Network Working Group J.L. Le Roux (Editor) Internet Draft France Telecom Category: Standard Track Expires: September 2006 J.P. Vasseur (Editor) Cisco System Inc. Yuichi Ikejiri NTT Communications Raymond Zhang BT Infonet March 2006 IGP protocol extensions for Path Computation Element (PCE) Discovery draft-ietf-pce-disco-proto-igp-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 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 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 et al. IGP extensions for PCE discovery [Page 1] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 PCE discovery consists of relying on IGP flooding. For that purpose this document defines OSPF and ISIS extensions for the advertisement of PCE Discovery information within an IGP area or the entire 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. OSPF extensions.............................................6 5.1. The OSPF PCED TLV...........................................6 5.1.1. PCE-ADDRESS sub-TLV.........................................8 5.1.2. PATH-SCOPE sub-TLV..........................................8 5.1.3. PCE-DOMAINS sub-TLV........................................10 5.1.3.1. IPv4 area ID DOMAIN sub-TLV..............................11 5.1.3.2. IPv6 area ID DOMAIN sub-TLV..............................11 5.1.3.3. AS Number sub-TLV........................................12 5.1.4. PCE-DEST-DOMAINS sub-TLV...................................12 5.1.5. GENERAL-CAP sub-TLV........................................13 5.1.6. The PATH-COMP-CAP sub-TLV..................................14 5.2. The OSPF PCES TLV..........................................15 5.2.1. The CONGESTION sub-TLV.....................................16 5.3. Elements of Procedure......................................16 5.3.1. PCED TLV Procedure.........................................17 5.3.2. PCES TLV procedure.........................................17 6. ISIS extensions............................................19 6.1. IS-IS PCED TLV format......................................19 6.1.1. PCE-ADDRESS sub-TLV........................................20 6.1.2. The PATH-SCOPE sub-TLV.....................................20 6.1.3. PCE-DOMAINS sub-TLV........................................22 6.1.3.1. Area ID DOMAIN sub-TLV...................................22 6.1.3.2. AS Number DOMAIN sub-TLV.................................23 6.1.4. PCE-DEST-DOMAINS sub-TLV...................................23 6.1.5. GENERAL-CAP sub-TLV........................................23 6.1.6. The PATH-COMP-CAP sub-TLV..................................24 6.2. The ISIS PCES TLV..........................................25 6.2.1. The CONGESTION sub-TLV.....................................25 6.3. Elements of Procedure......................................26 6.3.1. PCED TLV Procedure.........................................26 Le Roux, et al. IGP extensions for PCE discovery [Page 2] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 6.3.2. PCES TLV procedure.........................................27 7. Backward compatibility.....................................27 8. IANA considerations........................................28 8.1. OSPF TLVs..................................................28 8.2. ISIS TLVs..................................................28 8.3. Capability bits............................................29 9. Security Considerations....................................29 10. References.................................................29 10.1. Normative references........................................29 10.2. Informative references......................................30 11. Authors' Addresses:........................................30 12. Intellectual Property Statement............................31 1. Note This document specifies new TLVs and sub-TLVs to be carried within the OSPF Router information LSA ([OSPF-CAP]) and ISIS Router Capability TLV ([ISIS-CAP]) respectively. Because this document does not introduce any new element of procedure it will be discussed within the PCE Working Group with a review of the OSPF and ISIS Working Groups. Furthermore, once stabilized, it may be decided to split the document in two documents addressing the OSPF and ISIS aspects respectively. 2. Terminology Terminology used in this document ABR: IGP Area Border Router (OSPF ABR or ISIS 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. IGP Area: OSPF Area or ISIS level. Intra-area TE LSP: A TE LSP whose path does not cross IGP area boundaries. Inter-area TE LSP: A TE LSP whose path transits through two or more IGP areas. Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or more ASes or sub-ASes (BGP confederations). LSR: Label Switch Router. PCC: Path Computation Client: any client application requesting a Le Roux, et al. IGP extensions for PCE discovery [Page 3] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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 3. Introduction [PCE-ARCH] 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-DISCO-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 an IGP routing domain consists of relying on IGP advertisements. This document defines OSPF and ISIS extensions allowing a PCE participating in the IGP 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 IGP to advertise its potential processing congestion state. Le Roux, et al. IGP extensions for PCE discovery [Page 4] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 Generic capability mechanisms have been defined in [OSPF-CAP] and [ISIS-CAP] for OSPF and ISIS respectively the purpose of which is to allow a router to advertise its capability within an IGP area or an entire routing domain. Such IGP extensions fully satisfy the aforementioned dynamic PCE discovery requirements. This document defines two new TLVs (named the PCE Discovery (PCED) TLV and the PCE Status (PCES) TLV) for ISIS and OSPF to be carried within the ISIS Capability TLV ([ISIS-CAP]) and the OSPF Router Information LSA ([OSPF-CAP]). The PCE information advertised is detailed in section 4. Protocol extensions and procedures are defined in section 5 and 6 for ISIS and OSPF respectively. This document does not define any new OSPF or ISIS element of procedure but how the procedures defined in [OSPF-CAP] and [ISIS-CAP] should be used. The routing extensions defined in this document allow for PCE discovery within an IGP Routing domain. Solutions for PCE discovery across AS boundaries are beyond the scope of this document, and for further study. 4. Overview 4.1. PCE Information PCE information advertised within the IGP 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 is a set of one or more IPv4 and or IPv6 addresses that MUST be used to reach the PCE. It is RECOMMENDED to use loopback 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 domain(s) where the PCE has visibility and can compute paths. - The PCE Destination domain(s): This is the set of 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…). Le Roux, et al. IGP extensions for PCE discovery [Page 5] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 These are two variable length sets of bits flags, where each bit represent a given PCE capability. 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 or PCE deactivation/suppression. Hence, this information is not expected to change frequently. 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 dynamic information 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 IGP areas the PCE belongs to or can be extended across the entire 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. OSPF extensions 5.1. The OSPF PCED TLV The OSPF PCE Discovery TLV (PCED TLV) is made of a set of non-ordered sub-TLVs. The format of the OSPF PCED TLV and its sub-TLVs is the identical as the TLV format used by the Traffic Engineering Extensions to OSPF [OSPF-TE]. That is, the TLV is composed of 2 octets for the type, 2 octets specifying the TLV length and a value field. The Length field defines the length of the value portion in octets. The TLV is padded to four-octet alignment; padding is not included in the length field (so a three octet value would have a length of three, but the total size of the TLV would be eight octets). Nested TLVs are also 32-bit aligned. Unrecognized types are ignored. All types between 32768 and 65535 are reserved for vendor-specific Le Roux, et al. IGP extensions for PCE discovery [Page 6] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 extensions. All other undefined type codes are reserved for future assignment by IANA. The OSPF PCED TLV has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // sub-TLVs // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be defined by IANA (suggested value=2) Length Variable Value This comprises one or more sub-TLVs Sub-TLVs types are under IANA control. Currently five sub-TLVs are defined (type values to be assigned by IANA): Sub-TLV type Length Name 1 variable PCE-ADDRESS sub-TLV 2 4 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 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 MUST be present only in some specific inter-domain cases. The GENERAL-CAP and PATH-COMP-CAP sub-TLVs 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 information. The PCED TLV is carried within an OSPF Router Information LSA defined in [OSPF-CAP], the opaque type of which is determined by the desired flooding scope. Le Roux, et al. IGP extensions for PCE discovery [Page 7] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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 a loop-back address that is always reachable, provided that the PCE is alive. The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the PCED TLV. The PCE-ADDRESS sub-TLV MUST appear at least once in the PCED sub-TLV originated by a PCE. It MAY appear multiple times, for instance when the PCE has both an IPv4 and IPv6 address. The format of the PCE-ADDRESS sub-TLV is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | address-type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // PCE IP Address // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ PCE-ADDRESS sub-TLV format Type To be assigned by IANA (suggested value =1) Length 4 (IPv4) or 16 (IPv6) Address-type: 1 IPv4 2 IPv6 PCE IP Address: The IP address to be used to reach the PCE. This is the address that will be used for setting up PCC-PCE communication sessions. 5.1.2. PATH-SCOPE sub-TLV The PATH-SCOPE sub-TLV indicates the PCE path computation scope(s), 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). 