wdiff rfc8231v1.txt rfc8231.txt

Internet Engineering Task Force (IETF) E. Crabbe
Request for Comments: 8231 Oracle
Category: Standards Track I. Minei
ISSN: 2070-1721 Google, Inc.
J. Medved
Cisco Systems, Inc.
R. Varga
Pantheon Technologies SRO
August
September 2017

Path Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE

Abstract

The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Client (PCC) requests.

Although PCEP explicitly makes no assumptions regarding the
information available to the PCE, it also makes no provisions for PCE
control of timing and sequence of path computations within and across
PCEP sessions. This document describes a set of extensions to PCEP
to enable stateful control of MPLS-TE and GMPLS Label Switched Paths
(LSPs) via PCEP.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8231.
https://www.rfc-editor.org/info/rfc8231.

This document is subject to BCP 78 and the IETF Trust's Legal
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation and Objectives for Stateful PCE . . . . . . . . . 5
3.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Background . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Why a Stateful PCE? . . . . . . . . . . . . . . . . . 6
3.1.3. Protocol vs. Configuration . . . . . . . . . . . . . 7
3.2. Objectives . . . . . . . . . . . . . . . . . . . . . . . 7
4. New Functions to Support Stateful PCEs . . . . . . . . . . . 8
5. Overview of Protocol Extensions . . . . . . . . . . . . . . . 9
5.1. LSP State Ownership . . . . . . . . . . . . . . . . . . . 9
5.2. New Messages . . . . . . . . . . . . . . . . . . . . . . 9
5.3. Error Reporting . . . . . . . . . . . . . . . . . . . . . 10
5.4. Capability Advertisement . . . . . . . . . . . . . . . . 10
5.5. IGP Extensions for Stateful PCE Capabilities
Advertisement . . . . . . . . . . . . . . . . . . . . . . 11
5.6. State Synchronization . . . . . . . . . . . . . . . . . . 12
5.7. LSP Delegation . . . . . . . . . . . . . . . . . . . . . 15
5.7.1. Delegating an LSP . . . . . . . . . . . . . . . . . . 15
5.7.2. Revoking a Delegation . . . . . . . . . . . . . . . . 16
5.7.3. Returning a Delegation . . . . . . . . . . . . . . . 18
5.7.4. Redundant Stateful PCEs . . . . . . . . . . . . . . . 18
5.7.5. Redelegation on PCE Failure . . . . . . . . . . . . . 19
5.8. LSP Operations . . . . . . . . . . . . . . . . . . . . . 19
5.8.1. Passive Stateful PCE Path Computation
Request/Response . . . . . . . . . . . . . . . . . . 19
5.8.2. Switching from Passive Stateful to Active Stateful . 21
5.8.3. Active Stateful PCE LSP Update . . . . . . . . . . . 22
5.9. LSP Protection . . . . . . . . . . . . . . . . . . . . . 23
5.10. PCEP Sessions . . . . . . . . . . . . . . . . . . . . . . 23
6. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . . 23
6.1. The PCRpt Message . . . . . . . . . . . . . . . . . . . . 24
6.2. The PCUpd Message . . . . . . . . . . . . . . . . . . . . 26
6.3. The PCErr Message . . . . . . . . . . . . . . . . . . . . 29
6.4. The PCReq Message . . . . . . . . . . . . . . . . . . . . 29
6.5. The PCRep Message . . . . . . . . . . . . . . . . . . . . 30
7. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. OPEN Object . . . . . . . . . . . . . . . . . . . . . . . 31
7.1.1. Stateful PCE Capability STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . 31
7.2. SRP Object . . . . . . . . . . . . . . . . . . . . . . . 32
7.3. LSP Object . . . . . . . . . . . . . . . . . . . . . . . 33
7.3.1. LSP-IDENTIFIERS TLVs . . . . . . . . . . . . . . . . 35
7.3.2. Symbolic Path Name TLV . . . . . . . . . . . . . . . 38
7.3.3. LSP Error Code TLV . . . . . . . . . . . . . . . . . 39
7.3.4. RSVP Error Spec TLV . . . . . . . . . . . . . . . . . 40
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
8.1. PCE Capabilities in IGP Advertisements . . . . . . . . . 41
8.2. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 41
8.3. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . 42
8.4. LSP Object . . . . . . . . . . . . . . . . . . . . . . . 42
8.5. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 42
8.6. Notification Object . . . . . . . . . . . . . . . . . . . 43
8.7. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 44
8.8. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 44
8.9. LSP-ERROR-CODE TLV . . . . . . . . . . . . . . . . . . . 44
9. Manageability Considerations . . . . . . . . . . . . . . . . 45
9.1. Control Function and Policy . . . . . . . . . . . . . . . 45
9.2. Information and Data Models . . . . . . . . . . . . . . . 46
9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 46
9.4. Verifying Correct Operation . . . . . . . . . . . . . . . 47
9.5. Requirements on Other Protocols and Functional Components 47
9.6. Impact on Network Operation . . . . . . . . . . . . . . . 47
10. Security Considerations . . . . . . . . . . . . . . . . . . . 47
10.1. Vulnerability . . . . . . . . . . . . . . . . . . . . . 47
10.2. LSP State Snooping . . . . . . . . . . . . . . . . . . . 48
10.3. Malicious PCE . . . . . . . . . . . . . . . . . . . . . 48
10.4. Malicious PCC . . . . . . . . . . . . . . . . . . . . . 49
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 49
11.1. Normative References . . . . . . . . . . . . . . . . . . 49
11.2. Informative References . . . . . . . . . . . . . . . . . 50
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 52
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53

1. Introduction

[RFC5440] describes the Path Computation Element Communication
Protocol (PCEP). PCEP defines the communication between a Path
Computation Client (PCC) and a Path Computation Element (PCE), or
between PCEs, enabling computation of Multiprotocol Label Switching
(MPLS) for Traffic Engineering Label Switched Path (TE LSP)
characteristics. Extensions for support of Generalized MPLS (GMPLS)
in PCEP are defined in [PCEP-GMPLS].

This document specifies a set of extensions to PCEP to enable
stateful control of LSPs within and across PCEP sessions in
compliance with [RFC4657]. It includes mechanisms to effect Label
Switched Path (LSP) state synchronization State Synchronization between PCCs and PCEs,
delegation of control over LSPs to PCEs, and PCE control of timing
and sequence of path computations within and across PCEP sessions.

