PCENetwork Working Group J.L. Le Roux (Editor) Internet Draft France Telecom Category: Informational Expires: January 2006 July 2005 Requirements for Path Computation Element (PCE) Discovery draft-ietf-pce-discovery-reqs-00.txtdraft-ietf-pce-discovery-reqs-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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 their capabilities.certain information relevant for PCE selection. It is intended that solutions that specify procedures and protocolprotocol(s) or protocol(s) extensions for such PCE discovery satisfy these requirements. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119. Table of Contents 1. Contributors................................................2 2. Terminology.................................................3 3. Introduction................................................3 4. Problem Statement and Requirements overview.................4 4.1. Problem Statement...........................................4 4.2. Requirements overview.......................................5 5. Example of application scenario.............................6 6. Detailed Requirements.......................................7 6.1. PCE Information to be disclosed.............................7 6.1.1. Discovery of PCE Location...................................7 6.1.2. Discovery of PCE computation scopesscope(s) and domain(s) under control...................................................7control...............................................7 6.1.3. Discovery of PCE Capabilities...............................8 6.1.4. Discovery of Alternate PCEs.................................9PCEs.................................8 6.2. Scope of PCE Discovery......................................9 6.3. PCE Information Synchronization.............................9 6.4. Detecting PCE Liveliness...................................10Liveliness....................................9 6.5. Discovery of PCE capacity and congestion...................10 6.6. Extensibility..............................................10Security Requirements......................................10 6.7. Scalability................................................10Extensibility..............................................10 6.8. PCE Selection..............................................10Scalability................................................10 7. Security Considerations....................................11 8. Acknowledgments............................................11 9. References.................................................11 10. Authors' Addresses:........................................12Addresses:........................................11 11. Intellectual Property Statement............................13Statement............................12 1. Contributors The following are the authors that 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) 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. PCC: Path Computation Client: any client application requesting a path computation to be performed by a Path Computation Element. 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 ASes or sub-ASes (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. 3. Introduction The PCE Architecture [PCE-ARCH] defines a Path Computation Element (PCE) as an entity capable of computing TE-LSPs paths satisfying a set of constraints. The PCE function can be located on a router/LSR (composite PCE) or on a network server (external PCE).A PCE serves TE-LSPpath computation requests sent by Path Computation Clients (PCC). A Path Computation Client (PCC)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 [PCE-COM- REQ].[PCE-COM-REQ]. There are several motivations for the adoption of a PCE-based architecture to perform a TE-LSPpath computation. They are listed in [PCE-ARCH].[PCE- ARCH]. This includes applications such as CPU intensive path computation, inter-domain path computation and backup path computation. The PCE architecture requires, of course, that a PCC be aware of the location and capabilitiesof one or more PCEs in its domain, and also potentially of some relevantPCEs in other domains (in the context ofdomains, for inter-domain path computation).computation. 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 along with their capabilities,PCEs, including information required for PCE selection, and to dynamically detect new PCEs or any modification of the PCE capabilities.PCE's 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 3 points out the problem statement. Section 4 illustrates an application scenario. Finally section 5 addresses detailed requirements. It is intended that solutions that specify procedures and protocolprotocol(s) or protocol(s) extensions for such PCE discovery satisfy these requirements. There is no intent either to specify solution specific requirements or to make any assumption on the protocol(s) that could be used for the discovery. Note that requirements listed in this document apply equally to MPLS- TE and GMPLS-capable PCEs. It is also important to note that the notion of a PCC encompasses a PCE acting