Network Working Group J.-L. Le Roux (Editor) Internet Draft France Telecom Category: Informational Expires:
MayAugust 2006 February 2006 December 2005PCE Communication Protocol (PCECP) specific requirementsSpecific Requirements for Inter-Area (G)MPLS Traffic Engineering draft-ietf-pce-pcecp-interarea-reqs-00.txtdraft-ietf-pce-pcecp-interarea-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. 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 For scalability purposes a network may comprise multiple IGP areas. An inter-area TE-LSP is an LSP that transits through at least two IGP areas. In a multi-area network, topology visibility remains local to a given area, and a head-end LSR cannot compute alone an inter-area shortest constrained path. One key application of the Path Computation Element (PCE) based architecture is the computation of inter- areainter-area TE-LSP paths. In this context, thisThis document lists a detailed set of PCE Communication Protocol (PCECP) specific requirements for support of inter-area TE-LSP path computation. It complements generic requirements for a PCE Communication Protocol. 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................................................3 2. Terminology.................................................3 3. Introduction................................................4Introduction................................................3 4. Problem Statement...........................................5 5. Various approachesMotivations for PCE-based inter-area path computation...............................................6 5.1. Single PCE Computation......................................6 5.2. Multiple PCE path computation with inter-PCE communication.............................................8 6. Considerations on PCE location..............................9 7.Inter-Area Path Computation.......4 5. Detailed Inter-Area Specific Requirements on PCECP.............................10 7.1. Supported modes for PCE-based inter-area path computation..............................................10 7.2.PCECP..........5 5.1. Control of area crossing...................................10 7.3. Objective functions........................................11 7.4. TE metric / IGP metric.....................................11 7.5. Recording path attributes..................................11 7.6.crossing....................................5 5.2. Area Recording..............................................6 5.3. Strict Explicit pathPath and Loose Path........................12 7.7.Path.........................6 5.4. PCE-list enforcementEnforcement and recordingRecording in Multiple PCE Computation..............................................12 7.8.Computation.................................................6 5.5. Inclusion of Area IDs in request...........................13 7.9. Load-Balancing.............................................13 7.10.Request............................6 5.6. Inter-area Diverse Path computation...................................13 7.11. LSP failure handling.......................................14 7.11.1. LSP Rerouting..............................................14 7.11.2. Backup path computation....................................14 7.12.computation.........................7 5.7. Inter-Area policies........................................15 7.13. Scalability................................................15 8.Policies.........................................7 6. Manageability consideration................................16 9.Considerations................................7 7. Security Considerations....................................16 10. Acknowledgments............................................16 11.Considerations.....................................8 8. Acknowledgments.............................................8 9. Informative References.....................................16 12.References......................................8 10. Editor Address:............................................17 13.Address:.............................................9 11. Contributors' Addresses....................................17 14.Addresses.....................................9 12. Intellectual Property Statement............................18Statement............................10 1. Contributors The following are the authors that contributed to the present document: Jerry Ash (AT&T) Nabil Bitar (Verizon) Dean Cheng (Cisco) Kenji Kumaki (KDDI) J.L. Le Roux (France Telecom) Eiji Oki (NTT) Nabil Bitar (Verizon)Raymond Zhang (BT Infonet) Renhai Zhang (Huawei) 2. Terminology LSR: Label Switching RouterRouter. LSP: MPLS