PCE Working GroupInternet Engineering Task Force (IETF) E. OkiInternet-DraftRequest for Comments: 8282 Kyoto Universityof Electro-Communications Intended status:Category: Standards Track T. TakedaExpires: July 7, 2017ISSN: 2070-1721 NTT A. Farrel Juniper Networks F. Zhang Huawei Technologies Co., Ltd.January 3,November 2017 Extensions to the Path Computation ElementcommunicationCommunication Protocol (PCEP) for Inter-Layer MPLS and GMPLS Traffic Engineeringdraft-ietf-pce-inter-layer-ext-12Abstract 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 PCEcommunicationCommunication Protocol (PCEP) is designed as a communication protocol between Path Computation Clients (PCCs) and PCEs. This document presents PCEP extensions for inter-layer traffic engineering. Status of This Memo ThisInternet-Draftissubmitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documentsan Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF).Note that other groups may also distribute working documents as Internet-Drafts. The listIt represents the consensus ofcurrent Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents validthe IETF community. It has received public review and has been approved fora maximumpublication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status ofsix monthsthis document, any errata, and how to provide feedback on it may beupdated, replaced, or obsoleted by other documentsobtained atany time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 7, 2017.https://www.rfc-editor.org/info/rfc8282. Copyright Notice Copyright (c) 2017 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)(https://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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 2. Overview of PCE-Based Inter-Layer Path Computation . . . . . 4 3. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 4 3.1. INTER-LAYER Object . . . . . . . . . . . . . . . . . . .45 3.2. SWITCH-LAYER Object . . . . . . . . . . . . . . . . . . .78 3.3. REQ-ADAP-CAP Object . . . . . . . . . . . . . . . . . . . 9 3.4. New Metric Types . . . . . . . . . . . . . . . . . . . . 10 3.5. SERVER-INDICATION Object . . . . . . . . . . . . . . . .1011 4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.1. Path Computation Request . . . . . . . . . . . . . . . . 11 4.2. Path Computation Reply . . . . . . . . . . . . . . . . . 12 4.3. Stateful PCE and PCE Initiated LSPs . . . . . . . . . . . 13 5. Updated Format of PCEP Messages . . . . . . . . . . . . . . . 13 6. Manageability Considerations . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7.1. New PCEP Objects . . . . . . . . . . . . . . . . . . . . 16 7.2. New Registry for INTER-LAYER Object Flags . . . . . . . .1617 7.3. New Metric Types . . . . . . . . . . . . . . . . . . . . 17 8. Security Considerations . . . . . . . . . . . . . . . . . . .1718 9.AcknowledgmentsReferences . . . . . . . . . . . . . . . . . . . . . . . . . 1810. Contributors9.1. Normative References . . . . . . . . . . . . . . . . . . 18 9.2. Informative References . . . . . . .18 11. References. . . . . . . . . . 19 Acknowledgments . . . . . . . . . . . . . . .18 11.1. Normative References. . . . . . . . . . 21 Contributors . . . . . . . .18 11.2. Informative References. . . . . . . . . . . . . . . . .19. 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 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 networkgraph,graph and applying computational constraints. A Path Computation Client (PCC) may make requests to a PCE for paths to be computed, and a PCE may initiate or modify services in a network by supplying new paths([I-D.ietf-pce-stateful-pce], [I-D.ietf-pce-pce-initiated-lsp]).[RFC8231] [RFC8281]. A network may comprise multiple layers. These layers may representseparationsseparation of technologies (e.g., packet switch capable (PSC), time division multiplex (TDM), and lambda switch capable (LSC))[RFC3945],[RFC3945]; separation ofdata planedata-plane switching granularity levels (e.g.,VC4Virtual Circuit 4 (VC4) and VC12)[RFC5212],[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]. Discussion of other ways that network layering can be supported such that connectivity in ahigher layerhigher-layer network can be provided by LSPs in alower layerlower-layer network is provided in [RFC7926]. 