< draft-ietf-pce-segment-routing-12.txt   draft-ietf-pce-segment-routing-13.txt >
PCE S. Sivabalan PCE S. Sivabalan
Internet-Draft C. Filsfils Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems, Inc. Intended status: Standards Track Cisco Systems, Inc.
Expires: December 31, 2018 J. Tantsura Expires: April 15, 2019 J. Tantsura
Individual Individual
W. Henderickx W. Henderickx
Nokia Nokia
J. Hardwick J. Hardwick
Metaswitch Networks Metaswitch Networks
June 29, 2018 October 12, 2018
PCEP Extensions for Segment Routing PCEP Extensions for Segment Routing
draft-ietf-pce-segment-routing-12 draft-ietf-pce-segment-routing-13
Abstract Abstract
Segment Routing (SR) enables any head-end node to select any path 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 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- RSVP-TE). It depends only on "segments" that are advertised by Link-
State Interior Gateway Protocols (IGPs). A Segment Routed Path can State Interior Gateway Protocols (IGPs). A Segment Routed Path can
be derived from a variety of mechanisms, including an IGP Shortest be derived from a variety of mechanisms, including an IGP Shortest
Path Tree (SPT), explicit configuration, or a Path Computation Path Tree (SPT), explicit configuration, or a Path Computation
Element (PCE). This document specifies extensions to the Path Element (PCE). This document specifies extensions to the Path
Computation Element Protocol (PCEP) that allow a stateful PCE to Computation Element Communication Protocol (PCEP) that allow a
compute and initiate Traffic Engineering (TE) paths, as well as a PCC stateful PCE to compute and initiate Traffic Engineering (TE) paths,
to request a path subject to certain constraints and optimization as well as a PCC to request a path subject to certain constraints and
criteria in SR networks. optimization criteria in SR networks.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 31, 2018. This Internet-Draft will expire on April 15, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview of PCEP Operation in SR Networks . . . . . . . . . . 5 3. Overview of PCEP Operation in SR Networks . . . . . . . . . . 5
4. SR-Specific PCEP Message Extensions . . . . . . . . . . . . . 7 4. SR-Specific PCEP Message Extensions . . . . . . . . . . . . . 7
5. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7 5. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7 5.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7
5.1.1. The SR PCE Capability sub-TLV . . . . . . . . . . . . 7 5.1.1. The SR PCE Capability sub-TLV . . . . . . . . . . . . 7
5.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 8 5.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 8
5.3. ERO . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3. ERO . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . . . 9 5.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . . . 9
5.3.2. NAI Associated with SID . . . . . . . . . . . . . . . 11 5.3.2. NAI Associated with SID . . . . . . . . . . . . . . . 11
5.4. RRO . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.4. RRO . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.5. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 13 5.5. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 13
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 13 6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Exchanging the SR PCE Capability . . . . . . . . . . . . 13 6.1. Exchanging the SR PCE Capability . . . . . . . . . . . . 14
6.2. ERO Processing . . . . . . . . . . . . . . . . . . . . . 15 6.2. ERO Processing . . . . . . . . . . . . . . . . . . . . . 15
6.2.1. SR-ERO Validation . . . . . . . . . . . . . . . . . . 15 6.2.1. SR-ERO Validation . . . . . . . . . . . . . . . . . . 15
6.2.2. Interpreting the SR-ERO . . . . . . . . . . . . . . . 17 6.2.2. Interpreting the SR-ERO . . . . . . . . . . . . . . . 17
6.3. RRO Processing . . . . . . . . . . . . . . . . . . . . . 20 6.3. RRO Processing . . . . . . . . . . . . . . . . . . . . . 19
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 20 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 19
8. Management Considerations . . . . . . . . . . . . . . . . . . 21 8. Management Considerations . . . . . . . . . . . . . . . . . . 20
8.1. Controlling the Path Setup Type . . . . . . . . . . . . . 21 8.1. Controlling the Path Setup Type . . . . . . . . . . . . . 20
8.2. Migrating a Network to Use PCEP Segment Routed Paths . . 22 8.2. Migrating a Network to Use PCEP Segment Routed Paths . . 21
8.3. Verification of Network Operation . . . . . . . . . . . . 23 8.3. Verification of Network Operation . . . . . . . . . . . . 22
8.4. Relationship to Existing Management Models . . . . . . . 24 8.4. Relationship to Existing Management Models . . . . . . . 23
9. Security Considerations . . . . . . . . . . . . . . . . . . . 24 9. Security Considerations . . . . . . . . . . . . . . . . . . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10.1. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . 24 10.1. PCEP ERO and RRO subobjects . . . . . . . . . . . . . . 24
10.2. New NAI Type Registry . . . . . . . . . . . . . . . . . 24 10.2. New NAI Type Registry . . . . . . . . . . . . . . . . . 24
10.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 25 10.3. New SR-ERO Flag Registry . . . . . . . . . . . . . . . . 24
10.4. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 25 10.4. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 25
10.5. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 27 10.5. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 26
10.6. New Path Setup Type . . . . . . . . . . . . . . . . . . 27 10.6. New Path Setup Type . . . . . . . . . . . . . . . . . . 26
10.7. New Metric Type . . . . . . . . . . . . . . . . . . . . 27 10.7. New Metric Type . . . . . . . . . . . . . . . . . . . . 27
10.8. SR PCE Capability Flags . . . . . . . . . . . . . . . . 27 10.8. SR PCE Capability Flags . . . . . . . . . . . . . . . . 27
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
13.1. Normative References . . . . . . . . . . . . . . . . . . 28 13.1. Normative References . . . . . . . . . . . . . . . . . . 28
13.2. Informative References . . . . . . . . . . . . . . . . . 30 13.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction 1. Introduction
Segment Routing (SR) technology leverages the source routing and Segment Routing (SR) technology leverages the source routing and
tunneling paradigms. A source node can choose a path without relying 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 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 is specified as a set of "segments" advertised by link-state routing
protocols (IS-IS or OSPF). [I-D.ietf-spring-segment-routing] protocols (IS-IS or OSPF). [RFC8402] provides an introduction to the
provides an introduction to the SR architecture. The corresponding SR architecture. The corresponding IS-IS and OSPF extensions are
IS-IS and OSPF extensions are specified in specified in [I-D.ietf-isis-segment-routing-extensions] and
[I-D.ietf-isis-segment-routing-extensions] and
[I-D.ietf-ospf-segment-routing-extensions], respectively. The SR [I-D.ietf-ospf-segment-routing-extensions], respectively. The SR
architecture defines a "segment" as a piece of information advertised architecture defines a "segment" as a piece of information advertised
by a link-state routing protocols, e.g., an IGP prefix or an IGP by a link-state routing protocols, e.g., an IGP prefix or an IGP
adjacency. Several types of segments are defined. A Node segment adjacency. Several types of segments are defined. A Node segment
represents an ECMP-aware shortest-path computed by IGP to a specific represents an ECMP-aware shortest-path computed by IGP to a specific
node, and is always identified uniquely within the SR/IGP domain. An node, and is always identified uniquely within the SR/IGP domain. An
Adjacency Segment represents a unidirectional adjacency. An Adjacency Segment represents a unidirectional adjacency. An
Adjacency Segment is local to the node which advertises it. Both Adjacency Segment is local to the node which advertises it. Both
Node segments and Adjacency segments can be used for SR Traffic Node segments and Adjacency segments can be used for SR Traffic
Engineering (SR-TE). Engineering (SR-TE).