Label Switched PathPath. TE-LSP: Traffic Engineering Label Switched PathPath. IGP area: OSPF Area or IS-IS levellevel. ABR: IGP Area Border Router, a router that is attached to more than one IGP areas (ABR in OSPF or L1/L2 router in IS-IS)IS-IS). Inter-Area TE LSP: TE LSP that traverses more than one IGP areaarea. CSPF: ConstraintConstrained Shortest Path FirstFirst. SRLG: Shared Risk Link GroupGroup. PCE: Path Computation Element,Element: an entity (component, application or network node) that can computeis capable of computing a network path or route based on a network graph and applying computational constraintsconstraints. PCC: Path Computation Client, any application that request path computation to be performed by a PCEPCE. PCECP: PCE Communication Protocol, a protocol for communication between PCCs and PCEsPCEs, and between PCEs. 3. Introduction IGP hierarchy consists of separating an IGP domain into multiple IGP areas, and limiting the topology visibility local to an area. This mechanism significantly improves IGP scalability.[RFC4105] lists a set of motivations and requirements for setting up TE-LSPs across IGP area boundaries. These LSPs are called inter-area TE-LSPs. These requirements include the computation of inter- area shortest constrained paths with key guidelinesguideline being to respect the IGP hierarchy concept, and particularly the containment of topology information. The main challenge with inter-area MPLS-TE relies actually on path computation. TheIndeed the head-end LSR cannot compute an end-to-end shortesta constrained path,path across areas, as its topology visibility is limited to oneits own area. PathInter-area path computation can rely on loose hops with ERO expansion on each ABR, but this faces two issues: (1) it does not guaranteeis one of the computationkey applications of a shortest path that satisfiesthe TE- LSP constraints, and (2) itPCE based architecture [PCE-ARCH]. The computation of optimal inter-area paths may result in several signalling crankback messages before it successfully sets upbe achieved using the path. The Path Computation Element (PCE) Architecture, defined in [PCE- ARCH] can provide a suitable framework for computing anservices of one or more PCEs. Such PCE-based inter-area shortestpath computation could rely for instance on a TE-LSP. [PCE-ARCH] defines PCEs as entitiessingle multi-area PCE that has the TE database of all the areas in the IGP domain and can directly compute paths based on a network graph and applying computational constraints. A PCE function can be located on a LSR or a network server. It defines a Path Computation Client (PCC) as an application requesting a path computation to be performed by a PCE. Typically a PCC can be a head- end LSR, a transit LSR requesting a TE-LSP path computation, or a PCE requesting a path computation of another PCE, in a collaborative mode. One of the key applications of the PCE architecture is inter-domain path computation, where head-end LSRs have a limited topology view beyond its own domain. This includes both inter-area and inter-AS path computation. Inter-area path computation requirements expressed in [RFC4105] may be achieved using the services of one or more PCEs. PCE-based inter-area path computation could rely for instance on a single multi-area PCE that has the TE database of all the areas in the IGP domain and can directly compute an end-to-end shortest constrained path. Alternatively, PCE-based inter-area path computation could relyan end-to-end constrained shortest path. Alternatively, this could rely on the cooperation between PCEs whereby each PCE covers one or more IGP areas and the full set of PCEs covers all areas. The generic requirements for a PCE Communication Protocol (PCECP), allowingwhich allows a PCC to send path computation requests to a PCE and the PCE to sent path computation responseresponses to a PCCPCC, are listedset forth in [PCE-COM- REQ].[PCE-COM-REQ]. The use of a PCE-based approach,approach for inter-area path computation implies specific requirements on a PCE Communication Protocol, in addition to the generic requirements already listed in [PCE-COM-REQ]. This document complements these generic requirements by listing a detailed set of PCECP requirements specific to the PCE-based computation of inter-area TE-LSPs. The problem statement is discussed in section 4. Various PCE-based modes for inter-areainter- area path computation are described in section 5. Considerations for PCE location are provided in section 6. Finally detailed requirements are listed in section 7.computation. It is expected that a solution for a PCE Communication Protocol (PCECP)PCECP satisfies these requirements. Note that PCE-based inter-area path computation may require a mechanism for an automatic PCE discovery across areas, which is out of the scope of this document. Detailed requirements for such a mechanism are discussed in [PCE-DISCO-REQ]. 