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 pathcomputation),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 [RFC5623]. The PCE communication protocol (PCEP) is designed as a communication protocol between PCCs and PCEs and is defined in [RFC5440]. A set of requirements for PCEP extensions to support inter-layer traffic engineering is described in [RFC6457]. This document presents PCEP extensions for inter-layer traffic engineering that satisfy the requirements described in [RFC6457]. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in[RFC2119].BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Overview of PCE-Based Inter-Layer Path Computation [RFC4206] defines a way to signal a higher-layerLSPLSP, which has an explicit route that includes hops traversed by LSPs in lower layers. The computation of end-to-end paths across layers is calledInter- Layer Path Computation.inter- layer path computation. A Label Switching Router (LSR) in thehigher-layerhigher layer might not have information on the lower-layer topology, particularly in an overlay or augmented model[RFC3945], and hence[RFC3945]; hence, it may not be able to compute an end-to-end path across layers. 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. As described in [RFC5339], a hybrid node may advertise a single TE link with multiple switching capabilities.ThoseNormally, those TE links exist at the layer/regionboarder normally.boarder. In this case, a PCE needs to be capable of specifying theserver layerserver-layer path information when theserver layerserver-layer path information is required to be returned to the PCC. [RFC5623] describes models for inter-layer path computation in more detail. It introduces the Virtual Network Topology Manager (VNTM), a functional element that controls the VNT, and sets out three distinct models (and a fourth hybrid model) for inter-layer control involving a PCE, triggeredsignalling,signaling, and a Network Management System (NMS). 3. Protocol Extensions This section describes PCEP extensions for inter-layer path computation. Four new objects are defined: the INTER-LAYER object, the SWITCH-LAYER object, the REQ-ADAP-CAP object, and the SERVER- INDICATION object. Also, two new metric types are defined. 3.1. INTER-LAYER Object The INTER-LAYER object is optional and can be used inPCReqPath Computation Request (PCReq) andPCRepPath Computation Reply (PCRep) messages, and also inPCRpt, PCUpd,Path Computation State Report (PCRpt), Path Computation Update Request (PCUpd), andPCInitiatePath Computation LSP Initiate Request (PCInitiate) 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 whetherinter- layerinter-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. The applicability of this object to PCRpt and PCUpd messagesfollows asis theusage ofsame as for other objects on those messages as described in[I-D.ietf-pce-stateful-pce].[RFC8231]. The applicability of this object to the PCInitiate messagefollows asis theusage ofsame as for other objects on those messages as described in[I-D.ietf-pce-pce-initiated-lsp].[RFC8281]. These messages use the <attribute-list> as defined in [RFC5440] and extended by further PCEP extensions,andso the <attribute-list> as extended in Section 5 can be used to include the INTER-LAYER object on these messages. INTER-LAYER Object-ClassTBD1 to be assigned by IANA. INTER-LAYERis 36. Inter-layer Object-Type1 to be assigned by IANA.is 1. The format of the INTER-LAYER object body is shown in Figure 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |T|M|I| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: The INTER-LAYER Object 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 layereitherbecause either inter- layer path computation was not performed orbecausea 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 a mono-layer path or multi-layer path is requested. When the M flag is set (one), a multi-layer path is requested. When it is clear (zero), a mono-layer path is requested. The M flag is used by a PCE in a PCRep message to indicate to a PCC whether a mono-layer path or multi-layer path is returned. When the M flag is set (one), a multi-layer path is returned. When the M flag is clear (zero), a mono-layer path is returned. If the I flag is clear (zero), the M flag has no meaning and MUST be ignored. [RFC6457] describes two sub-options for mono-layer path. o A mono-layer path that is specified by strict hops. The path may include virtual TE links. o A mono-layer path that includes loose hops that span the lower- layer network. The choice of this sub-option can be specified by the use of the O flag in theRPRequest Parameter (RP) object specified in [RFC5440]. 