Network Working Group E. Oki Internet Draft UEC Tokyo Category: Standards Track Tomonori Takeda Created: December 2008 NTT Expires: June 2009 J-L Le Roux France Telecom A. Farrel Old Dog Consulting Extensions to the Path Computation Element communication Protocol (PCEP) for Inter-Layer MPLS and GMPLS Traffic Engineering draft-ietf-pce-inter-layer-ext-02.txt 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. Abstract The Path Computation Element (PCE) provides path computation functions in support of traffic engineering in Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks. MPLS and GMPLS networks may be constructed from layered service networks. It is advantageous for overall network efficiency to provide end-to-end traffic engineering across multiple network layers through a process called inter-layer traffic engineering. PCE is a candidate solution for such requirements. The PCE communication Protocol (PCEP) is designed as a communication protocol between Path Computation Clients (PCCs) and Oki, Takeda, Le Roux, and Farrel [Page 1] PCEP Extensions for Inter-Layer TE December 2008 PCEs. This document presents PCEP extensions for inter-layer traffic engineering. Table of Contents 1. Introduction.................................................2 2. Overview of PCE-Based Inter-Layer Path Computation...........3 3. Protocol Extensions..........................................4 3.1. INTER-LAYER Object........................................4 3.2. SWITCH-LAYER Object.......................................6 3.2.1. REQ-ADAP-CAP Object.....................................8 3.3. New Metric Type...........................................9 4. Procedure....................................................9 4.1. Path Computation Request..................................9 4.2. Path Computation Reply...................................10 5. Updated Format of PCEP Messages.............................10 6. Manageability Considerations................................11 7. IANA Considerations.........................................12 7.1. New PCEP Objects.........................................12 7.2. New Registry for INTER-LAYER Object Flags................12 7.3. METRIC Type..............................................13 8. Security Considerations.....................................13 9. Acknowledgments.............................................13 10. References................................................13 10.1. Normative Reference......................................13 10.2. Informative Reference....................................14 11. Authors' Addresses........................................14 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 The Path Computation Element (PCE) defined in [RFC4655] is an entity that is capable of computing a network path or route based on a network graph, and applying computational constraints. A Path Computation Client (PCC) may make requests to a PCE for paths to be computed. A network may comprise multiple layers. These layers may represent separations of technologies (e.g., packet switch capable (PSC), Oki, Takeda, Le Roux, and Farrel [Page 2] PCEP Extensions for Inter-Layer TE December 2008 time division multiplex (TDM), lambda switch capable (LSC)) [RFC3945], separation of data plane switching granularity levels (e.g., PSC-1 and PSC-2, or VC4 and VC12) [RFC5212], or a distinction between client and server networking roles (e.g., commercial or administrative separation of client and server networks). In this multi-layer network, Label Switched Paths (LSPs) in lower layers are used to carry higher-layer LSPs. The network topology formed by lower-layer LSPs and advertised as traffic engineering links (TE links) in the higher layer is called a Virtual Network Topology (VNT) [RFC5212]. It is important to optimize network resource utilization globally, i.e., taking into account all layers, rather than optimizing resource utilization at each layer independently. This allows better network efficiency to be achieved. This is what we call inter-layer traffic engineering. This includes mechanisms allowing the computation of end-to-end paths across layers (known as inter- layer path computation), and mechanisms for control and management of the VNT by setting up and releasing LSPs in the lower layers [RFC5212]. PCE can provide a suitable mechanism for resolving inter-layer path computation issues. The framework for applying the PCE-based path computation architecture to inter-layer traffic engineering is described in [PCE-INTER-LAYER-FRWK]. The PCE communication protocol (PCEP) is designed as a communication protocol between PCCs and PCEs and is defined in [PCEP]. A set of requirements for PCEP extensions to support inter- layer traffic engineering is described in [PCE-INTER-LAYER-REQ]. This document presents PCEP extensions for inter-layer traffic engineering that satisfy the requirements described in [PCE-INTER- LAYER-REQ]. 