4. Problem Statement In intra-area MPLS-TE, a head-end LSR has complete topology visibility of the area and can compute an end-to-end shortest constrained path.Motivations for PCE-based Inter-Area Path Computation IGP hierarchy allows improving IGP scalability, particularly in large networks with hundreds of nodes and thousands of links,by dividing the IGP domain into areas and limiting the flooding scope of topology information to area boundaries. A router in an area has full topology information for its own area but only reachability to routesdestinations in other areas._ Thus, a head-end LSR cannot compute an end-to-end constrained path that traverses more than one IGP area. A solution for computing inter-area TE-LSP path currently relies on a per domain path computation ([PD-COMP]). It is based on loose hop routing with an ERO expansion on each ABR. This can allow setting up a constrained path, but faces two major limitations: -This- This does not allow computing an optimal constrained path -This- This may lead to several signallingcrankback signaling messages and hence delay the LSP setup, and also invoke possible alternate routing activities. Note that, here, by optimal constrained path we mean the shortest constrained path across multiple areas, taking into account either the IGP or TE metric [METRIC]. In other words, such a path is the path that would have been computed by making use of some CSPF algorithm in the absence of multiple IGP areas. The PCE based architecture [PCE-ARCH] is well suited to inter-area path computation, as it allows overcoming the path computation limitations resulting from the limited topology visibility, by introducing path computation entities with more topology visibility, or by allowing cooperation between path computation entities in each area. Several PCE-based path computationThere are two main approaches can be used to computefor the computation of an inter-area optimal constrained paths, they are discussed in next section. The use of a PCE-based approach, to perform inter-area path computation requires specific functions in a PCECP, in addition to the generic requirements listed in [PCE-COM-REQ]. Detailed requirements are discussed in section 7. 5. Various approaches for PCE-based inter-area path computation There are various possible modes for PCE-Based inter-area path computation.path: - Single PCE computation: The computation of an inter-area optimalpath could be done by: -is computed by a single PCE,PCE that has enoughtopology visibility in all areas and can alone compute an end-to-endend- to-end optimal path,constrained path. - Multiple PCE computation with inter-PCE communication: the path computation is distributed on multiple PCEs, thatwhich have partial topology visibility. They compute path segments in their areas of visibility and collaborate with each other so as to arrive at an end-to-end optimal constrained path. These two modes are referred asSuch collaboration is ensured thanks to "Single PCE computation" and "Multiple PCE computation withinter-PCE communication" in [PCE- ARCH]. Note that these two modes may co-exist in a given multi-area network.communication. Note that the per-areause of a PCE-based approach, to perform inter-area path computation mode relying on route expansion performed directly by ABRs on the path (which function has composite PCEs) , or on external PCEs contacted byimplies specific functional requirements in a PCECP, in addition to the ABRsgeneric requirements listed in [PCE-COM-REQ]. These specific requirements are discussed in next section. 5. Detailed Inter-Area Specific Requirements on PCECP This section lists a set of additional requirements for the path, consistsPCECP that complement requirements listed in fact[PCE-COM-REQ] and are specific to inter-area (G)MPLS TE path computation. 5.1. Control of a simple concatenationarea crossing In addition to the path constraints specified in Section 6.1.16 of intra[PCE-COM-REQ], the request message MUST allow indicating whether area paths. It actually only impliescrossing is allowed or not. Indeed, when the source and destination reside in the same IGP area, there may be intra-area path computationsand does not allow computinginter-area optimalfeasible paths. Hence this mode is not discussedAs set forth in this document. 