Network Working Group Fatai Zhang Internet-Draft Huawei Intended status: Standards Track A. Farrel Old Dog Consulting G. Bernstein Grotto Networking Expires: February 31, 2013 August 31, 2012 Conveying Vendor-Specific Constraints in the Path Computation Element Protocol draft-ietf-pce-vendor-constraints-08.txt Abstract The Path Computation Element Protocol (PCEP) is used to convey path computation requests and responses between Path Computation Clients (PCCs) and Path Computation Elements (PCEs), and also between cooperating PCEs. In PCEP the path computation requests carry details of the constraints and objective functions that the PCC wishes the PCE to apply in its computation. The mechanisms defined for indicating objective functions include the capability to convey vendor-specific objective functions. This document defines a facility to carry vendor-specific constraints in PCEP. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 Farrel & Zhang Expires February 2013 [Page 1] draft-ietf-pce-vendor-constraints-08.txt August 2012 Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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 [RFC2119]. 1. Introduction A Path Computation Element (PCE) is 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. An architecture for the use of PCEs is defined in [RFC4655]. The Path Computation Element Protocol (PCEP) is defined in [RFC5440] to exchange path computation requests and responses between Path Computation Clients (PCCs) and PCEs. It is also used between cooperating PCEs. Path computations performed by a PCE depend on a set of constraints indicated by the PCC. These constraints include the end points of the path to compute (source and destination), and may include other simple constraints such as bandwidth requirements and metric maxima (for example, a maximum threshold for the hop count or the TE metric of the computed path). The PCE also needs to use an objective function to qualify the path it selects as meeting the requirements of the PCC. The PCE may have a default objective function, but the PCC can also indicate which objective function it wants applied by placing an Objective Function object in the path computation request message [RFC5541]. A core set Farrel & Zhang Expires February 2013 [Page 2] draft-ietf-pce-vendor-constraints-08.txt August 2012 of objective functions to be supported in PCEP messages is defined in the base PCEP requirements [RFC4657], and [RFC5541] defines each of these functions as an abstract formula. The registry of codepoints used to indicate objective functions is managed by IANA and new assignments can be made according to "IETF Review" and "First Come First Served" policies [RFC5226]. PCE implementations may also choose to offer proprietary, vendor-specific objective functions, and there is scope for this within the codepoint registry created by [RFC5541] using the codepoints that are flagged as "Reserved for Private Use." Proprietary objective functions may operate on non-standard constraints or metrics. The PCEP Metric Object defined in [RFC5440] has scope for the definition of new, standardized metrics, but no facility for the definition of vendor-specific metrics. At the same time, there is no mechanism in PCEP for carrying other, more complex, vendor-specific constraints. This document defines a new PCEP object, the Vendor Constraints object that can be used to carry arbitrary, proprietary constraint information. This document also defines a new PCEP TLV, the VENDOR-CONSTRAINT-TLV that can be used to carry arbitrary constraint information within any PCEP object that supports TLVs. 2. Procedures for The Vendor Constraints Object A PCC that wants to convey proprietary or vendor-specific constraints or metrics to a PCE does so by including a Vendor Constraints object in the PCReq message. The contents and format of the object are described in Section 4, but it is important to note that the object includes an Enterprise Number that is a unique identifier of an organization responsible for the definition of the content and meaning of the object. A PCE that receives a PCReq message containing a Vendor Constraints object MUST act according to the P-bit in the object header. That is, if the P flag is set, the object MUST be treated as mandatory and the request is either processed using the contents of the object or rejected as defined in [RFC5440]. If the P flag is clear, then as defined in [RFC5440], the object MAY be used by the PCE or MAY be ignored. The PCC sets the P flag according to how it wishes the request to be processed. The PCE determines how to interpret the Vendor Constraints object by Farrel & Zhang Expires February 2013 [Page 3] draft-ietf-pce-vendor-constraints-08.txt August 2012 examining the Enterprise Number it contains. If the Enterprise Number is unknown to the PCE, it MUST treat the Vendor Constraints object as unknown and handle it as described in [RFC5440] according to the setting of the P flag (see also Section 2.1). The Vendor Constraints object is OPTIONAL in a PCReq message. Multiple instances of the object