Extensions to permit the PCE to drive creation of an LSP are defined
in [PCE-Init-LSP], which specifies PCE-initiated LSP creation.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

2. Terminology

This document uses the following terms defined in [RFC5440]: PCC,
PCE, PCEP Peer, and PCEP Speaker. speaker.

This document uses the following terms defined in [RFC4655]: Traffic
Engineering Database (TED).

This document uses the following terms defined in [RFC3031]: LSP.

This document uses the following terms defined in [RFC8051]: Stateful
PCE, Passive Stateful PCE, Active Stateful PCE, Delegation, and LSP
State Database.

The following terms are defined in this document:

Revocation: an operation performed by a PCC on a previously
delegated LSP. Revocation revokes the rights granted to the PCE
in the delegation operation.

Redelegation Timeout Interval: the period of time a PCC waits for,
when a PCEP session is terminated, before revoking LSP delegation
to a PCE and attempting to redelegate LSPs associated with the
terminated PCEP session to an alternate PCE. The Redelegation
Timeout Interval is a PCC-local value that can be either operator
configured or dynamically computed by the PCC based on local
policy.

State Timeout Interval: the period of time a PCC waits for, when a
PCEP session is terminated, before flushing LSP state associated
with that PCEP session and reverting to operator-defined default
parameters or behaviors. The State Timeout Interval is a PCC-
local value that can be either operator configured or dynamically
computed by the PCC based on local policy.

LSP State Report: an operation to send LSP state (operational/
administrative status, LSP attributes configured at the PCC and
set by a PCE, etc.) from a PCC to a PCE.

LSP Update Request: an operation where an Active Stateful PCE
requests a PCC to update one or more attributes of an LSP and to
re-signal the LSP with updated attributes.

SRP-ID-number: a number used to correlate errors and LSP State
Reports to LSP Update Requests. It is carried in the Stateful PCE
Request Parameter (SRP) Object object described in Section 7.2.

Within this document, PCEP communications are described through PCC-
PCE relationships. The PCE architecture also supports PCE-PCE
communication, by having the requesting PCE fill the role of a PCC,
as usual.

The message formats in this document are specified using Routing
Backus-Naur Format (RBNF) encoding as specified in [RFC5511].

3. Motivation and Objectives for Stateful PCE

3.1. Motivation

[RFC8051] presents several use cases, demonstrating scenarios that
benefit from the deployment of a stateful PCE. The scenarios apply
equally to MPLS-TE and GMPLS deployments.

3.1.1. Background

Traffic engineering has been a goal of the MPLS architecture since
its inception [RFC2702] [RFC3031] [RFC3346]. In the traffic
engineering system provided by [RFC3209], [RFC3630], and [RFC5305],
information about network resources utilization is only available as
total reserved capacity by the traffic class on a per-interface
basis; individual LSP state is available only locally on each Label
Edge Router (LER) for its own LSPs. In most cases, this makes good
sense, as distribution and retention of total LSP state for all LERs
within in the network would be prohibitively costly.

Unfortunately, this visibility in terms of global LSP state may
result in a number of issues for some demand patterns, particularly
within a common setup and hold priority. This issue affects online
traffic engineering systems.

A sufficiently over-provisioned system will by definition have no
issues routing its demand on the shortest path. However, lowering
the degree to which network over-provisioning is required in order to
run a healthy, functioning network is a clear and explicit promise of
MPLS architecture. In particular, it has been a goal of MPLS to
provide mechanisms to alleviate congestion scenarios in which
"traffic streams are inefficiently mapped onto available resources;
causing subsets of network resources to become over-utilized while
others remain underutilized" [RFC2702].

3.1.2. Why a Stateful PCE?

[RFC4655] defines a stateful PCE to be one in which the PCE maintains
"strict synchronization between the PCE and not only the network
states (in term of topology and resource information), but also the
set of computed paths and reserved resources in use in the network."
[RFC4655] also expressed a number of concerns with regard to a
stateful PCE, specifically:

o Any reliable synchronization mechanism would result in significant
control-plane overhead

o Out-of-band TED synchronization would be complex and prone to race
conditions

o Path calculations incorporating total network state would be
highly complex

In general, stress on the control plane will be directly proportional
to the size of the system being controlled and the tightness of the
control loop and indirectly proportional to the amount of over-
provisioning in terms of both network capacity and reservation
overhead.

Despite these concerns in terms of implementation complexity and
scalability, several TE algorithms exist today that have been
demonstrated to be extremely effective in large TE systems, providing
both rapid convergence and significant benefits in terms of
optimality of resource usage [MXMN-TE]. All of these systems share
at least two common characteristics: the requirement for both global
visibility of a flow (or in this case, a TE LSP) state and for
ordered control of path reservations across devices within the system
being controlled. While some approaches have been suggested in order
to remove the requirements for ordered control (see [MPLS-PC]), these
approaches are highly dependent on traffic distribution and do not
allow for multiple simultaneous LSP priorities representing diffserv
classes.

The use cases described in [RFC8051] demonstrate a need for
visibility into global inter-PCC LSP state in PCE path computations
and for PCE control of sequence and timing in altering LSP path
characteristics within and across PCEP sessions.

3.1.3. Protocol vs. Configuration

Note that existing configuration tools and protocols can be used to
set LSP state, such as a Command Line Interface (CLI) tool. However,
this solution has several shortcomings:

o Scale & Performance: configuration operations often have
transactional semantics that are typically heavyweight and often
require processing of additional configuration portions beyond the
state being directly acted upon, with corresponding cost in CPU
cycles, negatively impacting both PCC stability LSP update Update rate
capacity.

o Security: when a PCC opens a configuration channel allowing a PCE
to send configuration, a malicious PCE may take advantage of this
ability to take over the PCC. In contrast, the PCEP extensions
described in this document only allow a PCE control over a very
limited set of LSP attributes.

o Interoperability: each vendor has a proprietary information model
for configuring LSP state, which limits interoperability of a
stateful PCE with PCCs from different vendors. The PCEP
extensions described in this document allow for a common
information model for LSP state for all vendors.

o Efficient State Synchronization: configuration channels may be
heavyweight and unidirectional; therefore, efficient state
synchronization State
Synchronization between a PCC and a PCE may be a problem.

