Network Working Group J.L. Le Roux (Editor) Internet Draft France Telecom Intended Status: Standard Track Expires:MarchApril 2008 J.P. Vasseur (Editor) Cisco System Inc. Yuichi Ikejiri NTT Communications Raymond Zhang BT InfonetSeptemberOctober 2007 IS-ISprotocol extensionsProtocol Extensions for Path Computation Element (PCE) Discoverydraft-ietf-pce-disco-proto-isis-07.txtdraft-ietf-pce-disco-proto-isis-08.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. Copyright Notice Copyright (C) The IETF Trust (2007). All rights reserved. Abstract There are various circumstances where it is highly desirable for a Path Computation Client (PCC) to be able to dynamically and automatically discover a set of Path Computation Elements(PCE),(PCEs), along withsomeinformation that can be used by the PCC for PCE selection. When the PCE is a Label Switching Router (LSR) participating in the Interior Gateway Protocol (IGP), or even a server participating passively in the IGP, a simple and efficient way todiscoverannounce PCEs consists of using IGP flooding. For that purpose this document defines extensions to the Intermediate System to Intermediate System (IS-IS) routing protocol for the advertisement of PCE Discovery information within an IS-IS area or within the entire IS-IS routing domain. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Table of ContentsTerminology........................................................31.3Terminology.................................................3 2. Introduction................................................4 3. Overview....................................................5 3.1. PCEInformation.............................................5 3.1.1. PCEDiscovery Information...................................53.1.2. PCE Overload Information....................................63.2. FloodingScope..............................................6Scope..............................................5 4. The IS-IS PCED Sub-TLV......................................6 4.1. PCE-ADDRESS Sub-TLV.........................................7 4.2. The PATH-SCOPE Sub-TLV......................................7 4.3. PCE-DOMAIN Sub-TLV..........................................9 4.4. NEIG-PCE-DOMAIN Sub-TLV....................................10 4.5. PCE-CAP-FLAGSSub-TLV......................................11 4.6. The OVERLOAD Sub-TLV.......................................11Sub-TLV......................................10 5. Elements ofProcedure......................................12 5.1. OVERLOAD Sub-TLV Specific Procedures.......................12Procedure......................................11 6. BackwardCompatibility.....................................13Compatibility.....................................12 7. IANAConsiderations........................................13Considerations........................................12 8. SecurityConsiderations....................................13Considerations....................................12 9. ManageabilityConsiderations...............................14Considerations...............................12 9.1. Control of Policy andFunctions............................14Functions............................12 9.2. Information and DataModel.................................14Model.................................13 9.3. Liveness Detection andMonitoring..........................14Monitoring..........................13 9.4. Verify CorrectOperations..................................14Operations..................................13 9.5. Requirements on Other Protocols and FunctionalComponents...............................................14Components...............................................13 9.6. Impact on NetworkOperations...............................15Operations...............................13 10.Acknowledgments............................................15Acknowledgments............................................14 11.References.................................................15References.................................................14 11.1. NormativeReferences.......................................15References.......................................14 11.2. InformativeReferences.....................................16References.....................................14 12. Editors'Addresses:........................................16Addresses:........................................15 13. Contributors'Adresses:....................................16Adresses:....................................15 14. Intellectual PropertyStatement............................17Statement............................15 