2. Overview of PCE-Based Inter-Layer Path Computation [RFC4206] defines a way to signal a higher-layer LSP which has an explicit route that includes hops traversed by LSPs in lower layers. The computation of end-to-end paths across layers is called Inter- Layer Path Computation. A Label Switching Router (LSR) in the higher-layer might not have information on the lower-layer topology, particularly in an overlay or augmented model [RFC3945], and hence may not be able to compute an end-to-end path across layers. Oki, Takeda, Le Roux, and Farrel [Page 3] PCEP Extensions for Inter-Layer TE December 2008 PCE-based inter-layer path computation consists of using one or more PCEs to compute an end-to-end path across layers. This could be achieved by relying on a single PCE that has topology information about multiple layers and can directly compute an end- to-end path across layers considering the topology of all of the layers. Alternatively, the inter-layer path computation could be performed using multiple cooperating PCEs where each PCE has information about the topology of one or more layers (but not all layers) and where the PCEs collaborate to compute an end-to-end path. [PCE-INTER-LAYER-FRWK] describes models for inter-layer path computation in more detail. 3. Protocol Extensions This section describes PCEP extensions for inter-layer path computation. Three new objects are defined: the INTER-LAYER object, the SWITCH-LAYER object, and the REQ-ADAP-CAP object. Also, a new metric type is defined. 3.1. INTER-LAYER Object The INTER-LAYER object is optional and can be used in PCReq and PCRep messages. In a PCReq message, the INTER-LAYER object indicates whether inter- layer path computation is allowed, the type of path to be computed, and whether triggered signaling (hierarchical LSPs per [RFC4206] or stitched LSPs per [RFC5150] depending on physical network technologies) is allowed. When the INTER-LAYER object is absent from a PCReq message, the receiving PCE MUST process as though inter-layer path computation had been explicitly disallowed (I-bit set to zero - see below). In a PCRep message, the INTER-LAYER object indicates whether inter- layer path computation has been performed, the type of path that has been computed, and whether triggered signaling is used. When a PCReq message includes more than one request, an INTER-LAYER object is used per request. When a PCRep message includes more than one path per request that is responded to, an INTER-LAYER object is used per path. INTER-LAYER Object-Class is to be assigned by IANA (recommended value=18) Oki, Takeda, Le Roux, and Farrel [Page 4] PCEP Extensions for Inter-Layer TE December 2008 INTER-LAYER Object-Type is to be assigned by IANA (recommended value=1) The format of the INTER-LAYER 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 |T|M|I| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I flag (1 bit): The I flag is used by a PCC in a PCReq message to indicate to a PCE whether an inter-layer path is allowed. When the I flag is set (one), the PCE MAY perform inter-layer path computation and return an inter-layer path. When the flag is clear (zero), the path that is returned MUST NOT be an inter-layer path. The I flag is used by a PCE in a PCRep message to indicate to a PCC whether the path returned is an inter-layer path. When the I flag is set (one), the path is an inter-layer path. When it is clear (zero), the path is contained within a single layer either because inter-layer path computation was not performed or because a mono- layer path (without any virtual TE link and without any loose hop that spans the lower-layer network) was found notwithstanding the use of inter-layer path computation. M flag (1 bit): The M flag is used by a PCC in a PCReq message to indicate to a PCE whether mono-layer path or multi-layer path is requested. When the M flag is set (one), multi-layer path is requested. When it is clear (zero), mono-layer path is requested. The M flag is used by a PCE in a PCRep message to indicate to a PCC whether mono-layer path or multi-layer path is returned. When M flag is set (one), multi-layer path is returned. When M flag is set (zero), mono-layer path is returned. If the I flag is clear (zero), the M flag has no meaning and MUST be ignored. [PCE-INTER-LAYER-REQ] describes two sub-options for mono-layer path. - A mono-layer path that is specified by strict hops. The path may include virtual TE links. - A mono-layer path that includes loose hops that span the lower- layer network. Oki, Takeda, Le Roux, and Farrel [Page 5] PCEP Extensions for Inter-Layer TE December 2008 The choice of this sub-option can be specified by the use of O flag in the RP object specified in [PCEP]. T flag (1 bit): The T flag is used by a PCC in a PCReq message to indicate to