PCE S. Sivabalan Internet-Draft C. Filsfils Intended status: Standards Track Cisco Systems, Inc. Expires: December 31, 2018 J. Tantsura Individual W. Henderickx Nokia J. Hardwick Metaswitch Networks June 29, 2018 PCEP Extensions for Segment Routing draft-ietf-pce-segment-routing-12 Abstract Segment Routing (SR) enables any head-end node to select any path without relying on a hop-by-hop signaling technique (e.g., LDP or RSVP-TE). It depends only on "segments" that are advertised by Link- State Interior Gateway Protocols (IGPs). A Segment Routed Path can be derived from a variety of mechanisms, including an IGP Shortest Path Tree (SPT), explicit configuration, or a Path Computation Element (PCE). This document specifies extensions to the Path Computation Element Protocol (PCEP) that allow a stateful PCE to compute and initiate Traffic Engineering (TE) paths, as well as a PCC to request a path subject to certain constraints and optimization criteria in SR networks. 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 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 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 https://datatracker.ietf.org/drafts/current/. Sivabalan, et al. Expires December 31, 2018 [Page 1] Internet-Draft PCEP Extensions for Segment Routing June 2018 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 December 31, 2018. Copyright Notice Copyright (c) 2018 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 (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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview of PCEP Operation in SR Networks . . . . . . . . . . 5 4. SR-Specific PCEP Message Extensions . . . . . . . . . . . . . 7 5. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7 5.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7 5.1.1. The SR PCE Capability sub-TLV . . . . . . . . . . . . 7 5.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 8 5.3. ERO . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . . . 9 5.3.2. NAI Associated with SID . . . . . . . . . . . . . . . 11 5.4. RRO . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.5. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 13 6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. Exchanging the SR PCE Capability . . . . . . . . . . . . 13 6.2. ERO Processing . . . . . . . . . . . . . . . . . . . . . 15 6.2.1. SR-ERO Validation . . . . . . . . . . . . . . . . . . 15 6.2.2. Interpreting the SR-ERO . . . . . . . . . . . . . . . 17 6.3. RRO Processing . . . . . . . . . . . . . . . . . . . . . 20 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 20 8. Management Considerations . . . . . . . . . . . . . . . . . . 21 8.1. Controlling the Path Setup Type . . . . . . . . . . . . . 21 8.2. Migrating a Network to Use PCEP Segment Routed Paths . . 22 8.3. Verification of Network Operation . . . . . . . . . . . . 23 Sivabalan, et al. Expires December 31, 2018 [Page 2] Internet-Draft PCEP Extensions for Segment Routing June 2018 8.4. Relationship to Existing Management Models . . . . . . . 24 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 10.1. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . 24 10.2. New NAI Type Registry . . . . . . . . . . . . . . . . . 24 10.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 25 10.4. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 25 10.5. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 27 10.6. New Path Setup Type . . . . . . . . . . . . . . . . . . 27 10.7. New Metric Type . . . . . . . . . . . . . . . . . . . . 27 10.8. SR PCE Capability Flags . . . . . . . . . . . . . . . . 27 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 13.1. Normative References . . . . . . . . . . . . . . . . . . 28 13.2. Informative References . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 1. Introduction Segment Routing (SR) technology leverages the source routing and tunneling paradigms. A source node can choose a path without relying on hop-by-hop signaling 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 the SR architecture. The corresponding IS-IS and OSPF extensions are specified in [I-D.ietf-isis-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions], respectively. The SR architecture defines a "segment" as a piece of information advertised by a link-state routing protocols, e.g., an IGP prefix or an IGP adjacency. Several types of segments are defined. A Node segment represents an ECMP-aware shortest-path computed by IGP to a specific node, and is always identified uniquely within the SR/IGP domain. An Adjacency Segment represents a unidirectional adjacency. An Adjacency Segment is local to the node which advertises it. Both Node segments and Adjacency segments can be used for SR Traffic Engineering (SR-TE). The SR architecture can be implemented using either an MPLS forwarding plane [I-D.ietf-spring-segment-routing-mpls] or an IPv6 forwarding plane [I-D.ietf-6man-segment-routing-header]. The MPLS forwarding plane can be applied to SR without any change, in which case an SR path corresponds to an MPLS Label Switching Path (LSP). This document is relevant to the MPLS forwarding plane only. In this document, "Node-SID" and "Adjacency-SID" denote Node Segment Identifier and Adjacency Segment Identifier respectively. Sivabalan, et al. Expires December 31, 2018 [Page 3] Internet-Draft PCEP Extensions for Segment Routing June 2018 A Segment Routed path (SR path) can be derived from an IGP Shortest Path Tree (SPT). SR-TE paths may not follow an IGP SPT. Such paths may be chosen by a suitable network planning tool and provisioned on the ingress node of the SR-TE path. [RFC5440] describes the Path Computation Element Protocol (PCEP) for communication between a Path Computation Client (PCC) and a Path Computation Element (PCE) or between a pair of PCEs. A PCE computes paths for MPLS Traffic Engineering LSPs (MPLS-TE LSPs) based on various constraints and optimization criteria. [RFC8231] specifies extensions to PCEP that allow a stateful PCE to compute and recommend network paths in compliance with [RFC4657] and defines objects and TLVs for MPLS-TE LSPs. Stateful PCEP extensions provide synchronization of LSP state between a PCC and a PCE or between a pair of PCEs, delegation of LSP control, reporting of LSP state from a PCC to a PCE, controlling the setup and path routing of an LSP from a PCE to a PCC. Stateful PCEP extensions are intended for an operational model in which LSPs are configured on the PCC, and control over them is delegated to the PCE. A mechanism to dynamically initiate LSPs on a PCC based on the requests from a stateful PCE or a controller using stateful PCE is specified in [RFC8281]. This mechanism is useful in Software Defined Networking (SDN) applications, such as on-demand engineering, or bandwidth calendaring. 