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. Le Roux, et al. IGP extensions for PCE discovery [Page 8] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 The PATH-SCOPE sub-TLV has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|1|2|3|4|5| Reserved |PrefL|PrefR|PrefS|PrefY| Res | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be defined by IANA (suggested value =3) Length Variable Value This comprises a 2 bytes flag where each bit represents a supported path scope, as well as four preference fields allowing to specify PCE preferences. The following bits are defined: 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. 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. 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 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). Le Roux, et al. IGP extensions for PCE discovery [Page 9] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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 load balance its path computation requests according to such PCE’s preference is 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 bit MUST respectively be set to 0. 5.1.3. PCE-DOMAINS sub-TLV The PCE-DOMAINS sub-TLV specifies the set of domains (areas, 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. The PCE-DOMAINS sub-TLV has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // DOMAIN sub-TLVs // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be defined by IANA (suggested value =3) 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. Le Roux, et al. IGP extensions for PCE discovery [Page 10] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 Sub-TLVs types are under IANA control. Currently three DOMAIN sub-TLVs are defined (suggested type values to be assigned by IANA): Sub-TLV type Length Name 1 variable IPv4 area ID sub-TLV 2 variable IPv6 area ID sub-TLV 3 variable AS number sub-TLV The PCE-DOMAINS sub-TLV MUST include at least one DOMAIN sub-TLV. Note than when the PCE visibility is an entire AS, the PCE-DOMAINS sub-TLV MUST uniquely include one AS number sub-TLV. 5.1.3.1. IPv4 area ID DOMAIN sub-TLV The IPv4 area ID DOMAIN sub-TLV carries an IPv4 OSPF area identifier. It has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Area ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be assigned by IANA (suggested value =1) Length 4 IPv4 OSPF area ID: The IPv4 identifier of the OSPF area 5.1.3.2. IPv6 area ID DOMAIN sub-TLV The IPv6 area ID sub-TLV carries an IPv6 OSPF area identifier. It has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 Area ID | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be assigned by IANA (suggested value =2) Length 16 Le Roux, et al. IGP extensions for PCE discovery [Page 11] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 IPv6 OSPF area ID: The IPv6 identifier of the OSPF area 5.1.3.3. AS Number sub-TLV The AS Number sub-TLV carries an AS number. It has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AS Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be assigned by IANA (suggested value =3) Length 4 AS Number: 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 sub-TLVs where each sub-TLV identifies a domain. The PCE-DEST-DOMAINS sub-TLV has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // DOMAIN sub-TLVs // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be defined by IANA (suggested value =3) Length Variable Value This comprises a set of one or more Area and/or AS DOMAIN sub-TLVs where each DOMAIN sub-TLV identifies a domain toward which a PCE can compute paths. Le Roux, et al. IGP extensions for PCE discovery [Page 12] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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. The value field of the GENERAL-CAP sub-TLV is made of bit flags, where each bit corresponds to a general PCE capability. It MAY also include optional sub-TLVs to encode more complex capabilities. The format of the GENERAL-CAP sub-TLV is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | General PCE Capabilities | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Optional sub-TLVs // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be assigned by IANA (suggested value =1) Length It is set to N x 4 octets. N starts from 1 and can be increased when there is a need. Each 4 octets are referred to as a capability flag. Value This comprises one or more capability flags. For each 4 octets, the bits are indexed from the most significant to the least significant, where each bit represents one general PCE capability. When the first 32 capabilities are defined, a new capability flag will be used to accommodate the next capability. Optional TLVs may be defined to specify more complex capabilities: there is no optional TLVs currently defined. IANA is requested to manage the space of general PCE capability bit flags. The following bits in the first capability flag are to be assigned by IANA: Le Roux, et al. IGP extensions for PCE discovery [Page 13] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 Bit Capabilities 0 P bit: Support for Request prioritization. 