Network Working Group J.L. Le Roux (Editor) Internet Draft France Telecom Category: Standard Track Expires: March 2007 J.P. Vasseur (Editor) Cisco System Inc. Yuichi Ikejiri NTT Communications Raymond Zhang BT Infonet September 2006 IS-IS protocol extensions for Path Computation Element (PCE) Discovery draft-ietf-pce-disco-proto-isis-00.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 There are various circumstances in which it is highly desirable for a Path Computation Client (PCC) to be able to dynamically and automatically discover a set of Path Computation Element(s) (PCE), along with some of information that can be used for PCE selection. When the PCE is an LSR participating to the IGP, or even a server participating passively to the IGP, a simple and efficient way for Le Roux, Vasseur et al. ISIS extensions for PCE Discovery [Page 1] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 PCE discovery consists of relying on IGP flooding. For that purpose this document defines ISIS extensions for the advertisement of PCE Discovery information within an ISIS area or within the entire ISIS 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 RFC-2119. Table of Contents 1. Note........................................................3 2. Terminology.................................................3 3. Introduction................................................4 4. Overview....................................................5 4.1. PCE Information.............................................5 4.1.1. PCE Discovery Information...................................5 4.1.2. PCE Status Information......................................6 4.2. Flooding scope..............................................6 5. ISIS extensions.............................................6 5.1. IS-IS PCED TLV format.......................................6 5.1.1. PCE-ADDRESS sub-TLV.........................................7 5.1.2. The PATH-SCOPE sub-TLV......................................7 5.1.3. PCE-DOMAINS sub-TLV.........................................9 5.1.3.1. Area ID DOMAIN sub-TLV...................................10 5.1.3.2. AS Number DOMAIN sub-TLV.................................10 5.1.4. PCE-DEST-DOMAINS sub-TLV...................................10 5.1.5. GENERAL-CAP sub-TLV........................................11 5.1.6. The PATH-COMP-CAP sub-TLV..................................12 5.1.6.1. Objective Functions sub-TLV..............................13 5.1.6.2. Opaque Objective Function sub-TLV........................13 5.1.6.3. Switch Caps sub-TLV......................................14 5.2. The ISIS PCES TLV..........................................14 5.2.1. The CONGESTION sub-TLV.....................................15 6. Elements of Procedure......................................16 6.1.1. PCES TLV specific procedure................................16 7. Backward compatibility.....................................17 8. IANA considerations........................................17 8.1. ISIS TLVs..................................................17 8.2. Capability bits............................................18 9. Security Considerations....................................19 10. References.................................................19 10.1. Normative references.......................................19 10.2. Informative references.....................................19 11. Authors' Addresses:........................................20 12. Intellectual Property Statement............................20 Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 2] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 1. Note This document specifies sub-TLVs to be carried within the ISIS Router Capability TLV ([ISIS-CAP]). Because this document does not introduce any new ISIS element of procedure it will be discussed within the PCE Working Group with a review of the ISIS Working Group. 2. Terminology Terminology used in this document ABR: IGP Area Border Router (L1L2 router). AS: Autonomous System. ASBR: AS Border Router. Domain: any collection of network elements within a common sphere of address management or path computational responsibility. Examples of domains include IGP areas and Autonomous Systems. Intra-area TE LSP: A TE LSP whose path does not cross IGP area boundaries. Intra-AS TE LSP: A TE LSP whose path does not cross AS boundaries. Inter-area TE LSP: A TE LSP whose path transits through two or more IGP areas. Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or more ASes or sub-ASes (BGP confederations). LSR: Label Switch Router. PCC: Path Computation Client: any client application requesting a path computation to be performed by a Path Computation Element. 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. PCECP: Path Computation Element Communication Protocol. TE LSP: Traffic Engineered Label Switched Path. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 3] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 3. Introduction [RFC4655] describes the motivations and architecture for a PCE-based path computation model for MPLS and GMPLS TE LSPs. The model allows the separation of PCE from PCC (also referred to as non co-located PCE) and allows cooperation between PCEs. This relies on a communication protocol between PCC and PCE, and between PCEs. The requirements for such communication protocol can be found in [PCECP- REQ] and the communication protocol is defined in [PCEP]. The PCE architecture requires, of course, that a PCC be aware of the location of one or more PCEs in its domain, and also potentially of some PCEs in other domains, e.g. in case of inter-domain TE LSP computation. A network may comprise a large number of PCEs with potentially distinct capabilities. In such context it would be highly desirable to have a mechanism for automatic and dynamic PCE discovery, which would allow PCCs to automatically discover a set of PCEs, along with additional information required for PCE selection, and to dynamically detect new PCEs or any modification of PCE information. Detailed requirements for such a PCE discovery mechanism are described in [PCE-DISC-REQ]. Moreover, it may also be useful to discover when a PCE experiences some processing congestion state and exits such state, in order for the PCCs to take some appropriate actions (e.g. redirect to another PCE). Note that the PCE selection algorithm is out of the scope of this document. When PCCs are LSRs participating to the IGP (OSPF, ISIS), and PCEs are LSRs or a servers also participating to the IGP, an efficient mechanism for PCE discovery within thisan IGP routing domain consists of relying on IGP advertisements. This document defines ISIS extensions allowing a PCE participating to the ISIS routing to advertise its location along with some information useful for PCE selection, so as to satisfy dynamic PCE discovery requirements set forth in [PCE-DISC-REQ]. This document also defines extensions allowing a PCE participating to the ISIS routing to advertise its potential processing congestion state. Generic capability mechanisms for ISIS have been defined in [ISIS- CAP] the purpose of which is to allow a router to advertise its capability within an ISIS area or an entire ISIS routing domain. Such ISIS extensions fully satisfy the aforementioned dynamic PCE discovery requirements. This document defines two new sub-TLVs (named the PCE Discovery (PCED) TLV and the PCE Status (PCES) TLV) for ISIS, to be carried within the ISIS Capability TLV ([ISIS-CAP]). The PCE information Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 4] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 advertised is detailed in section 4. Protocol extensions and procedures are defined in section 5 and 6. This document does not define any new ISIS element of procedure but how the procedures defined in [ISIS-CAP] should be used. The routing extensions defined in this document allow for PCE discovery within an ISIS Routing domain. Solutions for PCE discovery across AS boundaries are beyond the scope of this document, and for further study. Similar extensions to OSPF for PCE discovery can be found in [OSPF- PCE-DISCO]. 4. Overview 4.1. PCE Information PCE information advertised within ISIS includes PCE Discovery Information and PCE Status information. 4.1.1. PCE Discovery Information The PCE Discovery information is comprised of: - The PCE location: This an IPv4 and/or IPv6 address that must be used to reach the PCE. It is RECOMMENDED to use addresses always reachable; - The PCE inter-domain functions: this refers to the PCE path computation scope (i.e. inter-area, inter-AS, inter-layer…); - The PCE domain(s): This is the set of one or more domain(s) where the PCE has visibility and can compute paths; - The PCE Destination domain(s): This is the set of one or more destination domain(s) towards which a PCE can compute paths; - A set of general PCECP capabilities (e.g. support for request prioritization) and path computation specific capabilities (e.g. supported constraints, supported objective functions). It may also contain optional elements to describe more complex capabilities. PCE Discovery information is by nature a static information that does not change with PCE activity. Changes in PCE Discovery 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 change frequently. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 5] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 4.1.2. PCE Status Information The PCE Status is optional information that can be used to report a PCE processing congested state along with an estimated congestion duration. This is a dynamic information, which may change with PCE activity. Procedures for a PCE to move from a processing congested state to a non congested state are beyond the scope of this document, but the rate at which a PCE Status change is advertised MUST not impact by any mean the IGP scalability. Particular attention should be given on procedures to avoid state oscillations. 