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 Iflagand Mflagflags 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. o 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 LSPsetup, thus inter- layersetup; thus, the inter-layer path issetupset up even though the path computation result from a PCE to a PCCincludeincludes hops from the same layer only. o 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 that have not been pre-signaled 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 sent between a PCC and PCE in the same domain MUST be transmitted as zero and SHOULD be ignored on receipt. A PCE that forwards a path computation request to other PCEs MUST preserve the settings of reserved bits in the PCReq messages it sends and in the PCRep messages it forwards to PCCs. Note that the flags in the PCRpt message indicate the state of an LSP, whereas the flags in the PCUpd and the PCInitiate messages indicate the intended/desired state as determined by the PCE. 3.2. SWITCH-LAYER Object 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. When a SWITCH-LAYER object is used on aPCReqPCReq, it is interpreted in the context of the INTER-LAYER object on the same message. If no INTER-LAYER object is present, the PCE MUST process the SWITCH-LAYER object as though inter-layer path computation had been explicitly disallowed. In such a case, the SWITCH-LAYER object MUST NOT have more than one LSP Encoding Type and Switching Type with the I flag set. 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. TheSWTCH-LAYERSWITCH-LAYER object may be used on a PCRpt message consistent with how properties of existing LSPs are reported on that message[I-D.ietf-pce-stateful-pce].[RFC8231]. The PCRpt message uses the<attribute- list><attribute-list> as defined in [RFC5440] and extended by further PCEP extensions. This message can use the <attribute-list> as extended in Section 5 to carry the SWITCH-LAYER object. TheSWTCH-LAYERSWITCH-LAYER object is not used on a PCUpd or PCInitiate messages. SWITCH-LAYER Object-ClassTBD2isto be assigned by IANA. SWITCH-LAYER37. Switch-layer Object-Type1isto be assigned by IANA.1. The format of the SWITCH-LAYER object body is shown in Figure 2. 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| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: The SWITCH-LAYER Object Each row indicates a switching type and encoding type that must or must not be used for a specified layer(s) in the computed path. The format is based on[RFC3471],[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 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 the 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. 3.3. REQ-ADAP-CAP Object The REQ-ADAP-CAP object is optional and is used to specify a requested adaptation capability for both ends of thelower layerlower-layer LSP. The REQ-ADAP-CAP object is used in a PCReq message for inter-PCE communication, where the PCE that is responsible for computinghigher layerhigher-layer paths acts as a PCC to request a path computation from a PCE that is responsible for computinglower layerlower-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 an INTER- LAYERObject.object. The applicability of this object to PCRpt and PCUpd messagesfollows asis theusage ofsame as for other objects on those messages as described in[I-D.ietf-pce-stateful-pce].[RFC8231]. The applicability of this object to the PCInitiate messagefollows asis theusage ofsame as for other objects on those messages as described in[I-D.ietf-pce-pce-initiated-lsp].[RFC8281]. These messages use the <attribute-list> as defined in [RFC5440] and extended by further PCEP extensions. These messages can use the <attribute-list> as extended in Section 5 to carry the REQ-ADAP-CAP object. REQ-ADAP-CAP Object-ClassTBD3isto be assigned by IANA. REQ-ADAP-CAP38. Req-Adap-Cap Object-Type1isto be assigned by IANA.1. The format of the REQ-ADAP-CAP object body is shown in Figure 3. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: The REQ-ADAP-CAP Object The format is based on [RFC6001] and has equivalent semantics as the Interface Adjustment Capability Descriptor (IACD) Upper Switching Capability and Lower Switching Capability fields. Switching Capability (8 bits): see [RFC4203] for a description of parameters. 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 to zero. 3.4. New Metric Types This document defines two new metric types for use in the PCEP METRIC object. IANA has assigned the valueTBD518 to indicate the metric "Number of adaptations on apath."path". IANA has assigned the valueTBD619 to indicate the metric "Number of layersto be involvedon apath."path". SeeSectionSections 4.1,Section4.2, andSection4.3 for a description of how these metrics are applied. 3.5. SERVER-INDICATION Object The SERVER-INDICATION is optional and is used to indicate that path information included in theEROExplicit Route Object (ERO) isserverserver- layerinformationinformation, andspecifyit specifies the characteristics of the server layer, e.g., the switching capability and encoding of theserverserver- layer path. The format of the SERVER-INDICATION object body is shown in Figure 4. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Optional TLVs ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: The SERVER-INDICATION Object SERVER-INDICATION Object-ClassTBD4 to be assigned by IANA. SERVER-INDICATIONis 39. Server-indication Object-Type1 to be assigned by IANA.is 1. Switching Capability (8 bits): see [RFC4203] for a description of parameters. Encoding (8 bits): see [RFC3471] for a description of parameters. Optional TLVs: Optional TLVs MAY be included within the object to specify more specificserver layerserver-layer path information (e.g., traffic parameters). Such TLVs will be defined by other documents. 4. Procedures 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 asingle layersingle-layer GMPLS network. The REQ-ADAP-CAP object is optionally used to specify the interface switching capability of both ends of thelower layerlower-layer LSP. TheREQ- ADAP-CAPREQ-ADAP-CAP object is used in inter-PCE communication, where the PCE that is responsible for computinghigher layerhigher-layer paths makes a request as a PCC to a PCE that is responsible for computinglower layerlower-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 typeTBD518 is used, it indicates that path computation MUST minimize or bound the number of adaptations on a path. When metric typeTBD619 is used, it indicates that path computation MUST minimize or bound the number of layers to be involved on a path. Furthermore, in order to allow differentobjective functionsObjective Functions (OFs) to be applied within different network layers, multiple OF objects [RFC5541] MAY be present. In such a case, the first OF object specifies an objective 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, theI flag, M flag,I, M, and Tflagflags 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 [RFC5440]. The PCE MAY specify theserver layerserver-layer path information in the ERO. In this case, the requested PCE replies with a PCRep message that includes at least two sets of ERO information in thepath-list,path-list: one is for theclient layerclient-layer path information, and another one is theserver layerserver-layer path information. When SERVER-INDICATION is included in a PCRep message, it indicates that the path in the ERO is theserverserver- layer path information. Theserver layerserver-layer path specified in the ERO could be loose or strict. On receiving the replied path, the PCC (e.g.,NMS,NMS and ingress node) can trigger the signaling tosetupset up the LSPs according to the computed paths. In the case of unsuccessful path computation, the PCRep message also contains a NO-PATH object, and the SWITCH-TYPE object and/orthe REQ- ADAP-CAPREQ-ADAP-CAP MAY be used to indicate the set of constraints that could not be satisfied. 4.3. Stateful PCE and PCE Initiated LSPs Processing for stateful PCEs is described in[I-D.ietf-pce-stateful-pce].