Networking Working Group JP. Vasseur, Ed. Internet-Draft Cisco Systems Intended status: Standards Track JL. Le Roux, Ed. Expires: January 6, 2008 France Telecom July 5, 2007 Path Computation Element (PCE) communication Protocol (PCEP) draft-ietf-pce-pcep-08.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 6, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document specifies the Path Computation Element communication Protocol (PCEP) for communications between a Path Computation Client (PCC) and a Path Computation Element (PCE), or between two PCEs. Such interactions include path computation requests and path computation replies as well as notifications of specific states related to the use of a PCE in the context of Multiprotocol Label Switching (MPLS) and Generalized (GMPLS) Traffic Engineering. The Vasseur & Le Roux Expires January 6, 2008 [Page 1] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 PCEP protocol is designed to be flexible and extensible so as to easily allow for the addition of further messages and objects, should further requirements be expressed in the future. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Architectural Protocol Overview (Model) . . . . . . . . . . . 5 4.1. Problem . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Architectural Protocol Overview . . . . . . . . . . . . . 6 4.2.1. Initialization Phase . . . . . . . . . . . . . . . . . 7 4.2.2. Path computation request sent by a PCC to a PCE . . . 8 4.2.3. Path computation reply sent by the PCE to a PCC . . . 9 4.2.4. Notification . . . . . . . . . . . . . . . . . . . . . 11 4.2.5. Error . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.6. Termination of the PCEP Session . . . . . . . . . . . 13 5. Transport protocol . . . . . . . . . . . . . . . . . . . . . . 13 6. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . . 14 6.1. Common header . . . . . . . . . . . . . . . . . . . . . . 14 6.2. Open message . . . . . . . . . . . . . . . . . . . . . . . 15 6.3. Keepalive message . . . . . . . . . . . . . . . . . . . . 16 6.4. Path Computation Request (PCReq) message . . . . . . . . . 17 6.5. Path Computation Reply (PCRep) message . . . . . . . . . . 18 6.6. Notification (PCNtf) message . . . . . . . . . . . . . . . 20 6.7. Error (PCErr) Message . . . . . . . . . . . . . . . . . . 21 6.8. Close message . . . . . . . . . . . . . . . . . . . . . . 21 7. Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1. Common object header . . . . . . . . . . . . . . . . . . . 22 7.2. OPEN object . . . . . . . . . . . . . . . . . . . . . . . 23 7.3. RP Object . . . . . . . . . . . . . . . . . . . . . . . . 25 7.3.1. Object definition . . . . . . . . . . . . . . . . . . 25 7.3.2. Handling of the RP object . . . . . . . . . . . . . . 27 7.4. NO-PATH Object . . . . . . . . . . . . . . . . . . . . . . 28 7.5. END-POINT Object . . . . . . . . . . . . . . . . . . . . . 30 7.6. BANDWIDTH Object . . . . . . . . . . . . . . . . . . . . . 31 7.7. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 32 7.8. Explicit Route Object . . . . . . . . . . . . . . . . . . 35 7.9. Route Record Object . . . . . . . . . . . . . . . . . . . 35 7.10. LSPA Object . . . . . . . . . . . . . . . . . . . . . . . 36 Vasseur & Le Roux Expires January 6, 2008 [Page 2] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 7.11. Include Route Object Object . . . . . . . . . . . . . . . 38 7.12. SVEC Object . . . . . . . . . . . . . . . . . . . . . . . 38 7.12.1. Notion of Dependent and Synchronized path computation requests . . . . . . . . . . . . . . . . . 38 7.12.2. SVEC Object . . . . . . . . . . . . . . . . . . . . . 40 7.12.3. Handling of the SVEC Object . . . . . . . . . . . . . 41 7.13. NOTIFICATION Object . . . . . . . . . . . . . . . . . . . 42 7.14. PCEP-ERROR Object . . . . . . . . . . . . . . . . . . . . 45 7.15. LOAD-BALANCING Object . . . . . . . . . . . . . . . . . . 49 7.16. CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 50 8. Manageability Considerations . . . . . . . . . . . . . . . . . 51 8.1. Control of Function and Policy . . . . . . . . . . . . . . 51 8.2. Information and Data Models . . . . . . . . . . . . . . . 52 8.3. Liveness Detection and Monitoring . . . . . . . . . . . . 53 8.4. Verifying Correct Operation . . . . . . . . . . . . . . . 53 8.5. Requirements on Other Protocols and Functional Componentssection . . . . . . . . . . . . . . . . . . . . 53 8.6. Impact on Network Operation . . . . . . . . . . . . . . . 54 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 54 9.1. TCP Port . . . . . . . . . . . . . . . . . . . . . . . . . 54 9.2. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 54 9.3. PCEP Object . . . . . . . . . . . . . . . . . . . . . . . 54 9.4. Notification Object . . . . . . . . . . . . . . . . . . . 56 9.5. PCEP Error Object . . . . . . . . . . . . . . . . . . . . 56 9.6. CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 57 9.7. NO-PATH-VECTOR TLV . . . . . . . . . . . . . . . . . . . . 58 10. PCEP Finite State Machine (FSM) . . . . . . . . . . . . . . . 58 11. Security Considerations . . . . . . . . . . . . . . . . . . . 65 11.1. PCEP Authentication and Integrity . . . . . . . . . . . . 65 11.2. PCEP Privacy . . . . . . . . . . . . . . . . . . . . . . . 65 11.3. Protection against Denial of Service attacks . . . . . . . 66 11.4. Request input shaping/policing . . . . . . . . . . . . . . 66 12. Authors' addresses . . . . . . . . . . . . . . . . . . . . . . 66 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 68 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 68 14.1. Normative References . . . . . . . . . . . . . . . . . . . 68 14.2. Informative References . . . . . . . . . . . . . . . . . . 68 Appendix A. PCEP Variables . . . . . . . . . . . . . . . . . . . 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 71 Intellectual Property and Copyright Statements . . . . . . . . . . 72 Vasseur & Le Roux Expires January 6, 2008 [Page 3] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 1. Terminology Terminology used in this document AS: Autonomous System. Explicit path: full explicit path from start to destination made of a list of strict hops where a hop may be an abstract node such as an AS. IGP area: OSPF area or IS-IS level. Inter-domain TE LSP: A TE LSP whose path transits across at least two different domains where a domain can either be an IGP area, an Autonomous System or a sub-AS (BGP confederations). 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. PCEP Peer: an element involved in a PCEP session (i.e. a PCC or a PCE). TED: Traffic Engineering Database that contains the topology and resource information of the domain. The TED may be fed by IGP extensions or potentially by other means. TE LSP: Traffic Engineering Label Switched Path. Strict/loose path: mix of strict and loose hops comprising of at least one loose hop representing the destination where a hop may be an abstract node such as an AS. Within this document, when describing PCE-PCE communications, the requesting PCE fills the role of a PCC. This provides a saving in documentation without loss of function. 2. Introduction [RFC4655] describes the motivations and architecture for a PCE-based model for the computation of MPLS and GMPLS TE LSPs. The model allows for the separation of PCE from PCC, and allows for the cooperation between PCEs. This necessitates a communication protocol between PCC and PCE, and between PCEs. [RFC4657] states the generic Vasseur & Le Roux Expires January 6, 2008 [Page 4] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 requirements for such protocol including the requirement for using the same protocol between PCC and PCE, and between PCEs. Additional application-specific requirements (for scenarios such as inter-area, inter-AS, etc.) are not included in [RFC4657], but there is a requirement that any solution protocol must be easily extensible to handle other requirements as they are introduced in application- specific requirements documents. Examples of such application- specific requirements are [RFC4927], [I-D.ietf-pce-interas-pcecp-reqs] and [I-D.ietf-pce-inter-layer-req]. This document specifies the Path Computation Element communication Protocol (PCEP) for communications between a Path Computation Client (PCC) and a Path Computation Element (PCE), or between two PCEs, in compliance with [RFC4657]. Such interactions include path computation requests and path computation replies as well as notifications of specific states related to the use of a PCE in the context of MPLS and GMPLS Traffic Engineering. PCEP is designed to be flexible and extensible so as to easily allow for the addition of further messages and objects, should further requirements be expressed in the future. 3. Assumptions [RFC4655] describes various types of PCE. PCEP does not make any assumption and thus does not impose any constraint on the nature of the PCE. Moreover, it is assumed that the PCE gets the required information so as to perform the computation of TE LSP that usually requires network topology and resource information. Such information can be gathered by routing protocols or by some other means, the gathering of which is out of the scope of this document. Similarly, no assumption is made on the discovery method used by a PCC to discover a set of PCEs (e.g. via static configuration or dynamic discovery) and on the algorithm used to select a PCE. For the sake of reference [RFC4674] defines a list of requirements for dynamic PCE discovery and IGP-based solutions for such PCE discovery are specified in [I-D.ietf-pce-disco-proto-ospf] and [I-D.ietf-pce-disco-proto-isis]. 4. Architectural Protocol Overview (Model) The aim of this section is to describe the PCEP model in the spirit of [RFC4101]. An architecture protocol overview (the big picture of Vasseur & Le Roux Expires January 6, 2008 [Page 5] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 the protocol) is provided in this section. Protocol details can be found in further sections. 4.1. Problem The PCE-based architecture used for the computation of MPLS and GMPLS TE LSP is described in [RFC4655]. When the PCC and the PCE are not collocated, a communication protocol between the PCC and the PCE is needed. PCEP is such a protocol designed specifically for communications between a PCC and a PCE or between two PCEs in compliance with [RFC4657]: a PCC may use PCEP to send a path computation request for one or more TE LSP(s) to a PCE and the PCE may reply with a set of computed path(s) if one or more path(s) that satisfy the set of constraints can be found. 