| PCE | S. Sivabalan |
| Internet-Draft | C. Filsfils |
| Intended status: Standards Track | Cisco Systems, Inc. |
| Expires: April 13, 2018 | J. Tantsura |
| Individual | |
| W. Henderickx | |
| Nokia | |
| J. Hardwick | |
| Metaswitch Networks | |
| October 10, 2017 |
PCEP Extensions for Segment Routing
draft-ietf-pce-segment-routing-10
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 constraint(s) and optimization criteria in SR networks.
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].
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/.
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 April 13, 2018.
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 (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.
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 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. 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 global within SR/IGP domain. An Adjacency Segment represents 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 applied to the MPLS forwarding plane without any change, in which case an SR path corresponds to an MPLS Label Switching Path (LSP). This document is relevant to MPLS forwarding plane only and assumes that a 32-bit Segment Identifier (SID) represents an absolute value of MPLS label entry. In this document, "Node-SID" and "Adjacency-SID" denote Node Segment Identifier and Adjacency Segment Identifier respectively.
A Segment Routed path (SR path) can be derived from an IGP Shortest Path Tree (SPT). SR-TE paths may not follow 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 Path Computation Element Protocol (PCEP) for communication between a Path Computation Client (PCC) and a Path Computation Element (PCE) or between one a pair of PCEs. A PCE or a PCC operating as a PCE (in hierarchical PCE environment) computes paths for MPLS Traffic Engineering LSPs (MPLS-TE LSPs) based on various constraints and optimization criteria. [I-D.ietf-pce-stateful-pce] 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 [I-D.ietf-pce-pce-initiated-lsp]. Such mechanism is useful in Software Driven Networks (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 [I-D.ietf-pce-pce-initiated-lsp] 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 stateful or a stateless PCE. This specification relies on the PATH-SETUP-TYPE TLV and procedures specified in [I-D.ietf-pce-lsp-setup-type].
The following terminologies are used in this document:
In SR networks, an ingress node of an SR path appends all outgoing packets with an SR header consisting of a list of SIDs (or MPLS labels in the context of this document). The header has all necessary information to guide the packets from the ingress node to the egress node of the path, and hence there is no need for any signaling protocol.
In a PCEP session, LSP information is carried in the Explicit Route Object (ERO), which consists of a sequence of subobjects. Various types of ERO subobjects have been specified in [RFC3209], [RFC3473], and [RFC3477]. In SR networks, an ingress node of an SR path appends all outgoing packets with an SR header consisting of a list of SIDs (or MPLS labels in the context of this document). SR-TE LSPs computed by a PCE can be represented in one of the following forms:
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 [I-D.ietf-pce-pce-initiated-lsp], as well as in the PCEP LSP Update Request (PCUpd) and PCEP LSP State Report (PCRpt) messages defined in defined in [I-D.ietf-pce-stateful-pce].
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. Furthermore, an LSP initially established via RSVP-TE signaling can be updated with SR-TE path. This capability is useful when a network is migrated from RSVP-TE to SR-TE technology. Similarly, an LSP initially created with SR-TE signaling can be updated using RSVP-TE if necessary.
A PCC MAY include an RRO object containing the recorded LSP in PCReq and PCRpt messages as specified in [RFC5440] and [I-D.ietf-pce-stateful-pce] respectively. This document defines a new RRO subobject for SR networks. Methods used by a PCC to record SR-TE LSP are outside the scope of this document.
In summary, this document:
The extensions specified in this document complement the existing PCEP specifications to support SR-TE path. 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], [I-D.ietf-pce-stateful-pce], [I-D.ietf-pce-pce-initiated-lsp], and any other applicable PCEP specifications.
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 PCReq and PCRep messages specified in [RFC5440], PCInitiate message specified in [I-D.ietf-pce-pce-initiated-lsp], and PCRpt and PCUpd messages specified in [I-D.ietf-pce-stateful-pce]. However, PCEP messages pertaining to SR-TE LSP MUST include PATH-SETUP-TYPE TLV in the RP or SRP object to clearly identify that SR-TE LSP is intended. In other words, a PCEP speaker MUST not infer whether or not a PCEP message pertains to SR-TE LSP from any other object or TLV.
This document defines a new optional TLV for use in the OPEN Object.
The SR-PCE-CAPABILITY TLV is an optional TLV associated with the OPEN Object to exchange SR capability of PCEP speakers. The format of the SR-PCE-CAPABILITY TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=TBD | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |L| MSD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SR-PCE-CAPABILITY TLV format
The code point for the TLV type is to be defined by IANA. 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 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 octect long, and this document defines the following flag:
By including the SR-PCE-CAPABILITY TLV in the OPEN message destined to a PCE, a PCC indicates that it is capable of supporting the head-end functions for SR-TE LSP. By including the TLV in the OPEN message destined to a PCC, a PCE indicates that it is capable of computing SR-TE paths.