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 initiate an SR-TE path on a PCC using PCEP extensions specified in [RFC8281] using the SR specific PCEP extensions specified in this document. Additionally, using procedures described in this document, a PCC can request an SR path from either a stateful or a stateless PCE. This specification relies on the procedures specified in [I-D.ietf-pce-lsp-setup-type] to exchange the segment routing capability and to specify that the path setup type of an LSP is segment routing. 2. Terminology The following terminologies are used in this document: ERO: Explicit Route Object IGP: Interior Gateway Protocol IS-IS: Intermediate System to Intermediate System Sivabalan, et al. Expires December 31, 2018 [Page 4] Internet-Draft PCEP Extensions for Segment Routing June 2018 LSR: Label Switching Router MSD: Maximum SID Depth NAI: Node or Adjacency Identifier OSPF: Open Shortest Path First PCC: Path Computation Client PCE: Path Computation Element PCEP: Path Computation Element Protocol RRO: Record Route Object SID: Segment Identifier SR: Segment Routing SR-TE: Segment Routed Traffic Engineering 3. Overview of PCEP Operation in SR Networks In an SR network, the ingress node of an SR path prepends an SR header to all outgoing packets. The SR header consists of a list of SIDs (or MPLS labels in the context of this document). The header has all necessary information so that, in combination with the information distributed by the IGP, the packets can be guided from the ingress node to the egress node of the path; hence, there is no need for any signaling protocol. In PCEP messages, LSP route information is carried in the Explicit Route Object (ERO), which consists of a sequence of subobjects. In SR networks, an ingress node of an SR path prepends an SR header to all outgoing packets. The SR header consists of a list of SIDs (or MPLS labels in the context of this document). SR-TE paths computed by a PCE can be represented in an ERO in one of the following forms: o An ordered set of IP addresses representing network nodes/links: In this case, the PCC needs to convert the IP addresses into the corresponding MPLS labels by consulting its Link State Database (LSDB). o An ordered set of SIDs, with or without the corresponding IP addresses. Sivabalan, et al. Expires December 31, 2018 [Page 5] Internet-Draft PCEP Extensions for Segment Routing June 2018 o An ordered set of MPLS labels and IP addresses: In this case, the PCC needs to convert the IP addresses into the corresponding SIDs by consulting its LSDB. This document defines a new ERO subobject denoted by "SR-ERO subobject" capable of carrying a SID as well as the identity of the node/adjacency represented by the SID. SR-capable PCEP speakers should be able to generate and/or process such ERO subobject. An ERO containing SR-ERO subobjects can be included in the PCEP Path Computation Reply (PCRep) message defined in [RFC5440], the PCEP LSP Initiate Request message (PCInitiate) defined in [RFC8281], as well as in the PCEP LSP Update Request (PCUpd) and PCEP LSP State Report (PCRpt) messages defined in [RFC8231]. When a PCEP session between a PCC and a PCE is established, both PCEP speakers exchange their capabilites to indicate their ability to support SR-specific functionality. An PCE can update an LSP that is initially established via RSVP-TE signaling to use an SR-TE path, by sending a PCUpd to the PCC that delegated the LSP to it ([RFC8231]). Similarly, an LSP initially created with an SR-TE path can be updated to use RSVP-TE signaling, if necessary. This capability is useful when a network is migrated from RSVP-TE to SR-TE technology. A PCC MAY include an RRO containing the recorded LSP in PCReq and PCRpt messages as specified in [RFC5440] and [RFC8231], respectively. This document defines a new RRO subobject for SR networks. The methods used by a PCC to record the SR-TE LSP are outside the scope of this document. In summary, this document: o Defines a new ERO subobject, a new RRO subobject and new PCEP error codes. o Specifies how two PCEP speakers can establish a PCEP session that can carry information about SR-TE paths. o Specifies processing rules for the ERO subobject. o Defines a new path setup type to be used in the PATH_SETUP_TYPE and PATH_SETUP_TYPE_CAPABILITY TLVs ([I-D.ietf-pce-lsp-setup-type]). o Defines a new sub-TLV for the PATH_SETUP_TYPE_CAPABILITY TLV. Sivabalan, et al. Expires December 31, 2018 [Page 6] Internet-Draft PCEP Extensions for Segment Routing June 2018 The extensions specified in this document complement the existing PCEP specifications to support SR-TE paths. As such, the PCEP messages (e.g., Path Computation Request, Path Computation Reply, Path Computation Report, Path Computation Update, Path Computation Initiate, etc.,) MUST be formatted according to [RFC5440], [RFC8231], [RFC8281], and any other applicable PCEP specifications. 4. SR-Specific PCEP Message Extensions As defined in [RFC5440], a PCEP message consists of a common header followed by a variable length body made up of mandatory and/or optional objects. This document does not require any changes in the format of the PCReq and PCRep messages specified in [RFC5440], PCInitiate message specified in [RFC8281], and PCRpt and PCUpd messages specified in [RFC8231]. 5. Object Formats 5.1. The OPEN Object 5.1.1. The SR PCE Capability sub-TLV This document defines a new Path Setup Type (PST) for SR, as follows: o PST = 1: Path is setup using Segment Routing Traffic Engineering. A PCEP speaker SHOULD indicate its support of the function described in this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the OPEN object with this new PST included in the PST list. This document also defines the SR-PCE-CAPABILITY sub-TLV. PCEP speakers use this sub-TLV to exchange information about their SR capability. If a PCEP speaker includes PST=1 in the PST List of the PATH-SETUP-TYPE-CAPABILITY TLV then it MUST also include the SR-PCE- CAPABILITY sub-TLV inside the PATH-SETUP-TYPE-CAPABILITY TLV. The format of the SR-PCE-CAPABILITY sub-TLV is shown in the following figure: Sivabalan, et al. Expires December 31, 2018 [Page 7] Internet-Draft PCEP Extensions for Segment Routing June 2018 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=26 | Length=4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags |N|L| MSD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: SR-PCE-CAPABILITY sub-TLV format The code point for the TLV type is 26. The TLV length is 4 octets. The 32-bit value is formatted as follows. The "Maximum SID Depth" (1 octet) field (MSD) specifies the maximum number of SIDs (MPLS label stack depth in the context of this document) that a PCC is capable of imposing on a packet. The "Reserved" (2 octets) field is unused, and MUST be set to zero on transmission and ignored on reception. The "Flags" field is 1 octet long, and this document defines the following flags: o L flag: A PCC sets this flag to 1 to indicate that it does not impose any limit on the MSD. o N flag: A PCC sets this