4.2. Flooding scope The flooding scope for PCE Discovery Information can be limited to one or more ISIS areas the PCE belongs to or can be extended across the entire ISIS routing domain. Note that some PCEs may belong to multiple areas, in which case the flooding scope may comprise these areas. This could be the case of an ABR for instance advertising its PCE information within the backbone area and/or a subset of its attached IGP area(s). 5. ISIS extensions 5.1. IS-IS PCED TLV format The IS-IS PCED TLV is made of various non ordered sub-TLVs. The format of the IS-IS PCED TLV and its sub-TLVs is the same as the TLV format used by the Traffic Engineering Extensions to IS-IS [ISIS- TE]. That is, the TLV is composed of 1 octet for the type, 1 octet specifying the TLV length and a value field. The IS-IS PCED TLV has the following format: TYPE: To be assigned by IANA LENGTH: Variable VALUE: set of sub-TLVs Sub-TLVs types are under IANA control. Currently five sub-TLVs are defined (suggested type values to be assigned by IANA): Sub-TLV type Length Name 1 variable PCE-ADDRESS sub-TLV 2 3 PATH-SCOPE sub-TLV 3 variable PCE-DOMAINS sub-TLV 4 variable PCE-DEST-DOMAINS sub-TLV 5 variable GENERAL-CAP sub-TLV 6 variable PATH-COMP-CAP sub-TLV Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 6] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 The sub-TLVs PCE-ADDRESS and PATH-SCOPE MUST always be present within the PCED TLV. The sub-TLVs PCE-DOMAINS and PCE-DEST-DOMAINS are optional. They MAY be present in some specific inter-domain cases. The sub-TLVs GENERAL-CAP and PATH-COMP-CAP are optional and MAY be present in the PCED TLV to facilitate the PCE selection process. Any non recognized sub-TLV MUST be silently ignored. Additional sub-TLVs could be added in the future to advertise additional PCE information. The PCED TLV is carried within an ISIS CAPABILITY TLV defined in [ISIS-CAP], whose S bit is determined by the desired flooding scope. 5.1.1. PCE-ADDRESS sub-TLV The PCE-ADDRESS sub-TLV specifies the IP address that MUST be used to reach the PCE. It is RECOMMENDED to make use of an address that is always reachable, provided the PCE is alive. The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the PCED TLV. It MAY appear twice, when the PCE has both an IPv4 and IPv6 address. It MUST not appear more than twice. The PCE-ADDRESS sub-TLV has the following format: TYPE: To be assigned by IANA (Suggested value =1) LENGTH: 5 for IPv4 address and 17 for 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 5.1.2. The PATH-SCOPE sub-TLV The PATH-SCOPE sub-TLV indicates the PCE path computation scope which refers to the PCE ability to compute or take part into the computation of intra-area, inter-area, inter-AS or inter-layer_TE LSP(s). Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 7] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the PCED TLV. There MUST be exactly one PATH-SCOPE sub-TLV within each PCED TLV. The PATH-SCOPE sub-TLV contains a set of bit flags indicating the supported path scopes (intra-area, inter-area, inter-AS, inter-layer) and four fields indicating PCE preferences. The PATH-SCOPE sub-TLV has the following format: TYPE: To be assigned by IANA (Suggested value =2) LENGTH: 3 VALUE: This comprises a one-byte flag of bits where each bit represents a supported path scope, followed by a 2-bytes preferences field indicating PCE preferences. Here is the structure of the bits flag: +-+-+-+-+-+-+-+-+ |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 LSPs computation 2 Rd bit: Can act as a default PCE for inter-area TE LSPs computation 3 S bit: Can act as PCE for inter-AS TE LSPs 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 future usage. Here is the structure of the preferences field +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |PrefL|PrefR|PrefS|PrefY| Res | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Pref-L field: PCE's preference for intra-area TE LSPs computation. Pref-R field: PCE’s preference for inter-area TE LSPs computation. Pref-S field: PCE’s preference for inter-AS TE LSPs computation. Pref-Y field: PCE's preference for inter-layer TE LSPs computation. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 8] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 Res: Reserved for future usage. The bits L, R, S and Y bits are set when the PCE can act as a PCE for intra-area, inter-area, inter-AS and inter-layer TE LSPs computation respectively. These bits are non mutually exclusive. When set the Rd bit indicates that the PCE can act as a default PCE for inter-area TE LSPs computation (the PCE can compute path for any destination area). Similarly, when set the Sd bit indicates that the PCE can act as a default PCE for inter-AS TE LSPs computation (the PCE can compute path for any destination AS). When the Rd bit is set, the PCE-DEST-DOMAIN TLV (see 5.1.4) does not contain any Area ID DOMAIN sub-TLV. Similarly, when the Sd bit is set, the PCE-DEST-DOMAIN TLV does not contain any AS DOMAIN sub-TLV. The PrefL, PrefR, PrefS and PrefY fields are 3-bit long and allow the PCE to specify a preference for each computation scope, where 7 reflects the highest preference. Such preference can be used for weighted load balancing of requests. An operator may decide to configure a preference to each PCE so as to balance the path computation load among them, with respect to their respective CPU capacity. The algorithms used by a PCC to balance its path computation requests according to such PCE’s preference are out of the scope of this document. Same or distinct preferences may be used for different scopes. For instance an operator that wants a PCE capable of both inter-area and inter-AS computation to be used preferably for inter-AS computation may configure a PrefS higher than the PrefR. When the L bit, R bit, S or Y bit are cleared the PrefL, PrefR, PrefS, PrefY fields MUST respectively be set to 0. 5.1.3. PCE-DOMAINS sub-TLV The PCE-DOMAINS sub-TLV specifies the set of domains (areas or AS) where the PCE has topology visibility and can compute paths. It contains a set of one or more sub-TLVs where each sub-TLV identifies a domain. The PCE-DOMAINS sub-TLV MUST be present when PCE domains cannot be inferred by other IGP information, for instance when the PCE is inter-domain capable (i.e. when the R bit or S bit is set) and the flooding scope is the entire routing domain. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 9] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 The PCE-DOMAINS sub-TLV has the following format: TYPE: To be assigned by IANA (Suggested value =2) LENGTH: Variable VALUE: This comprises a set of one or more DOMAIN sub-TLVs where each DOMAIN sub-TLV identifies a domain where the PCE has topology visibility and can compute paths DOMAIN Sub-TLVs types are under IANA control. Currently two DOMAIN sub-TLVs are defined (suggested type values to be assigned by IANA): Sub-TLV type Length Name 1 variable Area ID sub-TLV 2 variable AS number sub-TLV At least one DOMAIN sub-TLV MUST be present in the PCE-DOMAINS sub- TLV. 5.1.3.1. Area ID DOMAIN sub-TLV This sub-TLV carries an ISIS area ID. It has the following format TYPE: To be assigned by IANA (Suggested value =1) LENGTH: Variable VALUE: This comprises a variable length ISIS area ID. This is the combination of an Initial Domain Part (IDP) and High Order part of the Domain Specific part (HO-DSP) 5.1.3.2. AS Number DOMAIN sub-TLV The AS Number sub-TLV carries an AS number. It has the following format: TYPE: To be assigned by IANA (Suggested value =2) LENGTH: 4 VALUE: AS number identifying an AS. When coded on two bytes (which is the current defined format as the time of writing this document), the AS Number field MUST have its left two bytes set to 0. 5.1.4. PCE-DEST-DOMAINS sub-TLV The PCE-DEST-DOMAINS sub-TLV specifies the set of destination domains (areas, AS) toward which a PCE can compute path. It means that the PCE can compute or take part in the computation of inter-domain LSPs whose destinations are located within one of these domains. It contains a set of one or more DOMAIN sub-TLVs where each DOMAIN sub- TLV identifies a domain. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 10] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 The PCE-DEST-DOMAINS sub-TLV has the following format: TYPE: To be assigned by IANA (Suggested value =3) LENGTH: Variable VALUE: This comprises a set of one or more Area or/and AS DOMAIN sub- TLVs where each sub-TLV identifies a destination domain toward which a PCE can compute path. The PCE-DEST-DOMAINS sub-TLV MUST be present if the R bit is set and the Rd bit is cleared, and/or, if the S bit is set and the Sd bit is cleared. The PCE-DEST-DOMAINS sub-TLV MUST include at least one DOMAIN sub- TLV. It MUST include at least one area ID sub-TLV, if the R bit of the PATH-SCOPE TLV is set and the Rd bit of the PATH-SCOPE TLV is cleared. Similarly, it MUST include at least one AS number sub-TLV if the S bit of the PATH-SCOPE TLV is set and the Sd bit of the PATH- SCOPE TLV is cleared. 5.1.5. GENERAL-CAP sub-TLV The GENERAL-CAP sub-TLV is an optional TLV used to indicate PCECP related capabilities. It carries a 32-bit flag, where each bit corresponds to a general PCE capability. It MAY also include optional sub-TLVs to encode more complex capabilities. The GENERAL-CAP sub-TLV has the following format: TYPE: To be assigned by IANA (Suggested value =4) LENGTH: Variable VALUE: This comprises a 32-bit General Capabilities flag where each bit corresponds to a general PCE capability, and optional sub-TLVs that may be defined to specify more complex capabilities. Currently no sub-TLVs are defined. The following bits in the General Capabilities 32-bit flag are to be assigned by IANA: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |P|M| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 11] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 Bit Capabilities 0 P bit: Support for Request prioritization. 