5.1. Single PCE Computation In this mode[RFC4105], if the inter-areashortest path computation is directly performed by a single PCE that has enough topology information to compute an end- to-end optimal path. No inter-PCE communication is required in this mode. This mode requires that the PCE have at least the TED of all the crossed areas for a given LSP. The actual distribution of PCEs may vary, i.e., a PCE may have TE database base from two, three or more IGP areas. If the head-end and tail-end LSRs are located in two peripheral areas, the PCE must have the TED of the source, backbone, and destination areas. In the particular case where the head- end/tail-End LSR is located in the backbone area and the tail- end/head-end LSRis located in a peripheral area, the PCE only needs the TED of the backbone area and the peripheral area to compute the path. Figure 1 below illustrates an example of single PCE inter-area computation. ------ | PCE0 | / ------ \ / | \ / | \ / | \ / | \ ------------------------------------------ | | | | | ABR2 ABR3 | R1 area1 | area0 | area2 R2 | ABR1 ABR4 | | | | | ------------------------------------------ Figure 1: Example of single PCE computation. In this multi area network PCE0 has topology visibility in area1, area0 and area2 and can compute and end-to-end path from area 1 to area 2. To setupan inter-area LSP from R1 in area 1 to R2 in area 2, R1 has to directly contact PCE0. Note that this mode may rely on PCEs that have knowledge of topology in all areas. Such a PCE is calledpath, an "all-areas" PCE. Particular attention should be given on the potential limitations of this "all-areas" PCE approach, in terms of scalability. Such all-area PCEsoperator either may have to maintain a large topology and this raises scalability issues both in terms of memory to maintain the TED and processingwant to synchronize TED information. Also such all-area PCEs would potentially serve a large number of PCCs,avoid, as far as possible, crossing areas and hencethus may faceprefer selecting a hugesub-optimal intra-area path computation request overload during a network event such as link or node failure (thator, conversely, may impact a large number of TE-LSPs onprefer to use a large number of head-end LSRs). This may significantly delay the TE-LSP recovery, and thus may diminish the benefits of such an approach. 5.2. Multiple PCE path computation with inter-PCE communication In this mode the computation of an optimal inter-area TE-LSP path is distributed across multiple PCEs. There is at least one PCE per area, and those PCEs do not have enough topology visibility to compute and inter-area optimal path. PCEs in each area compute path segments in their respective areas and collaborate together to arrive at an end-to-end inter-area optimal path. Such collaboration is ensured thanks to inter-PCE communication. The actual distribution of PCEs may vary, i.e. a PCE may have TE database from one, two, or more IGP areas, and the important thing is that the collection of topology and TE information maintained by a set of PCEs collectively must cover all the IGP areas where all inter-area LSPs traverse. Figure 2 and 3 below illustrate two examples of multiple PCE inter- area computation ------ ------ ------ | PCE1 |<------>| PCE0 |<---->| PCE2 | ------ ------ ------ | | | | | | -------------------------------------------- | | | | | ABR2 ABR3 | R1 area1 | area0 | area2 R2 | ABR1 ABR4 | | | | | -------------------------------------------- Figure 2: Cooperation between single-area PCEs Figure 2 above illustrates a multi-area network with 3 areas. PCE0, PCE1 and PCE2 are PCEs responsible for path computation respectively in area 0, 1 and 2. These PCEs have topology visibility limited to one area and are called single-area PCEs. To setup an inter-area LSP from R1 in area 1 to R2 in area 2, R1 has to contact PCE1. PCE1 then collaborates with PCE0, and PCE0 with PCE2 so as to compute an end-to-end shortest constrained path. ------ ------ | PCE1 | <----> | PCE2 | ------ ------ / \ / \ / \ / \ -------------------------------------------- | | | | | ABR2 ABR3 | R1 area1 | area0 | area2 R2 | ABR1 ABR4 | | | | | -------------------------------------------- Figure 3: Cooperation between multi-area PCEs Figure 3 above illustrates a multi-area network with 3 areas. PCE1, and PCE2 are PCEs responsible for path computation respectively in area 0+1 and in area 0+2. This means that PCE1 and PCE2 have topology visibility in area0+area1 and area0+area2 respectively. To setup an inter-area LSP from R1 in area 1 to R2 in area 2, R1 has to contact PCE1. PCE1 then collaborates with PCE2, so as to compute an end-to-end shortest constrained path. 6. Considerations on