[RFC8231]. That document defines the PCRpt message to allow a PCC to report to a PCE that an LSPthatalready exists in the network and to delegate control of that LSP to the PCE. When the LSP is a multi-layer LSP (or a mono-layer LSP for which specific adaptations exist), the message objects defined in this document are used on the PCRpt to describe an LSP that is delegated to the PCE so that the PCE may process the LSP. Furthermore,[I-D.ietf-pce-stateful-pce][RFC8231] defines the PCUpd message to allow a PCE to modify an LSP that has been delegated to it. When the LSP is a multi-layer LSP (or a mono-layer LSP for which specific adaptations exist), the message objects defined in this document are used on the PCUpd to describe the new attributes of the modified LSP. Processing forPCE initiatedPCE-initiated LSPs is described in[I-D.ietf-pce-pce-initiated-lsp].[RFC8281]. That document defines the PCInitiate message that is used by a PCE to request a PCC to set up a new LSP. When the LSP is a multi-layer LSP (or a mono-layer LSP for which specific adaptations exist), the message objects defined in this document are used on the PCInitiate to describe the attributes of the new LSP. The new metric types defined in this document can also be used with the stateful PCE extensions. The format of PCEP messages described in[I-D.ietf-pce-stateful-pce][RFC8231] and[I-D.ietf-pce-pce-initiated-lsp][RFC8281] uses <attribute-list> (which is extended in Section 5 for the purpose of including the newmetrics.metrics). The stateful PCE implementation MAY use the extension of PCReq and PCRep messages as defined in Section 5 to also enable the use ofinter- layerinter-layer parameters during passive statefuloperations too,operations, using the LSP object. 5. Updated Format of PCEP Messages Message formats in this section, as those in[RFC5440][RFC5440], are presented using Routing Backus-Naur Format (RBNF) as specified in [RFC5511]. The format of the PCReq message is updated as shown in Figure55. <PCReq Message>::= <Common Header> [<svec-list>] <request-list> where: <svec-list>::=<SVEC> [<svec-list>] <request-list>::=<request>[<request-list>] <request>::= <RP> <END-POINTS> [<LSP>] [<LSPA>] [<BANDWIDTH>] [<metric-list>] [<of-list>] [<RRO>[<BANDWIDTH>]] [<IRO>] [<LOAD-BALANCING>] [<INTER-LAYER> [<SWITCH-LAYER>]] [<REQ-ADAP-CAP>] where: <of-list>::=<OF>[<of-list>] <metric-list>::=<METRIC>[<metric-list>] Figure 5: The Updated PCReq Message The format of the PCRep message is updated as shown in Figure66. <PCRep Message> ::= <Common Header> <response-list> where: <response-list>::=<response>[<response-list>] <response>::=<RP> [<LSP>] [<NO-PATH>] [<attribute-list>] [<path-list>] <path-list>::=<path>[<path-list>] <path>::= <ERO><attribute-list> where: <attribute-list>::=[<of-list>] [<LSPA>] [<BANDWIDTH>] [<metric-list>] [<IRO>] [<INTER-LAYER>] [<SWITCH-LAYER>] [<REQ-ADAP-CAP>] [<SERVER-INDICATION>] <of-list>::=<OF>[<of-list>] <metric-list>::=<METRIC>[<metric-list>] Figure 6: The Updated PCRep Message 6. Manageability Considerations Implementations of this specification should provide a mechanism to configure any optional features (such as whether a PCE supports inter-layercomputation,computation and which metrics are supported). A Management Information Base (MIB) module for modeling PCEP is described in [RFC7420]. Systems that already use a MIB module to manage their PCEP implementations might want to augment that module to provide controls and indicators for support of inter-layer features defined in thisdocument,document and to add counters of messages sent and received containing the objects defined here. However, the preferred mechanism for configuration is through a YANG model. Work has started on a YANG model for PCEP[I-D.ietf-pce-pcep-yang],[PCEP-YANG], and this could be enhanced as described for the MIB module, above. Additional policy configuration might be provided to allow a PCE to discriminate between the computation services offered to different PCCs. A set of monitoring tools for the PCE-based architecture are provided in [RFC5886]. Systems implementing this specification and PCE monitoring should consider defining extensions to the mechanisms defined in [RFC5886] to help monitor inter-layer path computation requests. 7. IANA Considerations IANA maintains a registry calledthe"Path Computation Element Protocol (PCEP) Numbers".This document requestsPer this document, IANAto carryhas carried out actions on subregistries of that registry. 