3.2. Objectives

The objectives for the protocol extensions to support stateful PCE
described in this document are as follows:

o Allow a single PCC to interact with a mix of stateless and
stateful PCEs simultaneously using the same protocol, i.e., PCEP.

o Support efficient LSP state synchronization State Synchronization between the PCC and
one or more active or passive stateful PCEs.

o Allow a PCC to delegate control of its LSPs to an active stateful
PCE such that a given LSP is under the control of a single PCE at
any given time.

* A PCC may revoke this delegation at any time during the
lifetime of the LSP. If LSP delegation is revoked while the
PCEP session is up, the PCC MUST notify the PCE about the
revocation.

* A PCE may return an LSP delegation at any point during the
lifetime of the PCEP session. If LSP delegation is returned by
the PCE while the PCEP session is up, the PCE MUST notify the
PCC about the returned delegation.

o Allow a PCE to control computation timing and update timing across
all LSPs that have been delegated to it.

o Enable uninterrupted operation of a PCC's LSPs in the event of a
PCE failure or while control of LSPs is being transferred between
PCEs.

4. New Functions to Support Stateful PCEs

Several new functions are required in PCEP to support stateful PCEs.
A function can be initiated either from a PCC towards a PCE (C-E) or
from a PCE towards a PCC (E-C). The new functions are:

Capability advertisement (E-C,C-E): both the PCC and the PCE must
announce during PCEP session establishment that they support PCEP
Stateful PCE extensions defined in this document.

LSP state synchronization State Synchronization (C-E): after the session between the PCC
and a stateful PCE is initialized, the PCE must learn the state of
a PCC's LSPs before it can perform path computations or update LSP
attributes in a PCC.

LSP Update Request (E-C): a PCE requests modification of attributes
on a PCC's LSP.

LSP State Report (C-E): a PCC sends an LSP State Report to a PCE
whenever the state of an LSP changes.

LSP control delegation (C-E,E-C): a PCC grants to a PCE the right to
update LSP attributes on one or more LSPs; the PCE becomes the
authoritative source of the LSP's attributes as long as the
delegation is in effect (see Section 5.7); the PCC may withdraw
the delegation or the PCE may give up the delegation at any time.

Similarly to [RFC5440], no assumption is made about the discovery
method used by a PCC to discover a set of PCEs (e.g., via static
configuration or dynamic discovery) and on the algorithm used to
select a PCE.

5. Overview of Protocol Extensions

5.1. LSP State Ownership

In PCEP (defined in [RFC5440]), LSP state and operation are under the
control of a PCC (a PCC may be a Label Switching Router (LSR) or a
management station). Attributes received from a PCE are subject to
PCC's local policy. The PCEP extensions described in this document
do not change this behavior.

An active stateful PCE may have control of a PCC's LSPs that were
delegated to it, but the LSP state ownership is retained by the PCC.
In particular, in addition to specifying values for LSP's attributes,
an active stateful PCE also decides when to make LSP modifications.

Retaining LSP state ownership on the PCC allows for:

o a PCC to interact with both stateless and stateful PCEs at the
same time

o a stateful PCE to only modify a small subset of LSP parameters,
i.e., to set only a small subset of the overall LSP state; other
parameters may be set by the operator, for example, through CLI
commands

o a PCC to revert delegated LSP to an operator-defined default or to
delegate the LSPs to a different PCE, if the PCC gets disconnected
from a PCE with currently delegated LSPs

5.2. New Messages

In this document, we define the following new PCEP messages:

Path Computation State Report (PCRpt): a PCEP message sent by a PCC
to a PCE to report the status of one or more LSPs. Each LSP State
Report in a PCRpt message MAY contain the actual LSP's path,
bandwidth, operational and administrative status, etc. An LSP
Status Report carried on a PCRpt message is also used in
delegation or revocation of control of an LSP to/from a PCE. The
PCRpt message is described in Section 6.1.

Path Computation Update Request (PCUpd): a PCEP message sent by a
PCE to a PCC to update LSP parameters, on one or more LSPs. Each
LSP Update Request on a PCUpd message MUST contain all LSP
parameters that a PCE wishes to be set for a given LSP. An LSP
Update Request carried on a PCUpd message is also used to return
LSP delegations if at any point PCE no longer desires control of
an LSP. The PCUpd message is described in Section 6.2.

The new functions defined in Section 4 are mapped onto the new
messages as shown in the following table.

Table 1: New Function to Message Mapping

5.3. Error Reporting

Error reporting is done using the procedures defined in [RFC5440] and
reusing the applicable error types and error values of [RFC5440]
wherever appropriate. The current document defines new error values
for several error types to cover failures specific to stateful PCE.

5.4. Capability Advertisement

During the PCEP Initialization Phase, initialization phase, PCEP Speakers speakers (PCE or PCC)
advertise their support of stateful PCEP Stateful PCE extensions. A PCEP Speaker
speaker includes the "Stateful PCE Capability "STATEFUL-PCE-CAPABILITY TLV", described in
Section 7.1.1, in the OPEN object to advertise its support for PCEP
stateful extensions. The
Stateful PCE Capability extensions. The STATEFUL-PCE-CAPABILITY TLV includes
the 'LSP Update' Flag flag that indicates whether the PCEP Speaker speaker
supports LSP parameter updates.

The presence of the Stateful PCE Capability STATEFUL-PCE-CAPABILITY TLV in PCC's OPEN object
indicates that the PCC is willing to send LSP State Reports whenever
LSP parameters or operational status changes.

The presence of the Stateful PCE Capability STATEFUL-PCE-CAPABILITY TLV in PCE's OPEN message
indicates that the PCE is interested in receiving LSP State Reports
whenever LSP parameters or operational status changes.

The PCEP extensions for stateful PCEs MUST NOT be used if one or both
PCEP Speakers speakers have not included the Stateful PCE Capability STATEFUL-PCE-CAPABILITY TLV in
their respective OPEN message. If the PCEP Speaker speaker on the PCC
supports the extensions of this specification but did not advertise
this capability, then upon receipt of a PCUpd message from the PCE,
it MUST generate a PCEP Error (PCErr) with error-type 19 Error-type=19 (Invalid
Operation) and error-value 2 (Attempted LSP Update Request if the
stateful PCE capability was not advertised)(see Section 8.5), and it
SHOULD terminate the PCEP session. If the PCEP Speaker on the PCE
supports the extensions of this specification but did not advertise
this capability, then upon receipt of a PCRpt message from the PCC,
it MUST generate a PCErr with error-type 19 Error-type=19 (Invalid Operation) and
error-value 5 (Attempted LSP State Report if stateful PCE capability
was not advertised) (see Section 8.5), and it SHOULD terminate the
PCEP session.