PCE location As explained in [PCE-ARCH] a PCE can be a LSR or a network server. But note that in the inter-area context, it may be quite efficient for the ABRs to act as PCEs. Indeed, ABRs have topology information of the backbone area and at least one peripheral area. An inter-area TE-LSP optimal path computation could rely on a single ABR, if the path crosses only two IGP areas, or on collaboration between two ABRs in case the path crosses three IGP areas. For instance, in figure 2 above, ABR1 or ABR2 can play PCE1 role, and similarly ABR3 or ABR4 can play PCE2 role. Note that such ABRs are not necessarily transit LSRs on the computed inter-area TE LSP. With such PCE distribution on ABRs, the PCECP would run directly between LSRs. Note that if N peripheral areas are connected to one backbone area, with at least N ABRs, inter-area path computation would potentially require a full mesh of N^2 PCE-PCE communications between ABRs. This reinforces the requirement for communication protocol overhead minimization, expressed in [PCE-COM-REQ]. 7. Detailed Requirements on PCECP This section lists a set of additional requirements for the PCE Communication Protocol that complement requirements listed in [PCE- COM-REQ] and are specific to inter-area (G)MPLS TE path computation. 7.1. Supported modes for PCE-based inter-area path computation The PCECP MUST support the two PCE based inter-area path computation modes set forth in section 5. Multiple PCE inter-area path computation requires cooperation between PCEs. Hence the PCECP MUST support cooperation between PCEs so as to arrive at an inter-area optimal path. It MUST allow requests and replies for cooperative inter-area path computation. A simple cooperation may consists in exchanging intra or inter-area path Segments, and combine them to build an end-to-end optimal path. This is a basic cooperation level that allows building an inter-area optimal path in a recursive manner. The path segment combination could be done in the backward direction, in which case an inter-PCE response message includes a set of computed intra or inter-area path segments from a set of downstream ABRs to the destination, along with their respective cost. These path segments have to be completed by upstream PCEs in a recursive manner so as to build an end-to-end optimal path across areas. To support this collaboration mode, a response message MUST allow the inclusion of multiple intra-area or inter-area path segments from a set of downstream ABRs, to the destination, along with their respective cost (see also 8.4). Note that path segment combination in the forward direction is for further Study. 7.2. Control of area crossing In addition to the path constraints specified in section 6.1.16 of [PCE-COM-REQ] the request message MUST allow indicating whether area crossing is allowed or not. Indeed, for inter-area TE LSPs whose head-end and tail-end LSRs reside in the same IGP area, there may be intra-area and inter-area feasible paths, and, as set forth in [RFC4105], if the shortest path is an inter-area path, an operator either may want to avoid, as far as possible, crossing area and thus may prefer selecting a sub- optimal intra-area path or, conversely, may prefer to use a shortest path, even if it crosses areas. 7.3. Objective functions *Editorial note: This section will be moved to the generic requirement draft [PCE-COM-REQ] as this requirement applies to various PCE applications* As specified in [PCE-COM-REQ] an objective function corresponds to the optimization criteria used for the computation of one path, or the synchronized computation of a set of paths. In case of unsynchronized path computation, this can be, for example, the path cost or the residual bandwidth on the most loaded path link. In case of synchronized path computation, this can be, for example, the global bandwidth consumption or the residual bandwidth on the most loaded network link. For the purpose of inter-area path computation the PCECP MUST support the following "unsynchronized" objective functions: -Minimum cost path (shortest path) -Least loaded path (widest path) -To be completed Also the PCECP SHOULD 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. Note that the absence of an objective function in this list does not mean that it must not be supported. As per the extensibility requirement expressed in [PCE-COM-REQ], note that new objective functions can be added to this list without impacting the protocol. 7.4. TE metric / IGP metric The shortest path selection may rely either on the TE metric or on the IGP metric (see [METRIC]). Hence the PCECP request message MUST allow indicating the metric type (IGP or TE) to be used forshortest path selection. 