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case an SR path corresponds to an MPLS Label Switching Path (LSP). case an SR path corresponds to an MPLS Label Switching Path (LSP).
This document is relevant to the MPLS forwarding plane only. In this This document is relevant to the MPLS forwarding plane only. In this
document, "Node-SID" and "Adjacency-SID" denote Node Segment document, "Node-SID" and "Adjacency-SID" denote Node Segment
Identifier and Adjacency Segment Identifier respectively. Identifier and Adjacency Segment Identifier respectively.
A Segment Routed path (SR path) can be derived from an IGP Shortest 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 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 may be chosen by a suitable network planning tool and provisioned on
the ingress node of the SR-TE path. the ingress node of the SR-TE path.
[RFC5440] describes the Path Computation Element Protocol (PCEP) for [RFC5440] describes the Path Computation Element Communication
communication between a Path Computation Client (PCC) and a Path Protocol (PCEP) for communication between a Path Computation Client
Computation Element (PCE) or between a pair of PCEs. A PCE computes (PCC) and a Path Computation Element (PCE) or between a pair of PCEs.
paths for MPLS Traffic Engineering LSPs (MPLS-TE LSPs) based on A PCE computes paths for MPLS Traffic Engineering LSPs (MPLS-TE LSPs)
various constraints and optimization criteria. [RFC8231] specifies based on various constraints and optimization criteria. [RFC8231]
extensions to PCEP that allow a stateful PCE to compute and recommend specifies extensions to PCEP that allow a stateful PCE to compute and
network paths in compliance with [RFC4657] and defines objects and recommend network paths in compliance with [RFC4657] and defines
TLVs for MPLS-TE LSPs. Stateful PCEP extensions provide objects and TLVs for MPLS-TE LSPs. Stateful PCEP extensions provide
synchronization of LSP state between a PCC and a PCE or between a 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 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 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 a PCE to a PCC. Stateful PCEP extensions are intended for an
operational model in which LSPs are configured on the PCC, and operational model in which LSPs are configured on the PCC, and
control over them is delegated to the PCE. control over them is delegated to the PCE.
A mechanism to dynamically initiate LSPs on a PCC based on the A mechanism to dynamically initiate LSPs on a PCC based on the
requests from a stateful PCE or a controller using stateful PCE is requests from a stateful PCE or a controller using stateful PCE is
specified in [RFC8281]. This mechanism is useful in Software Defined specified in [RFC8281]. This mechanism is useful in Software Defined
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bandwidth calendaring. bandwidth calendaring.
It is possible to use a stateful PCE for computing one or more SR-TE It is possible to use a stateful PCE for computing one or more SR-TE
paths taking into account various constraints and objective paths taking into account various constraints and objective
functions. Once a path is chosen, the stateful PCE can initiate an functions. Once a path is chosen, the stateful PCE can initiate an
SR-TE path on a PCC using PCEP extensions specified in [RFC8281] SR-TE path on a PCC using PCEP extensions specified in [RFC8281]
using the SR specific PCEP extensions specified in this document. using the SR specific PCEP extensions specified in this document.
Additionally, using procedures described in this document, a PCC can Additionally, using procedures described in this document, a PCC can
request an SR path from either a stateful or a stateless PCE. request an SR path from either a stateful or a stateless PCE.
This specification relies on the procedures specified in This specification relies on the procedures specified in [RFC8408] to
[I-D.ietf-pce-lsp-setup-type] to exchange the segment routing exchange the segment routing capability and to specify that the path
capability and to specify that the path setup type of an LSP is setup type of an LSP is segment routing.
segment routing.
This specification provides a mechanism for a network controller
(acting as a PCE) to instantiate candidate paths for an SR Policy
onto a head-end node (acting as a PCC) using PCEP. For more
information on the SR Policy Architecture, see
[I-D.ietf-spring-segment-routing-policy].
2. Terminology 2. Terminology
The following terminologies are used in this document: The following terminologies are used in this document:
ERO: Explicit Route Object ERO: Explicit Route Object
IGP: Interior Gateway Protocol IGP: Interior Gateway Protocol
IS-IS: Intermediate System to Intermediate System IS-IS: Intermediate System to Intermediate System
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2. Terminology 2. Terminology
The following terminologies are used in this document: The following terminologies are used in this document:
ERO: Explicit Route Object ERO: Explicit Route Object
IGP: Interior Gateway Protocol IGP: Interior Gateway Protocol
IS-IS: Intermediate System to Intermediate System IS-IS: Intermediate System to Intermediate System
LSR: Label Switching Router LSR: Label Switching Router
MSD: Maximum SID Depth MSD: Maximum SID Depth
NAI: Node or Adjacency Identifier NAI: Node or Adjacency Identifier
OSPF: Open Shortest Path First OSPF: Open Shortest Path First
PCC: Path Computation Client PCC: Path Computation Client
PCE: Path Computation Element PCE: Path Computation Element
PCEP: Path Computation Element Protocol PCEP: Path Computation Element Communication Protocol
RRO: Record Route Object RRO: Record Route Object
SID: Segment Identifier SID: Segment Identifier
SR: Segment Routing SR: Segment Routing
SR-TE: Segment Routed Traffic Engineering SR-DB: Segment Routing Database (as defined in
[I-D.ietf-spring-segment-routing-policy])
SR-TE: Segment Routing Traffic Engineering
3. Overview of PCEP Operation in SR Networks 3. Overview of PCEP Operation in SR Networks
In an SR network, the ingress node of an SR path prepends an SR 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 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 SIDs (or MPLS labels in the context of this document). The header
has all necessary information so that, in combination with the has all necessary information so that, in combination with the
information distributed by the IGP, the packets can be guided from 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 the ingress node to the egress node of the path; hence, there is no
need for any signaling protocol. need for any signaling protocol.
In PCEP messages, LSP route information is carried in the Explicit In PCEP messages, LSP route information is carried in the Explicit
Route Object (ERO), which consists of a sequence of subobjects. In 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 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 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 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: 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: 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 o An ordered set of SIDs, with or without the corresponding IP
addresses. addresses.
o An ordered set of MPLS labels and IP addresses: In this case, the o An ordered set of MPLS labels, with or without corresponding IP
PCC needs to convert the IP addresses into the corresponding SIDs address.
by consulting its LSDB.
The PCC converts these into an MPLS label stack and next hop, as
described in Section 6.2.2.
This document defines a new ERO subobject denoted by "SR-ERO This document defines a new ERO subobject denoted by "SR-ERO
subobject" capable of carrying a SID as well as the identity of the subobject" capable of carrying a SID as well as the identity of the
node/adjacency represented by the SID. SR-capable PCEP speakers node/adjacency represented by the SID. SR-capable PCEP speakers
should be able to generate and/or process such ERO subobject. An ERO should be able to generate and/or process such ERO subobject. An ERO
containing SR-ERO subobjects can be included in the PCEP Path containing SR-ERO subobjects can be included in the PCEP Path
Computation Reply (PCRep) message defined in [RFC5440], the PCEP LSP Computation Reply (PCRep) message defined in [RFC5440], the PCEP LSP
Initiate Request message (PCInitiate) defined in [RFC8281], as well Initiate Request message (PCInitiate) defined in [RFC8281], as well
as in the PCEP LSP Update Request (PCUpd) and PCEP LSP State Report as in the PCEP LSP Update Request (PCUpd) and PCEP LSP State Report
(PCRpt) messages defined in [RFC8231]. (PCRpt) messages defined in [RFC8231].