4.2. Architectural Protocol Overview PCEP operates over TCP, which fulfils the requirements for reliable messaging and flow control without further protocol work. Several PCEP messages are defined: - Open and Keepalive messages are used to initiate and maintain a PCEP session respectively. - PCReq: a PCEP message sent by a PCC to a PCE to request a path computation. - PCRep: a PCEP message sent by a PCE to a PCC in reply to a path computation request. A PCRep message can either contain a set of computed path(s) if the request can be satisfied or a negative reply otherwise in which case the negative reply may also indicate the reason why no path could be found. - PCNtf: a PCEP notification message either sent by a PCC to a PCE or a PCE to a PCC to notify of a specific event. - PCErr: a PCEP message sent upon the occurrence of a protocol error condition. - Close message: a message used to close a PCEP session. The set of available PCE(s) may either be statically configured on a PCC or dynamically discovered. The mechanisms used to discover one or more PCE(s) and to select a PCE are out of the scope of this document. A PCC may have PCEP sessions with more than one PCE and similarly a Vasseur & Le Roux Expires January 6, 2008 [Page 6] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 PCE may have PCEP sessions with multiple PCCs. 4.2.1. Initialization Phase The initialization phase consists of two successive steps (described in a schematic form in Figure 1): 1) Establishment of a TCP connection (3-way handshake) between the PCC and the PCE. 2) Establishment of a PCEP session over the TCP connection. Once the TCP connection is established, the PCC and the PCE (also referred to as "PCEP peers") initiate a PCEP session establishment during which various session parameters are negotiated. These parameters are carried within Open messages and include the Keepalive timer, the Deadtimer and potentially other detailed capabilities and policy rules that specify the conditions under which path computation requests may be sent to the PCE. If the PCEP session establishment phase fails because the PCEP peers disagree on the session parameters or one of the PCEP peers does not answer after the expiration of the establishment timer, the TCP connection is immediately closed. Successive retries are permitted but an implementation should make use of an exponential back-off session establishment retry procedure. Keepalive messages are used to acknowledge Open messages and once the PCEP session has been successfully established, Keepalive messages may be exchanged between PCEP peers to ensure the liveness of the PCEP session. A single PCEP session can exist between a pair a PCEP peers. Details about the Open message and the Keepalive messages can be found inSection 6.2 and Section 6.3 respectively. Vasseur & Le Roux Expires January 6, 2008 [Page 7] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ | | |---- Open message --->| | | |<--- Open message ----| | | | | | | |<--- Keepalive -------| | | |---- Keepalive ------>| Figure 1: PCEP Initialization phase (initiated by a PCC) (Note that the exchange of Keepalive messages is optional) 4.2.2. Path computation request sent by a PCC to a PCE +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ 1)Path computation | | event | | 2)PCE Selection | | 3)Path computation |---- PCReq message--->| request sent to | | the selected PCE | | Figure 2: Path computation request Once a PCC has successfully established a PCEP session with one or more PCEs, if an event is triggered that requires the computation of a set of path(s), the PCC first selects one or more PCE(s). Note that the PCE selection decision process may have taken place prior to the PCEP session establishment. Once the PCC has selected a PCE, it sends a path computation request to the PCE (PCReq message) that contains a variety of objects that specify the set of constraints and attributes for the path to be computed. For example "Compute a TE LSP path with source IP address=x.y.z.t, destination IP address=x'.y'.z'.t', bandwidth=B Mbit/s, Setup/Hold priority=P, ...". Additionally, the PCC may desire to specify the urgency of such request by assigning a request Vasseur & Le Roux Expires January 6, 2008 [Page 8] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 priority. Each request is uniquely identified by a request-id number and the PCC-PCE address pair. The process is shown in a schematic form in figure 2. Details about the PCReq message can be found in Section 6.4 4.2.3. Path computation reply sent by the PCE to a PCC Vasseur & Le Roux Expires January 6, 2008 [Page 9] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ | | |---- PCReq message--->| | |1) Path computation | |request received | | | |2)Path successfully | |computed | | | |3) Computed path(s) sent | |to the PCC |<--- PCRep message ---| | (Positive reply) | Figure 3a: Path computation request with successful path computation +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ | | | | |---- PCReq message--->| | |1) Path computation | |request received | | | |2) No Path found that | |satisfies the request | | | |3) Negative reply sent to | |the PCC (optionally with | |various additional | |information) |<--- PCRep message ---| | (Negative reply) | Figure 3b: Path computation request with unsuccessful path computation Upon receiving a path computation request from a PCC, the PCE triggers a path computation, the result of which can either be: o Positive (Figure 3-a): the PCE manages to compute a path that satisfies the set of required constraints, in which case the PCE returns the set of computed path(s) to the requesting PCC. Note that PCEP supports the capability to send a single request that requires the computation of more than one path (e.g. computation Vasseur & Le Roux Expires January 6, 2008 [Page 10] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 of a set of link-diverse paths). o Negative (Figure 3-b): no path could be found that satisfies the set of constraints. In this case, a PCE may provide the set of constraints that led to the path computation failure. Upon receiving a negative reply, a PCC may decide to resend a modified request or take any other appropriate action. Details about the PCRep message can be found in Section 6.5. 4.2.4. Notification There are several circumstances whereby a PCE may want to notify a PCC of a specific event. For example, suppose that the PCE suddenly gets overloaded thus potentially leading to unacceptable response times. The PCE may want to notify one or more PCCs that some of their requests (listed in the notification) will not be satisfied or may experience unacceptable delays. Upon receiving such notification, the PCC may decide to redirect it(s) path computation request(s) to another PCE should an alternate PCE be available. Similarly, a PCC may desire to notify a PCE of a particular event such as the cancellation of pending request(s). Vasseur & Le Roux Expires January 6, 2008 [Page 11] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ 1)Path computation | | event | | 2)PCE Selection | | 3)Path computation |---- PCReq message--->| request X sent to | |4) Path computation the selected PCE | |triggered | | | | 5) Path computation| | request X cancelled| | |---- PCNtf message -->| | |6) Path computation | |request X cancelled Figure 4: Example of PCC notification (cancellation notification) sent to a PCE +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ 1)Path computation | | event | | 2)PCE Selection | | 3)Path computation |---- PCReq message--->| request X sent to | |4) Path computation the selected PCE | |triggered | | | | | |5) PCE gets overloaded | | | | | |6) Path computation | |request X cancelled | | |<--- PCNtf message----| Figure 5: Example of PCE notification (cancellation notification) sent to a PCC Details about the PCNtf message can be found in Section 6.6. 4.2.5. Error PCEP Error messages are sent when a protocol error condition is met (e.g. unknown object, non supported object, policy violation, ...). Vasseur & Le Roux Expires January 6, 2008 [Page 12] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ 1)Path computation | | event | | 2)PCE Selection | | 3)Path computation |---- PCReq message--->| request X sent to | |4) Path computation the selected PCE | |triggered => Policy | |violation ! | |5) Request discarded | | |<-- PCErr message ---| | | Figure 6: Example of Error message (policy violation) sent by a PCE Details about the PCErr message can be found in Section 6.7. 4.2.6. Termination of the PCEP Session When one of the PCEP peers desires to terminate a PCEP session it first sends a PCEP Close message and then closes the TCP connection. If the PCEP session is terminated by the PCE, the PCC clears all the states related to pending requests previously sent to the PCE. Similarly, if the PCC terminates a PCEP session the PCE clears all pending path computation requests sent by the PCC in question as well as the related states. A Close message can only be sent to terminate a PCEP session if the PCEP session has previously been established. In case of TCP connection failure, the PCEP session is immediately terminated. Details about the Close message can be found in Section 6.8. 5. Transport protocol PCEP operates over TCP using a well-known TCP port (to be assigned by IANA). This allows the requirements of reliable messaging and flow control to be met without further protocol work. An implementation may decide to keep the TCP connection alive for an unlimited time (this may for instance be appropriate when path computation requests are sent on a frequent basis so as to avoid to open a TCP connection each time a path computation request is needed, which would incur additional processing delays). Conversely, in some other circumstances, it may be desirable to systematically open and Vasseur & Le Roux Expires January 6, 2008 [Page 13] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 close the TCP connection for each PCEP request (for instance when sending a path computation request is a rare event). 6. PCEP Messages A PCEP message consists of a common header followed by a variable length body made of a set of objects that can either be mandatory or optional. In the context of this document, an object is said to be mandatory in a PCEP message when the object MUST be included for the message to be considered as valid. A PCEP message with a missing mandatory object MUST trigger an Error message (see Section 7.14). Conversely, if an object is optional, the object may or may not be present. A flag referred to as the P flag is defined in the common header of each PCEP object (see Section 7.1) that can be set by a PCEP peer to enforce a PCE to take into account the related information during the path computation. For example, the METRIC object defined in Section 7.7 allows a PCC to specify a bounded acceptable path cost. The METRIC object is optional but a PCC may set a flag to ensure that such constraint is taken into account. Similarly to the previous case, if such constraint cannot be taken into account by the PCE, the PCE MUST trigger an Error message. For each PCEP message type, rules are defined that specify the set of objects that the message can carry. We use the Backus-Naur Form (BNF) to specify such rules. Square brackets refer to optional sub- sequences. An implementation MUST form the PCEP messages using the object ordering specified in this document. 