7.5. Recording path attributes There are at least three aggregate path attributes defined in (G)MPLS-TE: the hop-count, the cumulated TE-metric, and the cumulated IGP-metric. The operator can actually give any semantic to the TE metric and IGP metric. As suggested in [METRIC], if the TE-metric encodes the link cost and the IGP metric the link delay, the cumulated TE-metric indicates the total cost of the LSP and the cumulated IGP metric the end-to-end propagation delay (provided that the LSR transit delay is neglected in a first approximation). A PCC may need to know the aggregate path attributes of an LSR, for instance to select a preferred path among a set of computed paths. In an inter-area context, a PCC may not be able to deduce this information from the supplied path. Therefore the PCECP request message MUST allow indicating the set of aggregate path attributes (hop-count, cumulated TE-metric, cumulated IGP-Metric) that are required in the reply and the PCECP response message MUST support the inclusion of a set of aggregate path attributes. Note thatpath, even if new TE link attributes are defined init crosses areas. Also, when the future to encode specific link parameters,source and allowing to define specific aggregate path constraints, such as, e.g. delay, distance or power loss,destinations reside in the PCEPC will have tosame area it may be extendeduseful to support them. Note that in caseknow whether the computedreturned path includes loose hopsis an inter-area path. Hence the PCEresponse message MUST allow indicating whether the computed path is crossing areas. 5.2. Area Recording It may notbe ableuseful for the PCC to giveknow the set of areas crossed by an accurate aggregateinter-area path attribute.and the corresponding path segments. Hence the response message MUST support the inclusion of the identifiers of the crossed areas and MUST allow indicating that an aggregateidentifying the corresponding path attribute is unknown. 7.6.segments. 5.3. Strict Explicit pathPath and Loose Path A Strict Explicit Path is defined as a set of strict hops. Ahops, while a Loose Path is defined as a set of strict andat least one loose hop and zero, one ore more strict hops. An inter-area path may be strictly explicit or loose (e.g. a list of ABRs as loose hops)hops). It may be useful to indicate to the PCE if a Strict Explicit path is required or not. Hence the PCECP request message MUST allow indicating ifwhether a Strict Explicit Path is required/desired. 126.96.36.199. PCE-list enforcementEnforcement and recordingRecording in Multiple PCE Computation In case of multiple-PCE inter-area path computation, a PCC may want to indicate a preferred list of PCEs to be used. Hence the PCECP request message MUST support the inclusion of a list of preferred PCEs. Note that this requires that a PCC in one area have knowledge of PCEs in other areas. This could rely on configuration or on a PCE discovery mechanism, allowing discovery across area boundaries (see [PCE-DISCO-REQ]). Also it would be useful to know the list of PCEs which effectively participated in the computation. Hence the request message MUST support requestinga request for PCE recording and the response message MUST support the recording of the set of one or more PCEs that took part intoin the computation. It may also be useful to know the path segments computed by each PCE. Hence the request message SHOULD allow requestinga request for the identification of path segmentsegments computed by a PCE, and the response message SHOULD allow identifying the path segments computed by each PCE. 188.8.131.52. Inclusion of Area IDs in requestRequest The knowledge of the areaareas in which the source and destination lie would allow selection of appropriate cooperating PCEs. A PCE may not be able to determine the location of the source and destination LSRs. Henceand in such a case it would be useful that a PCC indicates the source area IDand destination area IDs. For that purpose the request message MUST support the inclusion of the source and destination area IDs. Note that this information could be learned onby the PCC bythrough configuration. 