When a PCEP session between a PCC and a PCE is established, both PCEP When a PCEP session between a PCC and a PCE is established, both PCEP
speakers exchange their capabilites to indicate their ability to speakers exchange their capabilities to indicate their ability to
support SR-specific functionality. support SR-specific functionality.
An PCE can update an LSP that is initially established via RSVP-TE A 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 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 delegated the LSP to it ([RFC8231]). A PCC can update an undelegated
created with an SR-TE path can be updated to use RSVP-TE signaling, LSP that is initially established via RSVP-TE signaling to use an SR-
if necessary. This capability is useful when a network is migrated TE path as follows. First, it requests an SR-TE Path from a PCE by
from RSVP-TE to SR-TE technology. sending a PCReq message. If it receives a suitable path, it
establishes the path in the data plane, and then tears down the
original RSVP-TE path. If the PCE is stateful, then the PCC sends
PCRpt messages indicating that the new path is set up and the old
path is torn down, per [RFC8231].
Similarly, a PCE or PCC can update an LSP initially created with an
SR-TE path to use RSVP-TE signaling, if necessary. This capability
is useful for rolling back a change 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 A PCC MAY include an RRO containing the recorded LSP in PCReq and
PCRpt messages as specified in [RFC5440] and [RFC8231], respectively. PCRpt messages as specified in [RFC5440] and [RFC8231], respectively.
This document defines a new RRO subobject for SR networks. The 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 methods used by a PCC to record the SR-TE LSP are outside the scope
of this document. of this document.
In summary, this document: In summary, this document:
o Defines a new ERO subobject, a new RRO subobject and new PCEP o Defines a new ERO subobject, a new RRO subobject and new PCEP
error codes. error codes.
o Specifies how two PCEP speakers can establish a PCEP session that o Specifies how two PCEP speakers can establish a PCEP session that
can carry information about SR-TE paths. can carry information about SR-TE paths.
o Specifies processing rules for the ERO subobject. o Specifies processing rules for the ERO subobject.
o Defines a new path setup type to be used in the PATH_SETUP_TYPE o Defines a new path setup type to be used in the PATH-SETUP-TYPE
and PATH_SETUP_TYPE_CAPABILITY TLVs and PATH-SETUP-TYPE-CAPABILITY TLVs ([RFC8408]).
([I-D.ietf-pce-lsp-setup-type]).
o Defines a new sub-TLV for the PATH_SETUP_TYPE_CAPABILITY TLV. o Defines a new sub-TLV for the PATH-SETUP-TYPE-CAPABILITY TLV.
The extensions specified in this document complement the existing The extensions specified in this document complement the existing
PCEP specifications to support SR-TE paths. As such, the PCEP PCEP specifications to support SR-TE paths. As such, the PCEP
messages (e.g., Path Computation Request, Path Computation Reply, messages (e.g., Path Computation Request, Path Computation Reply,
Path Computation Report, Path Computation Update, Path Computation Path Computation Report, Path Computation Update, Path Computation
Initiate, etc.,) MUST be formatted according to [RFC5440], [RFC8231], Initiate, etc.,) MUST be formatted according to [RFC5440], [RFC8231],
[RFC8281], and any other applicable PCEP specifications. [RFC8281], and any other applicable PCEP specifications.
4. SR-Specific PCEP Message Extensions 4. SR-Specific PCEP Message Extensions
skipping to change at page 8, line 17 skipping to change at page 8, line 26
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=26 | Length=4 | | Type=26 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |N|L| MSD | | Reserved | Flags |N|L| MSD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SR-PCE-CAPABILITY sub-TLV format Figure 1: SR-PCE-CAPABILITY sub-TLV format
The code point for the TLV type is 26. The TLV length is 4 octets. 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 The 32-bit value is formatted as follows.
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 Reserved: MUST be set to zero by the sender and MUST be ignored by
impose any limit on the MSD. the receiver.
o N flag: A PCC sets this flag to 1 to indicate that it is capable Flags: This document defines the following flag bits. The other
of resolving a Node or Adjacency Identifier (NAI) to a SID. bits MUST be set to zero by the sender and MUST be ignored by the
receiver.
* N: A PCC sets this bit to 1 to indicate that it is capable of
resolving a Node or Adjacency Identifier (NAI) to a SID.
* L: A PCC sets this bit to 1 to indicate that it does not impose
any limit on the MSD.
Maximum SID Depth (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. Section 6.1 explains the
relationship between this field and the L bit.
5.2. The RP/SRP Object 5.2. The RP/SRP Object
To set up an SR-TE LSP using SR, the RP or SRP object MUST include 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], the PATH-SETUP-TYPE TLV, specified in [RFC8408], with the PST set to
with the PST set to 1 (path setup using SR-TE). 1 (path setup using SR-TE).
The LSP-IDENTIFIERS TLV MAY be present for the above PST type. The LSP-IDENTIFIERS TLV MAY be present for the above PST type.
5.3. ERO 5.3. ERO
An SR-TE path consists of one or more SIDs where each SID MAY be 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 associated with the identifier that represents the node or adjacency
corresponding to the SID. This identifier is referred to as the corresponding to the SID. This identifier is referred to as the
'Node or Adjacency Identifier' (NAI). As described later, a NAI can 'Node or Adjacency Identifier' (NAI). As described later, a NAI can
be represented in various formats (e.g., IPv4 address, IPv6 address, be represented in various formats (e.g., IPv4 address, IPv6 address,
skipping to change at page 9, line 17 skipping to change at page 9, line 33
SID and NAI. However, at least one of them MUST be present. 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 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 SR-ERO subobjects are organized as a last-in-first-out stack. The
first subobject relative to the beginning of ERO contains the first subobject relative to the beginning of ERO contains the
information about the topmost label. The last subobject contains information about the topmost label. The last subobject contains
information about the bottommost label. information about the bottommost label.
5.3.1. SR-ERO Subobject 5.3.1. SR-ERO Subobject
An SR-ERO subobject consists of a 32-bit header followed by the SID An SR-ERO subobject is formatted as shown in the following diagram.
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
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 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| |L| Type=36 | Length | NT | Flags |F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (optional) | | SID (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable, optional) // // NAI (variable, optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SR-ERO Subobject format Figure 2: SR-ERO subobject format
The fields in the SR-ERO Subobject are as follows: The fields in the SR-ERO Subobject are as follows:
The 'L' Flag indicates whether the subobject represents a loose-hop 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 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. overwrite the SID value present in the SR-ERO subobject.
Otherwise, a PCC MAY expand or replace one or more SID values in Otherwise, a PCC MAY expand or replace one or more SID values in
the received SR-ERO based on its local policy. the received SR-ERO based on its local policy.