LSP delegation and LSP update Update operations defined in this document may
only be used if both PCEP Speakers speakers set the LSP-UPDATE-CAPABILITY Flag flag
in the "Stateful Capability" STATEFUL-PCE-CAPABILITY TLV to 'Updates Allowed (U Flag flag = 1)'.
If this is not the case and LSP delegation or LSP update Update operations
are attempted, then a PCErr with error-type 19 Error-type=19 (Invalid Operation)
and error-value 1 (Attempted LSP Update Request for a non-delegated
LSP) (see Section 8.5) MUST be generated. Note that, even if one of
the PCEP speakers does not set the LSP-UPDATE-CAPABILITY flag in its
"Stateful Capability"
STATEFUL-PCE-CAPABILITY TLV, a PCE can still operate as a passive
stateful PCE by accepting LSP State Reports from the PCC in order to
build and maintain an up-to-date view of the state of the PCC's LSPs.

5.5. IGP Extensions for Stateful PCE Capabilities Advertisement

When PCCs are LSRs participating in the IGP (OSPF or IS-IS), and PCEs
are either LSRs or servers also participating in the IGP, an
effective mechanism for PCE discovery within an IGP routing domain
consists of utilizing IGP advertisements. Extensions for the
advertisement of PCE Discovery Information are defined for OSPF and
for IS-IS in [RFC5088] and [RFC5089], respectively.

The PCE-CAP-FLAGS sub-TLV, defined in [RFC5089], is an optional
sub-TLV used to advertise PCE capabilities. It MAY be present within
the PCE Discovery (PCED) sub-TLV carried by OSPF or IS-IS. [RFC5088]
and [RFC5089] provide the description and processing rules for this
sub-TLV when carried within OSPF and IS-IS, respectively.

The format of the PCE-CAP-FLAGS sub-TLV is included below for easy
reference:

Type: 5

Length: Multiple of 4.

Value: This contains an array of units of 32-bit flags with the most
significant bit as 0. Each bit represents one PCE capability.

PCE capability bits are defined in [RFC5088]. This document defines
new capability bits for the stateful PCE as follows:

Bit Capability
--- -------------------------------
11 Active Stateful stateful PCE capability
12 Passive Stateful stateful PCE capability

Note that while active and passive stateful PCE capabilities may be
advertised during discovery, PCEP Speakers speakers that wish to use stateful
PCEP MUST negotiate stateful PCEP capabilities during PCEP session
setup, as specified in the current document. A PCC MAY initiate
stateful PCEP capability negotiation at PCEP session setup even if it
did not receive any IGP PCE capability advertisements.

5.6. State Synchronization

The purpose of State Synchronization is to provide a
checkpoint-in-time state replica of a PCC's LSP state in a PCE.
State Synchronization is performed immediately after the
Initialization
initialization phase [RFC5440].

During State Synchronization, a PCC first takes a snapshot of the
state of its
LSP's state, LSPs, then it sends the snapshot to a PCE in a sequence
of LSP State Reports. Each LSP State Report sent during State
Synchronization has the SYNC Flag flag in the LSP Object object set to 1. The
set of LSPs for which state is synchronized with a PCE is determined
by the PCC's local configuration (see more details in Section 9.1)
and MAY also be determined by stateful PCEP capabilities defined in
other documents, such as [RFC8232].

The end of the synchronization marker is a PCRpt message with the
SYNC Flag flag set to 0 for an LSP Object object with PLSP-ID equal to the
reserved value 0 (see Section 7.3). In this case, the LSP Object object
SHOULD NOT include the SYMBOLIC-PATH-NAME TLV and SHOULD include the
LSP-IDENTIFIERS TLV with the special value of all zeroes. The PCRpt
message MUST include an empty Explicit Route Object (ERO) as its
intended path and SHOULD NOT include the optional Record Route Object
(RRO) for its actual path. If the PCC has no state to synchronize,
it SHOULD only send the end of the synchronization marker.

A PCE SHOULD NOT send PCUpd messages to a PCC before State
Synchronization is complete. A PCC SHOULD NOT send PCReq messages to
a PCE before State Synchronization is complete. This is to allow the
PCE to get the best possible view of the network before it starts
computing new paths.

Either the PCE or the PCC MAY terminate the session using the PCEP
session termination procedures during the synchronization phase. If
the session is terminated, the PCE MUST clean up the state it
received from this PCC. The session re-establishment MUST be
re-attempted per the procedures defined in [RFC5440], including use
of a backoff timer.

If the PCC encounters a problem that prevents it from completing the
LSP state synchronization, State Synchronization, it MUST send a PCErr message with
error-type 20 (LSP State Synchronization Error) and error-value 5
(indicating an internal PCC error) to the PCE and terminate the
session.

The PCE does not send positive acknowledgments for properly received
synchronization messages. It MUST respond with a PCErr message with
error-type 20
Error-type=20 (LSP State Synchronization Error) and error-value 1
(indicating an error in processing the PCRpt) (see Section 8.5) if it
encounters a problem with the LSP State Report it received from the
PCC, and it MUST terminate the session.

A PCE implementing a limit on the resources a single PCC can occupy
MUST send a PCEP Notify (PCNtf) message with Notification Type 4
(Stateful PCE resource limit exceeded) and Notification Value 1
(Entering resource limit exceeded state) in response to the PCRpt
message triggering this condition in the synchronization phase and
MUST terminate the session.

The successful State Synchronization sequence is shown in Figure 1.

+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|-----PCRpt, SYNC=1----->| (Sync start)
| |
|-----PCRpt, SYNC=1----->|
| . |
| . |
| . |
|-----PCRpt, SYNC=1----->|
| . |
| . |
| . |
| |
|-----PCRpt, SYNC=0----->| (End of sync marker
| | LSP State Report
| | for PLSP-ID=0)
| | (Sync done)

Figure 1: Successful State Synchronization

The sequence where the PCE fails during the State Synchronization
phase is shown in Figure 2.