7.9. Load-Balancing *Editorial note: This section will be moved to the generic requirement draft [PCE-COM-REQ] as this requirement applies to various PCE applications* In some cases a single inter-area path may not fit a TE-LSP bandwidth constraint. In this case it may be useful to setup a set of paths whose cumulated residual bandwidth fit the TE-LSP bandwidth request. This is what we call load balancing. So as to avoid ending up with a huge number of paths for a given request, and/or with low bandwidth paths, it is required to control the number of computed paths and the minimum path bandwidth. The request message MUST allow indicating if load-balancing is allowed or not. It MUST also include the number of paths in a load- balancing path group, and the minimum path bandwidth in a load- balancing path group. The response MUST support the inclusion of the set of computed paths of a load-balancing path group, as well as their respective bandwidth. 184.108.40.206. Inter-area Diverse Path computation For various reasonsreasons, including protection and load balancing, the computation of diverse inter-area paths may be required. There are various levels of diversity in an inter-area context: -Per area-Per-area diversity (intra-area path segments are link, node or SRLG disjoint) -Inter-Area-Inter-area diversity (end-to-end inter-area paths are link, node or SRLG disjoint) Note that two paths may be disjoint in the backbone area but sharednon- disjoint in peripheral areas. Also two paths may be node disjointsdisjoint within areas but may share ABRs.ABRs, in which case path segments within an area are node disjoint but end-to-end paths are not node-disjoint. The request message MUST allow requesting the computation of a set of inter-area diverse paths between athe same couple of nodesnode pair or between distinct couples of nodes.node pairs. It MUST allow indicating the required level of intra-area diversity (link, node, SRLG) on a per area basis, as well as the level of inter-area diversity (shared ABRs or ABR disjointness). The response message MUST allow indicating the level of diversity of a set of computed loose paths. Note that specific objective functionfunctions may be requested for diverse path computation, such as to minimize the cumulated cost of a set of diverse paths (see also 7.3). 7.11. LSP failure handling 7.11.1. LSP Rerouting *Editorial note: This section will be moved to the generic requirement draft [PCE-COM-REQ] as this requirement applies to various PCE applications* Upon LSP failure, due to link, node or SRLG failure, a head-end LSR may send a request to the PCE so as to reroute the LSP over an alternate path. So as to ease the computation such request should include the previous path and the failed element (if it can be identified). Hence the request message MUST allow indicating if the computation is for an LSP restoration, and MUST support the inclusion of the previously computed path as well as the failed element. Note that the old path is actually useful only if the old LSP is not torn down yet. This is up to the PCC to decide if it includes the old path or not. Note that a network failure may impact a large number of LSPs. A potentially large number of PCCs, are going to simultaneously send a request to the PCE. Some jittering may be used on PCCs so as to delay a request to the PCE, under network failure condition. The PCECP MAY support the inclusion, in a response message to a PCC, of an upper bound of the jitter to be used for further requests to the PCE (e.g. the PCC will wait for a random value between 0 and the upper bound before sending another request). This upper bound would depend on the level of congestion of the PCE. 7.11.2. Backup path computation ABRs can be protected using Fast Reroute (FRR) node protection [MPLS- FRR]. This requires setting up inter-area FRR backup LSPs (bypass or detour). The PCECP SHOULD support the computation of inter-area FRR backup LSPs (detour or bypass). Note that the objective function may be to minimize overhaul backup bandwidth consumption, by maximizing bandwidth sharing among backup LSPs protecting independent elements. Detailed requirements for intra and inter-area PCE-based backup path computation are for further study and will be addressed inminimizing the cumulated cost of a separate document. 7.12.set of diverse paths as set forth in [PCE-COM-REQ]. 5.7. Inter-Area policiesPolicies As already defined in Section 8.25.1, a request message MUST allow indicating whether area crossing is allowed or not. A PCE may want to apply policies based on the initiating PCC. In a multiple-PCE computation the address of the initiating PCC may no longer be part of the request messages sent between PCEs. Hence, the request message MUST support the inclusion of the address of the originatororiginating PCC. Note that in some case thiscases it is important to contain an inter-area path within a single AS. Hence the request message MUST allow indicating that AS crossing is not authorized. 