MAY be used on a single PCReq message and each MUST be treated according to its P-bit setting. The object can be present in two places within the PCReq message to enable it to apply to a single path computation request or to a set of synchronized requests. This usage mirrors the usage of the Objective Function object [RFC5541]. Thus, the PCReq message based on [RFC6006] is encoded as follows using the syntax described in [RFC5511]. ::= [] where ::= [] [] [] [] [] [] ::= [] ::= [] ::= [] ::= [] [] [] [] [] [] [] [] Farrel & Zhang Expires February 2013 [Page 4] draft-ietf-pce-vendor-constraints-08.txt August 2012 where ::= [] [] [] [] ::= [] [] ::= [] The Vendor Constraints object is included in a PCRep message in exactly the same way as any other object as defined in [RFC5440]. 2.1. Backward Compatibility A legacy implementation that does not recognize the Vendor Constraint object will act according to the procedures set out in [RFC5440]. If the P flag is set in the object, the message will be rejected using a PCErr message with an Error Type of 3 ("Unknown Object"). If the P flag is not set, the object can safely be ignored by the recipient. 3. Procedures for The Vendor Constraints TLV The Vendor Constraints TLV may be used to indicate a vendor-specific constraint that applies to a specific PCEP object by including it in the object. The PCE determines how to interpret the Vendor Constraints TLV by examining the Enterprise Number it contains. If the Enterprise Number is unknown to the PCE, it MUST treat the Vendor Constraints TLV as unknown and handle it as described in [RFC5440] (see also Section 3.1). Further specifications are needed to define the position and meaning of the Vendor Constraints TLV for specific PCEP objects. 3.1. Backward Compatibility A legacy implementation that does not recognize the Vendor Constraint TLV in an object will act according to the procedures set out in [RFC5440]. As described in Section 7.1 of [RFC5440], unrecognized TLVs MUST be ignored. Farrel & Zhang Expires February 2013 [Page 5] draft-ietf-pce-vendor-constraints-08.txt August 2012 4. Protocol Elements The Vendor Constraints object and TLV conform to the format for PCEP objects and TLVs defined in [RFC5440]. VENDOR-CONSTRAINT Object-Class is to be assigned by IANA. VENDOR-CONSTRAINT Object-Type 1 VENDOR-CONSTRAINT-TLV Type is to be assigned by IANA. The format of the VENDOR-CONSTRAINT object and the VENDOR-CONSTRAINT-TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Enterprise Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Enterprise-Specific Information ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Enterprise Number A unique identifier of an organization encoded as a 32-bit integer. Enterprise Numbers are assigned by IANA and managed through an IANA registry [RFC2578]. Enterprise-Specific Information The detailed enterprise-specific constraint information carried by the object. The format and interpretation of this information is a matter for the enterprise identified by the Enterprise Number. Such formats and interpretation may be published by the enterprise (possibly through an informational RFC or through commercial documentation) so that PCCs or PCEs that are not part of the organization can use the information. 5. IANA Considerations IANA maintains a registry of PCEP parameters called the "Path Computation Element Protocol (PCEP) Numbers". 5.1. New PCEP Object IANA is requested to make an allocation from the "PCEP Objects" sub-registry as follows. The value here is suggested for use by IANA. Farrel & Zhang Expires February 2013 [Page 6] draft-ietf-pce-vendor-constraints-08.txt August 2012 Object-Class Value Name Reference TBD1 VENDOR-CONSTRAINT [This.I-D] Object-Type 0: Unassigned 1: Vendor-Specific Constraints [This.I-D] 2-255: Unassigned 5.2. New PCEP TLV IANA is requested to make an allocation from the "PCEP TLV Type Indicators" sub-registry as follow. Value Description Reference TBD2 VENDOR-CONSTRAINT-TLV [This.I-D] 6. Management Considerations This section follows the guidance of [RFC5706] and [RFC6123]. 6.1. Control of Function and Policy A PCEP implementation SHUOLD allow configuring of various parameters as described in [RFC5440]. A PCC implementation that uses vendor- specific constraints MAY make the use of these constraints configurable either across the whole PCC, per PCE that the PCC uses, or per path computation request. A PCE that supports vendor-specific constraints MAY make the support of these constraints configurable, and MAY allow configuration of policies for the use of the constraints. 6.2. Information and Data Models A PCEP MIB module is defined in [PCE-MIB] that describes managed objects for modeling of PCEP communications. It is NOT RECOMMENDED that standard MIB modules are extended to include detailed information about the content of the Vendor Constaints object. However, the standard MIB module MAY be extended to report the use of the Vendor Specific object and the Enterprise Numbers that the objects contain. 