+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|-----PCRpt, SYNC=1----->|
| |
|-----PCRpt, SYNC=1----->|
| . |
| . |
| . |
|-----PCRpt, SYNC=1----->|
| |
|-PCRpt, SYNC=1 |
| \ ,-PCErr |
| \ / |
| \/ |
| /\ |
| / `-------->| (Ignored)
|<--------` |

Figure 2: Failed State Synchronization (PCE Failure)
The sequence where the PCC fails during the State Synchronization
phase is shown in Figure 3.

+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|-----PCRpt, SYNC=1----->|
| |
|-----PCRpt, SYNC=1----->|
| . |
| . |
| . |
|-------- PCErr=? ------>|
| |

Figure 3: Failed State Synchronization (PCC Failure)

Optimizations to the synchronization procedures and alternate
mechanisms of providing the synchronization function are outside the
scope of this document and are discussed elsewhere (see [RFC8232]).

5.7. LSP Delegation

If during Capability capability advertisement both the PCE and the PCC have
indicated that they support LSP Update, then the PCC may choose to
grant the PCE a temporary right to update (a subset of) LSP
attributes on one or more LSPs. This is called "LSP Delegation", delegation", and
it MAY be performed at any time after the Initialization initialization phase,
including during the State Synchronization phase.

A PCE MAY return an LSP delegation at any time if it no longer wishes
to update the LSP's state. A PCC MAY revoke an LSP delegation at any
time. Delegation, Revocation, and Return are done individually for
each LSP.

In the event of a delegation being rejected or returned by a PCE, the
PCC SHOULD react based on local policy. It can, for example, either
retry delegating to the same PCE using an exponentially increasing
timer or delegate to an alternate PCE.

5.7.1. Delegating an LSP

A PCC delegates an LSP to a PCE by setting the Delegate flag in the
LSP State Report to 1. If the PCE does not accept the LSP
Delegation,
delegation, it MUST immediately respond with an empty LSP Update
Request that has the Delegate flag set to 0. If the PCE accepts the
LSP Delegation, delegation, it MUST set the Delegate flag to 1 when it sends an
LSP Update Request for the delegated LSP (note that this may occur at
a later time). The PCE MAY also immediately acknowledge a delegation
by sending an empty LSP Update Request that has the Delegate flag set
to 1.

The delegation sequence is shown in Figure 4.

+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---PCRpt, Delegate=1--->| LSP delegated
| |
|---PCRpt, Delegate=1--->|
| . |
| . |
| . |
|<--(PCUpd,Delegate=1)---| Delegation confirmed
| |
|---PCRpt, Delegate=1--->|
| |

Figure 4: Delegating an LSP

Note that for an LSP to remain delegated to a PCE, the PCC MUST set
the Delegate flag to 1 on each LSP State Report sent to the PCE.

5.7.2. Revoking a Delegation

5.7.2.1. Explicit Revocation

When a PCC decides that a PCE is no longer permitted to modify an
LSP, it revokes that LSP's delegation to the PCE. A PCC may revoke
an LSP delegation at any time during the LSP's lifetime. A PCC
revoking an LSP delegation MAY immediately remove the updated
parameters provided by the PCE and revert to the operator-defined
parameters, but to avoid traffic loss, it SHOULD do so in a
make-before-break fashion. If the PCC has received but not yet acted
on PCUpd messages from the PCE for the LSP whose delegation is being
revoked, then it SHOULD ignore these PCUpd messages when processing
the message queue. All effects of all messages for which processing
started before the revocation took place MUST be allowed to complete,
and the result MUST be given the same treatment as any LSP that had
been previously delegated to the PCE (e.g., the state MAY immediately
revert to the operator-defined parameters).

If a PCEP session with the PCE to which the LSP is delegated exists
in the UP state during the revocation, the PCC MUST notify that PCE
by sending an LSP State Report with the Delegate flag set to 0, as
shown in Figure 5.

+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---PCRpt, Delegate=1--->|
| |
|<--(PCUpd,Delegate=1)---| Delegation confirmed
| . |
| . |
| . |
|---PCRpt, Delegate=0--->| PCC revokes delegation
| |

Figure 5: Revoking a Delegation

After an LSP delegation has been revoked, a PCE can no longer update
an LSP's parameters; an attempt to update parameters of a
non-delegated LSP will result in the PCC sending a PCErr message with
error-type 19
Error-type=19 (Invalid Operation) and error-value 1 (Attempted LSP
Update Request for a non-delegated LSP) (see Section 8.5).

5.7.2.2. Revocation on Redelegation Timeout

When a PCC's PCEP session with a PCE terminates unexpectedly, the PCC
MUST wait the time interval specified in the Redelegation Timeout
Interval before revoking LSP delegations to that PCE and attempting
to redelegate LSPs to an alternate PCE. If a PCEP session with the
original PCE can be re-established before the Redelegation Timeout
Interval timer expires, LSP delegations to the PCE remain intact.

Likewise, when a PCC's PCEP session with a PCE terminates
unexpectedly, and the PCC does not succeed in redelegating its LSPs,
the PCC MUST wait for the State Timeout Interval before flushing any
LSP state associated with that PCE. Note that the State Timeout
Interval timer may expire before the PCC has redelegated the LSPs to
another PCE, for example, if a PCC is not connected to any active
stateful PCE or if no connected active stateful PCE accepts the
delegation. In this case, the PCC MUST flush any LSP state set by
the PCE upon expiration of the State Timeout Interval and revert to
operator-defined default parameters or behaviors. This operation
SHOULD be done in a make-before-break fashion.

The State Timeout Interval MUST be greater than or equal to the
Redelegation Timeout Interval and MAY be set to infinity (meaning
that until the PCC specifically takes action to change the parameters
set by the PCE, they will remain intact).

5.7.3. Returning a Delegation

In order to keep a delegation, a PCE MUST set the Delegate flag to 1
on each LSP Update Request sent to the PCC. A PCE that no longer
wishes to update an LSP's parameters SHOULD return the LSP delegation
back to the PCC by sending an empty LSP Update Request that has the
Delegate flag set to 0. If a PCC receives an LSP Update Request with
the Delegate flag set to 0 (whether the LSP Update Request is empty
or not), it MUST treat this as a delegation return.

+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---PCRpt, Delegate=1--->| LSP delegated
| . |
| . |
| . |
|<--PCUpd, Delegate=0----| Delegation returned
| |
|---PCRpt, Delegate=0--->| No delegation for LSP
| |

Figure 6: Returning a Delegation

If a PCC cannot delegate an LSP to a PCE (for example, if a PCC is
not connected to any active stateful PCE or if no connected active
stateful PCE accepts the delegation), the LSP delegation on the PCC
will timeout within a configurable Redelegation Timeout Interval, and
the PCC MUST flush any LSP state set by a PCE at the expiration of
the State Timeout Interval and revert to operator-defined default
parameters or behaviors.