flag to 1 to indicate that it is capable of resolving a Node or Adjacency Identifier (NAI) to a SID. 5.2. The RP/SRP Object To set up an SR-TE LSP using SR, the RP or SRP object MUST include the PATH-SETUP-TYPE TLV, specified in [I-D.ietf-pce-lsp-setup-type], with the PST set to 1 (path setup using SR-TE). The LSP-IDENTIFIERS TLV MAY be present for the above PST type. 5.3. ERO An SR-TE path consists of one or more SIDs where each SID MAY be associated with the identifier that represents the node or adjacency corresponding to the SID. This identifier is referred to as the 'Node or Adjacency Identifier' (NAI). As described later, a NAI can be represented in various formats (e.g., IPv4 address, IPv6 address, etc). Furthermore, a NAI is used for troubleshooting purposes and, if necessary, to derive SID value as described below. The ERO specified in [RFC5440] is used to carry SR-TE path information. In order to carry SID and/or NAI, this document defines a new ERO subobject referred to as "SR-ERO subobject" whose format is Sivabalan, et al. Expires December 31, 2018 [Page 8] Internet-Draft PCEP Extensions for Segment Routing June 2018 specified in the following section. An ERO carrying an SR-TE path consists of one or more ERO subobjects, and MUST carry only SR-ERO subobjects. Note that an SR-ERO subobject does not need to have both SID and NAI. However, at least one of them MUST be present. When building the MPLS label stack from ERO, a PCC MUST assume that SR-ERO subobjects are organized as a last-in-first-out stack. The first subobject relative to the beginning of ERO contains the information about the topmost label. The last subobject contains information about the bottommost label. 5.3.1. SR-ERO Subobject An SR-ERO subobject consists of a 32-bit header followed by the SID and/or the NAI associated with the SID. The SID is a 32-bit number. The size of the NAI depends on its respective type, as described in the following sections. At least one of the SID and the NAI MUST be included in the SR-ERO subobject, and both MAY be included. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |L| Type=36 | Length | NT | Flags |F|S|C|M| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // NAI (variable, optional) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: SR-ERO Subobject format The fields in the SR-ERO Subobject are as follows: The 'L' Flag indicates whether the subobject represents a loose-hop in the LSP [RFC3209]. If this flag is set to zero, a PCC MUST NOT overwrite the SID value present in the SR-ERO subobject. Otherwise, a PCC MAY expand or replace one or more SID values in the received SR-ERO based on its local policy. Type is set to 36. Length contains the total length of the subobject in octets, including the L, Type and Length fields. The Length MUST be at least 8, and MUST be a multiple of 4. As mentioned earlier, an SR-ERO subobject MUST contain at least one of a SID or an NAI. Sivabalan, et al. Expires December 31, 2018 [Page 9] Internet-Draft PCEP Extensions for Segment Routing June 2018 The length should include the SID and NAI fields if and only if they are not absent. The flags described below indicate whether the SID or NAI fields are absent. NAI Type (NT) indicates the type and format of the NAI associated with the SID contained in the object body. This document describes the following NT values: NT=0 The NAI is absent. NT=1 The NAI is an IPv4 node ID. NT=2 The NAI is an IPv6 node ID. NT=3 The NAI is an IPv4 adjacency. NT=4 The NAI is an IPv6 adjacency. NT=5 The NAI is an unnumbered adjacency with IPv4 node IDs. Flags is used to carry additional information pertaining to the SID. This document defines the following flag bits. The other bits MUST be set to zero by the sender and MUST be ignored by the receiver. * M: If this bit is set to 1, the SID value represents an MPLS label stack entry as specified in [RFC3032]. Otherwise, the SID value is an administratively configured value which acts as an index into an MPLS label space. * C: If the M bit and the C bit are both set to 1, then the TC, S, and TTL fields in the MPLS label stack entry are specified by the PCE. However, a PCC MAY choose to override these values according its local policy and MPLS forwarding rules. If the M bit is set to 1 but the C bit is set to zero, then the TC, S, and TTL fields MUST be ignored by the PCC. The PCC MUST set these fields according to its local policy and MPLS forwarding rules. If the M bit is set to zero then the C bit MUST be set to zero. Sivabalan, et al. Expires December 31, 2018 [Page 10] Internet-Draft PCEP Extensions for Segment Routing June 2018 * S: When this bit is set to 1, the SID value in the subobject body is absent. In this case, the PCC is responsible for choosing the SID value, e.g., by looking up in its LSDB using the NAI which, in this case, MUST be present in the subobject. If the S bit is set to 1 then the M and C bits MUST be set to zero. * F: When this bit is set to 1, the NAI value in the subobject body is absent. The F bit MUST be set to 1 if NT=0, and otherwise MUST be set to zero. The S and F bits MUST NOT both be set to 1. SID is the Segment Identifier. NAI contains the NAI associated with the SID. The NAI's format depends on the value in the NT field, and is described in the following section. 5.3.2. NAI Associated with SID This document defines the following NAIs: 'IPv4 Node ID' is specified as an IPv4 address. In this case, the NT value is 1. 'IPv6 Node ID' is specified as an IPv6 address. In this case, the NT value is 2. 'IPv4 Adjacency' is specified as a pair of IPv4 addresses. In this case, the NT value is 3. The format of the NAI is shown in the following figure: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local IPv4 address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote IPv4 address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: NAI for IPv4 adjacency Sivabalan, et al. Expires December 31, 2018 [Page 11] Internet-Draft PCEP Extensions for Segment Routing June 2018 'IPv6 Adjacency' is specified as a pair of IPv6 addresses. In this case, the NT value is 4. The format of the NAI is shown in the following figure: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Local IPv6 address (16 bytes) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Remote IPv6 address (16 bytes) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: NAI for IPv6 adjacency 'Unnumbered Adjacency with IPv4 NodeIDs' is specified as a pair of Node ID / Interface ID tuples. In this case, the NT value is 5. The format of the NAI is shown in the following figure: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local Node-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote Node-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: NAI for Unnumbered adjacency with IPv4 Node IDs 5.4. RRO A PCC can record an SR-TE LSP and report the LSP to a PCE via the RRO. An RRO contains one or more subobjects