as PCC when requesting a TE-LSPpath computation of another PCE (inter-PCE communication). ThusHence, this document does not make the distinction between PCE discovery by PCCs and PCE discovery by PCEs. 4. Problem Statement and Requirements overview 4.1. Problem Statement A routing domain may in practice be comprised of 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...); -In an inter-domain context there can be several PCEs with distinct path computation scopes (intra-area, inter-area, inter-AS, inter-layer), each PCE being responsible for path computation in one or more domains within its scope. As an example, in a multi-area network made 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. In existing multi-area networks, N can be quite large (e.g. beyond fifty). In order to allow for efficient PCE selection by PCCs and efficient load balancing of requests, a PCC has to know the location of PCEs in its domain, along with their capabilities,some information relevant for PCE selection, and also potentially of some relevantPCEs in other domains (fordomains, for inter-domain path computation purpose).purpose. Such PCE information could be learnt through manual configuration, on each PCC, of the set of PCEs along with their capabilities and scope(s).capabilities. Such manual configuration approach may be sufficient, and even desired in some particular situations, but it obviously faces several limitations: -This may imply a substantial configuration overhead (see the above example with N PCEs); -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 capabilities.information. Furthermore, as with any manual configuration approach, this may lead to undesirable configuration errors. Hence, an automated PCE discovery mechanism allowing a PCC to dynamically discover a set of PCEs and their capabilitiesis highly desirable. 4.2. 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 PCEs in its domain and also, potentially, of PCEs in other domains, of interest for inter-domain path computation purpose. A PCE discovery mechanism MUST allow discovering the path computation scope(s) of a PCE.PCE (intra-area, inter-area, inter-ASą). It MUST also allow a PCC to discover the set of one or more domains under the path computation responsibility of a PCE. A PCE discovery mechanism MUST allow PCCs to dynamically discover that a new PCE has appeared or that there is a change in PCEPCE's information. It MUST also allow PCCs to dynamically discover that a PCE is no longer available. AThe PCE discovery MUST be secure. In particular, key consideration MUST be given in terms of how to establish a trust model for PCE discovery. OPTIONALLY a PCE discovery mechanism SHOULD also allow PCCsMAY be used so as to learn aboutdisclose a set of PCE path computationcapabilities. 5. 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 1.1 Figure 1 above illustrates a network with several PCEs: -The ABR R3 is a compositePCE that can take part in inter area path computation. It can compute paths in area 1 and area 0.0; -The ABR R6 is a compositePCE that can take part in inter-area path computation. It can compute paths in area 0 and area2area2; -The ASBR R9 is a compositePCE that can take part in inter-AS path computation, responsible for path computation in AS1 towards AS2.AS2; -The ASBR R12 is a compositePCE that can take part in inter-AS path computation, responsible for path computation in AS2 towards AS1.AS1; -The server S1 is an externala PCE that can be used to compute diverse paths and backup paths in area 1. The PCE discovery mechanism will allow: -each LSR in area 1 and 0 to dynamically discover R3, as a PCE for inter-area path computation as well as its path computation domains: area1 and area0.area0; -each LSR in area 0 and 2 to dynamically discover R6, as a PCE for inter-area path computation, as well as its path computation domains: area2 and area0.area0; -each LSR in AS1 and some PCEs in AS2 to dynamically discover R9 as a PCE for inter-AS path computation as well as its path computation domain:in AS1 towards AS2; -each LSR in area 1 to dynamically discover S1, as a PCE for diverse path computation and backup path computation in area1. 6. Detailed Requirements 6.1. PCE Information to be disclosed The PCE discovery mechanism MUST discloseallow disclosing some PCE information that will allow PCCs to select appropriate PCEs. This section details the kindWe distinguish two levels of information that hasto be disclosed.disclosed by the PCE discovery mechanism: -Mandatory information: This comprises discovery of PCE location, PCE computation scopes and domains under control -Optional information: This comprises discovery of PCE capabilities and alternate PCEs. Note that the latter information is optional in the context of the PCE discovery mechanism. It could also be obtained by other mechanisms, such as for instance the PCC-PCE communication protocol. 6.1.1. Discovery of PCE Location The PCE discovery mechanism MUST allow discovering, for a given PCE, the IPv4 and/or IPv6 address to be used to reach the PCE. This address will typically be a loop-back 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, thanks to a PCC-PCE communication protocol. 