5.7.4. Redundant Stateful PCEs

In a redundant configuration where one PCE is backing up another PCE,
the backup PCE may have only a subset of the LSPs in the network
delegated to it. The backup PCE does not update any LSPs that are
not delegated to it. In order to allow the backup to operate in a
hot-standby mode and avoid the need for state synchronization State Synchronization in case
the primary fails, the backup receives all LSP State Reports from a
PCC. When the primary PCE for a given LSP set fails, after expiry of
the Redelegation Timeout Interval, the PCC SHOULD delegate to the
redundant PCE all LSPs that had been previously delegated to the
failed PCE. Assuming that the State Timeout Interval had been
configured to be greater than the Redelegation Timeout Interval (as
MANDATORY), and assuming that the primary and redundant PCEs take
similar decisions, this delegation change will not cause any changes
to the LSP parameters.

5.7.5. Redelegation on PCE Failure

On failure, the goal is to: 1) avoid any traffic loss on the LSPs
that were updated by the PCE that crashed, 2) minimize the churn in
the network in terms of ownership of the LSPs, 3) not leave any
"orphan" (undelegated) LSPs, and 4) be able to control when the state
that was set by the PCE can be changed or purged. The values chosen
for the Redelegation Timeout and State Timeout values affect the
ability to accomplish these goals.

This section summarizes the behavior with regards to LSP delegation
and LSP state on a PCE failure.

If the PCE crashes but recovers within the Redelegation Timeout, both
the delegation state and the LSP state are kept intact.

If the PCE crashes but does not recover within the Redelegation
Timeout, the delegation state is returned to the PCC. If the PCC can
redelegate the LSPs to another PCE, and that PCE accepts the
delegations, there will be no change in LSP state. If the PCC cannot
redelegate the LSPs to another PCE, then upon expiration of the State
Timeout Interval, the state set by the PCE is removed and the LSP
reverts to operator-defined parameters, which may cause a change in
the LSP state. Note that an operator may choose to use an infinite
State Timeout Interval if he wishes to maintain the PCE state
indefinitely. Note also that flushing the state should be
implemented using make-before-break to avoid traffic loss.

If there is a standby PCE, the Redelegation Timeout may be set to 0
through policy on the PCC, causing the LSPs to be redelegated
immediately to the PCC, which can delegate them immediately to the
standby PCE. Assuming that the PCC can redelegate the LSP to the
standby PCE within the State Timeout Interval, and assuming the
standby PCE takes similar decisions as the failed PCE, the LSP state
will be kept intact.

5.8. LSP Operations

5.8.1. Passive Stateful PCE Path Computation Request/Response
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
1) Path computation |----- PCReq message --->|
request sent to | |2) Path computation
PCE | | request received,
| | path computed
| |
|<---- PCRep message ----|3) Computed paths
| (Positive reply) | sent to the PCC
| (Negative reply) |
4) LSP state change | |
event | |
| |
5) LSP State Report |----- PCRpt message --->|
sent to all | . |
stateful PCEs | . |
| . |
6) Repeat for each |----- PCRpt message --->|
LSP state change | |
| |

Figure 7: Passive Stateful PCE Path Computation Request/Response

Once a PCC has successfully established a PCEP session with a passive
stateful PCE and the PCC's LSP state is synchronized with the PCE
(i.e., the PCE knows about all of the PCC's existing LSPs), if an
event is triggered that requires the computation of a set of paths,
the PCC sends a path computation request to the PCE ([RFC5440],
Section 4.2.3). The PCReq message MAY contain the LSP Object object to
identify the LSP for which the path computation is requested.

Upon receiving a path computation request from a PCC, the PCE
triggers a path computation and returns either a positive or a
negative reply to the PCC ([RFC5440], Section 4.2.4).

Upon receiving a positive path computation reply, the PCC receives a
set of computed paths and starts to set up the LSPs. For each LSP,
it MAY send an LSP State Report carried on a PCRpt message to the
PCE, indicating that the LSP's status is "Going-up".

Once an LSP is up or active, the PCC MUST send an LSP State Report
carried on a PCRpt message to the PCE, indicating that the LSP's
status is 'Up' or 'Active', respectively. If the LSP could not be
set up, the PCC MUST send an LSP State Report indicating that the LSP
is 'Down' and stating the cause of the failure. Note that due to
timing constraints, the LSP status may change from 'Going-up' to 'Up'
(or 'Down') before the PCC has had a chance to send an LSP State
Report indicating that the status is 'Going-up'. In such cases, the
PCC MAY choose to only send the PCRpt indicating the latest status
('Active', 'Up', or 'Down').

Upon receiving a negative reply from a PCE, a PCC MAY resend a
modified request or take any other appropriate action. For each
requested LSP, it SHOULD also send an LSP State Report carried on a
PCRpt message to the PCE, indicating that the LSP's status is 'Down'.

There is no direct correlation between PCRep and PCRpt messages. For
a given LSP, multiple LSP State Reports will follow a single PCRep
message, as a PCC notifies a PCE of the LSP's state changes.

A PCC MUST send each LSP State Report to each stateful PCE that is
connected to the PCC.

Note that a single PCRpt message MAY contain multiple LSP State
Reports.

The passive stateful model for stateful PCEs is described in
[RFC4655], Section 6.8.

5.8.2. Switching from Passive Stateful to Active Stateful

This section deals with the scenario of an LSP transitioning from a
passive stateful to an active stateful mode of operation. When the
LSP has no working path, prior to delegating the LSP, the PCC MUST
first use the procedure defined in Section 5.8.1 to request the
initial path from the PCE. This is required because the action of
delegating the LSP to a PCE using a PCRpt message is not an explicit
request to the PCE to compute a path for the LSP. The only explicit
way for a PCC to request a path from the PCE is to send a PCReq
message. The PCRpt message MUST NOT be used by the PCC to attempt to
request a path from the PCE.

When the LSP is delegated after its setup, it may be useful for the
PCC to communicate to the PCE the locally configured intended
configuration parameters, so that the PCE may reuse them in its
computations. Such parameters MAY be acquired through an out-of-band
channel, or MAY be communicated in the PCRpt message delegating the
LSPs, by including them as part of the intended-attribute-list as
explained in Section 6.1. An implementation MAY allow policies on
the PCC to determine the configuration parameters to be sent to the
PCE.