6.3. Liveness Detection and Monitoring This document makes no change to the basic operation of PCEP and so there are no changes to the requirements for liveness detection and monitoring set out in [RFC4657] and [RFC5440]. Farrel & Zhang Expires February 2013 [Page 7] draft-ietf-pce-vendor-constraints-08.txt August 2012 6.4. Verifying Correct Operation This document makes no change to the basic operation of PCEP and so there are no changes to the requirements or techniques for monitoring the correct operation of the protocol out in [RFC4657] and [RFC5440]. Note that "correct operation" in this context referes to the operation of the protocol itself, and not to the operation of the computation algorithms which are out of scope for all PCEP work. Mechanisms for verifying the correct operation of computation algorithms might involve comparing the results returned by more than one PCE. Scope for this might be limited by the use of vendor constraints unless multiple PCEs support the same set of constraints. 6.5. Requirements on Other Protocols and Functional Components This document does not place any new requirements on other network components or protocols. However, it may be beneficial to consider whether a PCE should advertise the enterprise numbers and vendor constraints it supports. This advertisement could be within PCE Discovery ([RFC5088], [RFC5089]) or through extensions to PCEP [RFC5440]. Extensions for discovery and advertisement are outside the scope of this document. 6.6. Impact on Network Operation The availability of vendor constraints in PCEP messages may facilitate more complex and detailed path computations that may enhance the way in which the network is operated. On the other hand, the presence of additional vendor-specific information in PCEP messages may congest the operation of the protocol especially if the PCE does not support the constraints supplied by the PCC. Thus, a PCC SHOULD monitor the capabilities of a PCE either by discovery mechanisms as described in Section 6.5, or through the receipt of negative responses. A PCC SHOULD NOT include vendor constraints in a PCReq message to a PCE that it believes does not support the constraints and that will not forward the request to some other PCE that does support the constraints. Farrel & Zhang Expires February 2013 [Page 8] draft-ietf-pce-vendor-constraints-08.txt August 2012 7. Security Considerations The protocol extensions defined in this document do not substantially change the nature of PCEP. Therefore, the security considerations set out in [RFC5440] apply unchanged. Operators should note that an attack on PCEP may involve making PCEP messages as large as possible in order to consume bandwidth and processing power. The Vendor Constraints object may provide a mechanism for this type of attack. It may be protected against by using the authentication and integrity procedures described in [RFC5440]. 8. References 8.1. Normative References [RFC2119] S. Bradner, "Key words for use in RFCs to indicate requirements levels", RFC 2119, March 1997. [RFC5440] Vasseur, J.P., Le Roux, J.L., Ayyangar, A., Oki, E., Ikejiri, A., Atlas, A., Dolganow, A., "Path Computation Element (PCE) communication Protocol (PCEP)", RFC 5440, March 2009. [RFC5511] Farrel, A., "Reduced Backus-Naur Form (RBNF): A Syntax to Form Encoding Rules in Various Routing Protocol Specifications", RFC 5511, April 2007. [RFC6006] Q. Zhao, et al., "Extensions to the Path Computation Element Communication Protocol (PCEP) for Point-to- Multipoint Traffic Engineering Label Switched Paths", RFC 6006, September 2009. 8.2. Informative References [RFC2578] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation Element (PCE) Architecture", RFC 4655, August 2006. [RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, September 2006. Farrel & Zhang Expires February 2013 [Page 9] draft-ietf-pce-vendor-constraints-08.txt August 2012 [RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang, "OSPF Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5088, January 2008. [RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang, "IS-IS Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5089, January 2008. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Objective Function Encoding in Path Computation Element Communication and Discovery protocols", RFC 5541, June 2009. [RFC5706] Harrington, D., "Guidelines for Considering Operations and Management of New Protocols and Protocol Extensions", RFC 5706, November 2009. [RFC6123] Farrel, A., "Inclusion of Manageability Sections in Path Computation Element (PCE) Working Group Drafts", RFC 6123, February 2011. [PCE-MIB] Stephan, E. and K. Koushik, "PCE Communication Protocol (PCEP) Management Information Base", draft-ietf-pce-pcep- mib, work in progress. 9. Acknowledgements Thanks to Meral Shirazipour, Ramon Casellas, Cyril Margaria, and Dhruv Dhody for review and comments. 10. Authors' Addresses Adrian Farrel Old Dog Consulting EMail: adrian@olddog.co.uk Fatai Zhang Huawei Technologies Email: zhangfatai@huawei.com Greg Bernstein Grotto Networking EMail: gregb@grotto-networking.com Farrel & Zhang Expires February 2013 [Page 10]