a PCE whether triggered signaling is allowed. When the T flag is set (one), triggered signaling is allowed. When it is clear (zero), triggered signaling is not allowed. The T flag is used by a PCE in a PCRep message to indicate to a PCC whether triggered signaling is required to support the returned path. When the T flag is set (one), triggered signaling is required. When it is clear (zero), triggered signaling is not required. Note that triggered signaling is used to support hierarchical [RFC4206] or stitched [RFC5150] LSPs according to the physical attributes of the network layers. If the I flag is clear (zero), the T flag has no meaning and MUST be ignored. Note that the I flag and M flag differ in the following ways. - When the I flag is clear (zero), virtual TE links must not be used in path computation. In addition, loose hops that span the lower-layer network must not be specified. Only regular TE links from the same layer may be used. - When the I flag is set (one), the M flag is clear (zero), and the T flag is set (one), virtual TE links are allowed in path computation. In addition, when the O flag of the RP object is set, loose hops that span the lower-layer network may be specified. This will initiate lower-layer LSP setup, thus inter-layer path is setup even though the path computation result from a PCE to a PCC include hops from the same layer only. - However, when the I flag is set (one), the M flag is clear (zero), and the T flag is clear (zero), since triggered signaling is not allowed, virtual TE links must not be used in path computation. In addition, loose hops that span the lower-layer network must not be specified. Therefore, this is equivalent to the I flag being clear (zero). Reserved bits of the INTER-LAYER object SHOULD be transmitted as zero and SHOULD be ignored on receipt. A PCE that forwards a path computation request to other PCEs SHOULD preserve the settings of reserved bits in the PCReq messages it sends and in the PCRep messages it forwards to PCCs. 3.2. SWITCH-LAYER Object Oki, Takeda, Le Roux, and Farrel [Page 6] PCEP Extensions for Inter-Layer TE December 2008 The SWITCH-LAYER object is optional on a PCReq message and specifies switching layers in which a path MUST, or MUST NOT, be established. A switching layer is expressed as a switching type and encoding type. The SWITCH-LAYER object MUST NOT be used on a PCReq unless an INTER-LAYER object is also present on the PCReq message. The SWITCH-LAYER object is optional on a PCRep message, where it is used with the NO-PATH object in the case of unsuccessful path computation to indicate the set of constraints that could not be satisfied. SWITCH-LAYER Object-Class is to be assigned by IANA (recommended value=19) SWITCH-LAYER Object-Type is to be assigned by IANA (recommended value=1) The format of the SWITCH-LAYER 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LSP Enc. Type |Switching Type | Reserved |I| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | // . // | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LSP Enc. Type |Switching Type | Reserved |I| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Each row indicates a switching type and encoding type that must or must not be used for specified layer(s) in the computed path. The format is based on [RFC3471], and has equivalent semantics. LSP Encoding Type (8 bits): see [RFC3471] for a description of parameters. Switching Type (8 bits): see [RFC3471] for a description of parameters. I flag (1 bit): the I flag indicates whether a layer with the specified switching type and encoding type must or must not be used by the computed path. When the I flag is set (one), the computed path MUST traverse a layer with the specified switching type and encoding type. When the I flag is clear (zero), the computed path Oki, Takeda, Le Roux, and Farrel [Page 7] PCEP Extensions for Inter-Layer TE December 2008 MUST NOT enter or traverse any layer with the specified switching type and encoding type. When a combination of switching type and encoding type is not included in SWITCH-LAYER object, the computed path MAY traverse a layer with that combination of switching type and encoding type. A PCC may want to specify only a Switching Type and not an LSP Encoding Type. In this case, the LSP Encoding Type is set to zero. 3.2.1. REQ-ADAP-CAP Object The REQ-ADAP-CAP object is optional and is used to specify a requested adaptation capability for both ends of the lower layer LSP. The REQ-ADAP-CAP object is used in a PCReq message for inter- PCE communication, where the PCE that is responsible for computing higher layer paths acts as a PCC to request a path computation from a PCE that is responsible for computing lower layer paths. The REQ-ADAP-CAP object is used in a PCRep message in case of unsuccessful path computation (in this case, the PCRep message also contains a