5.8.3. Active Stateful PCE LSP Update

+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
1) LSP State |-- PCRpt, Delegate=1 -->|
Synchronization | . |
| . |2) PCE decides to
| . | update the LSP
| |
|<---- PCUpd message ----|3) PCUpd message sent
| | to the PCC
| |
| |
4) LSP State Report |---- PCRpt message ---->|
sent(->Going-up) | . |
| . |
| . |
5) LSP State Report |---- PCRpt message ---->|
sent (->Up|Down) | |
| |

Figure 8: Active Stateful PCE

Once a PCC has successfully established a PCEP session with an active
stateful PCE, the PCC's LSP state is synchronized with the PCE (i.e.,
the PCE knows about all of the PCC's existing LSPs). After LSPs have
been delegated to the PCE, the PCE can modify LSP parameters of
delegated LSPs.

To update an LSP, a PCE MUST send the PCC an LSP Update Request using
a PCUpd message. The LSP Update Request contains a variety of
objects that specify the set of constraints and attributes for the
LSP's path. Each LSP Update Request MUST have a unique identifier,
the SRP-ID-number, carried in the SRP Object object described in
Section 7.2. The SRP-ID-number is used to correlate errors and state
reports to LSP Update Requests. A single PCUpd message MAY contain
multiple LSP Update Requests.

Upon receiving a PCUpd message, the PCC starts to set up LSPs
specified in LSP Update Requests carried in the message. For each
LSP, it MAY send an LSP State Report carried on a PCRpt message to
the PCE, indicating that the LSP's status is 'Going-up'. If the PCC
decides that the LSP parameters proposed in the PCUpd message are
unacceptable, it MUST report this error by including the
LSP-ERROR-CODE TLV (Section 7.3.3) with LSP error-value="Unacceptable
parameters" in the LSP object in the PCRpt message to the PCE. Based
on local policy, it MAY react further to this error by revoking the
delegation. If the PCC receives a PCUpd message for an LSP object
identified with a PLSP-ID that does not exist on the PCC, it MUST
generate a PCErr with error-type 19 Error-type=19 (Invalid Operation), error-value
3, (Attempted LSP Update Request for an LSP identified by an unknown
PSP-ID) (see Section 8.5).

Once an LSP is up, the PCC MUST send an LSP State Report (PCRpt
message) to the PCE, indicating that the LSP's status is 'Up'. If
the LSP could not be set up, the PCC MUST send an LSP State Report
indicating that the LSP is 'Down' and stating the cause of the
failure. A PCC MAY compress LSP State Reports to only reflect the
most up to date state, as discussed in the previous section.

A PCC MUST send each LSP State Report to each stateful PCE that is
connected to the PCC.

PCErr and PCRpt messages triggered as a result of a PCUpd message
MUST include the SRP-ID-number from the PCUpd. This provides
correlation of requests and errors and acknowledgement of state
processing. The PCC MAY compress the state when processing PCUpd.
In this case, receipt of a higher SRP-ID-number implicitly
acknowledges processing all the updates with a lower SRP-ID-number
for the specific LSP (as per Section 7.2).

A PCC MUST NOT send to any PCE a path computation request for a
delegated LSP. Should the PCC decide it wants to issue a Path
Computation Request on a delegated LSP, it MUST perform the
Delegation Revocation procedure first.

5.9. LSP Protection

LSP protection and interaction with stateful PCE, as well as the
extensions necessary to implement this functionality, will be
discussed in a separate document.

5.10. PCEP Sessions

A permanent PCEP session MUST be established between a stateful PCE
and the PCC. In the case of session failure, session
re-establishment MUST be re-attempted per the procedures defined in
[RFC5440].

6. PCEP Messages

As defined in [RFC5440], a PCEP message consists of a common header
followed by a variable-length body made of a set of objects. For
each PCEP message type, a set of rules is defined that specifies the
set of objects that the message can carry.

6.1. The PCRpt Message

A Path Computation LSP State Report message (also referred to as a
PCRpt message) is a PCEP message sent by a PCC to a PCE to report the
current state of an LSP. A PCRpt message can carry more than one LSP
State Reports. A PCC can send an LSP State Report either in response
to an LSP Update Request from a PCE or asynchronously when the state
of an LSP changes. The Message-Type field of the PCEP common header
for the PCRpt message is 10.

The format of the PCRpt message is as follows:

<PCRpt Message> ::= <Common Header>
<state-report-list>
Where:

<state-report-list> ::= <state-report>[<state-report-list>]

<state-report> ::= [<SRP>]
<LSP>
<path>
Where:
<path>::= <intended-path>
[<actual-attribute-list><actual-path>]
<intended-attribute-list>

<actual-attribute-list>::=[<BANDWIDTH>]
[<metric-list>]

Where:
<intended-path> is represented by the ERO object defined in
Section 7.9 of [RFC5440].

<actual-attribute-list> consists of the actual computed and
signaled values of the <BANDWIDTH> and <metric-lists> objects
defined in [RFC5440].

<actual-path> is represented by the RRO object defined in
Section 7.10 of [RFC5440].

<intended-attribute-list> is the attribute-list defined in
Section 6.5 of [RFC5440] and extended by PCEP extensions.

The SRP object (see Section 7.2) is OPTIONAL. If the PCRpt message
is not in response to a PCupd message, the SRP object MAY be omitted.

When the PCC does not include the SRP object, the PCE MUST treat this
as an SRP object with an SRP-ID-number equal to the reserved value
0x00000000. The reserved value 0x00000000 indicates that the state
reported is not a result of processing a PCUpd message.

If the PCRpt message is in response to a PCUpd message, the SRP
object MUST be included and the value of the SRP-ID-number in the SRP
Object
object MUST be the same as that sent in the PCUpd message that
triggered the state that is reported. If the PCC compressed several
PCUpd messages for the same LSP by only processing the one with the
highest number, then it should use the SRP-ID-number of that request.
No state compression is allowed for state reporting, e.g., PCRpt
messages MUST NOT be pruned from the PCC's egress queue even if
subsequent operations on the same LSP have been completed before the
PCRpt message has been sent to the TCP stack. The PCC MUST
explicitly report state changes (including removal) for paths it
manages.