1 M bit: Support for multiple requests within the same request message. 2-31 Reserved for future assignments by IANA. 5.1.6. The PATH-COMP-CAP sub-TLV The PATH-COMP-CAP sub-TLV is an optional TLV used to indicate path computation specific capabilities of a PCE. It comprises a 32-bit flag, where each bit corresponds to a path computation capability. It MAY also include optional sub-TLVs to encode more complex capabilities. The PATH-COMP-CAP sub-TLV has the following format: TYPE: To be assigned by IANA (suggested value = 5) LENGTH: Variable VALUE: This comprises one 32 bit Path Computation Capabilities Flag, where each bit corresponds to a path computation capability, and optional sub-TLVs that may be defined to specify more complex capabilities. Three optional sub-TLVs are currently defined. The following bits in the Path Computation Capabilities 32-bit Flag are to be assigned by IANA: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |G|B|D|L|S|0|P| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Bit Capabilities 0 G bit: Capability to handle GMPLS link contraints 1 B bit: Capability to compute bidirectional paths 2 D bit: Capability to compute link/node/SRLG diverse paths 3 L bit: Capability to compute load-balanced paths 4 S bit: Capability to compute a set of paths in a synchronized Manner 5 O bit: Support for multiple objective functions 6 P bit: Capability to handle path constraints (e.g. max hop count, metric bound) 7-31 Reserved for future assignments by IANA. The G, B, D, L, S, O and P bits are not exclusive. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 12] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 Three optional sub-TLVs are currently defined for the PATH-COMP-CAP TLV: - The Objective Functions sub-TLV (type to be defined, suggested value =1) that carries a list of supported objective functions, where each objective function is identified by a 16 bit integer. - The Opaque Objective Function sub-TLV (type to be defined, suggested value =2) that allows the user to encode a specific objective function in any appropriate language. - The Switch Caps sub-TLV (type to be defined, suggested value =3) that carries a list of supported switching capabilities. This means that the PCE can compute paths for the listed switching capabilities. 5.1.6.1. Objective Functions sub-TLV The format of the Objective Functions sub-TLV is as follows: TYPE: To be defined by IANA (suggested value =1) LENGTH: Variable (N*2) VALUE: This comprises a set of one or more 16 bit function ids, where each function id identifies a supported objective functions. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | function 1 | function 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | function N | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Objectives functions and their identification will be defined in a separate document. The Objective Functions sub-TLV is optional. It MAY be present within the PATH-COMP-CAP TLV. When present it MUST be present only once in the PATH-COMP-CAP TLV. 5.1.6.2. Opaque Objective Function sub-TLV The format of the Opaque Objective Function sub-TLV is as follows: TYPE: To be defined by IANA (suggested value =2) LENGTH: Variable VALUE: This encodes a specific objective function in any appropriate language. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opaque objective function | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 13] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 The Opaque Objective function sub-TLV is optional. The PATH-COMP-CAP TLV MAY comprise 0, one or more Opaque Objective Functions. 5.1.6.3. Switch Caps sub-TLV The format of the Switch Caps sub-TLV is as follows: TYPE To be defined by IANA (suggested value =3) LENGTH Variable = N, where N is the number of supported switching capabilities VALUE This comprises a set of one or more 8-bit switching types, where each switching types identifies a supported switching capability. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SC type | SC type | SC type | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Switching type values are defined in [RFC4205]. The Switch Caps sub-TLV is optional. It MAY be present in the PATH-COMP- CAP TLV. When present it MUST be present only once in the PATH-COMP-CAP TLV. 5.2. The ISIS PCES TLV The ISIS PCE Status TLV (PCES TLV) carries information related to PCE processing congestion state. The PCES TLV is carried within an ISIS Capability TLV which is defined in [ISIS-CAP]. The ISIS PCES TLV has the following format: TYPE: To be assigned by IANA LENGTH: Variable VALUE: set of sub-TLVs Sub-TLVs types are under IANA control. Currently two sub-TLVs are defined (suggested type values to be assigned by IANA): Sub-TLV type Length Name 1 variable PCE-ADDRESS sub-TLV 2 3 CONGESTION sub-TLV The PCE-ADDRESS and CONGESTION sub-TLVs MUST be present once Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 14] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 in a PCES TLV. The PCE-ADDRESS sub-TLV is defined in section 6.1.1. It carries one of the PCE IP addresses and is used to identify the PCE the processing congestion state information is applied to. This is required as the PCES and PCED TLVs may be carried in separate ISIS Capability TLVs. Any non recognized sub-TLV MUST be silently ignored. Additional sub-TLVs could be added in the future to advertise additional congestion information. 