The number of SIDs that can be imposed on a packet depends on PCC's data plane's capability. An MSD value MUST be non-zero otherwise the receiver of the SR-PCE-CAPABILITY TLV MUST assume that the sender is not capable of imposing a MSD of any depth and hence is not SR-TE capable.
Note that the MSD value exchanged via SR-PCE-CAPABILITY TLV indicates the SID/label imposition limit for the PCC node. However, if a PCE learns 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.tantsura-idr-bgp-ls-segment-routing-msd], then it ignores the MSD value in the SR-PCE-CAPABILITY TLV. Furthermore, whenever a PCE learns MSD for a link via different means, it MUST use that value for that link regardless of the MSD value exchanged via SR-PCE-CAPABILITY 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 number of SIDs exceeding that MSD value. If a PCC needs to modify the MSD value, the PCEP session MUST be closed and re-established with the new MSD value. If a PCEP session is established with a non-zero MSD 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). 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.
The MSD value inside SR Capability TLV is meaningful only in the OPEN message sent from a PCC to a PCE. As such, a PCE does not need to set MSD value in outbound message to a PCC. Similarly, a PCC ignores any MSD value received from a PCE. If a PCE receives multiple SR-PCE-CAPABILITY TLVs in an OPEN message, it processes only the first TLV received.
In order to setup an SR-TE LSP using SR, RP or SRP object MUST include PATH-SETUP-TYPE TLV specified in [I-D.ietf-pce-lsp-setup-type]. This document defines a new Path Setup Type (PST) for SR as follows:
LSP-IDENTIFIERS TLV MAY be present for the above PST type.
An SR-TE path consists of one or more SID(s) 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 object 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 specified in the following section. An ERO object carrying an SR-TE path consists of one or more ERO subobject(s), and MUST carry only SR-ERO subobject(s). 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.
An SR-ERO subobject consists of a 32-bit header followed by the SID and 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.
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 | Length | ST | Flags |F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SR-ERO Subobject format
The fields in the SR-ERO Subobject are as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: NAI for IPv4 Adjacency
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 adjacenc y
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
This document defines the following NAIs:
A PCEP speaker that does not recognize the SR-ERO subobject in PCRep, PCInitiate, PCUpd or PCRpt messages MUST reject the entire PCEP message and MUST send a PCErr message with Error-Type=3 ("Unknown Object") and Error-Value=2 ("Unrecognized object Type") or Error-Type=4 ("Not supported object") and Error-Value=2 ("Not supported object Type"), defined in [RFC5440].
When the SID represents an MPLS label (i.e. the M bit is set), its value (20 most significant bits) MUST be larger than 15, unless it is special purpose label, such as an Entropy Label Indicator (ELI). If a PCEP speaker receives an invalid value, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error Value = TBD ("Bad label value"). If both M and C bits of an SR-ERO subobject are set, and if a PCEP speaker finds erroneous setting in one or more of TC, S, and TTL fields, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD ("Bad label format").
If a PCC receives a stack of SR-ERO subobjects, and the number of stack exceeds the maximum number of SIDs that the PCC can impose on the packet, it MAY send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD ("Unsupported number of Segment ERO subobjects").
When a PCEP speaker detects that all subobjects of ERO are not identical, and if it does not handle such ERO, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD ("Non-identical ERO subobjects").
If a PCEP speaker receives an SR-ERO subobject in which both SID and NAI are absent, it MUST consider the entire ERO object invalid and send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD ("Both SID and NAI are absent in ERO subobject").
When a PCEP speaker receives an SR-ERO subobject in which ST is 0, SID MUST be present and NAI MUST NOT be present(i.e., S-flag MUST be 0, F-flag MUST be 1, and the Length MUST be 8). Otherwise, it MUST consider the entire ERO object invalid and send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD ("Malformed object"). The PCEP speaker MAY include the malformed SR-ERO object in the PCErr message as well.
A PCC can record SR-TE LSP and report the LSP to a PCE via RRO. An RRO object contains one or more subobjects called "SR-RRO subobjects" whose format is shown below:
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 | Length | ST | Flags |F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: SR-RRO Subobject format
The format of SR-RRO subobject is the same as that of SR-ERO subobject without L flag.
A PCC MUST assume that SR-RRO subobjects are organized such that the first subobject relative to the beginning of RRO contains the information about the topmost label, and the last subobject contains information about the bottommost label of the SR-TE LSP.
Processing rules of SR-RRO subobject are identical to those of SR-ERO subobject.
If a PCEP speaker receives an SR-RRO subobject in which both SID and NAI are absent, it MUST consider the entire RRO object invalid and send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD ("Both SID and NAI are absent in RRO subobject").
If a PCE detects that all subobjects of RRO are not identical, and if it does not handle such RRO, it MUST send a PCErr message with Error-Type = 10 ("Reception of an invalid object") and Error-Value = TBD ("Non-identical RRO subobjects").
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:
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 TBD ("Default MSD is specified for the PCEP session").
A PCEP speaker that does not support the SR PCEP capability cannot recognize the SR-ERO or SR-RRO subobjects. As such, it MUST send a PCEP error with Error-Type = 4 (Not supported object) and Error-Value = 2 (Not supported object Type) as per [RFC5440].