1. Terminology ABR: IS-IS Area Border Router. AS: Autonomous System. IGP: Interior Gateway Protocol. Either of the two routing protocols Open Shortest Path First (OSPF) or Intermediate System to Intermediate system (IS-IS). Intra-area TE LSP: A TE LSP whose path does not cross an IGP areaboundaries.boundary. Intra-AS TE LSP: A TE LSP whose path does not cross an ASboundaries.boundary. Inter-area TE LSP: A TE LSP whose path transits two or more IGP areas. That is aTE-LSPTE LSP that crosses at least one IGP area boundary. Inter-AS TE LSP: A TE LSP whose path transits two or more ASes or sub-ASes (BGP confederations). That is aTE-LSPTE LSP that crosses at least one AS boundary. IS-IS LSP: Link State PDU LSR: Label Switching Router. PCC: Path ComputationClient:Client. Any client application requesting a path computation to be performed by a Path Computation Element. PCE: Path ComputationElement:Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph, and applying computational constraints. PCE-Domain: In a PCE context this refers to any collection of network elements within a common sphere of address management or path computational responsibility (referred to as a "domain" in [RFC4655]). Examples of PCE-Domains include IGP areas and ASes. This should be distinguished from an IS-IS routing domain as defined by [ISO]. PCEP: Path Computation Element communication Protocol. TE LSP: Traffic Engineered Label Switched Path. 2. Introduction [RFC4655] describes the motivations and architecture for a Path Computation Element (PCE)-based path computation model forMultiMulti- Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineered Label Switched Paths(TE-LSPs).(TE LSPs). The model allows for the separation of the PCE from a Path Computation Client (PCC) (also referred to as a non co-located PCE) and allows for cooperation betweenPCEs.PCEs (where one PCE acts as a PCC to make requests of the other PCE). This relies on a communication protocol between PCC and PCE, and also between PCEs. The requirements for such a communication protocol can be found in[RFC4657][RFC4657], and the communication protocol is defined in [PCEP]. The PCE architecture requires that a PCC be aware of the location of one or more PCEs in its domain, andalso potentiallyalso, potentially, ofsomePCEs in other domains,e.g.e.g., in the case of inter-domain TE LSP computation. A network may contain a large number ofPCEsPCEs, each with potentially distinct capabilities. In such a context it is highly desirable to have a mechanism for automatic and dynamic PCEdiscovery, whichdiscovery that allows PCCs to automatically discover a set ofPCEs,PCEs along with additional information about each PCE that may berequired for theused by a PCC to perform PCE selection. Additionally, it is valuable for a PCC to dynamically detect newPCEsPCEs, failed PCEs, or any modificationofto the PCE information. Detailed requirements for such a PCE discovery mechanism are provided in [RFC4674].Moreover, it may also be useful to discover when a PCE experiences processing overload and when it exits such a state, in order for the PCCs to take some appropriate actions (e.g. redirect their requests to another PCE).Note that the PCE selection algorithm applied by a PCC is out of the scope of this document. When PCCs are LSRs participating in the IGP (OSPF, IS-IS), and PCEs are either LSRs or servers also participating in the IGP, an effective mechanism for PCE discovery within an IGP routing domain consists of utilizing IGP advertisements. This document definesIS-ISextensions to IS-IS [ISO] to allow a PCE in an IS-IS routing domain to advertise its location along with some information useful to a PCC for PCE selection, so as to satisfy dynamic PCE discovery requirements set forth in [RFC4674].This document also defines extensions allowing a PCE in an IS-IS routing domain to advertise its processing overload state.Generic capability advertisement mechanisms for IS-IS are defined in [IS-IS-CAP]. These allow a router to advertise its capabilities within an IS-IS area or an entire IS-IS routing domain. This document leverages this generic capability advertisement mechanism to fully satisfy theaforementioneddynamic PCE discovery requirements. This document defines a new sub-TLV (named the PCE Discovery (PCED)) to be carried within the IS-IS Router Capability TLV ([IS-IS-CAP]). The PCE information advertised is detailed insectionSection 3. Protocol extensions and procedures are defined insectionSections 4 and 5. The IS-IS extensions defined in this document allow for PCE discovery within an IS-ISRoutingrouting domain. Solutions for PCE discovery across AS boundaries are beyond the scope of this document, and for further study. This document defines a set of sub-TLVs that are nested within each other. When the degree of nesting TLVs is 2 (a TLV is carried within another TLV) the TLV carried within a TLV is called a sub-TLV. Strictly speaking, when the degree of nesting is 3, a subsub-TLV is carried within a sub-TLV that is itself carried within a TLV. For the sake of terminology simplicity,we refer to sub-TLV,a TLV carried withinaanother TLV is called a sub-TLV regardless of the degree of nesting. 