use.3.  Example of Application Scenario   <----------------AS1-------------------->           <----AS2---    Area 1           Area 0        Area 2   R1---------R3-----R5-------R6-----------R9----------R11----R13             |               |             |           |             |               |             |           |   R2---------R4-----R7-------R8-----------R10---------R12----R14       |       |       --      |S1|       --                                 Figure 1   Figure 1 illustrates a multi-area/AS network with several PCEs:   - The ABR R3 is a PCE that can take part in inter-area path     computation.  It can compute paths in area 1 and area 0.   - The ABR R6 is a PCE that can take part in inter-area path     computation.  It can compute paths in area 0 and area 2.   - The ASBR R9 is a PCE that can take part in inter-AS path     computation.  It is responsible for path computation in AS1 towards     AS2.   - The ASBR R12 is a PCE that can take part in inter-AS path     computation.  It is responsible for path computation in AS2 towards     AS1.   - The server S1 is a PCE that can be used to compute diverse paths     and backup paths in area 1.Le Roux                      Informational                      [Page 6]

RFC 4674             Requirements for PCE Discovery         October 2006   By meeting the requirements set out in this document, the PCE   discovery mechanism will allow:   - each PCC in areas 1 and 0 to dynamically discover R3, as a PCE for     inter-area path computation, and that R3 can compute paths in area     0 and area 1.   - each PCC in areas 0 and 2 to dynamically discover R6, as a PCE for     inter-area path computation, and that R6 can compute paths in area     2 and area 0.   - each PCC in AS1 and one or more PCCs in AS2 to dynamically discover     R9 as a PCE for inter-AS path computation in AS1 towards AS2.   - each PCC in AS2 and one or more PCCs in AS1 to dynamically discover     R12 as a PCE for inter-AS path computation in AS2 towards AS1.   - each PCC in area 1 to dynamically discover S1, as a PCE for intra-     area path computation in area1, and optionally to discover its path     computation capabilities (diverse path computation and backup path     computation).4.  Detailed Requirements4.1.  PCE Information to Be Disclosed   We distinguish two levels of PCE information to be disclosed by a PCE   discovery mechanism:   - General information.  Disclosure MUST be supported by the PCE     discovery mechanism.   - Detailed information.  Disclosure MAY be supported by the PCE     discovery mechanism.   The PCE discovery mechanism MUST allow disclosure of general PCE   information that will allow PCCs to select appropriate PCEs.  This   comprises discovery of PCE location, PCE domains supported by the   PCEs, and PCE inter-domain functions.   The PCE discovery mechanism MAY also allow disclosure of detailed PCE   information.  This comprises any or all information about PCE path   computation capabilities and alternate PCEs.  This information is not   part of PCE discovery; this is additional information that can   facilitate the selection of a PCE by a PCC.  Support of the exchange   of this information is optional in the context of the PCE discovery   mechanism itself.  This does not mean that the availability of this   information is optional in the PCE-based architecture, but such   information could also be obtained by other mechanisms, such as the   PCC-PCE communication protocol.Le Roux                      Informational                      [Page 7]

RFC 4674             Requirements for PCE Discovery         October 20064.1.1.  General PCE Information (Mandatory Support)4.1.1.1.  Discovery of PCE Location   The PCE discovery mechanism MUST allow the discovery, for a given   PCE, of the IPv4 and/or IPv6 address to be used to reach the PCE.   This address will typically be an address that is always reachable,   if there is any connectivity to the PCE.   This address will be used by PCCs to communicate with a PCE, through   a PCC-PCE communication protocol.4.1.1.2.  Discovery of PCE Domains and Inter-domain Functions   Inter-domain path computation is a key application of the PCE-based   architecture.  This can rely on a multiple-PCE path computation,   where PCEs in each domain compute a part of the end-to-end path and   collaborate with each other to find the end-to-end-path.  Inter-   domain path computation can also rely on a single-PCE path   computation where a PCE has visibility inside multiple domains and   can compute an entire end-to-end inter-domain path (that is, a path   from the inter-domain TE-LSP head-end to the inter-domain TE-LSP tail   end).   Hence, the PCE discovery mechanism MUST allow the discovery of the   set of one or more domains where a PCE has visibility and can compute   paths.  These domains could be identified using a domain identifier:   For instance, an IGP area can be identified by the Area ID (OSPF or   ISIS), and an AS can be identified by the AS number.   Also the PCE discovery mechanism MUST allow discovery of the inter-   domain functions of a PCE, i.e., whether a PCE can be used to compute   or to take part in the computation of end-to-end paths across domain   borders.  The inter-domain functions include nonexhaustively: inter-   area, inter-AS and inter-layer path computation.  Note that these   functions are not mutually exclusive.   Note that the inter-domain functions are not necessarily inferred   from the set of domains where a PCE has visibility.  For instance, a   PCE may have visibility limited to a single domain, but may be able   to take part in the computation of inter-domain paths by   collaborating with PCEs in other domains.  Conversely, a PCE may have   visibility in multiple domains, but the operator may not want the PCE   to be used for inter-domain path computations.   The PCE discovery mechanisms MUST also allow discovery of the set of   one or more domains toward which a PCE can compute paths.  For   instance, in an inter-AS path computation context, there may beLe Roux                      Informational                      [Page 8]