Type is set to 36. Type: Set to 36.
Length contains the total length of the subobject in octets, Length: Contains the total length of the subobject in octets,
including the L, Type and Length fields. The Length MUST be at 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 least 8, and MUST be a multiple of 4. An SR-ERO subobject MUST
SR-ERO subobject MUST contain at least one of a SID or an NAI. contain at least one of a SID or an NAI. The length should
include the SID and NAI fields if and only if they are not absent.
The length should include the SID and NAI fields if and only if The flags described below indicate whether the SID or NAI fields
they are not absent. The flags described below indicate whether are absent.
the SID or NAI fields are absent.
NAI Type (NT) indicates the type and format of the NAI associated NAI Type (NT): Indicates the type and format of the NAI contained in
with the SID contained in the object body. This document the object body. This document describes the following NT values:
describes the following NT values:
NT=0 The NAI is absent. NT=0 The NAI is absent.
NT=1 The NAI is an IPv4 node ID. NT=1 The NAI is an IPv4 node ID.
NT=2 The NAI is an IPv6 node ID. NT=2 The NAI is an IPv6 node ID.
NT=3 The NAI is an IPv4 adjacency. NT=3 The NAI is an IPv4 adjacency.
NT=4 The NAI is an IPv6 adjacency. NT=4 The NAI is an IPv6 adjacency.
NT=5 The NAI is an unnumbered adjacency with IPv4 node IDs. NT=5 The NAI is an unnumbered adjacency with IPv4 node IDs.
Flags is used to carry additional information pertaining to the SID. Flags: Used to carry additional information pertaining to the SID.
This document defines the following flag bits. The other bits This document defines the following flag bits. The other bits
MUST be set to zero by the sender and MUST be ignored by the MUST be set to zero by the sender and MUST be ignored by the
receiver. receiver.
* M: If this bit is set to 1, the SID value represents an MPLS * M: If this bit is set to 1, the SID value represents an MPLS
label stack entry as specified in [RFC3032]. Otherwise, the label stack entry as specified in [RFC3032]. Otherwise, the
SID value is an administratively configured value which acts as SID value is an administratively configured value which
an index into an MPLS label space. represents an index into an MPLS label space (either SRGB or
SRLB) per [RFC8402].
* C: If the M bit and the C bit are both set to 1, then the TC, * 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 S, and TTL fields in the MPLS label stack entry are specified
by the PCE. However, a PCC MAY choose to override these values by the PCE. However, a PCC MAY choose to override these values
according its local policy and MPLS forwarding rules. If the M 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, 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 and TTL fields MUST be ignored by the PCC. The PCC MUST set
these fields according to its local policy and MPLS forwarding 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 rules. If the M bit is set to zero then the C bit MUST be set
to zero. to zero.
* S: When this bit is set to 1, the SID value in the subobject * 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 body is absent. In this case, the PCC is responsible for
choosing the SID value, e.g., by looking up in its LSDB using choosing the SID value, e.g., by looking up in the SR-DB using
the NAI which, in this case, MUST be present in the subobject. 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 If the S bit is set to 1 then the M and C bits MUST be set to
zero. zero.
* F: When this bit is set to 1, the NAI value in the subobject * 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 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 otherwise MUST be set to zero. The S and F bits MUST NOT both
be set to 1. be set to 1.
SID is the Segment Identifier. SID: The Segment Identifier. Depending on the M bit, it contains
either:
NAI contains the NAI associated with the SID. The NAI's format * A 4 octet index defining the offset into an MPLS label space
depends on the value in the NT field, and is described in the per [RFC8402].
following section.
* A 4 octet MPLS label, where the 20 most significant bits encode
the label value per [RFC3032].
NAI: 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.
At least one of the SID and the NAI MUST be included in the SR-ERO
subobject, and both MAY be included.
5.3.2. NAI Associated with SID 5.3.2. NAI Associated with SID
This document defines the following NAIs: This document defines the following NAIs:
'IPv4 Node ID' is specified as an IPv4 address. In this case, the 'IPv4 Node ID' is specified as an IPv4 address. In this case, the
NT value is 1. NT value is 1 and the NAI field length is 4 octets.
'IPv6 Node ID' is specified as an IPv6 address. In this case, the 'IPv6 Node ID' is specified as an IPv6 address. In this case, the
NT value is 2. NT value is 2 and the NAI field length is 16 octets.
'IPv4 Adjacency' is specified as a pair of IPv4 addresses. In this '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 case, the NT value is 3 and the NAI field length is 8 octets. The
following figure: format of the NAI is shown in the following figure:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 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 | | Local IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 address | | Remote IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: NAI for IPv4 adjacency Figure 3: NAI for IPv4 adjacency
'IPv6 Adjacency' is specified as a pair of IPv6 addresses. In this '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 case, the NT value is 4 and the NAI field length is 32 octets.
following figure: The format of the NAI is shown in the following figure:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 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) // // Local IPv6 address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 address (16 bytes) // // Remote IPv6 address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: NAI for IPv6 adjacency Figure 4: NAI for IPv6 adjacency
'Unnumbered Adjacency with IPv4 NodeIDs' is specified as a pair of 'Unnumbered Adjacency with IPv4 NodeIDs' is specified as a pair of
Node ID / Interface ID tuples. In this case, the NT value is 5. Node ID / Interface ID tuples. In this case, the NT value is 5
The format of the NAI is shown in the following figure: and the NAI field length is 16 octets. The format of the NAI is
shown in the following figure:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 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 Node-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID | | Local Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Node-ID | | Remote Node-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID | | Remote Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: NAI for Unnumbered adjacency with IPv4 Node IDs Figure 5: NAI for Unnumbered adjacency with IPv4 Node IDs
5.4. RRO 5.4. RRO
A PCC can record an SR-TE LSP and report the LSP to a PCE via the A PCC reports an SR-TE LSP to a PCE by sending a PCRpt message, per
RRO. An RRO contains one or more subobjects called "SR-RRO [RFC8231]. The RRO on this message represents the SID list that was
subobjects" whose format is shown below: applied by the PCC, that is, the actual path taken by the LSP. The
procedures of [RFC8231] with respect to the RRO apply equally to this
specification without change.
An RRO contains one or more subobjects called "SR-RRO subobjects"
whose format is shown below:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 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| | Type=36 | Length | NT | Flags |F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID | | SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable) // // NAI (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: SR-RRO Subobject format Figure 6: SR-RRO Subobject format
The format of the SR-RRO subobject is the same as that of the SR-ERO The format of the SR-RRO subobject is the same as that of the SR-ERO
subobject, but without the L flag. subobject, but without the L flag.
A PCC MUST assume that the SR-RRO subobjects are organized such that A PCC MUST order the SR-RRO subobjects such that the first subobject
the first subobject relative to the beginning of the RRO contains the relative to the beginning of the RRO identifies the first segment
information about the topmost label, and the last subobject contains visited by the SR-TE LSP, and the last subobject identifies the final
information about the bottommost label of the SR-TE LSP. segment of the SR-TE LSP, that is, its endpoint.