called "SR-RRO subobjects" whose format is shown below: Sivabalan, et al. Expires December 31, 2018 [Page 12] Internet-Draft PCEP Extensions for Segment Routing June 2018 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=36 | Length | NT | Flags |F|S|C|M| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // NAI (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: SR-RRO Subobject format The format of the SR-RRO subobject is the same as that of the SR-ERO subobject, but without the L flag. A PCC MUST assume that the SR-RRO subobjects are organized such that the first subobject relative to the beginning of the RRO contains the information about the topmost label, and the last subobject contains information about the bottommost label of the SR-TE LSP. 5.5. METRIC Object If a PCEP session is established with an MSD value of zero, then the PCC MAY specify the MSD for an individual path computation request using the METRIC object defined in [RFC5440]. This document defines a new type for the METRIC object to be used for this purpose as follows: o T = 11: Maximum SID Depth of the requested path. The PCC sets the metric-value to the MSD for this path. The PCC MUST set the B (bound) bit to 1 in the METRIC object, which specifies that the SID depth for the computed path MUST NOT exceed the metric-value. If a PCEP session is established with a non-zero MSD value, then the PCC MUST NOT send an MSD METRIC object. If the PCE receives a path computation request with an MSD METRIC object on a session with a non-zero MSD value then it MUST consider the request invalid and send a PCErr with Error-Type = 10 ("Reception of an invalid object") and Error-Value 9 ("Default MSD is specified for the PCEP session"). 6. Procedures 6.1. Exchanging the SR PCE Capability A PCC indicates that it is capable of supporting the head-end functions for SR-TE LSP by including the SR-PCE-CAPABILITY sub-TLV in the Open message that it sends to a PCE. A PCE indicates that it is Sivabalan, et al. Expires December 31, 2018 [Page 13] Internet-Draft PCEP Extensions for Segment Routing June 2018 capable of computing SR-TE paths by including the SR-PCE-CAPABILITY sub-TLV in the Open message that it sends to a PCC. If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV with a PST list containing PST=1, and supports that path setup type, then it checks for the presence of the SR-PCE-CAPABILITY sub-TLV. If that sub-TLV is absent, then the PCEP speaker MUST send a PCErr message with Error-Type 10 (Reception of an invalid object) and Error-Value TBD1 (to be assigned by IANA) (Missing PCE-SR-CAPABILITY sub-TLV) and MUST then close the PCEP session. If a PCEP speaker receives a PATH- SETUP-TYPE-CAPABILITY TLV with a SR-PCE-CAPABILITY sub-TLV, but the PST list does not contain PST=1, then the PCEP speaker MUST ignore the SR-PCE-CAPABILITY sub-TLV. If a PCC sets the N flag to 1, then the PCE MAY send NAI to the PCC within the SR-ERO subobject (see Section 6.2). Otherwise, the PCE MUST NOT send NAI to the PCC. The number of SIDs that can be imposed on a packet depends on the PCC's data plane's capability. If a PCC sets the L flag to 1 then the MSD is not used and MUST be set to zero. If a PCE receives an SR-PCE-CAPABILITY sub-TLV with the L flag set to 1 then it MUST ignore the MSD field and MUST assume that the sender can impose a SID stack of any depth. If a PCC sets the L flag to zero, then it sets the MSD field to the maximum number of SIDs that it can impose on a packet. If a PCE receives an SR-PCE-CAPABILITY sub-TLV with the L flag and MSD both set to zero then it MUST assume that the PCC is not capable of imposing a SID stack of any depth and hence is not SR-TE capable, unless it learns a non-zero MSD for the PCC through some other means. Note that the MSD value exchanged via the SR-PCE-CAPABILITY sub-TLV indicates the SID/label imposition limit for the PCC node. However, if a PCE learns the MSD value of a PCC node via different means, e.g routing protocols, as specified in: [I-D.ietf-isis-segment-routing-msd]; [I-D.ietf-ospf-segment-routing-msd]; [I-D.ietf-idr-bgp-ls-segment-routing-msd], then it ignores the MSD value in the SR-PCE-CAPABILITY sub-TLV. Furthermore, whenever a PCE learns the MSD for a link via different means, it MUST use that value for that link regardless of the MSD value exchanged in the SR-PCE- CAPABILITY sub-TLV. Once an SR-capable PCEP session is established with a non-zero MSD value, the corresponding PCE MUST NOT send SR-TE paths with a number of SIDs exceeding that MSD value. If a PCC needs to modify the MSD value, it MUST close the PCEP session and re-establish it with the new MSD value. If a PCEP session is established with a non-zero MSD Sivabalan, et al. Expires December 31, 2018 [Page 14] Internet-Draft PCEP Extensions for Segment Routing June 2018 value, and the PCC receives an SR-TE path containing more SIDs than specified in the MSD value, the PCC MUST send a PCErr message with Error-Type 10 (Reception of an invalid object) and Error-Value 3 (Unsupported number of Segment ERO subobjects). If a PCEP session is established with an MSD value of zero, then the PCC MAY specify an MSD for each path computation request that it sends to the PCE, by including a "maximum SID depth" metric object on the request, as defined in Section 5.5. The N flag, L flag and MSD value inside the SR-PCE-CAPABILITY sub-TLV are meaningful only in the Open message sent from a PCC to a PCE. As such, a PCE MUST set the N flag to zero, the L flag to 1 and MSD value to zero in an outbound message to a PCC. Similarly, a PCC MUST ignore any MSD value received from a PCE. If a PCE receives multiple SR-PCE-CAPABILITY sub-TLVs in an Open message, it processes only the first sub-TLV received. 6.2. ERO Processing 6.2.1. SR-ERO Validation If a PCC does not support the SR PCE Capability and thus cannot recognize the SR-ERO or SR-RRO subobjects, it will respond according to the rules for a malformed object per [RFC5440]. On receiving an SR-ERO, a PCC MUST validate that the Length field, the S bit, the F bit and the NT field are consistent, as follows. o If NT=0, the F bit MUST be 1, the S bit MUST be zero and the Length MUST be 8. o If NT=1, the F bit MUST be zero. If the S bit is 1, the Length MUST be 8, otherwise the Length MUST be 12. o If NT=2, the F bit MUST be zero. If the S bit is 1, the Length MUST be 20, otherwise the Length MUST be 24. o If NT=3, the F bit MUST be zero. If the S bit is 1, the Length MUST be 12, otherwise the Length MUST be 16. o If NT=4, the F bit MUST be zero. If the S bit is 1, the Length MUST be 36, otherwise the Length MUST be 40. o If NT=5, the F bit MUST be zero. If the S bit is 1, the Length MUST be 20, otherwise the Length MUST be 24. If a PCC finds that the NT field, Length field, S bit and F bit are not consistent, it MUST consider the entire ERO invalid and MUST send Sivabalan, et al. Expires December 31, 2018 [Page 15] Internet-Draft