5.2.1. The CONGESTION sub-TLV The CONGESTION sub-TLV is used to indicate whether a PCE experiences a processing congestion state or not along with optionally the PCE expected congestion duration. The CONGESTION sub-TLV is mandatory. It MUST be carried once within the PCES TLV. The format of the CONGESTION sub-TLV is as follows: TYPE: To be assigned by IANA (Suggested value =2) LENGTH: 3 VALUE: This comprises a one-byte flag of bits indicating the congestion status, followed by a 2-bytes field indicating the congestion duration. Here is the TLV structure +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |C| Reserved| Congestion Duration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Value -C bit: When set this indicates that the PCE experiences congestion and cannot support any new request. When cleared this indicates that the PCE does not experience congestion an can support a new request. -Congestion Duration: 2-bytes, the estimated PCE congestion duration in seconds. When C is set and the Congestion Duration field is equal to 0, this means that the Congestion Duration is unknown. When C is cleared the Congestion Duration MUST be set to 0. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 15] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 6. Elements of Procedure The PCED and PCES TLV are carried within an ISIS Capability TLV which is defined in [ISIS-CAP]. As PCES information is likely to change more frequently than the PCED information, it is RECOMMENDED to carry PCES and PCED TLVs in separate ISIS Capability TLVs, so as not to carry all PCED information each time the PCE status changes. An ISIS router MUST originate a new ISIS LSP whenever the content of any of the PCED TLV or PCES TLV changes or whenever required by the regular ISIS procedure (LSP refresh). When the scope of the PCED or PCES TLV is area local it MUST be carried within an ISIS CAPABILITY TLV having the S bit cleared. When the scope of the PCED or PCES TLV is the entire IGP domain, the PCED TLV MUST be carried within an ISIS 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 local. Note that the flooding scopes of the PCED and PCES TLVs may be distinct, in which case they are carried in distinct ISIS Capability TLVs. PCED and PCES sub-TLVs are OPTIONAL. When an ISIS LSP does not contain any PCED or PCES sub-TLV, this means that the PCE information of that node is unknown. Note that a change in PCED or PCES information MUST not trigger any SPF computation. The way PCEs retrieve their own information is out of the scope of this document. Some information may be configured (e.g. address, preferences, scope) and other information may be automatically retrieved (e.g. areas of visibility). 6.1.1. PCES TLV specific procedure When a PCE enters into a processing congestion state, the conditions of which are implementation dependent, it SHOULD originate a new ISIS LSP with a Capability TLV carrying a PCES TLV with the C bit set and optionally a non-null expected congestion duration. When a PCE leaves the processing congestion state, the conditions of which are implementation dependent, there are two cases: - If the congestion duration in the previously originated PCES TLV was null, it SHOULD originate a PCES TLV with the C bit cleared and a null congestion duration; Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 16] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 - If the congestion duration in the previously originated PCES TLV was non null, it MAY originate a PCES TLV. Note that in some particular cases it may be desired to originate a PCES TLV with the C bit cleared if the saturation duration was over estimated. The congestion duration allows reducing the amount of ISIS flooding, as only uncongested-congested state transitions are flooded. An implementation SHOULD support an appropriate dampening algorithm so as to dampen ISIS flooding in order to not impact the ISIS scalability. It is RECOMMENDED to introduce some hysteresis for congestion state transition, so as to avoid state oscillations that may impact ISIS performances. For instance two thresholds MAY be configured: A resource saturation upper-threshold and a resource saturation lower-threshold. An LSR enters the congested state when the CPU load reaches the upper threshold and leaves the congested state when the CPU load goes under the lower threshold. Upon receipt of an updated PCES TLV a PCC should take appropriate actions. In particular, the PCC SHOULD stop sending requests to a congested PCE, and SHOULD gradually start sending again requests to a no longer congested PCE. 7. Backward compatibility The PCED and PCES TLVs defined in this document do not introduce any interoperability issue. An ISIS router not supporting the PCED/PCES TLVs SHOULD just silently ignore the TLV as specified in [ISIS-CAP]. 