PCE Working Group Q. Zhao Internet-Draft Z. Li Intended status: Standards Track D. Dhody Expires: January 1, 2018 S. Karunanithi Huawei Technologies A. Farrel Juniper Networks, Inc C. Zhou Cisco Systems June 30, 2017 PCEP Procedures and Protocol Extensions for Using PCE as a Central Controller (PCECC) of SR-LSPs draft-zhao-pce-pcep-extension-pce-controller-sr-00 Abstract In certain networks deployment scenarios, service providers would like to keep all the existing MPLS functionalities in both MPLS and GMPLS while removing the complexity of existing signalling protocols such as LDP and RSVP-TE. PCE has been proposed to be used as a central controller (PCECC) so that LSP can be calculated/setup/ initiated and label forwarding entries are downloaded through a centralized PCE server to each network devices along the path while leveraging the existing PCE technologies as much as possible. This document specifies the procedures and PCEP protocol extensions when the PCE functions as one of the central controller components in Segment Routing(SR). Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 1, 2018. Zhao, et al. Expires January 1, 2018 [Page 1] Internet-Draft PCECC June 2017 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) 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. PCECC SR . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. PCEP Requirements . . . . . . . . . . . . . . . . . . . . . . 5 5. Procedures for Using the PCE as the Central Controller (PCECC) in Segment Routing . . . . . . . . . . . . . . . . . 5 5.1. Stateful PCE Model . . . . . . . . . . . . . . . . . . . 6 5.2. New LSP Functions . . . . . . . . . . . . . . . . . . . . 6 5.3. PCECC Capability Advertisement . . . . . . . . . . . . . 6 5.4. PCEP session IP address and TEDB Router ID . . . . . . . 6 5.5. LSP Operations . . . . . . . . . . . . . . . . . . . . . 7 5.5.1. PCECC Segment Routing (SR) . . . . . . . . . . . . . 7 5.5.1.1. PCECC SR Node/Prefix Label allocation . . . . . . 7 5.5.1.2. PCECC SR Adjacency Label allocation . . . . . . . 8 5.5.1.3. Redundant PCEs . . . . . . . . . . . . . . . . . 9 5.5.1.4. Session Termination . . . . . . . . . . . . . . . 10 5.5.1.5. LABEL-DB Synchronization . . . . . . . . . . . . 10 6. PCEP messages . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Label Operations . . . . . . . . . . . . . . . . . . . . 10 6.1.1. The PCLabelUpd message . . . . . . . . . . . . . . . 10 6.1.2. The PCLabelRpt message . . . . . . . . . . . . . . . 11 7. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . . . 12 7.1. OPEN Object . . . . . . . . . . . . . . . . . . . . . . . 12 7.1.1. PCECC Capability TLV . . . . . . . . . . . . . . . . 12 7.2. PATH-SETUP-TYPE TLV . . . . . . . . . . . . . . . . . . . 13 7.3. FEC Object . . . . . . . . . . . . . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 15 9. Manageability Considerations . . . . . . . . . . . . . . . . 15 9.1. Control of Function and Policy . . . . . . . . . . . . . 15 9.2. Information and Data Models . . . . . . . . . . . . . . . 15 Zhao, et al. Expires January 1, 2018 [Page 2] Internet-Draft PCECC June 2017 9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 15 9.4. Verify Correct Operations . . . . . . . . . . . . . . . . 15 9.5. Requirements On Other Protocols . . . . . . . . . . . . . 15 9.6. Impact On Network Operations . . . . . . . . . . . . . . 16 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 10.1. PCECC-CAPABILITY TLV . . . . . . . . . . . . . . . . . . 16 10.2. PCEP Object . . . . . . . . . . . . . . . . . . . . . . 16 10.3. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 16 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 12.1. Normative References . . . . . . . . . . . . . . . . . . 17 12.2. Informative References . . . . . . . . . . . . . . . . . 18 Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 1. Introduction The Path Computation Element communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform route computations in response to Path Computation Clients (PCCs) requests. PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model [I-D.ietf-pce-stateful-pce] describes a set of extensions to PCEP to enable active control of MPLS-TE and GMPLS tunnels. [I-D.ietf-pce-pce-initiated-lsp] describes the setup and tear down of PCE-initiated LSPs under the active stateful PCE model, without the need for local configuration on the PCC, thus allowing for a dynamic MPLS network that is centrally controlled and deployed. [I-D.ietf-teas-pce-central-control] introduces the architecture for PCE as a central controller, examines the motivations and applicability for PCEP as a southbound interface, and introduces