IETF Internet Draft PCE Working Group Jerry Ash (AT&T) Proposed Status: Informational Editor Expires: December 2006 J.L. Le Roux (France Telecom) Editor May 2006
draft-ietf-pce-comm-protocol-gen-reqs-05.txtdraft-ietf-pce-comm-protocol-gen-reqs-06.txt PCE Communication Protocol Generic Requirements 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. 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. This Internet-Draft will expire on December 18, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The PCE model is described in the "PCE Architecture" document and facilitates path computation requests from Path Computation Clients (PCCs) to Path Computation Elements (PCEs). This document specifies generic requirements for a communication protocol between PCCs and PCEs, and also between PCEs where cooperation between PCEs is desirable. Subsequent documents will specify application-specific requirements for the PCE communication protocol. Table of Contents 1. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . . . 3 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Overview of PCE Communication Protocol (PCECP) . . . . . . . . . 4 6. PCE Communication Protocol Generic Requirements . . . . . . . . . 5 6.1 Basic Protocol Requirements . . . . . . . . . . . . . . . . . 5 6.1.1 Commonality of PCC-PCE and PCE-PCE Communication . . . 5 6.1.2 Client-Server Communication . . . . . . . . . . . . . . 5 6.1.3 Transport . . . . . . . . . . . . . . . . . . . . . . . 5 6.1.4 Path Computation Requests . . . . . . . . . . . . . . . 6 6.1.5 Path Computation Responses . . . . . . . . . . . . . . 7 6.1.6 Cancellation of Pending Requests . . . . . . . . . . . 8 6.1.7 Multiple Requests and Responses . . . . . . . . . . . . 8 6.1.8 Reliable Message Exchange . . . . . . . . . . . . . . . 8 6.1.9 Secure Message Exchange . . . . . . . . . . . . . . . . 9 6.1.10 Request Prioritization . . . . . . . . . . . . . . . . 109 6.1.11 Unsolicited Notifications . . . . . . . . . . . . . . 10 6.1.12 Asynchronous Communication . . . . . . . . . . . . . . 10 6.1.13 Communication Overhead Minimization . . . . . . . . . 10 6.1.14 Extensibility . . . . . . . . . . . . . . . . . . . . 10 6.1.15 Scalability . . . . . . . . . . . . . . . . . . . . . 11 6.1.16 Constraints . . . . . . . . . . . . . . . . . . . . . 12 6.1.17 Objective Functions Supported . . . . . . . . . . . . 12 6.2 Deployment Support Requirements . . . . . . . . . . . . . . . 13 6.2.1 Support for Different Service Provider Environments . . 13 6.2.2 Policy Support . . . . . . . . . . . . . . . . . . . . 13 6.3 Aliveness Detection & Recovery Requirements . . . . . . . . . 13 6.3.1 Aliveness Detection . . . . . . . . . . . . . . . . . . 13 6.3.2 Protocol Recovery . . . . . . . . . . . . . . . . . . . 14 6.3.3 LSP Rerouting & Reoptimization . . . . . . . . . . . . 14 6.4 Requirements Summary . . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . . . 17 8. Manageability Considerations . . . . . . . . . . . . . . . . . . 17 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 18 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 18 11. Normative References . . . . . . . . . . . . . . . . . . . . . . 18 12. Informational References . . . . . . . . . . . . . . . . . . . . 18 13. Authors' & Contributors' Addresses . . . . . . . . . . . . . . . 19 Intellectual Property Statement . . . . . . . . . . . . . . . . . . 20 Disclaimer of Validity . . . . . . . . . . . . . . . . . . . . . . . 21 Copyright Statement . . . . . . . . . . . . . . . . . . . . . . . . 21 1. Contributors This document is the result of the PCE Working Group PCE Communication Protocol (PCECP) requirements design team joint effort. The following are the design team member authors that contributed to the present document: Jerry Ash (AT&T) Alia Atlas (Google, Inc.) Arthi Ayyangar (Juniper) Nabil Bitar (Verizon) Igor Bryskin (Independent Consultant) Dean Cheng (Cisco) Durga Gangisetti (MCI) Kenji Kumaki (KDDI) Jean-Louis Le Roux (France Telecom) Eiji Oki (NTT) Raymond Zhang (BT Infonet) 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 3. Introduction A Path Computation Element (PCE) [PCE-ARCH] supports requests for path computation issued by a Path Computation Client (PCC), which may be 'composite' (co-located) or 'external' (remote) from a PCE. When the PCC is external from the PCE, a request/response communication protocol is required to carry the path computation request and return the response. In order for the PCC and PCE to communicate, the PCC must know the location of the PCE: PCE discovery is described in [PCE-DISC-REQ]. The PCE operates on a network graph in order to compute paths based on the path computation request(s) issued by the PCC(s). The path computation request will include the source and destination of the paths to be computed, a set of constraints to be applied during the computation, and may also include an objective function. The PCE response includes the computed paths or the reason for a failed computation. This document lists a set of generic requirements for the PCECP. Application-specific requirements are beyond the scope of this document, and will be addressed in separate documents. For example, application-specific communication protocol requirements are given in [PCECP-INTER-AREA] and [PCECP-INTER-LAYER] for inter-area and inter-layer PCE applications, respectively. 