PCEP Extensions for Segment Routing June 2018 a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 11 ("Malformed object"). If a PCC does not recognise or support the value in the NT field, it MUST consider the entire ERO invalid and MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error- Value = TBD2 ("Unsupported NAI Type in Segment ERO subobject"). If a PCC receives an SR-ERO subobject in which the S and F bits are both set to 1 (that is, both the SID and NAI are absent), it MUST consider the entire ERO invalid and send a PCErr message with Error- Type = 10 ("Reception of an invalid object") and Error-Value = 6 ("Both SID and NAI are absent in SR-ERO subobject"). If a PCC receives an SR-ERO subobject in which the S bit is set to 1 and the F bit is set to zero (that is, the SID is absent and the NAI is present), but the PCC does not support NAI resolution, it MUST consider the entire ERO invalid and send a PCErr message with Error- Type = 4 ("Not supported object") and Error-Value = 4 ("Unsupported parameter"). If a PCC receives an SR-ERO subobject in which the S bit is set to 1 and either or both of the M or C bits is set to 1, it MUST consider the entire ERO invalid and send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 11 ("Malformed object"). If a PCC receives an SR-ERO subobject in which the S bit is set to zero and the M bit is set to 1 (that is, it represents an MPLS label value), its value (20 most significant bits) MUST be larger than 15, unless it is a special purpose label, such as an Entropy Label Indicator (ELI). If a PCC receives an invalid MPLS label value, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error Value = 2 ("Bad label value"). If both M and C bits of an SR-ERO subobject are set to 1, and if a PCC finds erroneous setting in one or more of TC, S, and TTL fields, it MAY overwrite those fields with values chosen according to its own policy. If the PCC does not overwite them, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 4 ("Bad label format"). If the M bit of an SR-ERO subobject is set to zero but the C bit is set to 1, then the PCC MUST consider the entire ERO invalid and MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 11 ("Malformed object"). Sivabalan, et al. Expires December 31, 2018 [Page 16] Internet-Draft PCEP Extensions for Segment Routing June 2018 If the first SR-ERO represents an MPLS label value then the NAI field MUST NOT be absent (that is, the F bit MUST be zero). The PCC needs the NAI field to determine the first hop router in the segment routed path. If the NAI is not present then the PCC MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error Value = TBD9 ("Cannot derive a next hop from SR-ERO"). If a PCC receives an SR-ERO subobject in which the S bit is set to zero and the M bit is set to zero (that is, it represents an index value), then the SID MUST be a node-SID, an adjacency-SID or a binding-SID. If the SID is not one of these types, the PCC MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error Value = TBD10 ("Bad SID type in SR-ERO"). If the SID is an Adjacency-SID then the L flag MUST NOT be set. If the L flag is set for an Adjacency-SID then the PCC MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 11 ("Malformed object"). If a PCC detects that the subobjects of an ERO are a mixture of SR- ERO subobjects and subobjects of other types, then it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 5 ("ERO mixes SR-ERO subobjects with other subobject types"). The SR-ERO subobjects can be classified according to whether they contain a SID representing an MPLS label value, a SID representing an index value, or no SID. If a PCC detects that the SR-ERO subobjects are a mixture of more than one of these types, then it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD11 ("Inconsistent SIDs in SR-ERO subobjects"). 6.2.2. Interpreting the SR-ERO The PCC creates a segment routed path by converting the sequence of SR-ERO subobjects into an MPLS label stack plus a next hop. The PCC sends packets along the segment routed path by prepending the MPLS label stack onto the packets and sending the resulting, modified packet to the next hop. The following subsections explain how the PCC converts the SR-ERO subobject sequence to an MPLS label stack and a next hop. 6.2.2.1. SR-ERO subobjects contain MPLS Labels If the SR-ERO subobjects contain SIDs with MPLS label values, then proceed as follows: (a) Initialize next_hop to null. Initialize label_stack to an empty label stack. Sivabalan, et al. Expires December 31, 2018 [Page 17] Internet-Draft PCEP Extensions for Segment Routing June 2018 (b) Get the first SR-ERO subobject from the ERO. Append its label value to label_stack, setting the TC, S and TTL fields according to the C bit and/or local policy. Set current_router and next_hop to the router identified by the NAI. If the NAI is absent from the first SR-ERO, then this is an error, and the ERO should have failed the validation checks of Section 6.2.1. (c) Loop through the remaining SR-ERO subobjects. For each SR-ERO subobject, append it to label_stack, setting the TC, S and TTL fields according to the C bit and/or local policy. 6.2.2.2. SR-ERO subobjects contain Index SIDs If the SR-ERO subobjects contain SIDs with index values, then proceed as follows: (a) Initialize current_router to the local router. Initialize next_hop to null. Initialize label_stack to an empty label stack. (b) Get the first SR-ERO subobject from the ERO and look the SID index up in the LSDB. * If the SID is a node-SID, set current_router to the node identified by the node-SID, compute the shortest path to that node and set next_hop to the next hop from the shortest path. If next_hop is the router identified by the node-SID, and that router advertised its node-SID with the P flag clear (indicating that PHP is allowed), then do not add a label to label_stack. Otherwise, look up the next_hop router's SRGB in the LSDB. Get the label that is at offset node-SID relative to the SRGB base label and append it to label_stack. * If the SID is an adjacency-SID, set next_hop to the corresponding routing adjacency. Do not add a label the label_stack. Set current_router to the adjacent router. * If the SID is a binding-SID, then append the binding SID's associated label stack to label_stack. Set next_hop to the first hop router in the binding SID tunnel. Set current_router to the router that is the endpoint of the binding-SID tunnel. * Any other type of SID is an error, and the SR-ERO should have failed the validation checks of Section 6.2.1. (c) Loop through the remaining SR-ERO subobjects. For each SR-ERO subobject, look the SID index up in the LSDB. Sivabalan, et al. Expires December 31, 2018 [Page 18] Internet-Draft PCEP Extensions for Segment Routing June 2018 * If the SID is a node-SID, then look up the current_router's SRGB in the LSDB. Get the label that is at offset node-SID relative to the SRGB base label and append it to label_stack. * If the SID is an adjacency-SID, then look up the current_router's SRLB in the LSDB. Get the label that is at offset adjacency-SID relative to the SRLB base label and append it to label_stack. * If the SID is a binding-SID, then look up the current_router's SRGB in the LSDB. Get the label that is at offset binding-SID relative to the SRGB base label and append it to label_stack. * Any other type of SID is an error, and the SR-ERO should have failed the validation checks of Section 6.2.1. 