6.1. Common header 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver | Flags | Message-Type | Message-Lenght | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: PCEP message common header Ver (Version - 3 bits): PCEP version number. Current version is version 1. Flags (5 bits): no flags are currently defined. Unassigned bits are considered as reserved and MUST be set to zero on transmission. Message-Type (8 bits): Vasseur & Le Roux Expires January 6, 2008 [Page 14] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The following message types are currently defined (to be confirmed by IANA). Value Meaning 1 Open 2 Keepalive 3 Path Computation Request 4 Path Computation Reply 5 Notification 6 Error 7 Close Message-Length (16 bits): total length of the PCEP message expressed in bytes including the common header. 6.2. Open message The Open message is a PCEP message sent by a PCC to a PCE and a PCE to a PCC in order to establish a PCEP session. The Message-Type field of the PCEP common header for the Open message is set to 1 (To be confirmed by IANA). Once the TCP connection has been successfully established, the first message sent by the PCC to the PCE or by the PCE to the PCC MUST be an Open message as specified in Section 10. Any message received prior to an Open message MUST trigger a protocol error condition and the PCEP session MUST be terminated. The Open message is used to establish a PCEP session between the PCEP peers. During the establishment phase the PCEP peers exchange several session characteristics. If both parties agree on such characteristics the PCEP session is successfully established. Open message ::= The Open message MUST contain exactly one OPEN object (see Section 7.2). Various session characteristics are specified within the OPEN object. Once the TCP connection has been successfully established the sender MUST start an initialization timer called OpenWait after the expiration of which if no Open message has been received it sends a PCErr message and releases the TCP connection (see Section 10 for details). Once an Open message has been sent to a PCEP peer, the sender MUST start an initialization timer called KeepWait after the expiration of which if neither a KeepAlive message has been received nor a PCErr message in case of disagreement of the session characteristics, a PCErr message MUST be sent and the TCP connection MUST be released (see Section 10 for details). Vasseur & Le Roux Expires January 6, 2008 [Page 15] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The KeepWait timer has a fixed value of 1 minute. Upon the receipt of an Open message, the receiving PCEP peer MUST determine whether the suggested PCEP session characteristics are acceptable. If at least one of the characteristic(s) is not acceptable by the receiving peer, it MUST send an Error message. The Error message SHOULD also contain the related Open object: for each unacceptable session parameter, an acceptable parameter value SHOULD be proposed in the appropriate field of the Open object in place of the originally proposed value. The PCEP peer MAY decide to resend an Open message with different session characteristics. If a second Open message is received with the same set of parameters or with parameters that are still unacceptable, the receiving peer MUST send an Error message and it MUST immediately close the TCP connection. Details about error message can be found in Section 7.14. If the PCEP session characteristics are acceptable, the receiving PCEP peer MUST consequently send a Keepalive message (defined in Section 6.3) that would serve as an acknowledgment. The PCEP session is considered as established once both PCEP peers have received a Keepalive message from their peer. 6.3. Keepalive message A Keepalive message is a PCEP message sent by a PCC or a PCE in order to keep the session in active state. The Message-Type field of the PCEP common header for the Keepalive message is set to 2 (To be confirmed by IANA). The Keepalive message does not contain any object. PCEP has its own keepalive mechanism used to ensure of the liveness of the PCEP session. This requires the determination of the frequency at which each PCEP peer sends keepalive messages. Asymmetric values may be chosen; thus there is no constraint mandating the use of identical keepalive frequencies by both PCEP peers. The DeadTimer is defined as the period of time after the expiration of which a PCEP peer declares the session down if no PCEP message has been received (keepalive or any other PCEP message: thus, any PCEP message acts as a keepalive message). Similarly, there is no constraints mandating the use of identical DeadTimers by both PCEP peers. The minimum KeepAlive timer value is 1 second. Keepalive messages are used to acknowledge an Open message if the receiving PCEP peer agrees on the session characteristics and to ensure the liveness of the PCEP session. Keepalive messages are sent at the frequency specified in the OPEN object carried within an Open message. Because any PCEP message may serve as Keepalive an Vasseur & Le Roux Expires January 6, 2008 [Page 16] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 implementation may either decide to send Keepalive messages at fixed intervals regardless on whether other PCEP messages might have been sent since the last sent Keepalive message or may decide to differ the sending of the next Keepalive message based on the time at which the last PCEP message (other than Keepalive) has been sent. Note that sending Keepalive messages to maintain the session alive is optional and PCEP peers may decide to not send Keepalive messages once the PCEP session is established. Keepalive message ::= 6.4. Path Computation Request (PCReq) message A Path Computation Request message (also referred to as a PCReq message) is a PCEP message sent by a PCC to a PCE so as to request a path computation. The Message-Type field of the PCEP common header for the PCReq message is set to 3 (To be confirmed by IANA). There are two mandatory objects that MUST be included within a PCReq message: the RP and the END-POINTS objects (see section Section 7). If one of these objects is missing, the receiving PCE MUST send an error message to the requesting PCC. Other objects are optional. Vasseur & Le Roux Expires January 6, 2008 [Page 17] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The format of a PCReq message is as follows: ::= [] where: ::=[] ::=[] ::= [] [] [] [] [] [] [] where: ::=[] The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, RRO, IRO and LOAD- BALANCING objects are defined in Section 7. The special case of two BANDWIDTH objects is discussed in details in Section 7.6. 6.5. Path Computation Reply (PCRep) message The PCEP Path Computation Reply message (also referred to as a PCRep message) is a PCEP message sent by a PCE to a requesting PCC in response to a previously received PCReq message. The Message-Type field of the PCEP common header is set to 4 (To be confirmed by IANA). The PCRep message MUST contain at least one RP object. For each reply that is bundled into a single PCReq message, an RP object MUST be included that contains a Request-ID-number identical to the one specified in the RP object carried in the corresponding PCReq message (see Section 7.3 for the definition of the RP object). A PCRep message may contain a set of computed path(s) corresponding to either a single path computation request with load-balancing (see Section 7.15) or multiple path computation requests originated by a requesting PCC. The PCRep message may also contain multiple acceptable paths corresponding to the same request. The bundling of multiple replies to a set of path computation Vasseur & Le Roux Expires January 6, 2008 [Page 18] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 requests within a single PCRep message is supported by PCEP. If a PCE receives non-synchronized path computation requests by means of one or more PCReq messages from a requesting PCC it MAY decide to bundle the computed paths within a single PCRep message so as to reduce the control plane load. Note that the counter side of such an approach is the introduction of additional delays for some path computation requests of the set. Conversely, a PCE that receives multiple requests within the same PCReq message MAY decide to provide each computed path in separate PCRep messages or within the same PCRep message. If the path computation request can be satisfied (the PCE finds a set of path(s) that satisfy the set of constraint(s)), the set of computed path(s) specified by means of ERO object(s) is inserted in the PCRep message. The ERO object is defined in Section 7.8. Such a situation where multiple computed paths are provided in a PCRep message is discussed in detail in Section 7.12. Furthermore, when a PCC requests the computation a set of paths for a total amount of bandwidth of X by means of a LOAD-BALANCING object carried within a PCReq message, the ERO of each computed path may be followed by a BANDWIDTH object as discussed in section Section 7.15. If the path computation request cannot be satisfied, the PCRep message MUST include a NO-PATH object. The NO-PATH object (described in Section 7.4) may also comprise other information (e.g reasons for the path computation failure). Vasseur & Le Roux Expires January 6, 2008 [Page 19] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The format of a PCRep message is as follows: ::= where: ::=[] ::= [] [] [] ::=[] ::= where: ::=[] [] [] [] ::=[] 6.6. Notification (PCNtf) message The PCEP Notification message (also referred to as the PCNtf message) can either be sent by a PCE to a PCC or by a PCC to a PCE so as to notify of a specific event. The Message-Type field of the PCEP common header is set to 5 (To be confirmed by IANA). The PCNtf message MUST carry at least one NOTIFICATION object and may contain several NOTIFICATION objects should the PCE or the PCC intend to notify of multiple events. The NOTIFICATION object is defined in Section 7.13. The PCNtf message MAY also contain an RP object (see Section 7.3 when the notification refers to a particular path computation request. The PCNtf message may be sent by a PCC or a PCE in response to a request or in an unsolicited manner. Vasseur & Le Roux Expires January 6, 2008 [Page 20] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The format of a PCNtf message is as follows: ::= ::= [] ::= [] :== := 6.7. Error (PCErr) Message The PCEP Error message (also referred to as a PCErr message) is sent when a protocol error condition is met. The Message-Type field of the PCEP common header is set to 6 (To be confirmed by IANA). The PCErr message is either sent by a PCC or a PCE in response to a request or in an unsolicited manner. In the former case, the PCErr message MUST include the set of RP objects related to the pending path computation request(s) that triggered the protocol error condition. In the later case (unsolicited), no RP object is inserted in the PCErr message. No RP object is inserted in a PCErr when the error condition occurred during the initialization phase. A PCErr message MUST contain a PCEP-ERROR object specifying the PCEP error condition. The PCEP-ERROR object is defined in section Section 7.14. The format of a PCErr message is as follows: ::= [] :==[] ::=[] :==[] :==[] The procedure upon the reception of a PCErr message is defined in Section 7.14. 