1 M bit: Support for multiple messages 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. It is made of a set of bit flags, where each bit correspond to a path computation capability. It MAY also include optional sub-TLVs to encode more complex capabilities. The format of the PATH-COMP-CAP sub-TLV is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Path Computation Capabilities | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Optional sub-TLVs // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be assigned by IANA (suggested value =1) Length It is set to N x 4 octets. N starts from 1 and can be increased when there is a need. Each 4 octets are referred to as a capability flag. Value This comprises one or more capability flags. For each 4 octets, the bits are indexed from the most significant to the least significant, where each bit represents one path computation PCE capability. When the first 32 capabilities are defined, a new capability flag will be used to accommodate the next capability. Optional TLVs may be defined to specify more complex capabilities: there is no optional TLVs currently defined. IANA is requested to manage the space of PCE path commutation capability bit flags. The following bits in the first capability flag are to be assigned by IANA: Le Roux, et al. IGP extensions for PCE discovery [Page 14] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 Bit Capabilities 0 G bit: Capability to handle GMPLS 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 6-31 Reserved for future assignments by IANA. The G, B, D, L, S and O bits are not exclusive. 5.2. The OSPF PCES TLV The OSPF PCE Status TLV (PCES TLV) carries information related to PCE processing congestion state. The PCES TLV is carried within an OSPF Router Information LSA which is defined in [OSPF-CAP]. The OSPF PCES TLV has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // PCE ADDRESS sub-TLV // // CONGESTION sub-TLV // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be defined by IANA (suggested value=3) Length Variable Value This comprises a PCE ADDRESS sub-TLV, identifying the PCE and a CONGESTION sub-TLV that contains congestion information. Sub-TLV types are under IANA control. Currently two sub-TLVs are defined (type values to be assigned by IANA): Sub-TLV type Length Name 1 variable PCE-ADDRESS sub-TLV 2 4 CONGESTION sub-TLV The PCE-ADDRESS and CONGESTION sub-TLVs MUST be present once in a PCES TLV. The PCE-ADDRESS sub-TLV is defined in section 5.1.1. 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 Le Roux, et al. IGP extensions for PCE discovery [Page 15] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 Router Information LSAs. 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 expected PCE 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: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |C| Reserved | Congestion Duration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type To be assigned by IANA (suggested value =2) Length 4 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 experiences 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. 5.3. Elements of Procedure The PCED and PCES TLV are carried within an OSPF Router information opaque LSA (opaque type of 4, opaque ID of 0) which is defined in [OSPF-CAP]. As the PCES information is likely to change more frequently than the PCED information, it is RECOMMENDED to carry PCES and PCED TLVs in separate Router Information LSAs, so as not to carry all PCED information each time the PCE status changes. Le Roux, et al. IGP extensions for PCE discovery [Page 16] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 5.3.1. PCED TLV Procedure A router MUST originate a new OSPF router information LSA whenever the content of the PCED TLV changes or whenever required by the regular OSPF procedure (LSA refresh (every LSRefreshTime)). The PCED TLV may be carried within a type 10 or 11 router information LSA depending on the flooding scope of the PCE information. If the flooding scope is local to an area then it MUST be carried within a type 10 router information LSA. If the flooding scope is the entire domain then it MUST be carried within type 11 router information LSA. Note that when the L bit of the PATH-SCOPE TLV is set and the R bit and S bit are cleared, the flooding scope MUST be local, and the PCED TLV MUST be carried within a type 10 Router Information LSA. PCED sub-TLVs are OPTIONAL. When an OSPF LSA does not contain any PCED sub-TLV, this means that the PCE information of that node is unknown. Note that a change in PCED 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 on the PCE (e.g. address, preferences, scope) and other information may be automatically retrieved by the PCE (e.g. areas of visibility). 5.3.2. PCES TLV procedure A router MUST originate a new OSPF router information LSA whenever the content of the PCES TLV changes or whenever required by the regular OSPF procedure (LSA refresh (every LSRefreshTime)). When a PCE enters into a processing congestion state, the conditions of which are implementation dependent, it SHOULD originate a Router Information LSA with 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; - If the congestion duration in the previously originated PCES TLV was non null, it MAY not 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 OSPF flooding, as only uncongested-congested state transitions are flooded. Le Roux, et al. IGP extensions for PCE discovery [Page 17] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 It is expected that a proper implementation will support dampening algorithms so as to dampen OSPF flooding in order to not impact the OSPF scalability. It is recommended to introduce some hysteresis for saturation state transition, so as to avoid state oscillations that may impact OSPF performances. For instance two thresholds could 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. Such PCC procedures are out of the scope of this document. Le Roux, et al. IGP extensions for PCE discovery [Page 18] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 6. ISIS extensions 6.1. 