the implications for the protocol. [I-D.ietf-teas-pcecc-use-cases] describes the use cases for the PCECC architecture. [I-D.zhao-pce-pcep-extension-for-pce-controller] specify the PCEP extention for the PCE as the central controller (PCECC). This document extends the PCECC procedures for Segment Routing (SR). Segment Routing (SR) technology leverage the source routing and tunnelling paradigms. A source node can choose a path without relying on hop-by-hop signalling protocols such as LDP or RSVP-TE. Each path is specified as a set of "segments" advertised by link- state routing protocols (IS-IS or OSPF). [I-D.ietf-spring-segment-routing] provides an introduction to SR technology. The corresponding IS-IS and OSPF extensions are Zhao, et al. Expires January 1, 2018 [Page 3] Internet-Draft PCECC June 2017 specified in [I-D.ietf-isis-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions] , respectively. A Segment Routed path (SR path) can be derived from an IGP Shortest Path Tree (SPT). Segment Routed Traffic Engineering paths (SR-TE paths) may not follow IGP SPT. Such paths may be chosen by a suitable network planning tool and provisioned on the source node of the SR-TE path. It is possible to use a stateful PCE for computing one or more SR-TE paths taking into account various constraints and objective functions. Once a path is chosen, the stateful PCE can instantiate an SR-TE path on a PCC using PCEP extensions specified in [I-D.ietf-pce-pce-initiated-lsp] using the SR specific PCEP extensions described in [I-D.ietf-pce-segment-routing]. PCECC may further use PCEP protocol for SR label distribution instead of IGP extensions with some benefits. The [I-D.zhao-pce-pcep-extension-for-pce-controller], specifies the procedures and PCEP protocol extensions for using the PCE as one of the the central controller components and user cases where LSPs are calculated/setup/initiated and label forwarding entries are downloaded on each hop along the path, through extending the existing PCE architectures and PCEP. This draft specify the procedures and PCEP protocol extensions for using the PCE as the central controller for SR label distribution and user cases where SR LSPs are calculated/setup/initiated/downloaded through extending the existing PCE architectures and PCEP. 1.1. 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 [RFC2119]. 2. Terminology Terminologies used in this document is same as described in the draft [I-D.ietf-teas-pcecc-use-cases]. 3. PCECC SR [I-D.ietf-pce-segment-routing] specifies extensions to PCEP that allow a stateful PCE to compute, update or initiate SR-TE paths. An ingress node of an SR-TE path appends all outgoing packets with a list of MPLS labels (SIDs). This is encoded in SR-ERO subobject, Zhao, et al. Expires January 1, 2018 [Page 4] Internet-Draft PCECC June 2017 capable of carrying a label (SID) as well as the identity of the node/adjacency label (SID). The notion of segment and SID is defined in [I-D.ietf-spring-segment-routing], which fits the MPLS architecture [RFC3031] as the label which is managed by a local allocation process of LSR (similarly to other MPLS signaling protocols) [I-D.ietf-spring-segment-routing-mpls]. The SR information such as node/adjacency label (SID) is flooded via IGP as specified in [I-D.ietf-isis-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions]. As per [I-D.ietf-teas-pce-central-control], PCE as a central controller can allocate and provision the node/adjacency label (SID) via PCEP. Rest of the processing is similar to existing stateful PCE with SR mechanism. For the purpose of this document, it is assumed that label range to be used by a PCE is set on both PCEP peers. Further, a global label range is assumed to be set on all PCEP peers in the SR domain. 4. PCEP Requirements Following key requirements for PCECC-SR should be considered when` designing the PCECC based solution: o PCEP speaker supporting this draft MUST have the capability to advertise its PCECC-SR capability to its peers. o PCEP speaker not supporting this draft MUST be able to reject PCECC-SR related message with a reason code that indicates no support for PCECC. o PCEP SHOULD provide a means to update (or cleanup) the label- map entry to the PCC. o PCEP SHOULD provide a means to synchronize the SR labels between PCE to PCC in PCEP messages. 