6.1.2. Discovery of PCE computation scopesscope(s) and domain(s) under control Inter-domain path computation is a key application of the PCE 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. This can also rely on a single-PCE path computation where a PCE has visibility inside multiple domains and can compute an inter-domain path. Hence the PCE discovery mechanism MUST allow discovering the path computation scope of a PCE, i.e. if a PCE can be used to compute or to take part in the computation of intra-area, inter-area or inter-AS TE-LSP. Note that these path computation scopes are not mutually exclusive. Also the PCE discovery mechanism MUST allow discovering the set of one or more domains under the path computation responsibility of a PCE, i.e. where a PCE has visibility and can compute TE-LSPpaths. These domains can 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. It MUST also allow discovering the set of one or more domain(s) towards which a PCE can compute paths. 6.1.3. Discovery of PCE Capabilities In the case where there are several PCEs with distinct capabilities,capabilities available, a PCC has to select one or more appropriate PCEs. For that purpose the PCE discovery mechanism SHOULD allow the discovery ofMAY be used so as to disclose some PCE capabilities. For the sake of illustration this could include for instance some path computation related capabilities: -The capability to compute MPLS-TE and/or GMPLS paths; -The type of link and path constraints supported: e.g. bandwidth, affinities, delay; -The objective functions supported: e.g. shortest constrained path, shortest bounded delay path; -The capability to compute multiple paths in a synchronized manner: e.g. diverse path computation, load balancing computation; -Some GMPLS specific capabilities: e.g. the supported interface switching capabilities, the capability to computesupport for multi-layer paths.path computation; And this could also include some general capabilities: -The capability to handle request prioritization; -The capability to authenticate PCCs and to be authenticated. 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 description of general and path computation specific PCE capabilities is out of the scope of this document. It is expected that this will be described in a separate document. It is paramount that dynamic capabilitydiscovery MUST NOTof PCE capabilities MUST NOT generate an excessive amount of information and SHOULD be limited to a small set of generic capabilities. If required, the exhaustive discovery of detailed capabilities could be ensured by means of the PCC-PCE communication protocol. Actually a tradeoff should be found between capability discovery by the PCE discovery mechanism and by the PCC-PCE communication protocol. One of the objectives of the PCE discovery mechanism is to help PCCs to select appropriate PCEs and limit the likelihood of PCC- PCE communication rejections that may occur in case a PCE cannot support a given capability. 6.1.4. 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, to indicate a set of one or more alternate PCEs that can be selected in case a given PCE fails. Hence the PCE Discovery mechanism SHOULD allow the advertising, for a given PCE of the location of one or more assigned alternate PCEs. 6.2. Scope of PCE Discovery The PCE Discovery mechanism MUST allow the control of the scope of the PCE information discovery (IGP Area, AS, set of AS) on a per PCE basis. In other words it MUST allow to control 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 the followings: -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 ASes -A set of one or more PCCs in a set of one or more ASes Particularly this also implies that the PCE Discovery mechanism MUST allow for the discovery of PCE information across IGP areas and across AS boundaries. Note that it MUST be possible to deactivate PCE discovery on a per PCE basis. 6.3. PCE Information Synchronization The PCE discovery mechanism MUST allow a PCC to detect any change in the information related to a PCE (e.g. capability modifications). In addition it MUST be possible to dynamically detect new PCEs. The PCE Discovery Mechanism SHOULD allow such detection under 60 seconds. Note that PCE capabilities areinformation is expected to be fairly stable and not to change frequently. 6.4. Detecting PCE Liveliness The PCE discovery mechanism MUST allow a PCC to detect when a PCE is no longer alive. This allows a PCC to rapidly switch to another PCE (for instance a predefined alternate PCE), and thus minimizes path computation service disruption. The PCE discovery mechanism SHOULD allow such PCE livelinessdetection under 60 seconds. 6.5. Discovery of PCE capacity and congestion PCE WG feedback is requested on the following items: -Is there a need for the discovery of PCE capacity in terms of computation power? This static parameter could be used to ensure weighted load balancing of requests in case PCEs do not have the same capacity. -Would it-May the PCE discovery mechanism be usefulused so that a PCE report its status as "congested" in case it is too busy? PCCs may then use this dynamic information to prefer a different PCE. 6.6. Security Requirements The PCE Discovery mechanism MUST address security issues across multiple ASes. 