5.5. METRIC Object 5.5. METRIC Object
If a PCEP session is established with an MSD value of zero, then the A PCC MAY request that PCE optimizes an individual path computation
PCC MAY specify the MSD for an individual path computation request request to minimize the SID depth of the computed path by using the
using the METRIC object defined in [RFC5440]. This document defines METRIC object defined in [RFC5440]. This document defines a new type
a new type for the METRIC object to be used for this purpose as for the METRIC object to be used for this purpose, as follows:
follows:
o T = 11: Maximum SID Depth of the requested path. 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 If the PCC includes a METRIC object of this type on a path
set the B (bound) bit to 1 in the METRIC object, which specifies that computation request, then the PCE MUST minimize the SID depth of the
the SID depth for the computed path MUST NOT exceed the metric-value. computed path. If the B (bound) bit is set to to 1 in the METRIC
object, then the PCE MUST NOT return a path whose SID depth exceeds
the given metric-value. If the PCC did not set the L bit in its SR-
PCE-CAPABILITY TLV, then it MUST set the B bit to 1. If the PCC set
the L bit in its SR-PCE-CAPABILITY TLV, then it MAY set the B bit to
1 or zero.
If a PCEP session is established with a non-zero MSD value, then the If a PCEP session is established with a non-zero default MSD value,
PCC MUST NOT send an MSD METRIC object. If the PCE receives a path then the PCC MUST NOT send an MSD METRIC object with an MSD greater
computation request with an MSD METRIC object on a session with a than the session's default MSD. If the PCE receives a path
non-zero MSD value then it MUST consider the request invalid and send computation request with an MSD METRIC object on such a session that
a PCErr with Error-Type = 10 ("Reception of an invalid object") and is greater than the session's default MSD, then it MUST consider the
Error-Value 9 ("Default MSD is specified for the PCEP session"). request invalid and send a PCErr with Error-Type = 10 ("Reception of
an invalid object") and Error-Value 9 ("MSD exceeds the default for
the PCEP session").
6. Procedures 6. Procedures
6.1. Exchanging the SR PCE Capability 6.1. Exchanging the SR PCE Capability
A PCC indicates that it is capable of supporting the head-end 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 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 the Open message that it sends to a PCE. A PCE indicates that it is
capable of computing SR-TE paths by including the SR-PCE-CAPABILITY capable of computing SR-TE paths by including the SR-PCE-CAPABILITY
sub-TLV in the Open message that it sends to a PCC. sub-TLV in the Open message that it sends to a PCC.
skipping to change at page 14, line 18 skipping to change at page 14, line 30
PST list containing PST=1, and supports that path setup type, then it 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 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 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 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 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- 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 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 PST list does not contain PST=1, then the PCEP speaker MUST ignore
the SR-PCE-CAPABILITY sub-TLV. the SR-PCE-CAPABILITY sub-TLV.
If a PCC sets the N flag to 1, then the PCE MAY send NAI to the PCC If a PCC sets the N flag to 1, then the PCE MAY send an SR-ERO
within the SR-ERO subobject (see Section 6.2). Otherwise, the PCE subobject containing NAI and no SID (see Section 6.2). Otherwise,
MUST NOT send NAI to the PCC. the PCE MUST NOT send an SR-ERO subobject containing NAI and no SID.
The number of SIDs that can be imposed on a packet depends on the 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 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 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 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 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 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 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 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 flag and MSD both set to zero then it MUST assume that the PCC is not
skipping to change at page 16, line 32 skipping to change at page 16, line 44
Type = 4 ("Not supported object") and Error-Value = 4 ("Unsupported Type = 4 ("Not supported object") and Error-Value = 4 ("Unsupported
parameter"). parameter").
If a PCC receives an SR-ERO subobject in which the S bit is set to 1 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 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 the entire ERO invalid and send a PCErr message with Error-Type = 10
("Reception of an invalid object") and Error-Value = 11 ("Malformed ("Reception of an invalid object") and Error-Value = 11 ("Malformed
object"). object").
If a PCC receives an SR-ERO subobject in which the S bit is set to 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 zero and the M bit is set to 1, then the subobject contains an MPLS
value), its value (20 most significant bits) MUST be larger than 15, label. The PCC MAY choose not to accept a label provided by the PCE,
unless it is a special purpose label, such as an Entropy Label based on it local policy. The PCC MUST NOT accept MPLS label value 3
Indicator (ELI). If a PCC receives an invalid MPLS label value, it (Implicit NULL), but it MAY accept other special purpose MPLS label
values. If the PCC decides not to accept an MPLS label value, it
MUST send a PCErr message with Error-Type = 10 ("Reception of an MUST send a PCErr message with Error-Type = 10 ("Reception of an
invalid object") and Error Value = 2 ("Bad label value"). 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 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, 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 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 policy. If the PCC does not overwrite them, it MUST send a PCErr
message with Error-Type = 10 ("Reception of an invalid object") and message with Error-Type = 10 ("Reception of an invalid object") and
Error-Value = 4 ("Bad label format"). Error-Value = 4 ("Bad label format").
If the M bit of an SR-ERO subobject is set to zero but the C bit is 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 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 send a PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = 11 ("Malformed object"). object") and Error-Value = 11 ("Malformed object").
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 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 zero and the M bit is set to zero, then the subobject contains a SID
value), then the SID MUST be a node-SID, an adjacency-SID or a index value. If the SID is an Adjacency-SID then the L flag MUST NOT
binding-SID. If the SID is not one of these types, the PCC MUST send be set. If the L flag is set for an Adjacency-SID then the PCC MUST
a PCErr message with Error-Type = 10 ("Reception of an invalid 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 object") and Error-Value = 11 ("Malformed object").
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- 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 ERO subobjects and subobjects of other types, then it MUST send a
PCErr message with Error-Type = 10 ("Reception of an invalid object") PCErr message with Error-Type = 10 ("Reception of an invalid object")
and Error-Value = 5 ("ERO mixes SR-ERO subobjects with other and Error-Value = 5 ("ERO mixes SR-ERO subobjects with other
subobject types"). subobject types").
The SR-ERO subobjects can be classified according to whether they The SR-ERO subobjects can be classified according to whether they
contain a SID representing an MPLS label value, a SID representing an 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 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 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") PCErr message with Error-Type = 10 ("Reception of an invalid object")
and Error-Value = TBD11 ("Inconsistent SIDs in SR-ERO subobjects"). and Error-Value = TBD9 ("Inconsistent SIDs in SR-ERO / SR-RRO
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.
(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 If an ERO specifies a new SR-TE path for an existing LSP and the PCC
failed the validation checks of Section 6.2.1. determines that the ERO contains SR-ERO subobjects that are not
valid, then the PCC MUST NOT update the LSP.
(c) Loop through the remaining SR-ERO subobjects. For each SR-ERO 6.2.2. Interpreting the SR-ERO
subobject, look the SID index up in the LSDB.
* If the SID is a node-SID, then look up the current_router's The SR-ERO contains a sequence of subobjects. According to
SRGB in the LSDB. Get the label that is at offset node-SID [I-D.ietf-spring-segment-routing-policy], each SR-ERO subobject in
relative to the SRGB base label and append it to label_stack. the sequence identifies a segment that the traffic will be directed
to, in the order given. That is, the first subobject identifies the
first segment the traffic will be directed to, the second SR-ERO
subobject represents the second segment, and so on.