8. IANA considerations 8.1. ISIS TLVs IANA will assign a new codepoint for the PCED TLV defined in this document and carried within the ISIS CAPABILITY TLV. IANA is requested to manage sub-TLV types for the PCED TLV. Five sub-TLVs types are defined for the PCED TLV and should be assigned by IANA: -PCE-ADDRESS sub-TLV (suggested value = 1) -PATH-SCOPE sub-TLV (suggested value = 2) -PCE-DOMAINS sub-TLV (suggested value = 3) -PCE-DEST-DOMAINS sub-TLV (suggested value = 4) -GENERAL-CAP sub-TLV (suggested value = 5) -PATH-COMP-CAP sub-TLV (suggested value = 6) Two sub-TLVs types are defined for the PCE-DOMAINS and PCE-DEST- DOMAINS TLVs and should be assigned by IANA: Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 17] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 -Area ID sub-TLV (suggested value = 1) -AS number sub-TLV (suggested value = 2) Three sub-TLV types are defined for the PATH-COMP-CAP TLV and should be assigned by IANA: -Objective Functions sub-TLV (suggested value =1) -Opaque Objective Function sub-TLV (suggested value =2) -Switch Caps sub-TLV (suggested value =3) IANA will assign a new codepoint for the ISIS PCES TLV defined in this document and carried within the ISIS CAPABILITY TLV. IANA is requested to manage sub-TLV types for the PCES TLV. Two sub- TLVs types are defined for this TLV and should be assigned by IANA: -PCE-ADDRESS sub-TLV (suggested value = 1) -CONGESTION sub-TLV (suggested value = 2) 8.2. Capability bits IANA is requested to manage the space of the General Capabilities 32-bit flag and the Path Computation Capabilities 32-bit flag defined in this document, numbering them in the usual IETF notation starting at zero and continuing through 31. New bit numbers may be allocated only by an IETF Consensus action. Each bit should be tracked with the following qualities: - Bit number - Defining RFC - Name of bit Currently two bits are defined in the General Capabilities flag. Here are the suggested values: -0: Support for Request prioritization. -1: Support for multiple messages within the same request message Currently six bits are defined in the Path Computation Capabilities flag. Here are the suggested values: -0: Capability to handle GMPLS Constraints -1: Capability to compute bidirectional paths -2: Capability to compute link/node/SRLG diverse paths -3: Capability to compute load-balanced paths -4: Capability to compute a set of paths in a synchronized Manner -5: Support for multiple objective function -6: Capability to handle path constraints (e.g. hop count, metric bound) Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 18] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 9. Security Considerations This document raises no new security issues for IS-IS. 10. References 10.1. Normative 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. [IS-IS] "Intermediate System to Intermediate System Intra-Domain Routing Exchange Protocol " ISO 10589. [IS-IS-IP] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [IS-IS-TE] 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. [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation Element (PCE)-based Architecture", RFC4655, august 2006. [PCE-DISCO-REQ] Le Roux, J.L., et al. "Requirements for PCE discovery", draft-ietf-pce-discovery-reqs, work in progress [RFC4205] Kompella, Rekhter, " IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC4205, October 2005. 10.2. Informative references [PCECP-REQ] Ash, J., Le Roux, J.L., " PCE Communication Protocol Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs, work in progress. [PCEP] Vasseur et al., “Path Computation Element (PCE) communication Protocol (PCEP) - Version 1”, draft-ietf-pce-pcep, work in progress. [OSPF-PCE-DISCO] Le Roux, Vasseur, et al., "OSPF Extensions for PCE Discovery", draft-ietf-pce-disco-proto-ospf, work in progress. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 19] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 11. Authors' Addresses: Jean-Louis Le Roux (Editor) France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex FRANCE Email: jeanlouis.leroux@orange-ft.com Jean-Philippe Vasseur (Editor) Cisco Systems, Inc. 1414 Massachusetts avenue Boxborough , MA - 01719 USA Email: jpv@cisco.com 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@infonet.com 12. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 20] Internet Draft draft-ietf-pce-disco-proto-isis-00.txt September 2006 rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Le Roux, Vasseur et al. ISIS extensions for PCE discovery [Page 21]