6.8. Close message The Close message is a PCEP message that is either sent by a PCC to a PCE or by a PCE to a PCC in order to close an established PCEP Vasseur & Le Roux Expires January 6, 2008 [Page 21] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 session. The Message-Type field of the PCEP common header for the Close message is set to 7 (To be confirmed by IANA). Close message ::= The Close message MUST contain exactly one CLOSE object (see Section 6.8). Upon the receipt of a Close message, the receiving PCEP peer MUST cancel all pending requests and MUST close the TCP connection. 7. Object Formats 7.1. Common object header A PCEP object carried within a PCEP message consists of one or more 32-bit words with a common header which has the following format: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Object-Class | OT |Res|P|I| Object Length (bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // (Object body) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: PCEP common object header Object-Class (8 bits): identifies the PCEP object class. OT (Object-Type - 4 bits): identifies the PCEP object type. The Object-Class and Object-Type fields are managed by IANA. The Object-Class and Object-Type fields uniquely identify each PCEP object. Res flags (2 bits). Reserved field. This field MUST be set to zero on transmission and MUST be ignored on receipt. o P flag (Processing-Rule - 1-bit): the P flag allows a PCC to specify in a PCReq message sent to a PCE whether the object must be taken into account by the PCE during path computation or is just optional. When the P flag is set, the object MUST be taken into account by the PCE. Conversely, when the P flag is cleared, Vasseur & Le Roux Expires January 6, 2008 [Page 22] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 the object is optional and the PCE is free to ignore it if not supported. o I flag (Ignore - 1 bit): the I flag is used by a PCE in a PCRep message to indicate to a PCC whether or not an optional object was processed. The PCE MAY include the ignored optional object in its reply and set the I flag to indicate that the optional object was ignored during path computation. When the I flag is cleared, the PCE indicates that the optional object was processed during the path computation. The setting of the I flag for optional objects is purely indicative and optional. The I flag has no meaning in a PCRep message when the P flag had been set in the corresponding PCRep message. If the PCE does not understand an object with the P flag set or understands the object but decides to ignore the object, the entire PCEP message MUST be rejected and the PCE MUST send a PCErr message with Error-Type="Unknown Object" or "Not supported Object". Object Length (16 bits). Specifies the total object length including the header, in bytes. The Object Length field MUST always be a multiple of 4, and at least 4. The maximum object content length is 65528 bytes. 7.2. OPEN object The OPEN object MUST be present in each Open message and MAY be present in a PCErr message. There MUST be only one OPEN object per Open or PCErr message. The OPEN object contains a set of fields used to specify the PCEP version, Keepalive frequency, DeadTimer, PCEP session ID along with various flags. The OPEN object may also contain a set of TLVs used to convey various session characteristics such as the detailed PCE capabilities, policy rules and so on. No TLVs are currently defined. OPEN Object-Class is to be assigned by IANA (recommended value=1) OPEN Object-Type is to be assigned by IANA (recommended value=1) Vasseur & Le Roux Expires January 6, 2008 [Page 23] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The format of the OPEN object body 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver | Flags | Keepalive | Deadtimer | SID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Optional TLV(s) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: OPEN Object format Ver (3 bits): PCEP version. Current version is 1. Flags (5 bits): No Flags are currently defined. Unassigned bits are considered as reserved and MUST be set to zero on transmission. Keepalive (8 bits): maximum period of time (in seconds) between the sending of PCEP messages. The minimum value for the Keepalive is 1 second. When set to 0, once the session is established, no further Keepalive messages need to be sent to the remote peer. A RECOMMENDED value for the keepalive frequency is 30 seconds. DeadTimer (8 bits): specifies the amount of time after the expiration of which the PCEP peer can declare the session with the sender of the Open message down if no PCEP message has been received. The DeadTimer MUST be set to 0 if the Keepalive is set to 0. A RECOMMENDED value for the DeadTimer is 4 times the value of the Keepalive. Example A sends an Open message to B with Keepalive=10 seconds and Deadtimer=30 seconds. This means that A sends Keepalive messages (or ay other PCEP message) to B every 30 seconds and B can declare the PCEP session with A down if no PCEP has been received from A. SID (PCEP session-ID - 8 bits): unsigned PCEP session number that identifies the current session. The SID MUST be incremented each time a new PCEP session is established and is mainly used for logging and troubleshooting purposes. Optional TLVs may be included within the OPEN object body to specify PCC or PCE characteristics. The specification of such TLVs is outside the scope of this document. When present in an Open message, the OPEN object specifies the proposed PCEP session characteristics. Upon receiving unacceptable Vasseur & Le Roux Expires January 6, 2008 [Page 24] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 PCEP session characteristics during the PCEP session initialization phase, the receiving PCEP peer (PCE) MAY include an OPEN object within the PCErr message so as to propose alternative acceptable session characteristic values. 7.3. RP Object The RP (Request Parameters) object MUST be carried within each PCReq and PCRep messages and MAY be carried within PCNtf and PCErr messages. The P flag of the RP object MUST be set in PCReq and PCReq messages and MUST be cleared in PCNtf and PCErr messages. The RP object is used to specify various characteristics of the path computation request. 7.3.1. Object definition RP Object-Class is to be assigned by IANA (recommended value=2) RP Object-Type is to be assigned by IANA (recommended value=1) The format of the RP object body 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags |O|B|R| Pri | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Request-ID-number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Optional TLV(s) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: RP object body format The RP object body has a variable length and may contain additional TLVs. No TLVs are currently defined. Reserved (8 bits): Reserved: This field MUST be set to zero on transmission and MUST be ignored on receipt. Flags (24 bits) The following flags are currently defined: o Pri (Priority - 3 bits): the Priority field may be used by the requesting PCC to specify to the PCE the request's priority from 1 to 7. The decision of which priority should be used for a Vasseur & Le Roux Expires January 6, 2008 [Page 25] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 specific request is of a local matter and MUST be set to 0 when unused. Furthermore, the use of the path computation request priority by the PCE's scheduler is implementation specific and out of the scope of this document. Note that it is not required for a PCE to support the priority field: in this case, it is RECOMMENDED to set the priority field to 0 by the PCC in the RP object. If the PCE does not take into account the request priority, it is RECOMMENDED to set the priority field to 0 in the RP object carried within the corresponding PCRep message, regardless of the priority value contained in the RP object carried within the corresponding PCReq message. A higher numerical value of the priority field reflects a higher priority. Note that it is the responsibility of the network administrator to make use of the priority values in a consistent manner across the various PCC(s). The ability of a PCE to support requests prioritization may be dynamically discovered by the PCC(s) by means of PCE capability discovery. If not advertised by the PCE, a PCC may decide to set the request priority and will learn the ability of the PCE to support request prioritization by observing the Priority field of the RP object received in the PCRep message. If the value of the Pri field is set to 0, this means that the PCE does not support the handling of request priorities: in other words, the path computation request has been honoured but without taking the request priority into account. o R (Reoptimization - 1 bit): when set, the requesting PCC specifies that the PCReq message relates to the reoptimization of an existing TE LSP in which case, in addition to the TE LSP attributes, the current path of the existing TE LSP to be reoptimized MUST be provided in the PCReq (except for 0-bandwidth TE LSP) message by means of an RRO object defined in Section 7.9. o B (Bi-directional - 1 bit): when set, the PCC specifies that the path computation request relates to a bidirectional TE LSP that has the same traffic engineering requirements including fate sharing, protection and restoration, LSRs, and resource requirements (e.g. latency and jitter) in each direction. When cleared, the TE LSP is unidirectional. o O (strict/lOose - 1 