PCEP implementation:
A PCEP MIB module is defined in [RFC7420]needs be extended to cover additional functionality provided by [RFC5440] and [I-D.ietf-pce-pce-initiated-lsp]. Such extension will cover the new functionality specified in this document.
The security considerations described in [RFC5440] and [I-D.ietf-pce-pce-initiated-lsp] are applicable to this specification. No additional security measure is required.
This document defines a new sub-object type for the PCEP explicit route object (ERO), and a new sub-object type for the PCEP record route object (RRO). The code points for sub-object types of these objects is maintained in the RSVP parameters registry, under the EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to allocate code points in the RSVP Parameters registry for each of the new sub-object types defined in this document, as follows:
| Object | Sub-Object | Sub-Object Type |
|---|---|---|
| --------------------- | -------------------------- | ------------------ |
| EXPLICIT_ROUTE | SR-ERO (PCEP-specific) | TBD (recommended 36) |
| ROUTE_RECORD | SR-RRO (PCEP-specific) | TBD (recommended 36) |
IANA is requested to allocate code-points in the PCEP-ERROR Object Error Types and Values registry for the following new error-values:
IANA is requested to allocate a new code point in the PCEP TLV Type Indicators registry, as follows:
| Value | Meaning | Reference |
|---|---|---|
| ------------------------- | ---------------------------- | -------------- |
| TBD (recommended 26) | SR-PCE-CAPABILITY | This document |
[I-D.ietf-pce-lsp-setup-type] defines the PATH-SETUP-TYPE TLV and requests that IANA creates a registry to manage the value of the PATH_SETUP_TYPE TLV's PST field. IANA is requested to allocate a new code point in the PCEP PATH_SETUP_TYPE TLV PST field registry, as follows:
| Value | Description | Reference |
|---|---|---|
| ------------------------- | ---------------------------- | -------------- |
| 1 | Traffic engineering path is setup using Segment Routing technique. | This document |
IANA is requested to allocate a new code point in the PCEP METRIC object T field registry, as follows:
| Value | Description | Reference |
|---|---|---|
| ------------------------- | ---------------------------- | -------------- |
| TBD (recommended 11) | Segment-ID (SID) Depth. | This document |
The following people contributed to this document:
We like to thank Ina Minei, George Swallow, Marek Zavodsky, Dhruv Dhody, Ing-Wher Chen and Tomas Janciga for the valuable comments.
| [I-D.ietf-isis-segment-routing-extensions] | Previdi, S., Filsfils, C., Bashandy, A., Gredler, H., Litkowski, S., Decraene, B. and j. jefftant@gmail.com, "IS-IS Extensions for Segment Routing", Internet-Draft draft-ietf-isis-segment-routing-extensions-11, March 2017. |
| [I-D.ietf-isis-segment-routing-msd] | Tantsura, J., Chunduri, U., Aldrin, S. and L. Ginsberg, "Signaling MSD (Maximum SID Depth) using IS-IS", Internet-Draft draft-ietf-isis-segment-routing-msd-03, March 2017. |
| [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", Internet-Draft draft-ietf-ospf-segment-routing-extensions-12, March 2017. |
| [I-D.ietf-ospf-segment-routing-msd] | Tantsura, J., Chunduri, U., Aldrin, S. and P. Psenak, "Signaling MSD (Maximum SID Depth) using OSPF", Internet-Draft draft-ietf-ospf-segment-routing-msd-04, March 2017. |
| [I-D.ietf-pce-lsp-setup-type] | Sivabalan, S., Medved, J., Minei, I., Crabbe, E., Varga, R., Tantsura, J. and J. Hardwick, "Conveying path setup type in PCEP messages", Internet-Draft draft-ietf-pce-lsp-setup-type-03, June 2015. |
| [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", Internet-Draft draft-ietf-pce-pce-initiated-lsp-09, March 2017. |
| [I-D.ietf-pce-stateful-pce] | Crabbe, E., Minei, I., Medved, J. and R. Varga, "PCEP Extensions for Stateful PCE", Internet-Draft draft-ietf-pce-stateful-pce-18, December 2016. |
| [I-D.ietf-spring-segment-routing] | Filsfils, C., Previdi, S., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", Internet-Draft draft-ietf-spring-segment-routing-11, February 2017. |
| [I-D.tantsura-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", Internet-Draft draft-tantsura-idr-bgp-ls-segment-routing-msd-02, January 2017. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC5440] | Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009. |
| [RFC5462] | Andersson, L. and R. Asati, "Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic Class" Field", RFC 5462, DOI 10.17487/RFC5462, February 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. |
| [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. |
| [RFC3473] | Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, DOI 10.17487/RFC3473, January 2003. |
| [RFC3477] | Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", RFC 3477, DOI 10.17487/RFC3477, January 2003. |
| [RFC4657] | Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, DOI 10.17487/RFC4657, September 2006. |