3. Overview 3.1. PCEInformation The PCE information advertised via IS-IS falls into two categories: PCE Discovery information and PCE Overload information. 3.1.1. PCEDiscovery Information The PCEDiscoverydiscovery information iscomprisedcomposed of: - The PCE location: an IPv4 and/or IPv6 address that is used to reach the PCE. It is RECOMMENDED to use an address that is alwaysreachable;reachable if there is any connectivity to the PCE; - The PCE path computation scope(i.e.(i.e., intra-layer, inter-area, inter-AS,inter- layer);or inter-layer); - The set of one or more PCE-Domain(s) into which the PCE has visibility and for which the PCE can compute paths; - The set of zero, one or more neighbor PCE-Domain(s)towardstoward whichathe PCE can compute paths; - A set of communication capabilities(e.g.(e.g., support for request prioritization) and pathcomputation specificcomputation-specific capabilities(e.g.(e.g., supported constraints). PCEDiscoverydiscovery information is by nature fairly static and does not change with PCE activity. Changes in PCEDiscoverydiscovery information may occur as a result of PCE configuration updates, PCE deployment/activation, PCE deactivation/suppression, or PCE failure. Hence, this information is not expected to changefrequently 3.1.2. PCE Overload Information The PCE Overload Information is optional and can be used to report a PCE's overload state in order to discourage the PCCs to send new path computation requests. A PCE may decide to clear the overload state according to local implementation triggers (e.g. CPU utilization, average queue length below some pre-defined thresholds). The rate at which a PCE status change is advertised MUST NOT impact by any means the IGP scalability. Particular attention should be given on procedures to avoid state oscillations.frequently. 3.2. Flooding Scope The flooding scope for PCE information advertised through IS-IS can be a single L1 area,aan L1 area and the L2 sub-domain, or the entire IS-IS routing domain. 4. The IS-IS PCED Sub-TLV The IS-IS PCED sub-TLVis made ofcontains a non-ordered set ofnon orderedsub-TLVs. The format of the IS-IS PCED sub-TLV and its sub-TLVs is identical to the TLV format used by the Traffic Engineering Extensions to IS-IS [RFC3784]. That is, the TLV is comprised of 1 octet for the type, 1 octet specifying the TLV length, and a value field. The Length field defines the length of the value portion in octets. The IS-IS PCED sub-TLV has the following format: TYPE: To be assigned by IANA (suggested value = 5) LENGTH: Variable VALUE: set of sub-TLVsSixFive sub-TLVs are defined: Sub-TLV type Length Name 1 variable PCE-ADDRESS sub-TLV 2 3 PATH-SCOPE sub-TLV 3 variable PCE-DOMAIN sub-TLV 4 variable NEIG-PCE-DOMAIN sub-TLV 5 variable PCE-CAP-FLAGS sub-TLV6 1 OVERLOAD sub-TLVThe PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within the PCED sub-TLV. The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional. They MAY be present in the PCED sub-TLV to facilitate selection of inter- domain PCEs. The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED sub-TLV to facilitate the PCE selection process.The OVERLOAD sub-TLV is optional and MAY be present in the PCED sub- TLV, to indicate a PCE's processing overload state.Anynon recognizedunrecognized sub-TLV MUST be silently ignored. The PCED sub-TLV is carried within an IS-IS CAPABILITY TLV defined in [IS-IS-CAP]. No additional sub-TLVs will be added to the PCED TLV in the future. If a future application requiresadvertisingthe advertisement of additional PCE information in IS-IS, this will not be carried in the CAPABILITY TLV. The following sub-sections describe the sub-TLVs which may be carried within the PCED sub-TLV. 4.1. PCE-ADDRESS Sub-TLV The PCE-ADDRESS sub-TLV specifiesthean IP address that can be used to reach the PCE. It is RECOMMENDED to make use of an address that is always reachable, provided the PCE isalive.alive and