4. Terminology Domain: any collection of network elements within a common sphere of address management or path computational responsibility. Examples of domains include IGP areas, Autonomous Systems (ASs), multiple ASs within a service provider network, or multiple ASs across multiple service provider networks. GMPLS: Generalized Multi-Protocol Label Switching LSP: MPLS/GMPLS Label Switched Path LSR: Label Switch Router MPLS: Multi-Protocol Label Switching PCC: Path Computation Client: any client application requesting a path computation to be performed by the PCE. 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 (see further description in [PCE-ARCH]). TED: Traffic Engineering Database, which contains the topology and resource information of the network or network segment used by a PCE. TE LSP: Traffic Engineering (G)MPLS Label Switched Path. See [PCE-ARCH] for further definitions of terms. 5. Overview of PCE Communication Protocol (PCECP) In the PCE model, path computation requests are issued by a PCC to a PCE that may be composite (co-located) or external (remote). If the PCC and PCE are not co-located, a request/response communication protocol is required to carry the request and return the response. If the PCC and PCE are co-located, a communication protocol is not required, but implementations may choose to utilize a protocol for exchanges between the components. In order that a PCC and PCE can communicate, the PCC must know the location of the PCE. This can be configured or discovered. The PCE discovery mechanism is out of scope of this document, but requirements are documented in [PCE-DISC-REQ]. The PCE operates on a network graph built from the TED in order to compute paths. The mechanism by which the TED is populated is out of scope for the PCECP. A path computation request issued by the PCC includes a specification of the path(s) needed. The information supplied includes, at a minimum, the source and destination for the paths, but may also include a set of further requirements (known as constraints) as described in Section 6. The response from the PCE may be positive in which case it will include the paths that have been computed. If the computation fails or cannot be performed, a negative response is required with an indication of the type of failure. A request/response protocol is also required for a PCE to communicate path computation requests to another PCE and for that PCE to return the path computation response. As described in [PCE-ARCH], there is no reason to assume that two different protocols are needed, and this document assumes that a single protocol will satisfy all requirements for PCC-PCE and PCE-PCE communication. [PCE-ARCH] describes four models of PCE: composite, external, multiple PCE path computation, and multiple PCE path computation with inter-PCE communication. In all cases except the composite PCE model, a PCECP is required. The requirements defined in this document are applicable to all models described in the [PCE-ARCH]. 6. PCE Communication Protocol Generic Requirements Section 6.4 contains a summary of the requirements in this section. 6.1 Basic Protocol Requirements 6.1.1 Commonality of PCC-PCE and PCE-PCE Communication A single protocol MUST be defined for PCC-PCE and PCE-PCE communication. A PCE requesting a path from another PCE can be considered as a PCC, and in the remainder of this document we refer to all communications as PCC-PCE regardless of whether they are PCC-PCE or PCE-PCE. 6.1.2 Client-Server Communication PCC-PCE communication is by nature client-server based. The PCECP MUST allow a PCC to send a request message to a PCE to request path computation, and for a PCE to reply with a response message to the requesting PCC once the path has been computed. In addition to this request-response mode, there are cases where there is unsolicited communication from the PCE to the PCC (see Section 6.1.11). 6.1.3 Transport The PCECP may utilize an existing transport protocol or operate directly over IP. If a transport protocol is used, it MAY be used to satisfy some requirements stated in other sections of this document (for example, reliability and security). Where requirements expressed in this document match the function of existing transport protocols, consideration MUST be given to the use of those protocols. If a transport protocol is used, it MUST NOT limit the size of the message used by the PCECP. 