RFC 4674             Requirements for PCE Discovery         October 2006   several PCEs in an AS, each one responsible for taking part in the   computation of inter-AS paths toward a set of one or more destination   ASs, and a PCC may have to discover the destination ASs each PCE is   responsible for.4.1.2.  Detailed PCE Information (Optional Support)4.1.2.1.  Discovery of PCE Capabilities   In the case where there are several PCEs with distinct capabilities   available, a PCC has to select one or more appropriate PCEs.   For that purpose, the PCE discovery mechanism MAY support the   disclosure of some detailed PCE capabilities.   For the sake of illustration, this could include the following path-   computation-related PCE capabilities:   - The link constraints supported: e.g., bandwidth, affinities.   - The path constraints supported: maximum IGP/TE cost, maximum hop     count.   - The objective functions supported: e.g., shortest path, widest     path.   - The capability to compute multiple correlated paths: e.g., diverse     paths, load balanced paths.   - The capability to compute bidirectional paths.   - The GMPLS-technology-specific constraints supported: e.g., the     supported interface switching capabilities, encoding types.   And this could also include some specific PCE capabilities:   - The capability to handle request prioritization.   - The maximum size of a request message.   - The maximum number of path requests in a request message.   - The PCE computation power (static parameters to be used for     weighted load balancing of requests).   Such information regarding PCE capabilities could then be used by a   PCC to select an appropriate PCE from a list of candidate PCEs.   Note that the exact definition and description of PCE capabilities   are out of the scope of this document.  It is expected that this will   be described in one or more separate documents which may be   application specific.Le Roux                      Informational                      [Page 9]

RFC 4674             Requirements for PCE Discovery         October 20064.1.2.2.  Discovery of Alternate PCEs   In the case of a PCE failure, a PCC has to select another PCE, if one   is available.  It could be useful in various situations for a PCE to   indicate a set of one or more alternate PCEs that can be selected in   case the given PCE fails.   Hence, the PCE discovery mechanism MAY allow the discovery, for a   given PCE, of the location of one or more assigned alternate PCEs.   The PCE discovery mechanism MAY also allow the discovery, for a given   PCE, of the set of one or more PCEs for which it acts as alternate   PCE.4.2.  Scope of PCE Discovery   The PCE discovery mechanism MUST allow control of the scope of the   PCE information disclosure on a per-PCE basis.  In other words, it   MUST allow control of to which PCC or group of PCCs the information   related to a PCE may be disclosed.   The choice for the discovery scope of a given PCE MUST include at   least the followings settings:   - All PCCs in a single IGP area.   - All PCCs in a set of adjacent IGP areas.   - All PCCs in a single AS.   - All PCCs in a set of ASs.   - A set of one or more PCCs in a set of one or more ASs.   In particular, this also implies that the PCE discovery mechanism   MUST allow for the discovery of PCE information across IGP areas and   across AS boundaries.   The discovery scope MUST be configurable on a per PCE basis.   It MUST be possible to deactivate PCE discovery on a per PCE basis.4.2.1.  Inter-AS Specific Requirements   When using a PCE-based approach for inter-AS path computation, a PCC   in one AS may need to learn information related to inter-AS capable   PCEs located in other ASs.  For that purpose, and as pointed out in   the previous section, the PCE discovery mechanism MUST allowLe Roux                      Informational                     [Page 10]