reachable. The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the PCED sub-TLV. It MAY appear twice, when the PCE has both an IPv4 and IPv6 address. It MUST NOT appear more than once for the same address type. If it appears more than once only the first occurrenceMUST beis processed andotherany others MUST be ignored. The PCE-ADDRESS sub-TLV has the following format: TYPE: 1 LENGTH: 5 for an IPv4 addressandor 17 for an IPv6 address VALUE: This comprises one octet indicating the address-type and 4 or 16 octets encoding the IPv4 or IPv6 address to be used to reach the PCE. Address-type: 1 IPv4 2 IPv6 4.2. The PATH-SCOPE Sub-TLV The PATH-SCOPE sub-TLV indicates the PCE path computation scope, which refers to the PCE's ability to compute or take part in the computation of paths for intra-area, inter-area, inter-AS, orinter-layer_TE LSP(s).inter- layer_TE LSPs. The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the PCED sub-TLV. There MUST be exactly one instance of the PATH-SCOPE sub-TLV within each PCED sub-TLV. If it appears more than once only the first occurrenceMUST beis processed andotherany others MUST be ignored. The PATH-SCOPE sub-TLV contains a set of bit flags indicating the supported path scopes, and four fields indicating PCE preferences. The PATH-SCOPE sub-TLV has the following format: TYPE: 2 LENGTH: 3 VALUE: This comprises a one-octet flags field where each flag represents a supported path scope, followed by a 2-octets preferences field indicating PCE preferences. Here is the structure of thebits flag:flags field: +-+-+-+-+-+-+-+-+ |0|1|2|3|4|5|Res| +-+-+-+-+-+-+-+-+ Bit Path Scope 0 L bit: Can compute intra-area path 1 R bit: Can act as PCE for inter-area TE LSP computation 2 Rd bit: Can act as a default PCE for inter-area TE LSP computation 3 S bit: Can act as PCE for inter-AS TE LSP computation 4 Sd bit: Can act as a default PCE for inter-AS TE LSPs computation 5 Y bit: Can compute or take part into the computation of paths across layers 6-7 Reserved for futureusage.use. Here is the structure of the preferences field +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |PrefL|PrefR|PrefS|PrefY| Res | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Res: Reserved for future usage.Pref-LPrefL field: PCE's preference for intra-area TE LSPs computation.Pref-RPrefR field: PCE's preference for inter-area TE LSPs computation.Pref-SPrefS field: PCE's preference for inter-AS TE LSPs computation. Pref-Y field: PCE's preference for inter-layer TE LSPs computation. Res: Reserved for futureusage.use. The L, R, S, and Y bits are set when the PCE can act as a PCE for intra-area, inter-area, inter-AS or inter-layer TE LSPs computation respectively. These bits are non-exclusive. Whensetset, the Rd bit indicates that the PCE can act as a default PCE for inter-area TE LSP computation (thatisis, the PCE can compute a pathtowardstoward any neighbor area). Similarly, when set, the Sd bit indicates that the PCE can act as a default PCE for inter-AS TE LSP computation (the PCE can compute a pathtowardstoward any neighbor AS). When the Rd and Sd bit are set, the PCED sub-TLV MUST NOT containanya NEIG-PCE-DOMAIN sub-TLV (see4.1.4).Section 4.4). When theR/SR bit iscleared,clear, theRd/SdRd bit SHOULD beclearedclear on transmission and MUST beignored.ignored on receipt. When the S bit is clear, the Sd bit SHOULD be clear on transmission and MUST be ignored on receipt. The PrefL, PrefR, PrefS and PrefY fields are each three bits long and allow the PCE to specify a preference for each computation scope, where 7 reflects the highest preference. Suchpreferencepreferences can be used for weighted load balancing of path computation requests. An operator may decide to configure a preference for each computation scopetoat each PCE so as to balance the path computation load among them. The algorithms used by a PCC to balance its path computation requests according to such PCEpreferencepreferences are out of the scope of this document andisare a matter for local ornetwork widenetwork-wide policy. The same ordistinctdifferent preferences may be used for eachscopes.scope. Forinstanceinstance, an operator that wants a PCE capable of both inter-area and inter-AS computation to beused preferablypreferred for use for inter-AScomputationcomputations may configureaPrefS higher thanthePrefR. When theL bit, R bit, S bitL, R, S, or Ybitbits areclearedclear, the PrefL, PrefR, PrefS, PrefY fields SHOULD respectively be set to 0 on transmission and MUST beignored.ignored on receipt. Both reserved fields SHOULD be set to zero on transmission and MUST be ignored on receipt. 