6.1.4 Path Computation Requests The path computation request message MUST include at least the source and destination. Note that the path computation request is for an LSP or LSP segment, and the source and destination supplied are the start and end of the computation being requested (i.e. of the LSP segment). The path computation request message MUST support the inclusion of a set of one or more path constraints, including but not limited to the requested bandwidth or resources (hops, affinities, etc.) to include/exclude. For example, a PCC may request the PCE to exclude points of failure in the computation of a new path if an LSP setup fails. The actual inclusion of constraints is a choice for the PCC issuing the request. A list of core constraints that must be supported by the PCECP is supplied in Section 6.1.16. Specification of constraints MUST be future-proofed as described in Section 6.1.14. The requester MUST be allowed to select or prefer from an advertised list or minimal subset of standard objective functions and functional options. An objective function is used by the PCE to process constraints to a path computation request when it computes a path in order to select the "best" candidate paths (e.g., minimum hop path), and corresponds to the optimization criteria used for the computation of one path, or the synchronized computation of a set of paths. In the case of unsynchronized path computation, this can be, for example, the path cost or the residual bandwidth on the most loaded path link. In the case of synchronized path computation, this can be, for example, the global bandwidth consumption or the residual bandwidth on the most loaded network link. A list of core objective functions that MUST be supported by the PCECP is supplied in Section 6.1.17. Specification of objective functions MUST be future-proofed as described in Section 6.1.14. The requester SHOULD also be able to select a vendor-specific or experimental objective function or functional option. Furthermore, the requester MUST be allowed to customize the function/options in use. That is, individual objective functions will often have parameters to be set in the request from PCC to PCE. Support for the specification of objective functions and objective parameters is required in the protocol extensibility specified in Section 6.1.14. A request message MAY include TE parameters carried by the MPLS/GMPLS LSP setup signaling protocol. Also, it MUST be possible for the PCE to apply additional objective functions. This might include policy based routing path computation for load balancing instructed by the management plane. Shortest path selection may rely either on the TE metric or on the IGP metric [METRIC]. Hence the PCECP request message MUST allow the PCC to indicate the metric type (IGP or TE) to be used for shortest path selection. Note that other metric types may be specified in the future. There may be cases where a single path cannot fit a given bandwidth request, while a set of paths could be combined to fit the request. Such path combination to serve a given request is called load-balancing. The request message MUST allow the PCC to indicate if load-balancing is allowed or not. It MUST also include the maximum number of paths in a load-balancing path group, and the minimum path bandwidth in a load-balancing path group. The request message MUST allow specification of the degree of disjointness of the members of the load-balancing group. 6.1.5 Path Computation Responses The path computation response message MUST allow the PCE to return various elements including, at least, the computed path(s). The protocol MUST be capable of returning any explicit path that would be acceptable for use for MPLS and GMPLS LSPs once converted to an Explicit Route Object for use in RSVP-TE signaling. In addition, anything that can be expressed in an Explicit Route Object MUST be capable of being returned in the computed path. Note that the resultant path(s) may be made up of a set of strict or loose hops, or any combination of strict and loose hops. Moreover, a hop may have the form of a non-simple abstract node. See [RFC 3209] for the definition of strict hop, loose hop, and abstract node. A positive response from the PCE MUST include the paths that have been computed. A positive PCECP computation response MUST support the inclusion of a set of attributes of the computed path, such as the path costs (e.g., cumulative link TE metrics and cumulative link IGP metrics) and the computed bandwidth. The latter is useful when a single path cannot serve the requested bandwidth and load balancing is applied. When a path satisfying the constraints cannot be found, or if the computation fails or cannot be performed, a negative response MUST be sent. This response MAY include further details of the reason(s) for the failure, and MAY include advice about which constraints might be relaxed to be more likely to achieve a positive result. The PCECP response message MUST support the inclusion of the set of computed paths of a load-balancing path group, as well as their respective bandwidths. 