bit): when set, in a PCReq message, this indicates that a loose path is acceptable. Otherwise, when cleared, this indicates to the PCE that a path exclusively made of strict hops is required. In a PCRep message, when the O bit is set this indicates that the returned path is a loose path, otherwise (the O bit is cleared), the returned path is made of strict hops. Unassigned bits are considered as reserved and MUST be set to zero on Vasseur & Le Roux Expires January 6, 2008 [Page 26] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 transmission. Request-ID-number (32 bits). The Request-ID-number value combined with the source IP address of the PCC and the PCE address uniquely identify the path computation request context. The Request-ID-number MUST be incremented each time a new request is sent to the PCE. The value 0x0000000 is considered as invalid. If no path computation reply is received from the PCE, and the PCC wishes to resend its request, the same Request-ID-number MUST be used. Conversely, different Request-ID-number MUST be used for different requests sent to a PCE. The same Request-ID-number may be used for path computation requests sent to different PCEs. The path computation reply is unambiguously identified by the IP source address of the replying PCE. 7.3.2. Handling of the RP object If a PCReq message is received without containing an RP object, the PCE MUST send a PCErr message to the requesting PCC with Error- type="Required Object missing" and Error-value="RP Object missing". If the O bit of the RP message carried within a PCReq message is cleared and local policy has been configured on the PCE to not provide explicit path(s) (for instance, for confidentiality reasons), a PCErr message MUST be sent by the PCE to the requesting PCC and the pending path computation request MUST be discarded. The Error-type is "Policy Violation" and Error-value is "O bit cleared". R bit: when the R bit of the RP object is set in a PCReq message, this indicates that the path computation request relates to the reoptimization of an existing TE LSP. In this case, the PCC MUST also provide the strict/loose path by including an RRO object in the PCReq message so as to avoid/limit double bandwidth counting if and only if the TE LSP is a non 0-bandwidth TE LSP. If the PCC has not requested a strict path (O bit set), a reoptimization can still be requested by the PCC but this implies for the PCE to be either stateful (keep track of the previously computed path with the associated list of strict hops) or to have the ability to retrieve the complete required path segment. Alternatively the PCC MUST be able to inform PCE of the working path with associated list of strict hops in PCReq. The absence of an RRO in the PCReq message for a non 0-bandwidth TE LSP when the R bit of the RP object is set MUST trigger the sending of a PCErr message with Error-type="Required Object Missing" and Error-value="RRO Object missing for reoptimization". If the PCC receives a PCRep message that contains a RP object referring to an unknown Request-ID-Number, the PCC MUST send a PCErr Vasseur & Le Roux Expires January 6, 2008 [Page 27] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 message with Error-Type="Unknown request reference". 7.4. NO-PATH Object The NO-PATH object is used in PCRep messages in response to an unsuccessful path computation request (the PCE could not find a path satisfying the set of constraints). When a PCE cannot find a path satisfying a set of constraints, it MUST include a NO-PATH object in the PCRep message. The NO-PATH object is used to report the impossibility to find a path that satisfies the set of constraints. There are potentially several categories of issues that can lead to a negative reply. For example, the PCE chain might be broken (should there be more than one PCE involved in the path computation) or no path obeying the set constraints could be found. The "NI (Nature of Issue)" field in the NO-PATH object is used to report the error category. Optionally, if the PCE supports such capability, the NO-PATH object MAY contain an optional NO-PATH-VECTOR TLV defined below used to provide more information on the reasons that led to a negative reply and the PCRep message MAY also contain a list of objects that specify the set of constraints that could not be satisfied. The PCE MAY just replicate the set of object(s) that was received that was the cause of the unsuccessful computation or MAY optionally report a suggested value for which a path could have been found. NO-PATH Object-Class is to be assigned by IANA (recommended value=3) NO-PATH Object-Type is to be assigned by IANA (recommended value=1) The format of the NO-PATH object body 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Nature Of Issue|C| Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Optional TLV(s) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11: NO-PATH object format NI - Nature Of Issue (8 bits): the NI field is used to report the nature of the issue that led to a negative reply. Two values are currently defined: Vasseur & Le Roux Expires January 6, 2008 [Page 28] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 0x00: No path satisfying the set of constraints could be found 0x01: PCE chain broken Flags (16 bits). The following flag is currently defined: C flag (1 bit): when set, the PCE indicates the set of unsatisfied constraints (reasons why a path could not be found) in the PCRep message by including the relevant PCEP objects. When cleared, no reason is specified. When the C bit is set, the NI field value MUST be 0x00. Reserved (8 bits): This field MUST be set to zero on transmission and MUST be ignored on receipt. The NO-PATH object body has a variable length and may contain additional TLVs. The only TLV currently defined is the NO-PATH- VECTOR TLV defined below. Example: consider the case of a PCC that sends a path computation request to a PCE for a TE LSP of X MBits/s. Suppose that PCE cannot find a path for X MBits/s. In this case, the PCE must include in the PCRep message a NO-PATH object. Optionally the PCE may also include the original BANDWIDTH object so as to indicate that the reason for the unsuccessful computation is the bandwidth constraint (in this case, the NI field value is 0x00 and C flag is set). If the PCE supports such capability it may alternatively include the BANDWIDTH Object and report a value of Y in the bandwidth field of the BANDWIDTH object (in this case, the C flag is set) where Y refers to the bandwidth for which a TE LSP with the same other characteristics could have been computed. When the NO-PATH object is absent from a PCRep message, the path computation request has been fully satisfied and the corresponding path(s) is/are provided in the PCRep message. An optional TLV named NO-PATH-VECTOR MAY be included in the NO-PATH object in order to provide more information on the reasons that led to a negative reply. The NO-PATH-VECTOR TLV is composed of 1 byte for the type, 1 byte specifying the number of bytes in the value field, followed by a fix length value field of 32-bits flags field used to report the reason(s) that led to unsuccessful path computation. The NO-PATH-VECTOR TLV is padded to eight-byte alignment. Vasseur & Le Roux Expires January 6, 2008 [Page 29] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 TYPE: To be assigned by IANA LENGTH: 4 VALUE: 32-bits flags field IANA is requested to manage the space of flags carried in the NO- PATH-VECTOR TLV (see Section 9). The following flags are currently defined: o 0x01: PCE currently unavailable o 0x02: Unknown destination o 0x03: Unknown source 7.5. END-POINT Object The END-POINTS object is used in a PCReq message to specify the source IP address and the destination IP address of the path for which a path computation is requested. Note that the source and destination addresses specified in the END-POINTS object may or may not correspond to the source and destination IP address of the TE LSP but rather to a path segment. Two END-POINTS objects (for IPv4 and IPv6) are defined. END-POINTS Object-Class is to be assigned by IANA (recommended value=4) END-POINTS Object-Type is to be assigned by IANA (recommended value=1 for IPv4 and 2 for IPv6) Vasseur & Le Roux Expires January 6, 2008 [Page 30] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The format of the END-POINTS object body for IPv4 (Object-Type=1) 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source IPv4 address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination IPv4 address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12: END-POINTS object body format for IPv4 The format of the END-POINTS object for IPv6 (Object-Type=2) 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Source IPv6 address (16 bytes) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Destination IPv6 address (16 bytes) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 13: END-POINTS object body format for IPv6 The END-POINTS object body has a fixed length of 8 bytes for IPv4 and 32 bytes for IPv6. 7.6. BANDWIDTH Object The BANDWIDTH object is used to specify the requested bandwidth for a TE LSP. If the requested bandwidth is equal to 0, the BANDWIDTH object is optional. Conversely, if the requested bandwidth is non equal to 0, the PCReq message MUST contain a BANDWIDTH object. In the case of the reoptimization of a TE LSP, the bandwidth of the existing TE LSP MUST also be included in addition to the requested bandwidth if and only if the two values differ. Consequently, two Object-Type are defined that refer to the requested bandwidth and the bandwidth of the TE LSP for which a reoptimization is being Vasseur & Le Roux Expires January 6, 2008 [Page 31] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 performed. The BANDWIDTH object may be carried within PCReq and PCRep messages. BANDWIDTH Object-Class is to be assigned by IANA (recommended value=5) Two Object-Type are defined for the BANDWIDTH object: o Requested bandwidth: BANDWIDTH Object-Type is to be assigned by IANA (recommended value=1) o Bandwidth of an existing TE LSP for which a reoptimization is requested. BANDWIDTH Object-Type is to be assigned by IANA (recommended value=2) The format of the BANDWIDTH object body 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 14: BANDWIDTH object body format Bandwidth: 32 bits. The requested bandwidth is encoded in 32 bits in IEEE floating point format, expressed in bytes per second. The BANDWIDTH object body has a fixed length of 4 bytes. 