6.2.2.3. SR-ERO subobjects contain NAI only If the SR-ERO subobjects do not contain SIDs (that is, contain only NAI), then look each NAI up in the LSDB to find the corresponding SID index. Then proceed as described above for SID index values. 6.2.2.4. Handling Errors During SR-ERO Conversion There are several errors that can occur during the process of converting an SR-ERO sequence to an MPLS label stack and a next hop. The PCC deals with them as follows. o If the PCC cannot find a SID index in the LSDB, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD3 ("Unknown SID"). o If the PCC cannot find an NAI in the LSDB, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD4 ("NAI cannot be resolved to a SID"). o If the PCC cannot find an SRGB in the LSDB, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD5 ("Could not find SRGB"). o If the PCC finds that a router's SRGB is not large enough for a SID index value, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD6 ("SID index exceeds SRGB size"). Sivabalan, et al. Expires December 31, 2018 [Page 19] Internet-Draft PCEP Extensions for Segment Routing June 2018 o If the PCC cannot find an SRLB in the LSDB, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD7 ("Could not find SRLB"). o If the PCC finds that a router's SRLB is not large enough for a SID index value, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD8 ("SID index exceeds SRLB size"). o If the number of labels in label_stack exceeds the maximum number of SIDs that the PCC can impose on the packet, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 3 ("Unsupported number of Segment ERO subobjects"). 6.3. RRO Processing The syntax checking rules that apply to the SR-RRO subobject are identical to those of the SR-ERO subobject, except as noted below. If a PCEP speaker receives an SR-RRO subobject in which both SID and NAI are absent, it MUST consider the entire RRO invalid and send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = 7 ("Both SID and NAI are absent in SR-RRO subobject"). If a PCE detects that all subobjects of the RRO are not identical, and if it does not support such an RRO, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error- Value = 10 ("Non-identical RRO subobjects"). 7. Backward Compatibility A PCEP speaker that does not support the SR PCEP capability cannot recognize the SR-ERO or SR-RRO subobjects. As such, it responds according to the rules for a malformed object, per [RFC5440]. Some implementations, which are compliant with an earlier version of this specification, do not send the PATH-SETUP-TYPE-CAPABILITY TLV in their OPEN objects. Instead, to indicate that they support SR, these implementations include the SR-CAPABILITY-TLV as a top-level TLV in the OPEN object. Unfortunately, some of these implementations made it into the field before this document was published in its final form. Therefore, if a PCEP speaker receives an OPEN object in which the SR-CAPABILITY-TLV appears as a top-level TLV, then it MUST interpret this as though the sender had sent a PATH-SETUP-TYPE- CAPABILITY TLV with a PST list of (0, 1) (that is, both RSVP-TE and SR-TE PSTs are supported) and with the SR-CAPABILITY-TLV as a sub- Sivabalan, et al. Expires December 31, 2018 [Page 20] Internet-Draft PCEP Extensions for Segment Routing June 2018 TLV. If a PCEP speaker receives an OPEN object in which both the SR- CAPABILITY-TLV and PATH-SETUP-TYPE-CAPABILITY TLV appear as top-level TLVs, then it MUST ignore the top-level SR-CAPABILITY-TLV and process only the PATH-SETUP-TYPE-CAPABILITY TLV. 8. Management Considerations This document adds a new path setup type to PCEP to allow LSPs to be set up using segment routing techniques. This path setup type may be used with PCEP alongside other path setup types, such as RSVP-TE, or it may be used exclusively. 8.1. Controlling the Path Setup Type The following factors control which path setup type is used for a given LSP. o The available path setup types are constrained to those that are supported by, or enabled on, the PCEP speakers. The PATH-SETUP- TYPE-CAPABILITY TLV indicates which path setup types a PCEP speaker supports. To use segment routing as a path setup type, it is a prerequisite that the PCC and PCE both include PST=1 in the list of supported path setup types in this TLV, and also include the SR-PCE-CAPABILITY sub-TLV. o When a PCE initiates an LSP, it proposes which path setup type to use by including it in the PATH-SETUP-TYPE TLV in the SRP object of the PCInitiate message. The PCE chooses the path setup type based on the capabilities of the network nodes on the path and on its local policy. The PCC MAY choose to accept the proposed path setup type, or to reject the PCInitiate request, based on its local policy. o When a PCC requests a path for an LSP, it can nominate a preferred path setup type by including it in the PATH-SETUP-TYPE TLV in the RP object of the PCInitiate message. The PCE MAY choose to reply with a path of the requested type, or to reply with a path of a different type, or to reject the request, based on the capabilities of the network nodes on the path and on its local policy. The operator can influence the path setup type as follows. o Implementations MUST allow the operator to enable and disable the segment routing path setup type on a PCEP-speaking device. Implementations MAY also allow the operator to enable and disable the RSVP-TE path setup type. Sivabalan, et al. Expires December 31, 2018 [Page 21] Internet-Draft PCEP Extensions for Segment Routing June 2018 o PCE implementations MUST allow the operator to specify that an LSP should be instantiated using segment routing or RSVP-TE as the proposed path setup type. o PCE implementations MAY allow the operator to configure a preference for the PCE to propose paths using segment routing or RSVP-TE in the absence of a specified path setup type. o PCC implementations MUST allow the operator to specify that a path requested for an LSP nominates segment routing or RSVP-TE as the path setup type. o PCC implementations MAY allow the operator to configure a preference for the PCC to nominate segment routing or RSVP-TE as the path setup type if none is specified for an LSP. o PCC implementations SHOULD allow the operator to configure a PCC to refuse to set up an LSP using an undesired path setup type. 8.2. Migrating a Network to Use PCEP Segment Routed