6.1.6 Cancellation of Pending Requests A PCC MUST be able to cancel a pending request using a notification message. A PCC that has sent a request to a PCE and no longer needs a response, for instance because it no longer wants to set up the associated service, MUST be able to notify the PCE that it can clear the request (i.e. stop the computation if already started, and clear the context). The PCE may also wish to cancel a pending request because of some congested state. 6.1.7 Multiple Requests and Responses It MUST be possible to send multiple path computation requests within the same request message. Such requests may be correlated (for example, requesting disjoint paths) or uncorrelated (requesting paths for unrelated services). It MUST be possible to limit by configuration of both PCCs and PCEs the number of requests that can be carried within a single message. Similarly, it MUST be possible to return multiple computed paths within the same response message, corresponding either to the same request (e.g. multiple suited paths, paths of a load balancing path group) or to distinct requests, correlated or not, of the same request message or distinct request messages. It MUST be possible to provide "continuation correlation" where all related requests or computed paths cannot fit within one message, and are carried in a sequence of correlated messages. The PCE MUST inform the PCC of its capabilities. Maximum acceptable message sizes and the maximum number of requests per message supported by a PCE MAY form part of PCE capabilities advertisement [PCE-DISC-REQ], or MAY be exchanged through information messages from the PCE as part of the protocol described here. It MUST be possible for a PCC to specify, in the request message, the maximum acceptable response message sizes and the maximum number of computed paths per response message it can support. It MUST be possible to limit the message size by configuration on PCCs and PCEs. 6.1.8 Reliable Message Exchange The PCECP MUST support reliable transmission of PCECP packets. This may form part of the protocol itself or may be achieved by the selection of a suitable transport protocol (see Section 6.1.3). In particular, it MUST allow for the detection and recovery of lost messages to occur quickly and not impede the operation of the PCECP. In some cases (e.g. after link failure), a large number of PCCs may simultaneously send requests to a PCE, leading to a potential saturation of the PCEs. The PCECP MUST support indication of congestion state and rate limitation state. This should enable, for example, a PCE to limit the rate of incoming request messages if the request rate is too high. The PCECP MUST provide: - Detection and report of lost or corrupted messages - Automatic attempts to retransmit lost messages without reference to the application - Handling of out-of-order messages - Handling of duplicate messages - Flow control and back-pressure to enable throttling of requests and responses - Rapid PCECP communication failure detection - Distinction between partner failure and communication channel failure after the PCECP communication is recovered If it is necessary to add functions to PCECP to overcome shortcomings in the chosen transport mechanisms, these functions SHOULD be based on and re-use where possible techniques developed in other protocols to overcome the same shortcomings. Functionality MUST NOT be added to the PCECP where the chosen transport protocol already provides it. 6.1.9 Secure Message Exchange The PCC-PCE communication protocol MUST include provisions to ensure the security of the exchanges between the entities. In particular, it MUST support mechanisms to prevent spoofing (e.g., authentication), snooping (e.g., encryption) and DOS attacks (e.g., rate limiting, no promiscuous listening). The PCC-PCE communication protocol MUST include provisions to ensure the security of the exchanges between the entities. In particular, it MUST support mechanisms to prevent spoofing (e.g., authentication), snooping (e.g., encryption) and DOS attacks (e.g.,packet filtering, rate limiting, no promiscuous listening). Where the PCE-PCC communication takes place entirely within one limited domain, the use of a private address space which is not available to customer systems MAY be used to help protect the information exchange, but other mechanisms MUST also be available. This function may be provided by the transport protocol or directly by the PCECP. See Section 7 for further discussion of security considerations. 6.1.10 Request Prioritization The PCECP MUST allow a PCC to specify the priority of a computation request. Implementation of priority-based activity within a PCE is subject to implementation and local policy. This application processing is out of scope of the PCECP. 