* If the SID is an adjacency-SID, then look up the The PCC interprets the SR-ERO by converting it to an MPLS label stack
current_router's SRLB in the LSDB. Get the label that is at plus a next hop. The PCC sends packets along the segment routed path
offset adjacency-SID relative to the SRLB base label and by prepending the MPLS label stack onto the packets and sending the
append it to label_stack. resulting, modified packet to the next hop.
* If the SID is a binding-SID, then look up the The PCC uses a different procedure to do this conversion, depending
current_router's SRGB in the LSDB. Get the label that is at on the information that the PCE has provided in the subobjects.
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 o If the subobjects contain SID index values, then the PCC converts
failed the validation checks of Section 6.2.1. them into the corresponding MPLS labels by following the procedure
defined in [I-D.ietf-spring-segment-routing-mpls].
6.2.2.3. SR-ERO subobjects contain NAI only o If the subobjects contain NAI only, then the PCC first converts
each NAI into a SID index value by looking it up in its local
database, and then proceeds as above.
If the SR-ERO subobjects do not contain SIDs (that is, contain only o If the subobjects contain MPLS labels, then the PCC looks up the
NAI), then look each NAI up in the LSDB to find the corresponding SID offset of the first subobject's label in its SRGB or SRLB. This
index. Then proceed as described above for SID index values. gives the first SID. The PCC pushes the labels in any remaining
subobjects onto the packet (with the final subobject specifying
the bottom-of-stack label) and then directs the packet to the
segment identified by the first SID.
6.2.2.4. Handling Errors During SR-ERO Conversion 6.2.2.1. Handling Errors During SR-ERO Conversion
There are several errors that can occur during the process of 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. converting an SR-ERO sequence to an MPLS label stack and a next hop.
The PCC deals with them as follows. The PCC deals with them as follows.
o If the PCC cannot find a SID index in the LSDB, it MUST send a o If the PCC cannot find a SID index in the SR-DB, it MUST send a
PCErr message with Error-Type = 10 ("Reception of an invalid PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = TBD3 ("Unknown SID"). object") and Error-Value = TBD3 ("Unknown SID").
o If the PCC cannot find an NAI in the LSDB, it MUST send a PCErr o If the PCC cannot find an NAI in the SR-DB, it MUST send a PCErr
message with Error-Type = 10 ("Reception of an invalid object") message with Error-Type = 10 ("Reception of an invalid object")
and Error-Value = TBD4 ("NAI cannot be resolved to a SID"). 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 o If the PCC needs to convert a SID into an MPLS label value but
message with Error-Type = 10 ("Reception of an invalid object") cannot find the corresponding router's SRGB in the SR-DB, it MUST
and Error-Value = TBD5 ("Could not find SRGB"). 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 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 SID index value, it MUST send a PCErr message with Error-Type = 10
("Reception of an invalid object") and Error-Value = TBD6 ("SID ("Reception of an invalid object") and Error-Value = TBD6 ("SID
index exceeds SRGB size"). index exceeds SRGB size").
o If the PCC cannot find an SRLB in the LSDB, it MUST send a PCErr o If the PCC needs to convert a SID into an MPLS label value but
message with Error-Type = 10 ("Reception of an invalid object") cannot find the corresponding router's SRLB in the SR-DB, it MUST
and Error-Value = TBD7 ("Could not find SRLB"). 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 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 SID index value, it MUST send a PCErr message with Error-Type = 10
("Reception of an invalid object") and Error-Value = TBD8 ("SID ("Reception of an invalid object") and Error-Value = TBD8 ("SID
index exceeds SRLB size"). index exceeds SRLB size").
o If the number of labels in label_stack exceeds the maximum number o If the number of labels in the computed label stack exceeds the
of SIDs that the PCC can impose on the packet, it MUST send a maximum number of SIDs that the PCC can impose on the packet, it
PCErr message with Error-Type = 10 ("Reception of an invalid MUST send a PCErr message with Error-Type = 10 ("Reception of an
object") and Error-Value = 3 ("Unsupported number of Segment ERO invalid object") and Error-Value = 3 ("Unsupported number of
subobjects"). Segment ERO subobjects").
If an ERO specifies a new SR-TE path for an existing LSP and the PCC
encounters an error while processing the ERO, then the PCC MUST NOT
update the LSP.
6.3. RRO Processing 6.3. RRO Processing
The syntax checking rules that apply to the SR-RRO subobject are The syntax checking rules that apply to the SR-RRO subobject are
identical to those of the SR-ERO subobject, except as noted below. 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 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 NAI are absent, it MUST consider the entire RRO invalid and send a
PCErr message with Error-Type = 10 ("Reception of an invalid object") PCErr message with Error-Type = 10 ("Reception of an invalid object")
and Error-Value = 7 ("Both SID and NAI are absent in SR-RRO and Error-Value = 7 ("Both SID and NAI are absent in SR-RRO
subobject"). subobject").
If a PCE detects that all subobjects of the RRO are not identical, If a PCE detects that the subobjects of an RRO are a mixture of SR-
and if it does not support such an RRO, it MUST send a PCErr message RRO subobjects and subobjects of other types, then it MUST send a
with Error-Type = 10 ("Reception of an invalid object") and Error- PCErr message with Error-Type = 10 ("Reception of an invalid object")
Value = 10 ("Non-identical RRO subobjects"). and Error-Value = 10 ("RRO mixes SR-RRO subobjects with other
subobject types").
The SR-RRO subobjects can be classified according to whether they
contain a SID representing an MPLS label value or a SID representing
an index value, or no SID. If a PCE detects that the SR-RRO
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 = TBD9 ("Inconsistent SIDs in SR-ERO
/ SR-RRO subobjects").
7. Backward Compatibility 7. Backward Compatibility
A PCEP speaker that does not support the SR PCEP capability cannot A PCEP speaker that does not support the SR PCEP capability cannot
recognize the SR-ERO or SR-RRO subobjects. As such, it responds recognize the SR-ERO or SR-RRO subobjects. As such, it responds
according to the rules for a malformed object, per [RFC5440]. according to the rules for a malformed object, per [RFC5440].
Some implementations, which are compliant with an earlier version of Some implementations, which are compliant with an earlier version of
this specification, do not send the PATH-SETUP-TYPE-CAPABILITY TLV in this specification, do not send the PATH-SETUP-TYPE-CAPABILITY TLV in
their OPEN objects. Instead, to indicate that they support SR, these their OPEN objects. Instead, to indicate that they support SR, these
skipping to change at page 21, line 39 skipping to change at page 20, line 51
o When a PCE initiates an LSP, it proposes which path setup type to 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 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 of the PCInitiate message. The PCE chooses the path setup type
based on the capabilities of the network nodes on the path and on 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 its local policy. The PCC MAY choose to accept the proposed path
setup type, or to reject the PCInitiate request, based on its setup type, or to reject the PCInitiate request, based on its
local policy. local policy.
o When a PCC requests a path for an LSP, it can nominate a preferred 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 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 RP object of the PCReq message. The PCE MAY choose to reply with
with a path of the requested type, or to reply with a path of a a path of the requested type, or to reply with a path of a
different type, or to reject the request, based on the different type, or to reject the request, based on the
capabilities of the network nodes on the path and on its local capabilities of the network nodes on the path and on its local
policy. policy.