7.13. Scalability As already pointed out in [PCE-COM-REQ] the PCECP MUST scale well, at least as good as linearly, with an increase of any of the following parameters: - number of PCCs communicating with a single PCE - number of PCEs communicated to by a single PCC - number of PCEs communicated to by another PCE - number of request per PCE per second in steady state - number of requests per PCE per second under emergency condition Note that these numbers will depend on the level of PCE distribution and on the PCE approach used (Single PCE computation, Multiple PCEs computation…) For instance in a network that comprises I IGP areas, with P PCCs per area and A ABRs per area boundary then -For single PCE computation with an all-areas PCE Server: -Number of PCCs communicating with a single PCE=I*P -Number of PCEs communicated to by a single PCC=1 -Number of PCEs communicated to by another PCE=0 -For multiple PCE computation with ABRs acting as PCEs: -Number of PCCs communicating with a single PCE=P -Number of PCE communicated to by a single PCC=I*A -Number of PCEs communicated to by another PCE=I*A Typical values for a large inter-area network can be: I=50, P=100, and A=2. Note also that the memory and CPU consumed to maintain and synchronize the TED on a PCE will directly depend on the number of areas under control of the PCE. This may diminish the benefits of "all area" PCEs, but this is beyond the scope of this document. 8. Manageability consideration6. Manageability ofConsiderations The inter-area PCEs must address the following consideration for section 7: - need for a MIB module for control plane and monitoring - need for built-in diagnostic tools - configuration implications for the protocol 9.application does not imply new manageability requirements beyond those already defined in [PCE-COM-REQ]. 7. Security Considerations IGP areas are administrated by the same entity. Hence the inter-area application does not imply a new trust model, or new security issues beyond those already defined in [PCE-COM-REQ]. 10.8. Acknowledgments We would also like to thank Adrian Farrel, Jean-Philippe Vasseur, Bruno Decraene andDecraene, Yannick Le Louedec and Dimitri Papadimitriou for their useful comments and suggestions. 11.9. Informative 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. [BCP79] Bradner, S., "Intellectual Property Rights in IETF Technology", RFC 3979, March 2005. [RFC4105] Le Roux J.L., Vasseur J.P., Boyle, J., et al. "Requirements for inter-area MPLS-TE" RFC 4105, June 2005. [PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, “Path Computation Element (PCE) Based Architecture”, draft-ietf-pce-architecture (workwork in progress).progress. [PCE-COM-REQ] J. Ash, J.L Le Roux etet. al., “PCE Communication Protocol Generic Requirements”, draft-ietf-pce-comm-protocol-gen-reqs (workwork in progress).progress. [PCE-DISC-REQ] J.L. Le Roux etet. al., “Requirements for Path Computation Element (PCE) Discovery”, draft-ietf-pce-discovery-reqs (workwork in progress).progress. [PD-COMP] Vasseur, J.P., Ayyangar, A., Zhang, R., " A"A Per-domain path computation method for computing Inter-domain Traffic Engineering (TE) Label Switched Path (LSP)", draft-ietf-ccamp-inter-domain-pd- path-comp,work in progressprogress. [METRIC] Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx, P., and T. Telkamp, "Use of Interior Gateway Protocol(IGP) Metric as a second MPLS Traffic Engineering (TE) Metric", BCP 87, RFC 3785, May 2004. [ID-RSVP] Ayyangar, A., Vasseur, J.P., "Inter domain GMPLS Traffic Engineering - RSVP-TE extensions", draft-ietf-ccamp-inter-domain- rsvp-te,work in progress. 12.10. Editor Address: Jean-Louis Le Roux France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex FRANCE Email: email@example.com 13.11. Contributors' Addresses Jerry Ash AT&T Room MT D5-2A01 200 Laurel Avenue Middletown, NJ 07748, USA Phone: +1-(732)-420-4578 Email: firstname.lastname@example.org Nabil Bitar Verizon 40 Sylvan Road Waltham, MA 02145 Email: email@example.com Dean Cheng Cisco Systems Inc. 3700 Cisco Way San Jose CA 95134 USA Phone: +1 408 527 0677 Email: firstname.lastname@example.org Kenji Kumaki KDDI Corporation Garden Air Tower Iidabashi, Chiyoda-ku, Tokyo 102-8460, JAPAN Phone: +81-3-6678-3103 Email: email@example.com Eiji Oki NTT Midori-cho 3-9-11 Musashino-shi, Tokyo 180-8585, JAPAN Email: firstname.lastname@example.org Raymond Zhang BT INFONET Services Corporation 2160 E. Grand Ave. El Segundo, CA 90245 USA Email: Raymond_zhang@bt.infonet.com email@example.com Renhai Zhang Huawei Technologies No. 3 Xinxi Road, Shangdi, Haidian District, Beijing City, P. R. China Email: firstname.lastname@example.org 12. 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