6.1.11 Unsolicited Notifications The normal operational mode is for the PCC to make path computation requests to the PCE, and for the PCE to respond. The PCECP MUST support unsolicited notifications from PCE to PCC, or PCC to PCE. This requirement facilitates the unsolicited communication of information and alerts between PCCs and PCEs. 6.1.12 Asynchronous Communication The PCC-PCE protocol MUST allow for asynchronous communication. A PCC MUST NOT have to wait for a response to one request before it can make another request. It MUST also be possible to have the order of responses differ from the order of the corresponding requests. This may occur, for instance, when path request messages have different priorities (see Requirement 6.1.10). A consequent requirement is that path computation responses MUST include a direct correlation to the associated request. 6.1.13 Communication Overhead Minimization The request and response messages SHOULD be designed so that the communication overhead is minimized. In particular, the overhead per message SHOULD be minimized, and the number of bytes exchanged to arrive at a computation answer SHOULD be minimized. Other considerations in overhead minimization include the following: - the number of background messages used by the protocol or its transport protocol to keep alive any session or association between the PCE and PCC - the processing cost at the PCE (or PCC) associated with request/response messages (as distinct from processing the computation requests themselves). 6.1.14 Extensibility The PCECP MUST provide a way for the introduction of new path computation constraints, diversity types, objective functions, optimization methods and parameters, etc., without requiring major modifications in the protocol. The PCECP MUST be easily extensible to support various PCE based applications that have been currently identified including: - intra-area path computation [PCECP-INTER-AREA] - inter-area path computation - inter-AS intra provider and inter-AS inter-provider path computation - inter-layer path computation [PCECP-INTER-LAYER] The PCECP MUST support the requirements specified in the application-specific requirements documents. The PCECP MUST also allow extensions as more PCE applications will be introduced in the future. The PCECP SHOULD also be extensible to support future applications not currently in the scope of the PCE working group, such as, for instance, point-to-multipoint path computations, multi-hop pseudowire path computation, etc. Note that application specific requirements are out of the scope of this document and will be addressed in separate requirements documents. 6.1.15 Scalability The PCECP MUST scale well, at least as good as linearly, with an increase of any of the following parameters (note, minimum order of magnitude estimates of what the PCECP should support are given in parenthesis): - number of PCCs (1000/domain) - number of PCEs (100/domain) - number of PCCs communicating with a single PCE (1000) - number of PCEs communicated to by a single PCC (100) - number of domains (20) - number of path request messages (average of 10/second/PCE) - handling bursts of requests (burst of 100/second/PCE within a 10- second interval). Note that path requests can be bundled in path request messages, for example, 10 PCECP request messages/second may correspond to 100 path requests/second. Bursts of requests may arise, for example, after a network outage when multiple recomputations are requested. The PCECP MUST handle the congestion in a graceful way so that it does not unduly impact the rest of the network, and so that it does not gate the ability of the PCE to perform computation. 6.1.16 Constraints This section provides a list of generic constraints that MUST be supported by the PCECP. Other constraints may be added to service specific applications as identified by separate application-specific requirements documents. Note that the absence of a constraint in this list does not mean that the constraint must not be supported. Note also that the provisions of Section 6.1.14 mean that new constraints can be added to this list without impacting the protocol to a level that requires major protocol changes. Here is the list of generic constraints that MUST be supported: o MPLS-TE and GMPLS generic constraints: - Bandwidth - Affinities inclusion/exclusion - Link, Node, SRLG inclusion/exclusion - Maximum end-to-end IGP metric - Maximum Hop Count - Maximum end-to-end TE metric - Degree of paths disjointess (Link, Node, SRLG) o MPLS-TE specific constraints - Class-type - Local protection - Node protection - Bandwidth protection o GMPLS specific constraints - Switching type, encoding type - Link protection type 6.1.17 Objective Functions Supported This section provides a list of generic objective functions that MUST be supported by the PCECP. Other objectives functions MAY be added to service specific