7.1. New PCEP Objects IANAis requested to makehas made the following assignmentsfromin the "PCEP Objects" subregistry. Object-Class Value|Name |Object-Type |Reference| Name | Object-Type | Reference -------------------+-------+-----------------------+----------- INTER-LAYER |TBD136 | 0: Reserved | RFC 8282 | | 1: Inter-layer |[This.I-D]| | 2-15: Unassigned | | | | SWITCH-LAYER |TBD237 | 0: Reserved | RFC 8282 | | 1: Switch-layer |[This.I-D]| | 2-15: Unassigned | | | | REQ-ADAP-CAP |TBD338 | 0: Reserved | RFC 8282 | | 1: Req-Adap-Cap |[This.I-D]| | 2-15: Unassigned | | | | SERVER-INDICATION |TBD439 | 0: Reserved | RFC 8282 | | 1: Server-indication |[This.I-D]Figure77: New PCEP Objects 7.2. New Registry for INTER-LAYER Object Flags IANAis requested to createhas created a new subregistry to manage the Flag field of theINTER-LayerINTER-LAYER object called the "Inter-Layer Object Path Property Bits" registry. New bit numbers may be allocated only byan"IETF Review"action [RFC5226].[RFC8126]. Each bit should be tracked with the following qualities: o Bit number (counting from bit 0 as the most significant bit up to a maximum of bit 31) o Capability Description o Defining RFC IANAis requested to pre-populatehas populated the registry as follows: Bit | Flag | Multi-Layer Path Property | Reference ----+------+-------------------------------+------------ 0-28| | Unassigned | 29 | T | TriggeredSignallingSignaling Allowed |[This.I-D]RFC 8282 30 | M | Multi-Layer Requested |[This.I-D]RFC 8282 31 | I | Inter-Layer Allowed |[This.I-D]RFC 8282 Figure88: New Registry for INTER-LAYER Object Flags 7.3. New Metric Types Two new metric types are defined in this document for the METRIC object (specified in [RFC5440]).TheIANAis requested to makehas made the following allocations from the "Metric Object T Field" registry. Value | Description | Reference ------+---------------------------------+------------TBD518 | Number of adaptations on a path |[This.I-D] TBD6RFC 8282 19 | Number of layers on a path |[This.I-D]RFC 8282 Figure99: New Metric Types IANAis further requested to updatehas updated the registry to showan assignment actionthe registration procedure of "IETFConsensus"Review" as already documented in [RFC5440]. 8. Security Considerations 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. The Path-Key-based mechanism defined in [RFC5520] MAY be applied to address the topology confidentiality between different layers.11.9. References11.1.9.1. Normative References[I-D.ietf-pce-pce-initiated-lsp] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model", draft-ietf-pce-pce-initiated-lsp-07 (work in progress), July 2016. [I-D.ietf-pce-stateful-pce] Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP Extensions for Stateful PCE", draft-ietf-pce-stateful- pce-18 (work in progress), December 2016.[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,<http://www.rfc-editor.org/info/rfc2119>.<https://www.rfc-editor.org/info/rfc2119>. [RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, DOI 10.17487/RFC3471, January 2003,<http://www.rfc-editor.org/info/rfc3471>.<https://www.rfc-editor.org/info/rfc3471>. [RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, DOI 10.17487/RFC3945, October 2004,<http://www.rfc-editor.org/info/rfc3945>.<https://www.rfc-editor.org/info/rfc3945>. [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,<http://www.rfc-editor.org/info/rfc4203>.<https://www.rfc-editor.org/info/rfc4203>. [RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE)", RFC 4206, DOI 10.17487/RFC4206, October 2005,<http://www.rfc-editor.org/info/rfc4206>. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008, <http://www.rfc-editor.org/info/rfc5226>.<https://www.rfc-editor.org/info/rfc4206>. [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009,<http://www.rfc-editor.org/info/rfc5440>.<https://www.rfc-editor.org/info/rfc5440>. [RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel, "Preserving Topology Confidentiality in Inter-Domain Path Computation Using a Path-Key-Based Mechanism", RFC 5520, DOI 10.17487/RFC5520, April 2009,<http://www.rfc-editor.org/info/rfc5520>. 11.2.<https://www.rfc-editor.org/info/rfc5520>. [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE", RFC 8231, DOI 10.17487/RFC8231, September 2017, <https://www.rfc-editor.org/info/rfc8231>. [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for PCE-initiated LSP Setup in a Stateful PCE Model", RFC 8281, DOI 10.17487/RFC8281, November 2017, <http://www.rfc-editor.org/info/rfc20>. 