5. Procedures for Using the PCE as the Central Controller (PCECC) in Segment Routing Zhao, et al. Expires January 1, 2018 [Page 5] Internet-Draft PCECC June 2017 5.1. Stateful PCE Model Active stateful PCE is described in [I-D.ietf-pce-stateful-pce]. PCE as a central controller (PCECC) reuses existing Active stateful PCE mechanism as much as possible to control the LSP. 5.2. New LSP Functions This document uses the same PCEP messages and its extenstions which are described in [I-D.zhao-pce-pcep-extension-for-pce-controller] for PCECC-SR as well. PCEP messages PCRpt, PCInitiate, PCUpd are also used to send PCECC-SR Reports, LSP setup and LSP update respectively. PCLabelUpd message described in [I-D.zhao-pce-pcep-extension-for-pce-controller] is used to download or cleanup SR Label entry. PCLabelRpt message described in [I-D.zhao-pce-pcep-extension-for-pce-controller] is also used to report the set of SR Label entries from PCC to PCE for which explicit action is required from PCE (update or cleanup or do nothing for these Label entries). 5.3. PCECC Capability Advertisement During PCEP Initialization Phase, PCEP Speakers (PCE or PCC) advertise their support of PCECC extensions. A PCEP Speaker includes the "PCECC Capability" TLV, described in [I-D.zhao-pce-pcep-extension-for-pce-controller]. A new S-bit is added in PCECC-CAPABILITY TLV to indicate support for PCECC-SR. A PCC MUST set S-bit in PCECC-CAPABILITY TLV and include SR-PCE-CAPABILITY TLV ([I-D.ietf-pce-segment-routing]) in OPEN Object to support the PCECC SR extensions defined in this document. If S-bit is set in PCECC-CAPABILITY TLV and SR-PCE-CAPABILITY TLV is not advertised in OPEN Object, PCE SHOULD send a PCErr message with Error-Type=19 (Invalid Operation) and Error-value=TBD(SR capability was not advertised) and terminate the session. 5.4. PCEP session IP address and TEDB Router ID PCE may construct its TEDB by participating in the IGP ([RFC3630] and [RFC5305] for MPLS-TE; [RFC4203] and [RFC5307] for GMPLS). An alternative is offered by BGP-LS [RFC7752] and [I-D.dhodylee-pce-pcep-ls]. Zhao, et al. Expires January 1, 2018 [Page 6] Internet-Draft PCECC June 2017 PCEP [RFC5440] speaker MAY use any IP address while creating a TCP session. It is important to link the session IP address with the Router ID in TEDB for successful PCECC operations. During PCEP Initialization Phase, PCC SHOULD advertise the TE mapping information. Thus a PCC includes the "Node Attributes TLV" [I-D.dhodylee-pce-pcep-ls] with "IPv4/IPv6 Router-ID of Local Node", in the OPEN Object for this purpose. [RFC7752] describes the usage as auxiliary Router-IDs that the IGP might be using, e.g., for TE purposes. If there are more than one auxiliary Router-ID of a given type, then multiple TLVs are used to encode them. If "IPv4/IPv6 Router-ID" TLV is not present, the TCP session IP address is directly used for the mapping purpose. 5.5. LSP Operations The PCEP messages pertaining to PCECC-SR MUST include PATH-SETUP-TYPE TLV [I-D.ietf-pce-lsp-setup-type] in the SRP object to clearly identify the PCECC-SR LSP is intended. 5.5.1. PCECC Segment Routing (SR) Segment Routing (SR) as described in [I-D.ietf-spring-segment-routing] depends on "segments" that are advertised by Interior Gateway Protocols (IGPs). The SR-node allocates and advertises the SID (node, adj etc) and flood via the IGP. This document proposes a new mechanism where PCE allocates the SID (label) centrally and uses PCEP to advertise the SID. In some deployments PCE (and PCEP) are better suited than IGP because of centralized nature of PCE and direct TCP based PCEP session to the node. 5.5.1.1. PCECC SR Node/Prefix Label allocation Each node (PCC) is allocated a node-SID (label) by the PCECC. The PCECC sends PCLabelUpd to update the label map of each node to all the nodes in the domain. The TE router ID is determined from the TEDB or from "IPv4/IPv6 Router-ID" Sub-TLV [I-D.dhodylee-pce-pcep-ls], in the OPEN Object Section 5.4. It is RECOMMENDED that PCEP session with PCECC SR capability to use a different session IP address during TCP session establishment than the node Router ID in TEDB, to make sure that the PCEP session does not get impacted by the SR Node/Prefix Label maps (Section 5.4). If a node (PCC) receives a PCLabelUpd message with a Label, out of the range set aside for the global label, it MUST send a PCErr Zhao, et al. Expires January 1, 2018 [Page 7] Internet-Draft PCECC June 2017 message with Error-type=TBD (label download failure) and Error- value=TBD (Label out of range) and MUST include the SRP object to specify the error is for the corresponding label update [I-D.zhao-pce-pcep-extension-for-pce-controller]. On receiving the label map, each node (PCC) uses the local information to determine the next-hop and download the label forwarding instructions accordingly. The PCLabelUpd message in this case MUST NOT have LSP object but uses new FEC object. +---------+ +-------+ |PCC | | PCE | |192.0.2.3| +-------+ +------| | | | PCC +---------+ | | 192.0.2.2| | | +------| | | | |PCC +----------+ | | |192.0.2.1| | | | +---------+ | | | | | | | |<------- PCLabelUpd, FEC=192.0.2.1---------------- | Label Map | | | Label=X | update |Find | | | |Nexthop|<------- PCLabelUpd, FEC=192.0.2.1-------- | Label Map |locally| | Label=X | update | | | | | | |<--- PCLabelUpd, FEC=192.0.2.1---- | Label Map | | | Label=X | update | | | | The forwarding behaviour and the end result is similar to IGP based "Node-SID" in SR. Thus, from anywhere in the domain, it enforces the ECMP-aware shortest-path forwarding of the packet towards the related node. PCE relies on the Node/Prefix Label cleanup using the same PCLabelUpd message. 