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 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 MUST be present only in some specific inter-domain cases. The 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. Le Roux, et al. IGP extensions for PCE discovery [Page 19] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 6.1.1. 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 a loop-back addresse that is always reachable, provided the PCE is alive. The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the PCED TLV. The PCE-ADDRESS sub-TLV has the following format: TYPE: To be assigned by IANA (Suggested value =1) LENGTH: 4 for IPv4 address and 16 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 The PCE-ADDRESS sub-TLV MUST appear at least once in the PCED sub-LTV originated by a PCE. It MAY appear multiple times, for instance when the PCE has both an IPv4 and IPv6 address. 6.1.2. 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). 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 bit flag: +-+-+-+-+-+-+-+-+ |0|1|2|3|4|5|Res| +-+-+-+-+-+-+-+-+ Le Roux, et al. IGP extensions for PCE discovery [Page 20] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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. 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 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 Le Roux, et al. IGP extensions for PCE discovery [Page 21] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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 is 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 bit MUST respectively be set to 0. 6.1.3. 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. 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. 6.1.3.1. 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 Le Roux, et al. IGP extensions for PCE discovery [Page 22] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 combination of an Initial Domain Part (IDP) and High Order part of the Domain Specific part (HO-DPS) 6.1.3.2. 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. 6.1.4. 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. 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. 6.1.5. GENERAL-CAP sub-TLV The GENERAL-CAP sub-TLV is an optional TLV used to indicate PCECP related capabilities. This is a series of bits flags, where each bit corresponds to a general PCE capability. It MAY also include optional sub-TLVs to encode more complex capabilities. Le Roux, et al. IGP extensions for PCE discovery [Page 23] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 The GENERAL-CAP sub-TLV has the following format: TYPE: To be assigned by IANA (Suggested value =4) LENGTH: It is set to N. N starts from 1 and can be increased when there is a need. Each octet is referred to as a capability flag. VALUE: This comprises one or more general PCE capability flags. The following bits in the first capability flag are to be assigned by IANA: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |P|M| Reserved | +-+-+-+-+-+-+-+-+ P bit: Support for request prioritization. M bit: Support for multiple messages within the same request message. Reserved bits are for future assignment by IANA. 6.1.6. 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. This is a series of bit flags, where each bit correspond 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: It is set to N. N starts from 1 and can be increased when there is a need. Each octet is referred to as a capability flag. VALUE: This comprises one or more Path Computation specific PCE capability flags. The following bits in the first capability flag are to be assigned by IANA. 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |M|G|D|L|S|0|Res| +-+-+-+-+-+-+-+-+ G bit: Capability to handle GMPLS constraints B bit: Capability to compute bidirectional paths D bit: Capability to compute link/node/SRLG diverse paths L bit: Capability to compute load-balanced paths Le Roux, et al. IGP extensions for PCE discovery [Page 24] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 S bit: Capability to compute a set of paths in a synchronized Manner O bit: Support for multiple objective functions Reserved bits are for future assignment by IANA. The G, B, D, L, S and O bits are not exclusive. 6.2. 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 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. 6.2.1. 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) Le Roux, et al. IGP extensions for PCE discovery [Page 25] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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 experiences 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. 6.3. 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. 