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 ore more trust model(s). The PCE discovery mechanism MUST deliver the operational security objectives where required. The overall security objectives of privacy, authentication, and integrity may take on varying level of importance. These objectives MAY be met by other established means and protocols. Particularly, mechanisms MUST be defined to ensure authentication, integrity and privacy of PCE discovery information. It MUST be possible to restrict the scope of discovery to a set of authorized PCCs. In particular, the identity of any PCE MUST only be learnt by authorized PCCs. It MUST be possible for PCEs to authenticate PCCs and for PCCs to authenticate PCEs. It MUST also be possible to encrypt discovery information. 6.7. Extensibility The PCE discovery mechanism MUST be flexible and extensible so as to easily allow for the additioninclusion of some additional PCE information that could be defined in the future. 220.127.116.11. Scalability The PCE discovery mechanism MUST be designed to scale well with an increase of any of the following parameters: -Number of PCCs; -Number of PCEs; -Number of IGP Areas in the discovery scope; -Number of ASs in the discovery scope. Particularly, in case routing protocols (IGP, BGP) are extended to support PCE discovery, the extensions MUST NOT cause a degradation in routing protocol performance. The same applies to a signaling solution that could serve for this communication. 6.8. PCE Selection A PCC may have to select among a set of candidate PCEs that have the same capabilities. A specific PCE selection procedure SHOULD be defined in order to ensure consistent behaviour when doing load balancing and avoid that all PCCs send the requests to only one PCE. The precise requirements and mechanisms for this function are out of the scope of this document. It is expected that this requirement will be covered in another document.discovery. 7. Security Considerations PCE discoveryThis document is a requirement document and particularly inter-AS PCE discovery mayhence does not raise new security issues. PCE discovery procedures or protocol extensions MUST deliver the operational security objectives where required. The overall security objectives of confidentiality, integrity and availability may take on varying level of importance. These objectives MAY be metby other established means and protocols. The PCE discovery mechanism MUST be able to restrict the scope of discovery to aitself any particular security issue. A set of authorized PCCs. The identity of any PCE MUST only be learnt by authorized PCCs. Itsecurity requirements that MUST be possible to encrypt discovery information. Note that a threat analysis ofaddressed when considering the proposed procedures and/or protocol extensions SHOULD address masquerade, eavesdropping, unauthorized access, loss or corruption of information (includes replay attacks), repudiation, forgerydesign and denialdeployment of service attacks.a PCE Discovery mechanism have been identified in section 6.6. 8. Acknowledgments We would like to thank Benoit Fondeviole, Thomas Morin, Emile Stephan, Jean-Philippe Vasseur, Dean Cheng andCheng, Adrian Farrel, Renhai Zhang, Mohamed BoucadairBoucadair, Eric Gray, Igor Bryskin and Dimitri Papadimitriou, for their useful comments and suggestions. 9. References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC 3667, February 2004. [RFC3668] Bradner, S., "Intellectual Property Rights in IETF Technology", BCP 79, RFC 3668, February 2004. [PCE-ARCH] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation Element (PCE) Architecture", draft-ietf-pce-architecture-00.txt,draft-ietf-pce-architecture, work in progress. [PCE-COM-REQ] Ash, J., Le Roux, J.L., " PCE Communication Protocol Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs-00.txt,draft-ietf-pce-comm-protocol-gen-reqs, work in progress. 10. Authors' Addresses: Jean-Louis Le Roux France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex FRANCE Email: email@example.com Paul Mabey Qwest Communications 950 17th Street, Denver, CO 80202, USA Email: firstname.lastname@example.org Eiji Oki NTT Midori-cho 3-9-11 Musashino-shi, Tokyo 180-8585, JAPAN Email: email@example.com Richard Rabbat Fujitsu Laboratories of America 1240 East Arques Ave, MS 345 Sunnyvale, CA 94085 USA Email: firstname.lastname@example.org Ting Wo Chung Bell Canada 181 Bay Street, Suite 350 Toronto, Ontario, M5J 2T3 CANADA, Email: email@example.com Raymond Zhang BT Infonet 2160 E. Grand Ave. El Segundo, CA 90025 USA Email: firstname.lastname@example.org 11. Intellectual Property Statement 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 in BCP 78 and BCP 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 at http://www.ietf.org/ipr. 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