applications as identified by separate application-specific requirements documents. Note that the absence of an objective function in this list does not mean that the objective function may not be supported. Note also that the provisions of Section 6.1.14 mean that new objective functions MAY be added to this list without impacting the protocol. The PCECP MUST support the following "unsynchronized" objective functions: - Minimum cost path with respect to a specified metric(shortest path) - Least loaded path - Maximum available bandwidth path Also the PCECP MUST support the following "synchronized" objective functions: - Minimize aggregate bandwidth consumption on all links - Maximize the residual bandwidth on the most loaded link - Minimize the cumulative cost of a set of diverse paths. 6.2 Deployment Support Requirements 6.2.1 Support for Different Service Provider Environments The PCECP MUST operate in various different service provider network environments that utilize an IP-based control plane, including - MPLS-TE and GMPLS networks - packet and non-packet networks - centralized and distributed PCE path computation - single and multiple PCE path computation Definitions of centralized, distributed, single, and multiple PCE path computation can be found in [PCE-ARCH]. 6.2.2 Policy Support The PCECP MUST allow for the use of policies to accept/reject requests, and include the ability for a PCE to supply sufficient detail when it rejects a request for policy reasons to allow the PCC to determine the reason for rejection or failure. For example, filtering could be required for a PCE that serves one domain (perhaps an AS) such that all requests that come from another domain (AS) are rejected. However, specific policy details are left to application-specific PCECP requirements. Actual policies, configuration of policies, and applicability of policies are out of scope. Note that work on supported policy models and the corresponding requirements/implications is being undertaken as a separate work item in the PCE working group. PCECP messages MUST be able to carry transparent policy information. 6.3 Aliveness Detection & Recovery Requirements 6.3.1 Aliveness Detection The PCECP MUST allow a PCC to - check the liveliness of the PCC-PCE communication - rapidly detect PCC-PCE communication failure (indifferently to partner failure or connectivity failure), - distinguish PCC/PCE node failures from PCC-PCE connectivity failures, after the PCC-PCE communication is recovered. The aliveness detection mechanism MUST ensure reciprocal knowledge of PCE and PCC liveness. 6.3.2 Protocol Recovery In the event of the failure of a sender or of the communication channel, the PCECP, upon recovery, MUST support resynchronization of information and requests between the sender and the receiver, and this SHOULD be arranged so as to minimize repeat data transfer. 6.3.3 LSP Rerouting & Reoptimization If an LSP fails owing to the failure of a link or node that it traverses, a new computation request may be made to a PCE in order to repair the LSP. Since the PCC cannot know that the PCE's TED has been updated to reflect the failure network information, it is useful to include this information in the new path computation request. Also, in order to re-use the resources used by the old LSP, it may be advantageous to indicate the route of the old LSP as part of the new path computation request. Hence the path computation request message MUST allow an indication of whether the computation is for LSP restoration, and MUST support the inclusion of the previously computed path as well as the identity of the failed element. Note that the old path might only be useful if the old LSP has not yet been torn down. Note that a network failure may impact a large number of LSPs. In this case, a potentially large number of PCCs is going to simultaneously send requests to the PCE. The PCECP MUST properly handle such overload situations, such as for instance through throttling of requests as set forth in section 6.1.8. The path computation request message MUST support TE LSP path reoptimization and the inclusion of a previously computed path. This will help ensure optimal routing of a reoptimized path, since it will allow the PCE to avoid double bandwidth accounting and help reduce blocking issues. 