Paths This section discusses the steps that the operator takes when migrating a network to enable PCEP to set up paths using segment routing as the path setup type. o The operator enables the segment routing PST on the PCE servers. o The operator enables the segment routing PST on the PCCs. o The operator resets each PCEP session. The PCEP sessions come back up with segment routing enabled. o If the operator detects a problem, they can roll the network back to its initial state by disabling the segment routing PST on the PCEP speakers and resetting the PCEP sessions. Note that the data plane is unaffected if a PCEP session is reset. Any LSPs that were set up before the session reset will remain in place and will still be present after the session comes back up. An implementation SHOULD allow the operator to manually trigger a PCEP session to be reset. An implementation MAY automatically reset a PCEP session when an operator reconfigures the PCEP speaker's capabilities. However, note that if the capabilities at both ends of the PCEP session are not reconfigured simultaneously, then the session could be reset twice, which could lead to unnecessary network traffic. Therefore, such Sivabalan, et al. Expires December 31, 2018 [Page 22] Internet-Draft PCEP Extensions for Segment Routing June 2018 implementations SHOULD allow the operator to override this behaviour and wait instead for a manual reset. Once segment routing is enabled on a PCEP session, it can be used as the path setup type for future LSPs. User traffic is not automatically be migrated from existing LSPs onto segment routed LSPs just by enabling the segment routing PST in PCEP. The migration of user traffic from existing LSPs onto segment routing LSPs is beyond the scope of this document. 8.3. Verification of Network Operation The operator needs the following information to verify that PCEP is operating correctly with respect to the segment routing path setup type. o An implementation SHOULD allow the operator to view whether the PCEP speaker sent the segment routing PST capability to its peer. If the PCEP speaker is a PCC, then the implementation SHOULD also allow the operator to view the value of the L flag that was sent, and the value of the MSD field that was sent. o An implementation SHOULD allow the operator to view whether the peer sent a the segment routing PST capability. If the peer is a PCC, then the implementation SHOULD also allow the operator to view the values of the L flag and MSD fields that the peer sent sent. o An implementation SHOULD allow the operator to view whether the segment routing PST is enabled on the PCEP session. o If one PCEP speaker advertises the segment routing PST capability, but the other does not, then the implementation SHOULD create a log to inform the operator of the capability mismatch. o An implementation SHOULD allow the operator to view the PST that was proposed, or requested, for an LSP, and the PST that was actually used. o If a PCEP speaker decides to use a different PST to the one that was proposed, or requested, for an LSP, then the implementation SHOULD create a log to inform the operator that the expected PST has not been used. The log SHOULD give the reason for this choice (local policy, equipment capability etc.) Sivabalan, et al. Expires December 31, 2018 [Page 23] Internet-Draft PCEP Extensions for Segment Routing June 2018 o If a PCEP speaker rejects a segment routed path, then it SHOULD create a log to inform the operator, giving the reson for the decision (local policy, MSD exceeded etc.) 8.4. Relationship to Existing Management Models The PCEP YANG module [I-D.ietf-pce-pcep-yang] should include: o advertised PST capabilities and MSD per PCEP session. o the PST configured for, and used by, each LSP. The PCEP MIB [RFC7420] could also be updated to include this information. 9. Security Considerations The security considerations described in [RFC5440], [RFC8281] and [I-D.ietf-pce-lsp-setup-type] are applicable to this specification. No additional security measure is required. 10. IANA Considerations 10.1. PCEP Objects This document defines a new subobject type for the PCEP explicit route object (ERO), and a new subobject type for the PCEP record route object (RRO). The code points for subobject types of these objects is maintained in the RSVP parameters registry, under the EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to confirm the early allocation of the following code points in the RSVP Parameters registry for each of the new subobject types defined in this document. Object Subobject Subobject Type --------------------- -------------------------- ------------------ EXPLICIT_ROUTE SR-ERO (PCEP-specific) 36 ROUTE_RECORD SR-RRO (PCEP-specific) 36 10.2. New NAI Type Registry IANA is requested to create a new sub-registry within the "Path Computation Element Protocol (PCEP) Numbers" registry called "PCEP SR-ERO NAI Types". The allocation policy for this new registry should be by IETF Review. The new registry should contain the following values: Sivabalan, et al. Expires December 31, 2018 [Page 24] Internet-Draft PCEP Extensions for Segment Routing June 2018 Value Description Reference 0 NAI is absent. This document 1 NAI is an IPv4 node ID. This document 2 NAI is an IPv6 node ID. This document 3 NAI is an IPv4 adjacency. This document 4 NAI is an IPv6 adjacency. This document 5 NAI is an unnumbered This document adjacency with IPv4 node IDs. 10.3. New SR-ERO Flag Registry IANA is requested to create a new sub-registry, named "SR-ERO Flag Field", within the "Path Computation Element Protocol (PCEP) Numbers" registry to manage the Flag field of the SR-ERO subobject. New values are to be assigned by Standards Action [RFC8126]. 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 The following values are defined in this document: Bit Description Reference 0-7 Unassigned 8 NAI is absent (F) This document 9 SID is absent (S) This document 10 SID specifies TC, S This document and TTL in addition to an MPLS label (C) 11 SID specifies an MPLS This document label (M) 10.4. PCEP-Error Object IANA is requested to confirm the early allocation of the code-points in the PCEP-ERROR Object Error Types and Values registry for the following new error-values: Error-Type Meaning ---------- ------- 10 Reception of an invalid object. Sivabalan, et al. Expires December 31, 2018 [Page 25] Internet-Draft PCEP Extensions for Segment Routing June 2018 Error-value = 2: Bad label value Error-value = 3: Unsupported number of SR-ERO subobjects Error-value = 4: Bad label format Error-value = 5: ERO mixes SR-ERO subobjects with other subobject types Error-value = 6: Both SID and NAI are absent in SR- ERO subobject Error-value = 7: Both SID and NAI are absent in SR- RRO subobject Error-value = 9: Default MSD is specified for the PCEP session Error-value = 10: RRO mixes SR-RRO subobjects with other subobject types Error-value = TBD1: Missing