7.7. METRIC Object The METRIC object is optional and can be used for several purposes. In a PCReq message, a PCC MAY insert a METRIC object: o To indicate the metric that MUST be optimized by the path computation algorithm (IGP metric, TE metric, Hop counts). Currently, three metrics are defined: the IGP cost, the TE metric (see [RFC3785]) and the number of hops traversed by a TE LSP. o To indicate a bound on the path cost that MUST NOT be exceeded for the path to be considered as acceptable by the PCC. In a PCRep message, the METRIC object MAY be inserted so as to provide the cost for the computed path. It MAY also be inserted within a PCRep with the NO-PATH object to indicate that the metric constraint could not be satisfied. Vasseur & Le Roux Expires January 6, 2008 [Page 32] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The path computation algorithmic aspects used by the PCE to optimize a path with respect to a specific metric are outside the scope of this document. It must be understood that such path metric is only meaningful if used consistently: for instance, if the delay of a path computation segment is exchanged between two PCEs residing in different domains, consistent ways of defining the delay must be used. The absence of the METRIC object MUST be interpreted by the PCE as a path computation request for which the PCE may choose the metric to be used. METRIC Object-Class is to be assigned by IANA (recommended value=6) METRIC Object-Type is to be assigned by IANA (recommended value=1) The format of the METRIC object body 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags |C|B| T | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | metric-value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 15: METRIC object body format The METRIC object body has a fixed length of 8 bytes. Reserved (16 bits): This field MUST be set to zero on transmission and MUST be ignored on receipt. T (Type - 8 bits): Specifies the metric type. Three values are currently defined: o T=1: IGP metric o T=2: TE metric o T=3: Hop Counts Flags (8 bits): Two flags are currently defined: o B (Bound - 1 bit): When set in a PCReq message, the metric-value indicates a bound (a maximum) for the path cost that must not be exceeded for the PCC to consider the computed path as acceptable. Vasseur & Le Roux Expires January 6, 2008 [Page 33] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 When the B flag is cleared, the metric-value field is not used to reflect a bound constraint. o C (Cost - 1 bit): When set in a PCReq message, this indicates that the PCE MUST provide the computed path cost (should a path satisfying the constraints be found) in the PCRep message for the corresponding metric. Unassigned flags MUST be set to zero on transmission and MUST be ignored on receipt. Metric-value (32 bits): metric value encoded in 32 bits in IEEE floating point format. Multiple METRIC Objects MAY be inserted in a PCRep or the PCReq message. There MUST be at most one instance of the METRIC object for each metric type with the same B flag value. If two or more instances of a METRIC object with the same B flag value are present for a metric type, only the first instance MUST be considered and other instances MUST be ignored. In a PCReq message the presence of multiple METRIC objects can be used to specify a multi-parameters (e.g. a metric may be a constraint or a parameter to minimize/maximize) objective function or multiple bounds for different constraints where at most one METRIC object must be used to indicate the metric to optimize (B-flag is cleared): the other METRIC object MUST be used to reflect bound constraints (B-Flag is set). A METRIC object used to indicate the metric to optimize during the path computation MUST have the B-Flag cleared and the T-Flag set to the appropriate value. When the path computation relates to the reoptimization of an exiting TE LSP (in which case R-Flag of the RP object is set) an implementation MAY decide to set the metric-value field to the cost of the TE LSP to be reoptimized with regards to a specific metric type. A METRIC object used to reflect a bound MUST have the B-Flag set, the T-Flag and metric-value field set to the appropriate values. In a PCRep message, unless not allowed by PCE policy, at least one METRIC object MUST be present that reports the computed path cost in particular if the C bit of the METRIC object was set in the corresponding path computation request (the B-flag MUST be cleared); optionally the PCRep message MAY contain additional METRIC objects that correspond to bound constraints, in which case the metric-value MUST be equal to the corresponding path metric cost (the B-flag MUST be set). If no path satisfying the constraints could be found by the Vasseur & Le Roux Expires January 6, 2008 [Page 34] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 PCE, the METRIC objects MAY also be present in the PCRep message with the NO-PATH object to indicate the constraint metric that could be satisfied. Example: if a PCC sends a path computation request to a PCE where the metric to optimize is the IGP metric and the TE metric must not exceed the value of M, two METRIC object are inserted in the PCReq message: o First METRIC Object with B=0, T=1, C=1, metric-value=0x0000 o Second METRIC Object with B=1, T=2, metric-value=M If a path satisfying the set of constraints can be found by the PCE and no policy preventing to provide the path cost is in place, the PCE inserts one METRIC object with B=0, T=1, metric-value= computed IGP path cost. Additionally, the PCE may insert a second METRIC object with B=1, T=2, metric-value= computed TE path cost. 7.8. Explicit Route Object The ERO is used to encode a TE LSP. The ERO is carried within a PCRep message to provide the computed TE LSP should have the path computation been successful. The contents of this object are identical in encoding to the contents of the Explicit Route Object defined in [RFC3209], [RFC3473] and [RFC3477]. That is, the object is constructed from a series of sub- objects. Any RSVP ERO sub-object already defined or that could be defined in the future for use in the ERO is acceptable in this object. PCEP ERO sub-object types correspond to RSVP ERO sub-object types. Since the explicit path is available for immediate signaling by the MPLS or GMPLS control plane, the meanings of all of the sub-objects and fields in this object are identical to those defined for the ERO. ERO Object-Class is to be assigned by IANA (recommended value=7) ERO Object-Type is to be assigned by IANA (recommended value=1) 7.9. Route Record Object The RRO is used to record the route followed by a TE LSP. The PCEP RRO is exclusively carried within a PCReq message so as to specify the route followed by a TE LSP for which a reoptimization is desired. Vasseur & Le Roux Expires January 6, 2008 [Page 35] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The contents of this object are identical in encoding to the contents of the Route Record Object defined in [RFC3209], [RFC3473] and [RFC3477]. That is, the object is constructed from a series of sub- objects. Any RSVP RRO sub-object already defined or that could be defined in the future for use in the RRO is acceptable in this object. The meanings of all of the sub-objects and fields in this object are identical to those defined for the RRO. PCEP RRO sub-object types correspond to RSVP RRO sub-object types. RRO Object-Class is to be assigned by IANA (recommended value=8) RRO Object-Type is to be assigned by IANA (recommended value=1) 7.10. LSPA Object The LSPA object is optional and specifies various TE LSP attributes to be taken into account by the PCE during path computation. The LSPA (LSP Attributes) object can either be carried within a PCReq message or a PCRep message in case of unsuccessful path computation (in this case, the PCRep message also contains a NO-PATH object and the LSPA object is used to indicate the set of constraint(s) that could not be satisfied). Most of the fields of the LSPA object are identical to the fields of the SESSION-ATTRIBUTE object defined in [RFC3209] and [RFC4090]. When absent from the PCReq message, this means that the Setup and Holding priorities are equal to 0, and there are no affinity constraints. LSPA Object-Class is to be assigned by IANA (recommended value=9) LSPA Object-Types is to be assigned by IANA (recommended value=1) Vasseur & Le Roux Expires January 6, 2008 [Page 36] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 The format of the LSPA object body is: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Exclude-any | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Include-any | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Include-all | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Setup Prio | Holding Prio | Flags |L| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Optional TLV(s) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 16: LSPA object body format Setup Prio (Setup Priority - 8 bits). The priority of the session with respect to taking resources, in the range of 0 to 7. The value 0 is the highest priority. The Setup Priority is used in deciding whether this session can preempt another session. Holding Prio (Holding Priority - 8 bits). The priority of the session with respect to holding resources, in the range of 0 to 7. The value 0 is the highest priority. Holding Priority is used in deciding whether this session can be preempted by another session. Flags (8 bits) The flag L corresponds to the "Local protection desired" bit ([RFC3209]) of the SESSION-ATTRIBUTE Object. L Flag (Local protection desired). When set, this means that the computed path must include links protected with Fast Reroute as defined in [RFC4090]. Unassigned flags MUST be set to zero on transmission and MUST be ignored on receipt. Reserved (8 bits): This field MUST be set to zero on transmission and MUST be ignored on receipt. Note that the Optional TLV field may contain additional TE LSP attributes as defined in [RFC4420]. Vasseur & Le Roux Expires January 6, 2008 [Page 37] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 7.11. Include Route Object Object The IRO (Include Route Object) is optional and can be used to specify that the computed path MUST traverse a set of specified network elements. The IRO MAY be carried within PCReq and PCRep messages. When carried within a PCRep message with the NO-PATH object, the IRO indicates the set of elements that fail the PCE to find a path. IRO Object-Class is to be assigned by IANA (recommended value=10) IRO Object-Type is to be assigned by IANA (recommended value=1) 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // (Subobjects) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 17: IRO body format Subobjects The IRO is made of sub-object(s) identical to the ones defined in [RFC3209], [RFC3473] and [RFC3477] for use in EROs. The following subobject types are supported. Type