RFC 4674             Requirements for PCE Discovery         October 2006   disclosure of information related to inter-AS-capable PCEs across AS   boundaries.   Such inter-AS PCE discovery must be carefully controlled.  For   security and confidentiality reasons, particularly in an inter-   provider context, the discovery mechanism MUST allow the discovery   scope to be limited to a set of ASs and MUST also provide control of   the PCE information to be disclosed across ASs.  This is achieved by   applying policies (see alsoSection 4.4).  This implies the   capability to contain a PCE advertisement to a restricted set of one   or more ASs, and to filter and translate any PCE parameter (PCE   domains, PCE inter-domain functions, PCE capabilities, etc.) in   disclosures that cross AS borders.  For the sake of illustration, it   may be useful to disclose detailed PCE information (such as detailed   capabilities) locally in the PCE's AS but only general information   (such as location and supported domains) in other ASs.4.3.  PCE Information Synchronization   The PCE discovery mechanism MUST allow a PCC to discover any change   in the information related to a PCE that it has previously   discovered.  This includes changes to both general information (e.g.,   a change in the PCE domains supported) and detailed information if   supported (e.g., a modification of the PCE's capabilities).   In addition, the PCE discovery mechanism MUST allow dynamic discovery   of new PCEs in a given discovery scope.   Note that there is no requirement for real-time detection of these   changes; the PCE discovery mechanism SHOULD rather allow discovery of   these changes in a range of 60 seconds, and the operator should have   the ability to configure the discovery delay.   Note that PCE information is relatively static and is expected to be   fairly stable and not to change frequently.4.4.  Discovery of PCE Deactivation   The PCE discovery mechanism MUST allow a PCC to discover when a PCE   that it has previously discovered is no longer alive or is   deactivated.  This may help in reducing or avoiding path computation   service disruption.   Note that there is no requirement for real-time detection of PCE   failure/deactivation; the PCE discovery mechanism SHOULD rather allow   such discovery in a range of 60 seconds, and the operator should have   the ability to configure the discovery delay.Le Roux                      Informational                     [Page 11]

RFC 4674             Requirements for PCE Discovery         October 20064.5.  Policy Support   The PCE discovery mechanism MUST allow for policies to restrict the   discovery scope to a set of authorized domains, to control and   restrict the type and nature of the information to be disclosed, and   also to filter and translate some information at domains borders.  It   MUST be possible to apply these policies on a per-PCE basis.   Note that the discovery mechanisms MUST allow disclosing policy   information so as to control the disclosure policies at domain   boundaries.   Also, it MUST be possible to apply different policies when disclosing   PCE information to different domains.4.6.  Security Requirements   The five major threats related to PCE discovery mechanisms are   - impersonation of PCE;   - interception of PCE discovery information (sniffing);   - falsification of PCE discovery information;   - information disclosure to non-authorized PCCs (PCC spoofing);   - Denial of Service (DoS) Attacks.   Note that security of the PCE discovery procedures is of particular   importance in an inter-AS context, where PCE discovery may increase   the vulnerability to attacks and the consequences of these attacks.   Hence, mechanisms MUST be defined to ensure authenticity, integrity,   confidentiality, and containment of PCE discovery information:   - There MUST be a mechanism to authenticate discovery information.   - There MUST be a mechanism to verify discovery information     integrity.   - There MUST be a mechanism to encrypt discovery information.   - There MUST be a mechanism to restrict the scope of discovery to a     set of authorized PCCs and to filter PCE information disclosed at     domain boundaries (as per defined inSection 4.5).   A PCE and PCC MUST be identified by a globally unique ID, which may   be, for instance, a combination of AS number and IP address.   Mechanisms MUST be defined in order to limit the impact of a DoS   attack on the PCE discovery procedure (e.g., filter out excessive PCE   information change and flapping PCEs).  Note also that DoS attacks   may be either accidental (caused by a misbehaving PCE system) or   intentional.  As discussed in [RFC4657], such mechanisms may includeLe Roux                      Informational                     [Page 12]