The operator can influence the path setup type as follows. The operator can influence the path setup type as follows.
o Implementations MUST allow the operator to enable and disable the o Implementations MUST allow the operator to enable and disable the
segment routing path setup type on a PCEP-speaking device. segment routing path setup type on a PCEP-speaking device.
Implementations MAY also allow the operator to enable and disable Implementations MAY also allow the operator to enable and disable
the RSVP-TE path setup type. the RSVP-TE path setup type.
skipping to change at page 23, line 10 skipping to change at page 22, line 23
operator reconfigures the PCEP speaker's capabilities. However, note operator reconfigures the PCEP speaker's capabilities. However, note
that if the capabilities at both ends of the PCEP session are not that if the capabilities at both ends of the PCEP session are not
reconfigured simultaneously, then the session could be reset twice, reconfigured simultaneously, then the session could be reset twice,
which could lead to unnecessary network traffic. Therefore, such which could lead to unnecessary network traffic. Therefore, such
implementations SHOULD allow the operator to override this behaviour implementations SHOULD allow the operator to override this behaviour
and wait instead for a manual reset. and wait instead for a manual reset.
Once segment routing is enabled on a PCEP session, it can be used as Once segment routing is enabled on a PCEP session, it can be used as
the path setup type for future LSPs. the path setup type for future LSPs.
User traffic is not automatically be migrated from existing LSPs onto User traffic is not automatically migrated from existing LSPs onto
segment routed LSPs just by enabling the segment routing PST in PCEP. segment routed LSPs just by enabling the segment routing PST in PCEP.
The migration of user traffic from existing LSPs onto segment routing The migration of user traffic from existing LSPs onto segment routing
LSPs is beyond the scope of this document. LSPs is beyond the scope of this document.
8.3. Verification of Network Operation 8.3. Verification of Network Operation
The operator needs the following information to verify that PCEP is The operator needs the following information to verify that PCEP is
operating correctly with respect to the segment routing path setup operating correctly with respect to the segment routing path setup
type. type.
o An implementation SHOULD allow the operator to view whether the o An implementation SHOULD allow the operator to view whether the
PCEP speaker sent the segment routing PST capability to its peer. PCEP speaker sent the segment routing PST capability to its peer.
If the PCEP speaker is a PCC, then the implementation SHOULD also 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, allow the operator to view the values of the L and N flags that
and the value of the MSD field that was sent. were sent, and the value of the MSD field that was sent.
o An implementation SHOULD allow the operator to view whether the o An implementation SHOULD allow the operator to view whether the
peer sent a the segment routing PST capability. If the peer is a peer sent the segment routing PST capability. If the peer is a
PCC, then the implementation SHOULD also allow the operator to PCC, then the implementation SHOULD also allow the operator to
view the values of the L flag and MSD fields that the peer sent view the values of the L and N flags and MSD fields that the peer
sent. sent.
o An implementation SHOULD allow the operator to view whether the o An implementation SHOULD allow the operator to view whether the
segment routing PST is enabled on the PCEP session. segment routing PST is enabled on the PCEP session.
o If one PCEP speaker advertises the segment routing PST capability, o If one PCEP speaker advertises the segment routing PST capability,
but the other does not, then the implementation SHOULD create a but the other does not, then the implementation SHOULD create a
log to inform the operator of the capability mismatch. log to inform the operator of the capability mismatch.
o An implementation SHOULD allow the operator to view the PST that o An implementation SHOULD allow the operator to view the PST that
was proposed, or requested, for an LSP, and the PST that was was proposed, or requested, for an LSP, and the PST that was
actually used. actually used.
o If a PCEP speaker decides to use a different PST to the one that 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 was proposed, or requested, for an LSP, then the implementation
SHOULD create a log to inform the operator that the expected PST 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 has not been used. The log SHOULD give the reason for this choice
(local policy, equipment capability etc.) (local policy, equipment capability etc.)
o If a PCEP speaker rejects a segment routed path, then it SHOULD 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 create a log to inform the operator, giving the reason for the
decision (local policy, MSD exceeded etc.) decision (local policy, MSD exceeded etc.)
8.4. Relationship to Existing Management Models 8.4. Relationship to Existing Management Models
The PCEP YANG module [I-D.ietf-pce-pcep-yang] should include: The PCEP YANG module [I-D.ietf-pce-pcep-yang] should include:
o advertised PST capabilities and MSD per PCEP session. o advertised PST capabilities and MSD per PCEP session.
o the PST configured for, and used by, each LSP. o the PST configured for, and used by, each LSP.
The PCEP MIB [RFC7420] could also be updated to include this The PCEP MIB [RFC7420] could also be updated to include this
information. information.
9. Security Considerations 9. Security Considerations
The security considerations described in [RFC5440], [RFC8281] and The security considerations described in [RFC5440], [RFC8281] and
[I-D.ietf-pce-lsp-setup-type] are applicable to this specification. [RFC8408] are applicable to this specification. No additional
No additional security measure is required. security measure is required.
Note that this specification enables a network controller to
instantiate a path in the network without the use of a hop-by-hop
signaling protocol (such as RSVP-TE). This creates an additional
vulnerability if the security mechanisms of [RFC5440] and [RFC8281]
are not used, because an attacker could create a path which is not
subjected to the further verification checks that would be performed
by the signaling protocol.
Note that this specification adds the MSD field to the OPEN message
(see Section 5.1.1) which discloses how many MPLS labels the sender
can push onto packets that it forwards into the network. If the
security mechanisms of [RFC5440] and [RFC8281] are not used then an
attacker could use this new field to gain intelligence about the
capabilities of the edge devices in the network.
10. IANA Considerations 10. IANA Considerations
10.1. PCEP Objects 10.1. PCEP ERO and RRO subobjects
This document defines a new subobject type for the PCEP explicit 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 (ERO), and a new subobject type for the PCEP record
route object (RRO). The code points for subobject types of these route object (RRO). The code points for subobject types of these
objects is maintained in the RSVP parameters registry, under the objects is maintained in the RSVP parameters registry, under the
EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to
confirm the early allocation of the following code points in the RSVP confirm the early allocation of the following code points in the RSVP
Parameters registry for each of the new subobject types defined in Parameters registry for each of the new subobject types defined in
this document. this document.