6.4 Requirements Summary The following is a summary of the requirements in Section 6: Requirement Necessity Ref. ------------------------------------------------------------------ Commonality of PCC-PCE and PCE-PCE communication MUST 6.1.1 Client-server communication MUST 6.1.2 Support PCC/PCE request message to request path computation MUST 6.1.2 Support PCE response message with computed path MUST 6.1.2 Support unsolicited communication PCE-PCC SHOULD 6.1.2 Maintain PCC-PCE session NON-RQMT 6.1.2 Use of existing transport protocol MAY 6.1.3 Transport protocol satisfy reliability & security requirements MAY 6.1.3 Transport protocol limits size of message MUST NOT 6.1.3 Support path computation requests MUST 6.1.4 Path computation request includes source & destination MUST 6.1.4 Support path constraints (e.g., bandwidth, hops, affinities) to include/exclude MUST 6.1.4 Allow to select/prefer from advertised list of standard objective functions/options MUST 6.1.4 Allow to customize objective function/options MUST 6.1.4 Allow indicating the metric type (IGP or TE) to be used for shortest path selection MUST 6.1.4 Allow indicating the set of path attributes required in response message MUST 6.1.4 Allow indicating if load-balancing is allowed MUST 6.1.4 Support path computation responses MUST 6.1.5 Negative response support reasons for failure, constraints to relax to achieve positive result SHOULD 6.1.5 Support inclusion of set of path attributes MUST 6.1.5 Support inclusion of set of computed paths of a load-balancing path group, as well as their respective bandwidth MUST 6.1.5 Cancellation of pending requests MUST 6.1.6 Multiple requests and responses MUST 6.1.7 Limit by configuration number of requests within a message MUST 6.1.7 Support multiple computed paths in response MUST 6.1.7 Support "continuation correlation" where related requests or computed paths cannot fit within one message MUST 6.1.7 Maximum message size & maximum number of requests per message exchanged through PCE messages to PCC, or indicated in request message MAY 6.1.7 Reliable message exchange (achieved by PCECP itself or transport protocol) MUST 6.1.8 Allow detection & recovery of lost messages to occur quickly & not impede operation of PCECP MUST 6.1.8 Handle overload situations without significant decrease in performance, e.g., through throttling of requests MUST 6.1.8 Detect/report lost/corrupted messages, retransmit lost messages, handle out-of-order messages & duplicate messages, provide flow control/ back-pressure to throttle messages, detect PCECP communication failure detection MUST 6.1.8 Functionality added to PCECP if transport protocol provides it SHOULD NOT 6.1.8 Secure message exchange (provided by PCECP or transport protocol MUST 6.1.9 Support mechanisms to prevent spoofing (e.g., authentication), snooping (e.g., encryption), DOS attacks MUST 6.1.9 Request prioritization MUST 6.1.10 Unsolicited notifications SHOULD 6.1.11 Allow asynchronous communication MUST 6.1.12 PCC has to wait for response before making another request MUST NOT 6.1.12 Allow order of responses differ from order of requests MUST 6.1.12 Communication overhead minimization SHOULD 6.1.13 Give particular attention to message size SHOULD 6.1.13 Extensibility without requiring modifications to protocol MUST 6.1.14 Easily extensible to support intra-area, inter-area, inter-AS intra provider, inter-AS inter-provider, multi-layer path & virtual network topology path computation MUST 6.1.14 Easily extensible to support future applications not in scope (e.g., point-to-multipoint path computations) SHOULD 6.1.14 Scale at least linearly with number of PCCs, PCEs, PCCs communicating with single PCE, PCEs communicated to by single PCC, domains, path requests, handling bursts of requests MUST 6.1.15 Support path computation constraints MUST 6.1.16 Support "unsynchronized" & "synchronized" objective functions MUST 6.1.17 Support different service provider environments (e.g., MPLS-TE and GMPLS networks, centralized & distributed PCE path computation, single & multiple PCE path computation) MUST 6.2.1 Policy support for policies to accept/reject requests, PCC to determine reason for rejection, notification of policy violation MUST 6.2.2 Aliveness detection of PCCs/PCEs, PCECP failure detection MUST 6.3.1 Protocol recovery support resynchronization of information & requests between sender & receiver MUST 6.3.2 Minimize repeat data transfer, allow PCE to respond to computation requests issued before failure without requests being re-issued SHOULD 6.3.2 Stateful PCE able to resynchronize/recover states (e.g., LSP status, paths) after restart SHOULD 6.3.2 Allow indicating if computation is for LSP restoration (support inclusion of previously computed path & failed element) MUST 6.3.3 Support path reoptimization & inclusion of a previously computed path MUST 6.3.3 7. Security Considerations The impact of the use of a PCECP MUST be considered in the light of the impact that it has on the security of the existing routing and signaling protocols and techniques in use within the network. Intra-domain security is impacted since there is a new interface, protocol and element in the network. Any host in the network could impersonate a PCC, and receive detailed information on network paths. Any host could also impersonate a PCE, both gathering information about the network before passing the request on to a real PCE, and spoofing responses. Some protection here depends on the security of the PCE discovery process (see [PCE-DISC-REQ]). An increase in inter-domain information flows may increase the vulnerability to security attacks, and the facilitation of inter-domain paths may increase the impact of these security attacks. Of particular relevance are the implications for confidentiality inherent in a PCECP for multi-domain networks. It is not necessarily the case that a multi-domain PCE solution will compromise security, but solutions MUST examine their impacts in this area. Applicability statements for particular combinations of signaling, routing and path computation techniques are expected to contain detailed security sections. It should be observed that the use of an external PCE introduces additional security issues. Most notable amongst these are: - interception of PCE requests or responses - impersonation of PCE or PCC - DoS attacks on PCEs or PCCs The PCECP MUST address these issues in detail using authentication, encryption and DoS protection techniques. See also Section 6.1.9. 8. Manageability Considerations Manageability of the PCECP MUST address the following considerations: - the need for a MIB module for control and monitoring of PCECP - the need for built-in diagnostic tools to test the operation of the protocol (e.g., partner failure detection, OAM, etc.) - configuration implications for the protocol PCECP operations MUST be modeled and controlled through appropriate MIB modules. Statistics gathering will form an important part of the operation of the PCECP. The operator MUST be able to determine PCECP historical interactions and the success rate of requests using data from MIB modules. Similarly, it is important for an operator to be able to determine PCECP and PCE load and whether an individual PCC is responsible for a disproportionate amount of the load. It MUST be possible, through use of MIB modules, to record and inspect statistics about the PCECP communications, including issues such as malformed messages, unauthorized messages and messages discarded owing to congestion. The new MIB modules should also be used to provide notifications (traps) when thresholds are crossed or when important events occur. PCECP techniques must enable a PCC to determine the liveness of a PCE both before it sends a request and in the period between sending a request and receiving a response. It is also important for a PCE to know about the liveness of PCCs to gain a predictive view of the likely loading of a PCE in the future, and to allow a PCE to abandon processing of a received request. The PCECP MUST support indication of congestion state and rate limitation state, and MAY allow the operator to control such a function. 9. IANA Considerations This document makes no requests for IANA action. 10. Acknowledgements The authors would like to extend their warmest thanks to (in alphabetical order) Lou Berger, Ross Callon, Adrian Farrel, Thomas Morin, Dimitri Papadimitriou, and JP Vasseur for their review and suggestions. 11. Normative References [PCE-ARCH] Farrel, A., Vasseur, JP, Ash, J., "Path Computation Element (PCE) Architecture", work in progress. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 12. Informational References [METRIC] Le Faucheur, F., et. al., "Use of Interior Gateway Protocol (IGP) Metric as a second MPLS Traffic Engineering (TE) Metric", BCP 87, RFC 3785, May 2004. [PCE-DISC-REQ] Le Roux, JL, et. al., "Requirements for Path Computation Element (PCE) Discovery," work in progress. [PCECP-INTER-AREA] Le Roux, JL, et. al., "PCE Communication Protocol (PCECP) specific requirements for Inter-Area (G)MPLS Traffic Engineering," work in progress. [PCECP-INTER-LAYER] Oki, E., et. al., "PCC-PCE Communication Requirements for Inter-Layer Traffic Engineering," work in progress. 13. Authors' & Contributors' Addresses Jerry Ash (Editor) AT&T Room MT D5-2A01 200 Laurel Avenue Middletown, NJ 07748, USA Phone: (732)-420-4578 Email: firstname.lastname@example.org Jean-Louis Le Roux (Editor) France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex, FRANCE Email: email@example.com Alia K. Atlas Google Inc. 1600 Amphitheatre Parkway Mountain View, CA 94043 Email: firstname.lastname@example.org Arthi Ayyangar Juniper Networks, Inc. 1194 N.Mathilda Ave Sunnyvale, CA 94089 USA Email: email@example.com Nabil Bitar Verizon 40 Sylvan Road Waltham, MA 02145 Email: firstname.lastname@example.org Igor Bryskin Independent Consultant Email: email@example.com Dean Cheng Cisco Systems Inc. 3700 Cisco Way San Jose CA 95134 USA Phone: 408 527 0677 Email: firstname.lastname@example.org Durga Gangisetti MCI Email: email@example.com Kenji Kumaki KDDI Corporation Garden Air Tower Iidabashi, Chiyoda-ku, Tokyo 102-8460, JAPAN Phone: 3-6678-3103 Email: firstname.lastname@example.org Eiji Oki NTT Midori-cho 3-9-11 Musashino-shi, Tokyo 180-8585, JAPAN Email: email@example.com Raymond Zhang BT INFONET Services Corporation 2160 E. 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