4.3. PCE-DOMAIN Sub-TLV The PCE-DOMAIN sub-TLV specifies a PCE-Domain (areas and/or ASes) where the PCE has topology visibility and through which the PCE can compute paths. The PCE-DOMAIN sub-TLVMAYSHOULD be present when PCE-Domains for which the PCE can operate cannot be inferred by other IGP information, for instance when the PCE is inter-domain capable(i.e.(i.e., when the R bit or S bit is set) and the flooding scope is the entire routing domain (seesectionSection 5 for a discussion of how the flooding scope is set and interpreted). A PCED sub-TLVMAYmay include multiple PCE-DOMAIN sub-TLVs when the PCE has visibilityininto multiple PCE-Domains. The PCE-DOMAIN sub-TLV has the following format: TYPE: 3 LENGTH: Variable VALUE: This iscomprisedcomposed of one octet indicating the domain-type (area ID or AS Number) and a variable length IS-IS area ID or a 32 bits AS number, identifying a PCE-domain where the PCE hasvisibility.visibility and can compute paths. Two domain types are defined: 1 Area ID 2 AS Number The Area ID is the area address as defined in [ISO]. When the AS number is coded in twooctets (which is the current defined format as the time of writing this document),octets, the AS Number field MUST have itsleftfirst two octets set to 0. 4.4. NEIG-PCE-DOMAIN Sub-TLV The NEIG-PCE-DOMAIN sub-TLV specifies aneighbourneighbor PCE-domain(area,(area or AS) toward which a PCE can compute paths. It means that the PCE can take part in the computation of inter-domain TE LSPswhose path transitswith paths that transit thisneighbourneighbor PCE-domain. A PCED sub-TLVMAYmay include several NEIG-PCE-DOMAIN sub-TLVs when the PCE can compute paths towards several neighbour PCE-domains. The NEIG-PCE-DOMAIN sub-TLV has the same format as the PCE-DOMAIN sub-TLV: TYPE: 4 LENGTH: Variable VALUE: This comprises one octet indicating the domain-type (area ID or AS Number) and a variable length IS-IS area ID or a 32 bits AS number, identifying a PCE-domaintowardstoward which the PCE can compute paths. Two domain types are defined: 1 Area ID 2 AS Number The Area ID is the area address as defined in [ISO]. When the AS number is coded in twooctets (which is the current defined format as the time of writing this document),octets, the AS Number field MUST have its first two octets set to 0. The NEIG-PCE-DOMAIN sub-TLV MUST be present at least once with domain type 1 if the R bit is set and the Rd bit iscleared, and/or,clear, and MUST be present at least once with domain type 2 if the S bit is set and the Sd bit iscleared.clear. 4.5. PCE-CAP-FLAGS Sub-TLV The PCE-CAP-FLAGs sub-TLV is an optional sub-TLV used to indicate PCEP related capabilities. It MAY be present within the PCED sub-TLV. It MUST NOT be present more than once. If it appears more than once only the first occurrenceMUST beis processed andotherany others MUST be ignored. The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array of units of 32bit flagsbit-flags numbered from the most significant as bit zero, where each bit represents one PCE capability. The PCE-CAP-FLAGS sub-TLV has the following format: TYPE: 5 LENGTH: Multiple of 4 VALUE: This contains an array of units of 32 bit flags numbered from the most significant as bit zero, where each bit represents one PCE capability. The PCE capability registry is managed by IANA, it is common with OSPF and defined in [PCED-OSPF]. Reserved bits SHOULD be set to zero on transmission and MUST be ignored on receipt.4.6. The OVERLOAD Sub-TLV The OVERLOAD sub-TLV is used to indicate that a PCE is experiencing a processing overload state and may optionally include expected PCE overload duration. The OVERLOAD sub-TLV is optional, it MAY be carried within the PCED sub-TLV. It MUST NOT be present more than once. If it appears more than once only the first occurrence MUST be processed and other MUST be ignored. The format of the OVERLOAD sub-TLV is as follows: TYPE: 6 LENGTH: 1 VALUE: This comprises a one octet of bit flags indicating the overload status. Currently only the first flag is defined. Here is the TLV structure +-+-+-+-+-+-+-+-+ |C| Reserved| +-+-+-+-+-+-+-+-+ Value -C bit: When set this indicates that the PCE is overloaded and cannot accept any new request. When cleared this indicates that the PCE is not overloaded and can accept new requests.5. Elements of Procedure The PCED sub-TLV is advertised within an IS-IS Router Capability TLV defined in [IS-IS-CAP]. As such, elements of procedures are inherited from those defined in [IS-IS-CAP]. The flooding scope is controlled by the S flag in