RFC 4674             Requirements for PCE Discovery         October 2006   packet filtering, rate limiting, no promiscuous listening, and where   applicable use of private addresses spaces.   Also, key consideration MUST be given in terms of how to establish a   trust model for PCE discovery.  The PCE discovery mechanism MUST   explicitly support a specific set of one or more trust models.4.7.  Extensibility   The PCE discovery mechanism MUST be flexible and extensible so as to   easily allow for the inclusion of additional PCE information that   could be defined in the future.4.8.  Scalability   The PCE discovery mechanism MUST be designed to scale well with an   increase of any of the following parameters:   - Number of PCCs discovering a given PCE.   - Number of PCEs to be discovered by a given PCC.   - Number of domains in the discovery scope.   The PCE discovery mechanism MUST NOT have an adverse effect in the   performance of other protocols (especially routing and signaling)   already operating in the network.   Note that there is no scalability requirement with regards to the   amount of information to be exchanged.   Information disclosed in the PCE discovery mechanism is relatively   static.  Changes in PCE information may occur as a result of PCE   configuration updates, PCE deployment/activation, or PCE   deactivation/suppression, and should not occur as a result of the PCE   activity itself.  Hence, this information is quite stable and will   not change frequently.4.9.  Operational Orders of Magnitudes   This section gives minimum order of magnitude estimates of what the   PCE discovery mechanism should support.   - Number of PCCs discovering a given PCE: 1000   - Number of PCEs to be discovered by a given PCC: 100Le Roux                      Informational                     [Page 13]

RFC 4674             Requirements for PCE Discovery         October 20064.10.  Manageability Considerations   Mechanisms are REQUIRED to manage PCE discovery operations.  This   includes the configuration of PCE discovery functions and policies,   as well as the monitoring of the discovery protocol activity.4.10.1.  Configuration of PCE Discovery Parameters   It MUST be possible to enable and disable the PCE discovery function   at a PCC and at a PCE.   On the PCC, it MUST be possible for an operator to   activate/deactivate automatic PCE discovery.  The activation of   automatic discovery MUST not prevent static configuration of PCE   information that may supplement discovered information.   On the PCE, it MUST be possible for an operator to control the   application of discovery policies by which the specific PCE is   discovered.  As described inSection 4.5, this control MUST include   the ability to   - restrict the discovery scope to a set of authorized domains;   - define the type and nature of the information disclosed;   - specify the filtering and translation to be applied to the PCE     information disclosed at domain borders.   These configuration options MAY be supported through an   implementation-specific local configuration interface, or MAY be   supported via a standardised interface (such as a MIB module, as   below).4.10.2.  PCE Discovery MIB Modules   PCE discovery MIB modules MUST be specified for the control of the   function on PCCs and PCEs.4.10.2.1.  PCC MIB Module   The MIB module that will run on PCCs MUST include at least the   following:   - A control to disable automatic discovery by the PCC,   - The set of known PCEs,   - The number of known PCEs, and the number of discovered PCEs.   For each PCE reported in the MIB module, the following information   MUST be available:Le Roux                      Informational                     [Page 14]

RFC 4674             Requirements for PCE Discovery         October 2006   - Information advertised by the PCE (i.e., discovered information),   - Information locally configured about the PCE,   - The time since the PCE was discovered,   - The time since any change to the discovered information for the     PCE.   Note that when a PCE is no longer alive (seeSection 4.4), it SHOULD   no longer be reported in the PCC MIB module.   The MIB module SHOULD also provide the average and maximum rates of   arrival, departure, and modification of PCE discovery to enable   effective analysis of the operation of the protocols.  Furthermore,   the MIB module SHOULD report on the operation of the discovery   protocol by counting the number of unacceptable and incomprehensible   information exchanges.   The PCC MIB module SHOULD also be used to provide notifications when   thresholds (e.g., on the maximum rate of change, on the number of   unacceptable messages) are crossed, or when important events occur   (e.g., the number of discovered PCEs decreases to zero).4.10.2.2.  PCE MIB module   The MIB module that will run on PCEs MUST include at least   - a control to disable automatic discovery announcements by the PCE;   - information to be advertised by the PCE, although this information     MAY be present as read-only;   - the discovery policies active on the PCE, although this information     MAY be present as read-only.   The MIB module SHOULD also include   - the time since the last change to the advertised PCE information;   - the time since the last change to the advertisement policies;   - control of on which interfaces the PCE issues advertisements where     this is applicable to the protocol solution selected.   Note that a PCE MAY also be configured to discover other PCEs.  In   this case, it SHOULD operate the MIB module described inSection4.10.2.1 as well as the module described here.4.10.3.  Monitoring Protocol Operations   It MUST be possible to monitor the operation of any PCE discovery   protocol.  Where an existing protocol is used to support the PCE   discovery function, this monitoring SHOULD be achieved using the   techniques already defined for that protocol, enhanced by the MIBLe Roux                      Informational                     [Page 15]