skipping to change at page 26, line 20 skipping to change at page 25, line 44
Error-value = 5: ERO mixes SR-ERO Error-value = 5: ERO mixes SR-ERO
subobjects with subobjects with
other subobject other subobject
types types
Error-value = 6: Both SID and NAI Error-value = 6: Both SID and NAI
are absent in SR- are absent in SR-
ERO subobject ERO subobject
Error-value = 7: Both SID and NAI Error-value = 7: Both SID and NAI
are absent in SR- are absent in SR-
RRO subobject RRO subobject
Error-value = 9: Default MSD is Error-value = 9: MSD exceeds the
specified for the default for the
PCEP session PCEP session
Error-value = 10: RRO mixes SR-RRO Error-value = 10: RRO mixes SR-RRO
subobjects with subobjects with
other subobject other subobject
types types
Error-value = TBD1: Missing PCE-SR- Error-value = TBD1: Missing PCE-SR-
CAPABILITY sub-TLV CAPABILITY sub-TLV
Error-value = TBD2: Unsupported NAI Error-value = TBD2: Unsupported NAI
Type in SR-ERO Type in SR-ERO
subobject subobject
Error-value = TBD3: Unknown SID Error-value = TBD3: Unknown SID
Error-value = TBD4: NAI cannot be Error-value = TBD4: NAI cannot be
resolved to a SID resolved to a SID
Error-value = TBD5: Could not find SRGB Error-value = TBD5: Could not find SRGB
Error-value = TBD6: SID index exceeds Error-value = TBD6: SID index exceeds
SRGB size SRGB size
Error-value = TBD7: Could not find SRLB Error-value = TBD7: Could not find SRLB
Error-value = TBD8: SID index exceeds Error-value = TBD8: SID index exceeds
SRLB size SRLB size
Error-value = TBD9: Cannot derive a Error-value = TBD9: Inconsistent SIDs
next hop from SR- in SR-ERO / SR-RRO
ERO
Error-value = TBD10: Bad SID type in SR-
ERO
Error-value = TBD11: Inconsistent SIDs
in SR-ERO
subobjects subobjects
Note to IANA: this draft originally had an early allocation for Note to IANA: this draft originally had an early allocation for
Error-value=11 (Malformed object) in the above list. However, we Error-value=11 (Malformed object) in the above list. However, we
have since moved the definition of that code point to draft-ietf-pce- have since moved the definition of that code point to RFC8408.
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 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 the early allocation took place, and so do not currently have a code
point assigned. Please assign code points from the indicated point assigned. Please assign code points from the indicated
registry and replace each instance of "TBD1", "TBD2" etc. in this registry and replace each instance of "TBD1", "TBD2" etc. in this
document with the respective code points. document with the respective code points.
Note to IANA: some of the Error-value descriptive strings above have Note to IANA: some of the Error-value descriptive strings above have
changed since the early allocation. Please refresh the registry. changed since the early allocation. Please refresh the registry.
skipping to change at page 27, line 28 skipping to change at page 26, line 47
IANA is requested to confirm the early allocation of the following IANA is requested to confirm the early allocation of the following
code point in the PCEP TLV Type Indicators registry. code point in the PCEP TLV Type Indicators registry.
Value Meaning Reference Value Meaning Reference
------------------------- ---------------------------- -------------- ------------------------- ---------------------------- --------------
26 SR-PCE-CAPABILITY This document 26 SR-PCE-CAPABILITY This document
10.6. New Path Setup Type 10.6. New Path Setup Type
[I-D.ietf-pce-lsp-setup-type] requests that IANA creates a sub- [RFC8408] requests that IANA creates a sub-registry within the "Path
registry within the "Path Computation Element Protocol (PCEP) Computation Element Protocol (PCEP) Numbers" registry called "PCEP
Numbers" registry called "PCEP Path Setup Types". IANA is requested Path Setup Types". IANA is requested to allocate a new code point
to allocate a new code point within this registry, as follows: within this registry, as follows:
Value Description Reference Value Description Reference
------------------------- ---------------------------- -------------- ------------------------- ---------------------------- --------------
1 Traffic engineering path is This document 1 Traffic engineering path is This document
setup using Segment Routing. setup using Segment Routing.
10.7. New Metric Type 10.7. New Metric Type
IANA is requested to confirm the early allocation of the following IANA is requested to confirm the early allocation of the following
code point in the PCEP METRIC object T field registry: code point in the PCEP METRIC object T field registry:
skipping to change at page 28, line 43 skipping to change at page 28, line 16
We thank Ina Minei, George Swallow, Marek Zavodsky, Dhruv Dhody, Ing- We thank Ina Minei, George Swallow, Marek Zavodsky, Dhruv Dhody, Ing-
Wher Chen and Tomas Janciga for the valuable comments. Wher Chen and Tomas Janciga for the valuable comments.
13. References 13. References
13.1. Normative References 13.1. Normative References
[I-D.ietf-idr-bgp-ls-segment-routing-msd] [I-D.ietf-idr-bgp-ls-segment-routing-msd]
Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
"Signaling Maximum SID Depth using Border Gateway Protocol "Signaling MSD (Maximum SID Depth) using Border Gateway
Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01 Protocol Link-State", draft-ietf-idr-bgp-ls-segment-
(work in progress), October 2017. routing-msd-02 (work in progress), August 2018.
[I-D.ietf-isis-segment-routing-extensions] [I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura, Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
"IS-IS Extensions for Segment Routing", draft-ietf-isis- "IS-IS Extensions for Segment Routing", draft-ietf-isis-
segment-routing-extensions-18 (work in progress), June segment-routing-extensions-19 (work in progress), July
2018. 2018.
[I-D.ietf-isis-segment-routing-msd] [I-D.ietf-isis-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling MSD (Maximum SID Depth) using IS-IS", draft- "Signaling MSD (Maximum SID Depth) using IS-IS", draft-
ietf-isis-segment-routing-msd-12 (work in progress), May ietf-isis-segment-routing-msd-16 (work in progress),
2018. September 2018.
[I-D.ietf-ospf-segment-routing-extensions] [I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment- Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-25 (work in progress), April 2018. routing-extensions-25 (work in progress), April 2018.
[I-D.ietf-ospf-segment-routing-msd] [I-D.ietf-ospf-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling MSD (Maximum SID Depth) using OSPF", draft- "Signaling MSD (Maximum SID Depth) using OSPF", draft-
ietf-ospf-segment-routing-msd-14 (work in progress), May ietf-ospf-segment-routing-msd-20 (work in progress),
2018. August 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] [I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
YANG Data Model for Path Computation Element YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", draft-ietf-pce-pcep- Communications Protocol (PCEP)", draft-ietf-pce-pcep-
yang-08 (work in progress), June 2018. 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 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>. <https://www.rfc-editor.org/info/rfc3032>.
skipping to change at page 30, line 37 skipping to change at page 29, line 42
Extensions for Stateful PCE", RFC 8231, Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017, DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>. <https://www.rfc-editor.org/info/rfc8231>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP) Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>. <https://www.rfc-editor.org/info/rfc8281>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8408] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
Hardwick, "Conveying Path Setup Type in PCE Communication
Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
July 2018, <https://www.rfc-editor.org/info/rfc8408>.
13.2. Informative References 13.2. Informative References
[I-D.ietf-6man-segment-routing-header] [I-D.ietf-6man-segment-routing-header]
Previdi, S., Filsfils, C., Leddy, J., Matsushima, S., and Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-13 (work in (SRH)", draft-ietf-6man-segment-routing-header-14 (work in
progress), May 2018. progress), June 2018.
[I-D.ietf-spring-segment-routing-mpls] [I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-14 data plane", draft-ietf-spring-segment-routing-mpls-14
(work in progress), June 2018. (work in progress), June 2018.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-01 (work in progress), June 2018.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>. <https://www.rfc-editor.org/info/rfc3209>.
[RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <https://www.rfc-editor.org/info/rfc4657>. 2006, <https://www.rfc-editor.org/info/rfc4657>.
 End of changes. 99 change blocks. 
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