6.3.1. PCED TLV Procedure An ISIS router MUST originate a new ISIS LSP whenever the content of any of the PCED TLV changes or whenever required by the regular ISIS procedure (LSP refresh). When the scope of the PCED TLV is area local it MUST be carried within an ISIS CAPABILITY TLV having the S bit cleared. When the scope of the PCED TLV is the entire 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 and the flooding scope MUST be local. PCED sub-TLVs are OPTIONAL. When an ISIS LSP does not contain any PCED sub-TLV, this means that the PCE information of that node is unknown. Note that a change in PCED information MUST not trigger any SPF computation. Le Roux, et al. IGP extensions for PCE discovery [Page 26] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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). 6.3.2. PCES TLV procedure An ISIS router MUST originate a new ISIS LSP whenever the content of any of the PCES TLV changes or whenever required by the regular IS-IS procedure (LSP refresh). 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; - If the congestion duration in the previously originated PCES TLV was non null, it MAY not 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. It is expected that a proper implementation will support dampening algorithms 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 could 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. Such PCC procedures are out of the scope of this document. 7. Backward compatibility The PCED and PCEs TLVs defined in this document do not introduce any interoperability issue. For OSPF, a router not supporting the PCED/PCES TLVs SHOULD just silently ignore the TLVs as specified in [RFC2370]. Le Roux, et al. IGP extensions for PCE discovery [Page 27] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 For ISIS a router not supporting the PCED/PCES TLVs SHOULD just silently ignore the TLV. 8. IANA considerations 8.1. OSPF TLVs IANA will assign a new codepoint for the OSPF PCED TLV defined in this document and carried within the Router Information LSA. Five sub-TLVs types are defined for this 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) Three sub-TLVs types are defined for the PCE-DOMAINS and PCE-DEST- DOMAINS TLVs and should be assigned by IANA: -IPv4 area ID sub-TLV (suggested value = 1) -IPv6 area ID sub-TLV (suggested value = 2) -AS number sub-TLV (suggested value = 3) IANA will assign a new codepoint for the OSPF PCES TLV defined in this document and carried within the Router Information LSA. 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. ISIS TLVs IANA will assign a new codepoint for the PCED TLV defined in this document and carried within the ISIS CAPABILITY 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-DEST-DOMAINS sub-TLV (suggested value = 3) -PCE-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: -Area ID sub-TLV (suggested value = 1) -AS number sub-TLV (suggested value = 2) IANA will assign a new codepoint for the ISIS PCES TLV defined in this document and carried within the ISIS CAPABILITY TLV. Le Roux, et al. IGP extensions for PCE discovery [Page 28] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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) 8.3. Capability bits IANA is requested to manage the space of general and path computation specific PCE capability bits flags, numbering them in the usual IETF notation starting at zero and continuing at least 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 first general PCE capability 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 first path computation specific PCE capability 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 functions 9. Security Considerations To be completed in further revisions. 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. [OSPF-v2] Moy, J., "OSPF Version 2", RFC 2328, April 1998. Le Roux, et al. IGP extensions for PCE discovery [Page 29] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 [RFC2370] Coltun, R., “The OSPF Opaque LSA Option”, RFC 2370, July 1998. [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. [OSPF-TE] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering Extensions to OSPF Version 2", RFC 3630, September 2003. [IS-IS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic Engineering", RFC 3784, June 2004. [OSPF-CAP] Lindem, A., Shen, N., Aggarwal, R., Shaffer, S., Vasseur, J.P., "Extensions to OSPF for advertising Optional Router Capabilities", draft-ietf-ospf-cap, work in progress. [IS-IS-CAP] Vasseur, J.P. et al., "IS-IS extensions for advertising router information", draft-ietf-isis-caps, work in progress. [PCE-ARCH] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation Element (PCE) Architecture", draft-ietf-pce-architecture, work in progress. [PCE-DISCO-REQ] Le Roux, J.L., et al. "Requirements for PCE discovery", draft-ietf-pce-discovery-reqs, work in progress 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-01.txt, work in progress. 11. Authors' Addresses: Jean-Louis Le Roux (Editor) France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex FRANCE Email: jeanlouis.leroux@francetelecom.com Jean-Philippe Vasseur (Editor) Cisco Systems, Inc. 1414 Massachusetts avenue Boxborough , MA - 01719 Le Roux, et al. IGP extensions for PCE discovery [Page 30] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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 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 Le Roux, et al. IGP extensions for PCE discovery [Page 31] Internet Draft draft-ietf-pce-disco-proto-igp-01.txt March 2006 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, et al. IGP extensions for PCE discovery [Page 32]