9.2. Informative References[I-D.ietf-pce-pcep-yang][PCEP-YANG] Dhody, D., Hardwick, J., Beeram, V., and j. jefftant@gmail.com, "A YANG Data Model for Path Computation Element Communications Protocol (PCEP)",draft-ietf-pce-pcep-yang-01 (workWork inprogress), October 2016.Progress, draft-ietf-pce-pcep-yang-05, June 2017. [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006,<http://www.rfc-editor.org/info/rfc4655>.<https://www.rfc-editor.org/info/rfc4655>. [RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel, "Label Switched Path Stitching with Generalized Multiprotocol Label Switching Traffic Engineering (GMPLS TE)", RFC 5150, DOI 10.17487/RFC5150, February 2008,<http://www.rfc-editor.org/info/rfc5150>.<https://www.rfc-editor.org/info/rfc5150>. [RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux, M., and D. Brungard, "Requirements for GMPLS-Based Multi- Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, DOI 10.17487/RFC5212, July 2008,<http://www.rfc-editor.org/info/rfc5212>.<https://www.rfc-editor.org/info/rfc5212>. [RFC5339] Le Roux, JL., Ed. and D. Papadimitriou, Ed., "Evaluation of Existing GMPLS Protocols against Multi-Layer and Multi- Region Networks (MLN/MRN)", RFC 5339, DOI 10.17487/RFC5339, September 2008,<http://www.rfc-editor.org/info/rfc5339>.<https://www.rfc-editor.org/info/rfc5339>. [RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax Used to Form Encoding Rules in Various Routing Protocol Specifications", RFC 5511, DOI 10.17487/RFC5511, April 2009,<http://www.rfc-editor.org/info/rfc5511>.<https://www.rfc-editor.org/info/rfc5511>. [RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of Objective Functions in the Path Computation Element Communication Protocol (PCEP)", RFC 5541, DOI 10.17487/RFC5541, June 2009,<http://www.rfc-editor.org/info/rfc5541>.<https://www.rfc-editor.org/info/rfc5541>. [RFC5623] Oki, E., Takeda, T., Le Roux, JL., and A. Farrel, "Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic Engineering", RFC 5623, DOI 10.17487/RFC5623, September 2009,<http://www.rfc-editor.org/info/rfc5623>.<https://www.rfc-editor.org/info/rfc5623>. [RFC5886] Vasseur, JP., Ed., Le Roux, JL., and Y. Ikejiri, "A Set of Monitoring Tools for Path Computation Element (PCE)-Based Architecture", RFC 5886, DOI 10.17487/RFC5886, June 2010,<http://www.rfc-editor.org/info/rfc5886>.<https://www.rfc-editor.org/info/rfc5886>. [RFC6001] Papadimitriou, D., Vigoureux, M., Shiomoto, K., Brungard, D., and JL. Le Roux, "Generalized MPLS (GMPLS) Protocol Extensions for Multi-Layer and Multi-Region Networks (MLN/ MRN)", RFC 6001, DOI 10.17487/RFC6001, October 2010,<http://www.rfc-editor.org/info/rfc6001>.<https://www.rfc-editor.org/info/rfc6001>. [RFC6457] Takeda, T., Ed. and A. Farrel, "PCC-PCE Communication and PCE Discovery Requirements for Inter-Layer Traffic Engineering", RFC 6457, DOI 10.17487/RFC6457, December 2011,<http://www.rfc-editor.org/info/rfc6457>.<https://www.rfc-editor.org/info/rfc6457>. [RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J. Hardwick, "Path Computation Element Communication Protocol (PCEP) Management Information Base (MIB) Module", RFC 7420, DOI 10.17487/RFC7420, December 2014,<http://www.rfc-editor.org/info/rfc7420>.<https://www.rfc-editor.org/info/rfc7420>. [RFC7926] Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G., Ceccarelli, D., and X. Zhang, "Problem Statement and Architecture for Information Exchange between Interconnected Traffic-Engineered Networks", BCP 206, RFC 7926, DOI 10.17487/RFC7926, July 2016,<http://www.rfc-editor.org/info/rfc7926>. 9.<https://www.rfc-editor.org/info/rfc7926>. Acknowledgments The authors would like to thank Cyril Margaria for his valuable comments. Helpful comments and suggested text were offered by DhruvDhodyDhody, who also fixed the RBNF. Jonathan Hardwick provided a helpful review as document shepherd.10.Contributors Jean-Louis Le Roux France Telecom R&D Av Pierre Marzin LannionFrance22300 France Email: jeanlouis.leroux@orange.com Authors' Addresses Eiji Oki Kyoto Universityof Electro-Communications TokyoYoshida-honmachi, Sakyo-ku, Kyoto Japan Email:oki@ice.uec.ac.jpoki@i.kyoto-u.ac.jp Tomonori Takeda NTT 3-9-11 Midori-cho Musashino-shi, Tokyo Japan Email: tomonori.takeda@ntt.com Adrian Farrel Juniper Networks Email: afarrel@juniper.net Fatai Zhang Huawei Technologies Co., Ltd. F3-5-B R&D Center, Huawei Base Bantian, Longgang District, Shenzhen 518129P. R.China Phone: +86-755-28972912 Email: zhangfatai@huawei.com