PCE-SR- CAPABILITY sub-TLV Error-value = TBD2: Unsupported NAI Type in SR-ERO subobject Error-value = TBD3: Unknown SID Error-value = TBD4: NAI cannot be resolved to a SID Error-value = TBD5: Could not find SRGB Error-value = TBD6: SID index exceeds SRGB size Error-value = TBD7: Could not find SRLB Error-value = TBD8: SID index exceeds SRLB size Error-value = TBD9: Cannot derive a next hop from SR- ERO Error-value = TBD10: Bad SID type in SR- ERO Error-value = TBD11: Inconsistent SIDs in SR-ERO subobjects Note to IANA: this draft originally had an early allocation for Error-value=11 (Malformed object) in the above list. However, we have since moved the definition of that code point to draft-ietf-pce- Sivabalan, et al. Expires December 31, 2018 [Page 26] Internet-Draft PCEP Extensions for Segment Routing June 2018 lsp-setup-type and we included an instruction in that draft for you to update the reference in the indicated registry. Please ensure that this has happened when you process the present draft. Note to IANA: some Error-values in the above list were defined after the early allocation took place, and so do not currently have a code point assigned. Please assign code points from the indicated registry and replace each instance of "TBD1", "TBD2" etc. in this document with the respective code points. Note to IANA: some of the Error-value descriptive strings above have changed since the early allocation. Please refresh the registry. 10.5. PCEP TLV Type Indicators IANA is requested to confirm the early allocation of the following code point in the PCEP TLV Type Indicators registry. Value Meaning Reference ------------------------- ---------------------------- -------------- 26 SR-PCE-CAPABILITY This document 10.6. New Path Setup Type [I-D.ietf-pce-lsp-setup-type] requests that IANA creates a sub- registry within the "Path Computation Element Protocol (PCEP) Numbers" registry called "PCEP Path Setup Types". IANA is requested to allocate a new code point within this registry, as follows: Value Description Reference ------------------------- ---------------------------- -------------- 1 Traffic engineering path is This document setup using Segment Routing. 10.7. New Metric Type IANA is requested to confirm the early allocation of the following code point in the PCEP METRIC object T field registry: Value Description Reference ------------------------- ---------------------------- -------------- 11 Segment-ID (SID) Depth. This document 10.8. SR PCE Capability Flags IANA is requested to create a new sub-registry, named "SR Capability Flag Field", within the "Path Computation Element Protocol (PCEP) Numbers" registry to manage the Flag field of the SR-PCE-CAPABILITY Sivabalan, et al. Expires December 31, 2018 [Page 27] Internet-Draft PCEP Extensions for Segment Routing June 2018 TLV. New values are to be assigned by Standards Action [RFC8126]. 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 The following values are defined in this document: Bit Description Reference 0-5 Unassigned 6 Node or Adjacency This document Identifier (NAI) is supported (N) 7 Unlimited Maximum SID This document Depth (L) 11. Contributors The following people contributed to this document: - Lakshmi Sharma - Jan Medved - Edward Crabbe - Robert Raszuk - Victor Lopez 12. Acknowledgements We thank Ina Minei, George Swallow, Marek Zavodsky, Dhruv Dhody, Ing- Wher Chen and Tomas Janciga for the valuable comments. 13. References 13.1. Normative References [I-D.ietf-idr-bgp-ls-segment-routing-msd] Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, "Signaling Maximum SID Depth using Border Gateway Protocol Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 (work in progress), October 2017. Sivabalan, et al. Expires December 31, 2018 [Page 28] Internet-Draft PCEP Extensions for Segment Routing June 2018 [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS Extensions for Segment Routing", draft-ietf-isis- segment-routing-extensions-18 (work in progress), June 2018. [I-D.ietf-isis-segment-routing-msd] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling MSD (Maximum SID Depth) using IS-IS", draft- ietf-isis-segment-routing-msd-12 (work in progress), May 2018. [I-D.ietf-ospf-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Extensions for Segment Routing", draft-ietf-ospf-segment- routing-extensions-25 (work in progress), April 2018. [I-D.ietf-ospf-segment-routing-msd] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, "Signaling MSD (Maximum SID Depth) using OSPF", draft- ietf-ospf-segment-routing-msd-14 (work in progress), May 2018. [I-D.ietf-pce-lsp-setup-type] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J. Hardwick, "Conveying path setup type in PCEP messages", draft-ietf-pce-lsp-setup-type-10 (work in progress), May 2018. [I-D.ietf-pce-pcep-yang] Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A YANG Data Model for Path Computation Element Communications Protocol (PCEP)", draft-ietf-pce-pcep- yang-08 (work in progress), June 2018. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf-spring-segment-routing-15 (work in progress), January 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Sivabalan, et al. Expires December 31, 2018 [Page 29] Internet-Draft PCEP Extensions for Segment Routing June 2018 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, . [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [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, December 2017, . 13.2. Informative References [I-D.ietf-6man-segment-routing-header] Previdi, S., Filsfils, C., Leddy, J., Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-segment-routing-header-13 (work in progress), May 2018. [I-D.ietf-spring-segment-routing-mpls] Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing with MPLS data plane", draft-ietf-spring-segment-routing-mpls-14 (work in progress), June 2018. Sivabalan, et al. Expires December 31, 2018 [Page 30] Internet-Draft PCEP Extensions for Segment Routing June 2018 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, . [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, DOI 10.17487/RFC4657, September 2006, . [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, . Authors' Addresses Siva Sivabalan Cisco Systems, Inc. 2000 Innovation Drive Kanata, Ontario K2K 3E8 Canada Email: msiva@cisco.com Clarence Filsfils Cisco Systems, Inc. Pegasus Parc De kleetlaan 6a, DIEGEM BRABANT 1831 BELGIUM Email: cfilsfil@cisco.com Jeff Tantsura Individual 444 San Antonio Rd, 10A Palo Alto, CA 94306 USA Email: jefftant.ietf@gmail.com Sivabalan, et al. Expires December 31, 2018 [Page 31] Internet-Draft PCEP Extensions for Segment Routing June 2018 Wim Henderickx Nokia Copernicuslaan 50 Antwerp 2018, CA 95134 BELGIUM Email: wim.henderickx@alcatel-lucent.com Jon Hardwick Metaswitch Networks 100 Church Street Enfield, Middlesex UK Email: jonathan.hardwick@metaswitch.com Sivabalan, et al. Expires December 31, 2018 [Page 32]