the IS-IS Router Capability TLV (see [IS-IS-CAP]). When the scope of the PCED sub-TLV is area local it MUST be carried within an IS-IS Router Capability TLV having the S bit cleared. When the scope of the PCED sub-TLV is the entire IS-IS routing domain, it MUST be carried within an IS-IS Router Capability TLV having the S bit set. Note that when only the L bit of the PATH-SCOPE sub-TLV is set, the flooding scope MUST be area local. Note that a L1L2 node may includeboth in its L1 and L2 LSPsa PCED TLV in a Router Capability TLV with the S bitcleared.cleared in both in its L1 and L2 LSPs. This allowsrestrictingthe flooding scope to be restricted to the L1 area and the L2sub-domain. An IS-IS router MUST originate a new IS-IS LSP whenever there is a change in a PCED TLV associated with a PCE it advertises.sub- domain. Whenathe PCE function is deactivated, the IS-ISRouterspeaker advertising this PCE MUST originate a new IS-IS LSP that no longer includes the corresponding PCED TLV. The PCEaddress(s), i.e.address (i.e., theaddress(s)address indicated within the PCE ADDRESSsub-TLV,sub-TLV) SHOULD be reachable via someprefix(es)prefixes advertised byIS-IS; thisIS-IS. This allowsspeeding upthe detection of a PCEfailure. Note that whenfailure to be sped up. When the PCE address is no longer reachable,this means thatthe PCE node hasfailed orfailed, has been torn down, orthatthere is no longer IP connectivity to the PCE node. A change inPCEDinformation in the PCED sub-TLV MUSTnotNOT trigger any SPF computation at a receiving router. The way PCEs determine the information they advertise is out of the scope of this document. Some information may be configured (e.g., address, preferences, scope) and other information may be automatically determined by the PCE (e.g. areas of visibility).5.1. OVERLOAD Sub-TLV Specific Procedures When a PCE enters into an overload state, the conditions of which are implementation dependent, a new IS-IS LSP with an OVERLOAD sub-TLV with the C bit set MAY be generated. When a PCE exists from an overload state, the conditions of which are implementation dependent (e.g. CPU utilization, average queue length below some pre-defined thresholds), a new IS-IS LSP with an OVERLOAD sub-TLV with the C bit cleared SHOULD be generated, if an OVERLOAD sub-TLV with the C bit set had previously been generated. A PCE implementation supporting the IS-IS extensions defined in this document SHOULD support an appropriate dampening algorithm so as to dampen flooding of PCE Overload information in order to not impact the IS-IS scalability. It is RECOMMENDED to introduce some hysteresis for overload state transition, so as to avoid state oscillations that may impact IS-IS performance. For instance two thresholds MAY be configured: an upper-threshold and a lower-threshold. An LSR enters the overload state when the CPU load reaches the upper threshold and leaves the overload state when the CPU load goes under the lower threshold. Upon receipt of an updated OVERLOAD sub-TLV a PCC should take appropriate actions. In particular, the PCC SHOULD stop sending requests to an overloaded PCE, and SHOULD gradually start sending again requests to a PCE that is no longer overloaded.6. Backward Compatibility The PCED sub-TLV defined in this document does not introduce any interoperability issues. An IS-IS router not supporting the PCED sub-TLV will just silently ignore theTLVsub-TLV as specified in [IS-IS-CAP]. 7. IANA ConsiderationsOnceIANA has defined a registry for the sub-TLVs carried in the IS-IS Router Capabilitysub-TLVs,sub-TLVs defined in[IS-IS-CAP] has been assigned,[IS-IS-CAP]. IANAwillis requested to assign a new sub-TLVcode- pointcode-point for the PCED sub-TLV carried within the Router CapabilityTLV.sub-TLV. Value Sub-TLV References ----- -------- ---------- 5 PCED sub-TLV (this document) 8. Security Considerations This document defines IS-IS extensions for PCE discovery within an administrative domain. Hence the security of the PCE discovery relies on the security of IS-IS. Mechanisms defined to ensure authenticity and integrity of IS-IS LSPs [RFC3567], and their TLVs, can be used to secure the PCED sub-TLV as well. IS-IS provides no encryption mechanism for protecting the privacy of LSPs, and in particular the privacy of the PCE discovery information. 9. Manageability Considerations Manageability considerations for PCE Discovery are addressed insectionSection 4.10 of [RFC4674]. 