RFC 4674             Requirements for PCE Discovery         October 2006   modules described above.  Where those techniques are inadequate, new   techniques MUST be developed.   Monitoring of the protocol operation demands support for at least the   following functions:   - Correlation of information advertised against information received.   - Counts of dropped, corrupt, and rejected information elements.   - Detection of 'segmented' networks, that is, the ability to detect     and diagnose the failure of a PCE advertisement to reach a PCC.4.10.4.  Impact on Network Operations   Frequent changes in PCE information may have a significant impact on   PCCs that receive the advertisements, might destabilize the operation   of the network by causing the PCCs to swap between PCEs, and might   harm the network through excessive advertisement traffic.  Hence, 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.5.  Security Considerations   This document is a requirement document and hence does not raise by   itself any particular security issue.   A set of security requirements that MUST be addressed when   considering the design and deployment of a PCE discovery mechanism   has been identified inSection 4.6.6.  Acknowledgements   We would like to thank, in chronological order, Benoit Fondeviole,   Thomas Morin, Emile Stephan, Jean-Philippe Vasseur, Dean Cheng,   Adrian Farrel, Renhai Zhang, Mohamed Boucadair, Eric Gray, Igor   Bryskin, Dimitri Papadimitriou, Arthi Ayyangar, Andrew Dolganow, Lou   Berger, Nabil Bitar, and Kenji Kumaki.   Thanks also to Ross Callon, Ted Hardie, Dan Romascanu, Russ Housley   and Sam Hartman for their review and constructive discussions during   the final stages of publication.Le Roux                      Informational                     [Page 16]

RFC 4674             Requirements for PCE Discovery         October 20067.  Contributors   The following are the authors who contributed to the present   document:   Jean-Louis Le Roux (France Telecom)   Paul Mabey (Qwest Communications)   Eiji Oki (NTT)   Richard Rabbat (Fujitsu)   Ting Wo Chung (Bell Canada)   Raymond Zhang (BT Infonet)8.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path              Computation Element (PCE)-Based Architecture",RFC 4655,              August 2006.8.2.  Informative References   [RFC4657]  Ash, J., Ed. and J.L. Le Roux, Ed., "Path Computation              Element (PCE) Communication Protocol Generic              Requirements",RFC 4657, September 2006.Contributors' Addresses   Paul Mabey   Qwest Communications   950 17th Street   Denver, CO 80202   USA   EMail: pmabey@qwest.com   Eiji Oki   NTT   Midori-cho 3-9-11   Musashino-shi, Tokyo 180-8585   JAPAN   EMail: oki.eiji@lab.ntt.co.jpLe Roux                      Informational                     [Page 17]

RFC 4674             Requirements for PCE Discovery         October 2006   Richard Rabbat   Fujitsu Laboratories of America   1240 East Arques Ave, MS 345   Sunnyvale, CA 94085   USA   EMail: richard@us.fujitsu.com   Ting Wo Chung   Bell Canada   181 Bay Street, Suite 350   Toronto, Ontario, M5J 2T3   CANADA   EMail: ting_wo.chung@bell.ca   Raymond Zhang   BT Infonet   2160 E. Grand Ave.   El Segundo, CA 90025   USA   EMail: raymond_zhang@infonet.comEditor's Address   Jean-Louis Le Roux (Editor)   France Telecom   2, avenue Pierre-Marzin   22307 Lannion Cedex   FRANCE   EMail: jeanlouis.leroux@orange-ft.comLe Roux                      Informational                     [Page 18]

RFC 4674             Requirements for PCE Discovery         October 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Le Roux                      Informational                     [Page 19]