5.5.1.2. PCECC SR Adjacency Label allocation [I-D.ietf-pce-segment-routing] extends PCEP to allow a stateful PCE to compute and initiate SR-TE paths, as well as a PCC to request a path subject to certain constraint(s) and optimization criteria in SR networks. Zhao, et al. Expires January 1, 2018 [Page 8] Internet-Draft PCECC June 2017 For PCECC SR, apart from node-SID, Adj-SID is used where each adjacency is allocated an Adj-SID (label) by the PCECC. The PCECC sends PCLabelUpd to update the label map of each Adj to the corresponding nodes in the domain. Each node (PCC) download the label forwarding instructions accordingly. Similar to SR Node/Prefix Label allocation, the PCLabelUpd message in this case MUST NOT have LSP object but uses new FEC object. +---------+ +-------+ |PCC | | PCE | |192.0.2.3| +-------+ +------| | | | PCC +---------+ | | 192.0.2.2| | | +------| | | | |PCC +----------+ | | |192.0.2.1| | | | +---------+ | | | | | | | |<------ PCLabelUpd, FEC=192.0.2.1 / ------------ | Label Map | | | 192.0.2.2 | update | | | Label=A | | | | | | |<----- PCLabelUpd, FEC=192.0.2.2------- | Label Map | | | 192.0.2.1 | update | | | Label=B | | | | | The forwarding behavior and the end result is similar to IGP based "Adj-SID" in SR. The Path Setup Type for segment routing MUST be set for PCECC SR (see Section 7.2). All PCEP procedures and mechanism are similar to [I-D.ietf-pce-segment-routing]. PCE relies on the Adj label cleanup using the same PCLabelUpd message. 5.5.1.3. Redundant PCEs [I-D.litkowski-pce-state-sync] describes synchronization mechanism between the stateful PCEs. The SR Labels allocated by a PCE should also be synchronized among PCEs for PCECC SR state synchronization. Note that the SR labels are downloaded independent to the PCECC LSP, and remains intact till any topology change. The redundant PCEs MUST have a common view of all SR labels allocated in the domain. Zhao, et al. Expires January 1, 2018 [Page 9] Internet-Draft PCECC June 2017 Incase the session to the PCE that allocated the SR labels is down, similar to the LSP re-delegation mechanims, the SR labels are re- delegated to a redundant PCE using the PCLabelRpt message. This is done so that the SR labels remains intact and cosntant in case of session disconnect. 5.5.1.4. Session Termination [I-D.zhao-pce-pcep-extension-for-pce-controller] describes the action needed for label provisioned for the Basic PCECC LSP on this terminated session. Similarly actions should be applied for SR Labels as well. Additionally, if PCC has any alternate PCEP session with another PCE, then PCC MUST deligate the SR labels of this session to this alternate PCE in a sequence of PCLabelRpt message. PCE can accept it and can send PCLabelUpd message to update or clean the label. Extensions for PCLabelUpd and PCLabelRpt message for SR label are described in Section 6.1. 5.5.1.5. LABEL-DB Synchronization [I-D.zhao-pce-pcep-extension-for-pce-controller] describes LABEL-DB Synchronization procedures needed for the labels provisioned for the Basic PCECC LSP. Same procedures should be applied for SR labels as well. 6. PCEP messages As defined in [RFC5440], a PCEP message consists of a common header followed by a variable-length body made of a set of objects that can be either mandatory or optional. An object is said to be mandatory in a PCEP message when the object must be included for the message to be considered valid. For each PCEP message type, a set of rules is defined that specify the set of objects that the message can carry. An implementation MUST form the PCEP messages using the object ordering specified in this document. 6.1. Label Operations 6.1.1. The PCLabelUpd message Label Update Message (PCLabelUpd) defined in [I-D.zhao-pce-pcep-extension-for-pce-controller] is extended to update the label map at the PCC. The format of the extended PCLabelUpd message is as follows: Zhao, et al. Expires January 1, 2018 [Page 10] Internet-Draft PCECC June 2017 ::= Where: ::= [] ::= (|) Where: ::=