Subobject 1 IPv4 prefix 2 IPv6 prefix 4 Unnumbered Interface ID 32 Autonomous system number The L bit of such sub-object has no meaning within an IRO. 7.12. SVEC Object 7.12.1. Notion of Dependent and Synchronized path computation requests Independent versus dependent path computation requests: path computation requests are said to be independent if they are not related to each other. Conversely a set of dependent path computation requests is such that their computations cannot be performed independently of each other (a typical example of dependent requests is the computation of a set of diverse paths). Synchronized versus non-synchronized path computation requests: a set of path computation requests is said to be non-synchronized if their respective treatment (path computations) can be performed by a PCE in a serialized and independent fashion. Vasseur & Le Roux Expires January 6, 2008 [Page 38] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 There are various circumstances where the synchronization of a set of path computations may be beneficial or required. Consider the case of a set of N TE LSPs for which a PCC needs to send path computation requests to a PCE. The first solution consists of sending N separate PCReq messages to the selected PCE. In this case, the path computation requests are non synchronized. Note that the PCC may chose to distribute the set of N requests across K PCEs for load balancing purpose. Considering that M (with M+-+-+-+-+-+-+ | | | | | KeepWait |----+ | | +--| |<---+ | |+-----+-+-+-+-+-+-+ | | || | | | || | | | || V | | || +->+-+-+-+-+-+-+----+ | || | | OpenWait |-------+ || +--| |<------+ ||+----+-+-+-+-+-+-+<---+ | ||| | | | ||| | | | ||| V | | ||| +->+-+-+-+-+-+-+ | | ||| | |TCPPending |----+ | ||| +--| | | |||+---+-+-+-+-+-+-+<---+ | |||| | | | |||| | | | |||| V | | |||+--->+-+-+-+-+ | | ||+---->| Idle |-------+ | |+----->| |----------+ +------>+-+-+-+-+ Figure 23: PCEP Finite State Machine for the PCC PCEP defines the following set of variables: Connect: timer (in seconds) started after having initialized a TCP connection using the PCEP well-known TCP port. The value of the TCPConnect timer is 60 seconds. ConnectRetry: specifies the number of times the system has tried to establish a TCP connection with a PCEP peer without success. ConnectMaxRetry: Maximum number of times the system tries to establish a TCP connection using the PCEP well-known TCP port before going back to the Idle state. The value of the ConnectMaxRetry is 5. Vasseur & Le Roux Expires January 6, 2008 [Page 59] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 OpenWait: timer that corresponds to the amount of time a PCEP peer will wait to receive an Open message from the PCEP peer after the expiration of which the system releases the PCEP resource and go back to the Idle state. The OpenWait timer has a fixed value of 60 seconds. KeepWait: timer that corresponds to the amount of time a PCEP peer will wait to receive a KeepAlive or a PCErr message from the PCEP peer after the expiration of which the system releases the PCEP resource and go back to the Idle state. The KeepWait timer has a fixed value of 60 seconds. OpenRetry: specifies the number of times the system has received an Open message with unacceptable PCEP session characteristics. The following two states variable are defined: RemoteOK: the RemoteOK variable is a Boolean set to 1 if the system has received an acceptable Open message. LocalOK: the LocalOK variable is a Boolean set to 1 if the system has received a Keepalive message acknowledging that the Open message sent to the peer was valid. Idle State: The idle state is the initial PCEP state where PCEP (also referred to as "the system") waits for an initialization event that can either be manually triggered by the user (configuration) or automatically triggered by various events. In Idle state, PCEP resources are allocated (memory, potential process, ...) but no PCEP messages are accepted from any PCEP peer. The system listens the well-known PCEP TCP port. The following set of variable are initialized: TCPRetry=0, LocalOK=0, RemoteOK=0, OpenRetry=0. Upon detection of a local initialization event (e.g. user configuration to establish a PCEP session with a particular PCEP peer, local event triggering the establishment of a PCEP session with a PCEP peer such as the automatic detection of a PCEP peer, ...), the Vasseur & Le Roux Expires January 6, 2008 [Page 60] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 system: o Initiates of a TCP connection with the PCEP peer, o Starts the Connect timer, o Moves to the TCPPending state. Upon receiving a TCP connection on the well-known PCEP TCP port, if the TCP connection establishment succeeds, the system: o Sends an Open message, o Starts the OpenWait timer, o Moves to the OpenWait state. If the connection establishment fails, the system remains in the Idle state. Any other event received in the Idle state is ignored. It is expected that an implementation will use an exponentially increase timer between automatically generated Initialization events and between retrials of TCP connection establishments. TCPPending State If the TCP connection establishment succeeds, the system: o Sends an Open message, o Starts the OpenWait timer, o Moves to the OpenWait state. If the TCP connection establishment fails (an error is detected during the TCP connection establishment) or the Connect timer expires: If ConnectRetry =ConnectMaxRetry the system moves to the Idle State If ConnectRetry < ConnectMaxRetry the system: o Initiates of a TCP connection with the PCEP peer, o Increments the ConnectRetry variable, o Restarts the Connect timer, Vasseur & Le Roux Expires January 6, 2008 [Page 61] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 o Stays in the TPCPending state. If the system detects that the PCEP peer tries to simultaneously establish a TCP connection, it stops the TCP connection establishment if and only if the PCEP peer has a higher IP address and moves to the Idle state. This guarantees that in case of "collision" a single TCP connection is established. In response to any other event the system releases the PCEP resources for that peer and moves back to the Idle state. OpenWait State: In the OpenWait state, the system waits for an Open message from its PCEP peer. If the system receives an Open message from the PCEP peer before the expiration of the OpenWait timer, PCEP checks the PCEP session attributes (Keepalive frequency, DeadTimer, ...). If an error is detected (e.g. malformed Open message, presence of two Open objects, ...), PCEP generates an error notification, the PCEP peer sends a PCErr message with Error-Type=1 and Error-value=1. The system releases the PCEP resources for the PCEP peer, closes the TCP connection and moves to the Idle state. If no errors are detected, PCEP increments the OpenRetry variable. If no errors are detected, OpenRetry=1 and the session characteristics are unacceptable, the PCEP peer sends a PCErr with Error-Type=1 and Error-value=5, the system releases the PCEP resources for that peer and moves back to the Idle state. If no errors are detected and the session characteristics are acceptable to the local system, the system: o Sends a Keepalive message to the PCEP peer, o Starts the Keepalive timer, o Sets the RemoteOK variable to 1. If LocalOK=1 the system clears the OpenWait timer and moves to the UP state. If LocalOK=0 the system clears the OpenWait timer, starts the KeepWait timer and moves to the KeepWait state. Vasseur & Le Roux Expires January 6, 2008 [Page 62] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 If no errors are detected but the session characteristics are unacceptable and non-negotiable, the PCEP peer sends a PCErr with Error-Type=1 and Error-value=3, the system releases the PCEP resources for that peer, and moves back to the Idle state. If no errors are detected, OpenRetry=0, the session characteristics are unacceptable but negotiable (such as the Keepalive period or the DeadTimer), the system: o Increments the OpenRetry variable, o Sends a PCErr message with Error-Type=1 and Error-value=4 that contains proposed acceptable session characteristics, o If LocalOK=1, the system restarts the OpenWait timer and stays in the OpenWait state o If LocalOK=0, the system clears the OpenWait timer, starts the KeepWait timer and moves to the KeepWait state If no Open message is received before the expiration of the OpenWait timer, the PCEP peer sends a PCErr message with Error-Type=1 and Error-value=2, the system releases the PCEP resources for the PCEP peer, closes the TCP connection and moves to the Idle state. In response to any other event the system releases the PCEP resources for that peer and moves back to the Idle state. KeepWait State In the Keepwait state, the system waits for the receipt of a Keepalive from its PCEP peer acknowledging its Open message or a PCErr message in response to unacceptable PCEP session characteristics proposed in the Open message. If an error is detected (e.g. malformed Keepalive message), PCEP generates an error notification, the PCEP peer sends a PCErr message with Error-Type=1 and Error-value=1. The system releases the PCEP resources for the PCEP peer, closes the TCP connection and moves to the Idle state. If a Keepalive message is received before the expiration of the KeepWait timer, then the system sets LocalOK=1 and: o If RemoteOK=1, the system clears the KeepWait timer and moves to the UP state. Vasseur & Le Roux Expires January 6, 2008 [Page 63] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 o If RemoteOK=0, the system clears the KeepWait timer, starts the OpenWait timer and moves to the OpenWait State. If a PCErr message is received before the expiration of the KeepWait timer: 1. If the proposed values are unacceptable, the PCEP peer sends a PCErr message with Error-Type=1 and Error-value=6 and the system releases the PCEP resources for that PCEP peer, closes the TCP connection and moves to the Idle state. 