NO-PATH object, and the REQ-ADAP-CAP object is used to indicate the set of constraints that could not be satisfied). The REQ-ADAP-CAP object MAY be used in a PCReq message in a mono- layer network to specify a requested adaptation capability for both ends of the LSP. In this case, it MAY be carried without INTER- LAYER Object. REQ-ADAP-CAP Object-Class is to be assigned by IANA (recommended value=20) REQ-ADAP-CAP Object-Type is to be assigned by IANA (recommended value=1) The format of the REQ-ADAP-CAP 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Switching Cap | Encoding | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format is based on [MLN-SOL] and has equivalent semantics. Switching Capability (8 bits): see [RFC4203] for a description of parameters. Oki, Takeda, Le Roux, and Farrel [Page 8] PCEP Extensions for Inter-Layer TE December 2008 Encoding (8 bits): see [RFC3471] for a description of parameters. A PCC may want to specify a Switching Capability, but not an Encoding. In this case, the Encoding MUST be set zero. 3.3. New Metric Type A new metric type is defined for the METRIC object in PCEP. Type 11 (suggested value, to be assigned by IANA): Number of adaptations on a path. 4. Procedure 4.1. Path Computation Request A PCC requests or allows inter-layer path computation in a PCReq message by including the INTER-LAYER object with the I flag set. The INTER-LAYER object indicates whether inter-layer path computation is allowed, which path type is requested, and whether triggered signaling is allowed. The SWITCH-LAYER object, which MUST NOT be present unless the INTER-LAYER object is also present, is optionally used to specify the switching types and encoding types that define layers that must, or must not, be used in the computed path. When the SWITCH-LAYER object is used with the INTER-LAYER object I flag clear (zero), inter-layer path computation is not allowed, but constraints specified in the SWITCH-LAYER object apply. Example usage includes path computation in a single layer GMPLS network. The REQ-ADAP-CAP object is optionally used to specify the interface switching capability of both ends of the lower layer LSP. The REQ- ADAP-CAP object is used in inter-PCE communication, where the PCE that is responsible for computing higher layer paths makes a request as a PCC to a PCE that is responsible for computing lower layer paths. Alternatively, the REQ-ADAP-CAP object may be used in the NMS-VNTM model, where the VNTM makes a request as a PCC to a PCE that is responsible for computing lower-layer paths. The METRIC object is optionally used to specify metric types to be optimized or bounded. When metric type 11 (TBC by IANA) is used, it indicates that path computation MUST minimize or bound the number of adaptations on a path. Furthermore, in order to allow different objective functions to be applied within different network layers, multiple OF objects MAY be present. In such a case, the first OF object specifies an objective Oki, Takeda, Le Roux, and Farrel [Page 9] PCEP Extensions for Inter-Layer TE December 2008 function for the higher-layer network, and subsequent OF objects specify objection functions of the subsequent lower-layer networks. 4.2. Path Computation Reply In the case of successful path computation, the requested PCE replies to the requesting PCC for the inter-layer path computation result in a PCRep message that MAY include the INTER-LAYER object. When the INTER-LAYER object is included in a PCRep message, the I flag, M flag, and T flag indicate semantics of the path as described in Section 3.1. Furthermore, when the C flag of the METRIC object in a PCReq is set, the METRIC object MUST be included in the PCRep to provide the computed metric value, as specified in [PCEP]. In the case of unsuccessful path computation, the PCRep message also contains a NO-PATH object, and the SWITCH-TYPE object and/or the REQ-ADAP-CAP MAY be used to indicate the set of constraints that could not be satisfied. 5. Updated Format of PCEP Messages Message formats in this section, as those in [PCEP] are presented using Backus-Naur Format as specified in [RBNF]. The format of the PCReq message is updated as follows: ::= [] where: ::= [] ::=[] ::= [] [] [] [] [[]] [] Oki, Takeda, Le Roux, and Farrel [Page 10] PCEP Extensions for Inter-Layer TE December 2008 [] [ []] [] where: ::=[] ::=[] The format of the PCRep message is updated as follows: ::= where: ::=[] ::= [] [] [] ::=[] ::= where: ::=[] [] [] [] [] [] [] [] ::=[] ::=[] 6. Manageability Considerations TBD Manageability of inter-layer traffic engineering with PCE must Oki, Takeda, Le Roux, and Farrel [Page 11] PCEP Extensions for Inter-Layer TE December 2008 address the following consideration for section 5.1. - need for a MIB module for control and monitoring - need for built-in diagnostic tools - configuration implication for the