9.1. Control of Policy and Functions Requirementsonfor the configuration of PCE discovery parameters on PCCs and PCEs are discussed insectionSection 4.10.1 of [RFC4674].Particularly,In particular, a PCE implementation SHOULD allowconfiguringthe following parameters to be configured on the PCE: -The PCE IPv4/IPv6 address(es) (seesection 4.1.1)Section 4.1) -The PCE Scope, including the inter-domain functions (inter- area, inter-AS, inter-layer), the preferences, and whether the PCE can act as default PCE (seesection 4.1.2)Section 4.2) -The PCE domains (seesection 4.1.3)Section 4.3) -The neighbour PCE domains (seesection 4.1.4)Section 4.4) -The PCE capabilities (seesection 4.1.5)Section 4.5) 9.2. Information and Data Model A MIB module for PCE Discovery is defined in [PCED-MIB]. 9.3. Liveness Detection and Monitoring PCE Discovery Protocol liveness detection relies upon IS-IS liveness detection. IS-IS already includes a liveness detection mechanism (Hello PDUs), and PCE discovery does not require additional capabilities. Procedures defined insection 5.1Section 5 allow a PCCdetectingto detect when a PCE has been deactivated, or is no longer reachable. 9.4. Verify Correct Operations The correlation of information advertised against information received can be achieved by comparing thePCEDinformation in thePCC and inPCED sub-TLV received by thePCE, which isPCC with that storedinat the PCE using the PCED MIB [PCED-MIB]. The number of dropped, corrupt, and rejected information elements arestored inavailable through the PCED MIB. 9.5. Requirements on Other Protocols and Functional Components The IS-IS extensions defined in this document do not imply any requirement on other protocols. 9.6. Impact on Network Operations Frequent changes in PCEinformation, and particularlyinformation advertised inPCE overload information,the PCED sub-TLV may have a significant impact on IS-IS and might destabilize the operation of the network by causing the PCCs to swap between PCEs. As discussed insection 5.1, a PCE implementation SHOULD support an appropriate dampening algorithm so as to dampen IS-IS flooding in order to not impact the IS-IS scalability. Also, as discussed in sectionSection 4.10.4 of [RFC4674], it MUST be possible to apply at least the following controls: - Configurable limit on the rate of announcement of changed parameters at a PCE. - Control of the impact on PCCs such as throughdiscovery messages rate-limiting.rate-limiting the processing of PCED sub-TLVs. - Configurable control of triggers that cause a PCC to swap to another PCE. 10. Acknowledgments We would like to thank Lucy Wong, Adrian Farrel, Les Ginsberg, Mike Shand, Lou Berger, and David Ward, for their useful comments and suggestions. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [ISO] "Intermediate System to Intermediate System Intra-Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service(ISO 8473)", ISO DP 10589, February 1990.ISO/IEC 10589:2002 Second Edition. [RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic Engineering", RFC 3784, June 2004. [IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising router information", draft-ietf-isis-caps, work in progress. [RFC3567] Li, T. and R. Atkinson, "Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, July 2003. [PCED-OSPF] Le Roux, Vasseur, et al. "OSPF protocol extensions for Path Computation Element (PCE) Discovery", draft-ietf-pce-disco- proto-ospf, work in progress. 11.2. Informative References [RFC4657] Ash, J., Le Roux, J.L., "PCE Communication Protocol Generic Requirements", RFC4657, September 2006. [PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE) communication Protocol (PCEP) - Version 1", draft-ietf-pce-pcep, work in progress. [PCED-MIB] Stephan, E., "Definitions of Managed Objects for Path Computation Element Discovery", draft-ietf-pce-disc-mib, work in progress. [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation Element (PCE)-based Architecture", RFC4655, august 2006. [RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery", RFC4674, October 2006. 12. Editors' Addresses: Jean-Louis Le Roux (Editor) France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex FRANCE Email: jeanlouis.leroux@orange-ftgroup.com Jean-Philippe Vasseur (Editor) Cisco Systems, Inc. 1414 Massachusetts avenue Boxborough , MA - 01719 USA Email: jpv@cisco.com 13. Contributors' Adresses: Yuichi Ikejiri NTT Communications Corporation 1-1-6, Uchisaiwai-cho, Chiyoda-ku Tokyo 100-8019 JAPAN Email: y.ikejiri@ntt.com Raymond Zhang BT Infonet 2160 E. Grand Ave. El Segundo, CA 90025 USA Email: raymond_zhang@bt-infonet.com 14. 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. 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