2. If the proposed values are acceptable, the system adjusts its PCEP session characteristics according to the proposed values received in the PCErr message restarts the KeepWait timer and sends a new Open message. If RemoteOK=1, the system restarts the KeepWait timer and stays in the KeepWait state. If RemoteOK=0, the system clears the KeepWait timer, start the OpenWait timer and moves to the OpenWait state. If neither a Keepalive nor a PCErr is received after the expiration of the KeepWait timer, the PCEP peer sends a PCErr message with Error-Type=1 and Error-value=7 and, system releases the PCEP resources for that PCEP peer, closes the TCP connection and moves to the Idle State. In response to any other event the system releases the PCEP resources for that peer and moves back to the Idle state. UP State In the UP state, the PCEP peer starts exchanging PCEP messages according to the session characteristics. If the Keepalive timer expires, the system restarts the Keepalive timer and sends a Keepalive message. If no PCEP message (Keepalive, PCReq, PCRep, PCNtf) is received from the PCEP peer after the expiration of the DeadTimer, the system terminates PCEP session according to the procedure defined in Section 6.8, releases the PCEP resources for that PCEP peer, closes the TCP connection and moves to the Idle State. If a malformed message is received, the system terminates the PCEP session according to the procedure defined in Section 6.8, releases the PCEP resources for that PCEP peer, closes the TCP connection and moves to the Idle State. If the system detects that the PCEP peer tries to setup a second TCP Vasseur & Le Roux Expires January 6, 2008 [Page 64] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 connection, it stops the TCP connection establishment and sends a PCErr with Error-Type=9. If the TCP connection fails, the system releases the PCEP resources for that PCEP peer, closes the TCP connection and moves to the Idle State. 11. Security Considerations PCEP could be the target of the following attacks: o Spoofing (PCC or PCE impersonation) o Snooping (message interception) o Falsification o Denial of Service A PCEP attack may have significant impact, particularly in an inter-AS context as PCEP facilitates inter-AS path establishment. Several mechanisms are proposed below, so as to ensure authentication, integrity and privacy of PCEP Communications, and also to protect against DoS attacks. 11.1. PCEP Authentication and Integrity It is RECOMMENDED to use TCP-MD5 [RFC1321] signature option to provide for the authenticity and integrity of PCEP messages. This will allow protecting against PCE or PCC impersonation and also against message content falsification. This requires the maintenance, exchange and configuration of MD-5 keys on PCCs and PCEs. Note that such maintenance may be especially onerous to the operators as pointed out in [I-D.ietf-rpsec-bgpsecrec]. Hence it is important to limit the number of keys while ensuring the required level of security. MD-5 signature faces some limitations, as per explained in [RFC2385]. Note that when one digest technique stronger than MD5 is specified and implemented, PCEP could be easily upgraded to use it. 11.2. PCEP Privacy Ensuring PCEP communication privacy is of key importance, especially in an inter-AS context, where PCEP communication end-points do not reside in the same AS, as an attacker that intercept a PCE message Vasseur & Le Roux Expires January 6, 2008 [Page 65] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 could obtain sensitive information related to computed paths and resources. Privacy can be ensured thanks to encryption. To ensure privacy of PCEP communication, IPSec [RFC4303] tunnels MAY be used between PCC and PCEs or between PCEs. Note that this could also be used to ensure Authentication and Integrity, in which case, TCP MD-5 option would not be required. 11.3. Protection against Denial of Service attacks PCEP can be the target of TCP DoS attacks, such as for instance SYN attacks, as all protocols running on top of TCP. PCEP can use the same mechanisms as defined in [RFC3036] to mitigate the threat of such attacks: o A PCE should avoid promiscuous TCP listens for PCEP TCP connection establishment. It should use only listens that are specific to authorized PCCs. o The use of the MD5 option helps somewhat since it prevents a SYN from being accepted unless the MD5 segment checksum is valid. However, the receiver must compute the checksum before it can decide to discard an otherwise acceptable SYN segment. o The use of access-list on the PCE so as to restrict access to authorized PCCs. 11.4. Request input shaping/policing A PCEP implementation may be subject to Denial Of Service attacks consisting of sending a very large number of PCEP messages (e.g. PCReq messages). Thus, especially in multi-Service Providers environments, a PCE implementation should implement request input shaping/policing so as to throttle the amount of received PCEP messages without compromising the implementation behavior. 12. Authors' addresses This document was the collective work of several authors. The content of this document was contributed by the editors and the co- authors listed below: Arthi Ayyangar Nuova Systems 2600 San Tomas Expressway Santa Clara, CA 95051 USA Vasseur & Le Roux Expires January 6, 2008 [Page 66] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 Email: arthi@nuovasystems.com Eiji Oki NTT Midori 3-9-11 Musashino, Tokyo, 180-8585 JAPAN Email: oki.eiji@lab.ntt.co.jp Alia Atlas Google 1600 Amphitheatre Parkway Montain View, CA 94043 USA Email: akatlas@alum.mit.edu Andrew Dolganow Alcatel 600 March Road Ottawa, ON K2K 2E6 CANADA Email: andrew.dolganow@alcatel.com Yuichi Ikejiri NTT Communications Corporation 1-1-6 Uchisaiwai-cho, Chiyoda-ku Tokyo, 100-819 JAPAN Email: y.ikejiri@ntt.com Kenji Kumaki KDDI Corporation Garden Air Tower Iidabashi, Chiyoda-ku, Tokyo, 102-8460 JAPAN Email: ke-kumaki@kddi.com Vasseur & Le Roux Expires January 6, 2008 [Page 67] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 13. Acknowledgements The authors would like to thank Dave Oran, Dean Cheng, Jerry Ash, Igor Bryskin, Carol Iturrade, Siva Sivabalan, Rich Bradford, Richard Douville, Jon Parker and Martin German for their very valuable input. Special thank to Adrian Farrel for his very valuable suggestions. 14. References 14.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003. [RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", RFC 3477, January 2003. [RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005. 14.2. Informative References [I-D.ietf-ccamp-inter-domain-rsvp-te] Ayyangar, A., "Inter domain Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering - RSVP-TE extensions", draft-ietf-ccamp-inter-domain-rsvp-te-06 (work in progress), April 2007. [I-D.ietf-pce-disco-proto-isis] Roux, J., "IS-IS protocol extensions for Path Computation Element (PCE) Discovery", draft-ietf-pce-disco-proto-isis-06 (work in progress), Vasseur & Le Roux Expires January 6, 2008 [Page 68] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 June 2007. [I-D.ietf-pce-disco-proto-ospf] Roux, J., "OSPF protocol extensions for Path Computation Element (PCE) Discovery", draft-ietf-pce-disco-proto-ospf-06 (work in progress), June 2007. [I-D.ietf-pce-inter-layer-req] Oki, E., "PCC-PCE Communication Requirements for Inter- Layer Traffic Engineering", draft-ietf-pce-inter-layer-req-04 (work in progress), March 2007. [I-D.ietf-pce-interas-pcecp-reqs] Bitar, N., "Inter-AS Requirements for the Path Computation Element Communication Protocol (PCECP)", draft-ietf-pce-interas-pcecp-reqs-01 (work in progress), October 2006. [I-D.ietf-pce-manageability-requirements] Farrel, A., "Inclusion of Manageability Sections in PCE Working Group Drafts", draft-ietf-pce-manageability-requirements-01 (work in progress), March 2007. [I-D.ietf-rpsec-bgpsecrec] Christian, B. and T. Tauber, "BGP Security Requirements", draft-ietf-rpsec-bgpsecrec-07 (work in progress), February 2007. [I-D.kkoushik-pce-pcep-mib] Stephan, E. and K. Koushik, "PCE communication protocol(PCEP) Management Information Base", draft-kkoushik-pce-pcep-mib-00 (work in progress), February 2007. [I-D.vasseur-pce-monitoring] Vasseur, J., "A set of monitoring tools for Path Computation Element based Architecture", draft-vasseur-pce-monitoring-03 (work in progress), May 2007. [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 Signature Option", RFC 2385, August 1998. Vasseur & Le Roux Expires January 6, 2008 [Page 69] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 [RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A., and B. Thomas, "LDP Specification", RFC 3036, January 2001. [RFC3785] Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx, P., and T. Telkamp, "Use of Interior Gateway Protocol (IGP) Metric as a second MPLS Traffic Engineering (TE) Metric", BCP 87, RFC 3785, May 2004. [RFC4022] Raghunarayan, R., "Management Information Base for the Transmission Control Protocol (TCP)", RFC 4022, March 2005. [RFC4101] Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101, June 2005. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. [RFC4420] Farrel, A., Papadimitriou, D., Vasseur, J., and A. Ayyangar, "Encoding of Attributes for Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Establishment Using Resource ReserVation Protocol-Traffic Engineering (RSVP-TE)", RFC 4420, February 2006. [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. [RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, September 2006. [RFC4674] Le Roux, J., "Requirements for Path Computation Element (PCE) Discovery", RFC 4674, October 2006. [RFC4927] Le Roux, J., "Path Computation Element Communication Protocol (PCECP) Specific Requirements for Inter-Area MPLS and GMPLS Traffic Engineering", RFC 4927, June 2007. Appendix A. PCEP Variables PCEP defines the following configurable variables: KeepAlive timer: minimum period of time between the sending of PCEP messages (Keepalive, PCReq, PCRep, PCNtf) to a PCEP peer. A suggested value for the Keepalive timer is 30 seconds. DeadTimer: period of timer after the expiration of which a PCEP peer Vasseur & Le Roux Expires January 6, 2008 [Page 70] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 declared the session down if no PCEP message has been received. SyncTimer: the SYNC timer is used in the case of synchronized path computation request using the SVEC object defined in Section 7.12.3. Consider the case where a PCReq message is received by a PCE that contains the SVEC object referring to M synchronized path computation requests. If after the expiration of the SYNC timer all the M path computation requests have not been received, a protocol error is triggered and the PCE MUST cancel the whole set of path computation requests. A RECOMMENDED value for the SYNC timer is 60 seconds. Authors' Addresses JP Vasseur (editor) Cisco Systems 1414 Massachusetts Avenue Boxborough, MA 01719 USA Email: jpv@cisco.com JL Le Roux (editor) France Telecom 2, Avenue Pierre-Marzin Lannion, 22307 FRANCE Email: jeanlouis.leroux@orange-ftgroup.com Vasseur & Le Roux Expires January 6, 2008 [Page 71] Internet-Draft draft-ietf-pce-pcep-08.txt July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. 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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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Vasseur & Le Roux Expires January 6, 2008 [Page 72]