protocol 7. IANA Considerations 7.1. New PCEP Objects Three new objects: the INTER-LAYER object, the SWITCH-LAYER object, and the REQ-ADAP-CAP object. INTER-LAYER Object-Class is to be assigned by IANA (recommended value=18) INTER-LAYER Object-Type is to be assigned by IANA (recommended value=1) SWITCH-LAYER Object-Class is to be assigned by IANA (recommended value=19) SWITCH-LAYER Object-Type is to be assigned by IANA (recommended value=1) REQ-ADAP-CAP Object-Class is to be assigned by IANA (recommended value=20) REQ-ADAP-CAP Object-Type is to be assigned by IANA (recommended value=1) 7.2. New Registry for INTER-LAYER Object Flags IANA is requested to create a registry to manage the Flag field of the INTER-Layer object. New bit numbers may be allocated only by an IETF Consensus action. Each bit should be tracked with the following qualities: o Bit number (counting from bit 0 as the most significant bit) o Capability Description o Defining RFC Several bits are defined for the INTER-LAYER object flag fields in this document. The following values have been assigned: Oki, Takeda, Le Roux, and Farrel [Page 12] PCEP Extensions for Inter-Layer TE December 2008 Bit Number Description Reference 29 T flag this document 30 M flag this document 31 I flag this document 7.3. METRIC Type A new metric type is defined in this document for the METRIC object (specified in [PCEP]). The IANA is requested to make the following allocation (suggested value): - Type 11 : Number of adaptations on a path 8. Security Considerations TBD Inter-layer traffic engineering with PCE may raise new security issues when PCE-PCE communication is done between different layer networks for inter-layer path computation. Security issues may also exist when a single PCE is granted full visibility of TE information that applies to multiple layers. It is expected that solutions for inter-layer protocol extensions will address these issues in detail using security techniques such as authentication. 9. Acknowledgments 10. References 10.1. Normative Reference [RFC2119] S. Bradner, "Key words for use in RFCs to indicate requirements levels", RFC 2119, March 1997. [RFC3471] L. Burger, "Generalized Multi-Protocol Label Switching (GMPLS)", RFC 3471, January 2003. [RFC3945] E. Mannie, "Generalized Multi-Protocol Label Switching Architecture", RFC 3945, October 2004. [RFC4203] K. Kompella and Y. Rekhter, "OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203, October 2005. Oki, Takeda, Le Roux, and Farrel [Page 13] PCEP Extensions for Inter-Layer TE December 2008 [RFC4206] K. Kompella, and Y. Rekhter, "Label Switched Paths (LSP) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005. [PCEP] JP. Vasseur et al, "Path Computation Element (PCE) communication Protocol (PCEP)" draft-ietf-pce-pcep, work in progress. [PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication Requirements for Inter-Layer Traffic Engineering", draft- ietf-pce-inter-layer-req, work in progress. [PCE-INTER-LAYER-FRWK] E. Oki et al., "Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic Engineering", draft- ietf-pce-inter-layer-frwk, work in progress. 10.2. Informative Reference [RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, September 2006. [RFC5212] K. Shiomoto et al., "Requirements for GMPLS-based multi- region and multi-layer networks (MRN/MLN)", RFC 5212, July 2008. [MLN-SOL] D. Papadimitriou et al., " Generalized Multi-Protocol Label Switching (GMPLS) Protocol Extensions for Multi- Layer and Multi-Region Networks (MLN/MRN)", draft-ietf- ccamp-gmpls-mln-extensions, work in progress. [RFC5150] A. Ayyangar et al., "Label Switched Path Stitching with Generalized Multiprotocol Label Switching Traffic Engineering (GMPLS TE)", RFC 5150, February 2008. [RBNF] Farrel, A., "Reduced Backus-Naur Form (RBNF) A Syntax Used in Various Protocol Specifications", draft-farrel- rtg-common-bnf, work in progress. 11. Authors' Addresses Eiji Oki University of Electro-Communications Tokyo Japan Email: oki@ice.uec.ac.jp Tomonori Takeda Oki, Takeda, Le Roux, and Farrel [Page 14] PCEP Extensions for Inter-Layer TE December 2008 NTT 3-9-11 Midori-cho, Musashino-shi, Tokyo 180-8585, Japan Email: takeda.tomonori@lab.ntt.co.jp Jean-Louis Le Roux France Telecom R&D, Av Pierre Marzin, 22300 Lannion, France Email: jeanlouis.leroux@orange-ftgroup.com Adrian Farrel Old Dog Consulting Email: adrian@olddog.co.uk Full Copyright Statement Copyright (c) 2008 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. 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No language to the contrary, or terms, conditions or rights that differ from or are inconsistent with the rights and licenses granted under RFC 5378, shall have any effect and shall be null and void, whether published or posted by such Contributor, or included with or in such Contribution. Oki, Takeda, Le Roux, and Farrel [Page 16]