The LSP object (see Section 7.3) is REQUIRED, and it MUST be included
in each LSP State Report on the PCRpt message. If the LSP object is
missing, the receiving PCE MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value 8 (LSP object
missing).

If the LSP transitioned to non-operational state, the PCC SHOULD
include the LSP-ERROR-TLV (Section 7.3.3) with the relevant LSP Error
Code to report the error to the PCE.

The intended path, represented by the ERO object, is REQUIRED. If
the ERO object is missing, the receiving PCE MUST send a PCErr
message with Error-type=6 (Mandatory Object missing) and Error-value
9 (ERO object missing). The ERO may be empty if the PCE does not
have a path for a delegated LSP.

The actual path, represented by the RRO object, SHOULD be included in
a PCRpt by the PCC when the path is up or active, but it MAY be
omitted if the path is down due to a signaling error or another
failure.

The intended-attribute-list maps to the attribute-list in Section 6.5
of [RFC5440] and is used to convey the requested parameters of the
LSP path. This is needed in order to support the switch from passive
to active stateful PCE as described in Section 5.8.2. When included
as part of the intended-attribute-list, the meaning of the BANDWIDTH
object is the requested bandwidth as intended by the operator. In
this case, the BANDWIDTH Object-Type of 1 SHOULD be used. Similarly,
to indicate a limiting constraint, the METRIC object SHOULD be
included as part of the intended-attribute-list with the B flag set
and with a specific metric value. To indicate the optimization
metric, the METRIC object SHOULD be included as part of the
intended-attribute-list with the B flag unset and the metric value
set to zero. Note that the intended-attribute-list is optional and
thus may be omitted. In this case, the PCE MAY use the values in the
actual-attribute-list as the requested parameters for the path.

The actual-attribute-list consists of the actual computed and
signaled values of the BANDWIDTH and METRIC objects defined in
[RFC5440]. When included as part of the actual-attribute-list,
Object-Type 2 [RFC5440] SHOULD be used for the BANDWIDTH object, and
the C flag SHOULD be set in the METRIC object [RFC5440].

Note that the ordering of intended-path, actual-attribute-list,
actual-path, and intended-attribute-list is chosen to retain
compatibility with implementations of an earlier version of this
standard.

A PCE may choose to implement a limit on the resources a single PCC
can occupy. If a PCRpt is received that causes the PCE to exceed
this limit, the PCE MUST notify the PCC using a PCNtf message with
Notification Type 4 (Stateful PCE resource limit exceeded) and
Notification Value 1 (Entering resource limit exceeded state), and it
MUST terminate the session.

6.2. The PCUpd Message

A Path Computation LSP Update Request message (also referred to as
PCUpd message) is a PCEP message sent by a PCE to a PCC to update
attributes of an LSP. A PCUpd message can carry more than one LSP
Update Request. The Message-Type field of the PCEP common header for
the PCUpd message is 11.

The format of a PCUpd message is as follows:

<PCUpd Message> ::= <Common Header>
<update-request-list>
Where:

<update-request-list> ::= <update-request>[<update-request-list>]

<update-request> ::= <SRP>
<LSP>
<path>
Where:
<path>::= <intended-path><intended-attribute-list>

Where:
<intended-path> is represented by the ERO object defined in
Section 7.9 of [RFC5440].

<intended-attribute-list> is the attribute-list defined in
[RFC5440] and extended by PCEP extensions.

There are three mandatory objects that MUST be included within each
LSP Update Request in the PCUpd message: the SRP Object object (see
Section 7.2), the LSP object (see Section 7.3) and the ERO object (as
defined in [RFC5440], which represents the intended path. If the SRP
object is missing, the receiving PCC MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value=10 (SRP
object missing). If the LSP object is missing, the receiving PCC
MUST send a PCErr message with Error-type=6 (Mandatory Object
missing) and Error-value=8 (LSP object missing). If the ERO object
is missing, the receiving PCC MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value=9 (ERO object
missing).

The ERO in the PCUpd may be empty if the PCE cannot find a valid path
for a delegated LSP. One typical situation resulting in this empty
ERO carried in the PCUpd message is that a PCE can no longer find a
strict SRLG-disjoint path for a delegated LSP after a link failure.
The PCC SHOULD implement a local policy to decide the appropriate
action to be taken: either tear down the LSP or revoke the delegation
and use a locally computed path, or keep the existing LSP.

A PCC only acts on an LSP Update Request if permitted by the local
policy configured by the network manager. Each LSP Update Request
that the PCC acts on results in an LSP setup operation. An LSP
Update Request MUST contain all LSP parameters that a PCE wishes to
be set for the LSP. A PCC MAY set missing parameters from locally
configured defaults. If the LSP specified in the Update Request is
already up, it will be re-signaled.

The PCC SHOULD minimize the traffic interruption and MAY use the
make-before-break procedures described in [RFC3209] in order to
achieve this goal. If the make-before-break procedures are used, two
paths will briefly coexist. The PCC MUST send separate PCRpt
messages for each, identified by the LSP-IDENTIFIERS TLV. When the
old path is torn down after the head end switches over the traffic,
this event MUST be reported by sending a PCRpt message with the
LSP-IDENTIFIERS-TLV of the old path and the R bit set. The
SRP-ID-number that the PCC associates with this PCRpt MUST be
0x00000000. Thus, a make-before-break operation will typically
result in at least two PCRpt messages, one for the new path and one
for the removal of the old path (more messages may be possible if
intermediate states are reported).

If the path setup fails due to an RSVP signaling error, the error is
reported to the PCE. The PCC will not attempt to re-signal the path
until it is prompted again by the PCE with a subsequent PCUpd
message.

A PCC MUST respond with an LSP State Report to each LSP Update
Request it processed to indicate the resulting state of the LSP in
the network (even if this processing did not result in changing the
state of the LSP). The SRP-ID-number included in the PCRpt MUST
match that in the PCUpd. A PCC MAY respond with multiple LSP State
Reports to report LSP setup progress of a single LSP. In that case,
the SRP-ID-number MUST be included for the first message; for
subsequent messages, the reserved value 0x00000000 SHOULD be used.

Note that a PCC MUST process all LSP Update Requests -- for example,
an LSP Update Request is sent when a PCE returns delegation or puts
an LSP into non-operational state. The protocol relies on TCP for
message-level flow control.

If the rate of PCUpd messages sent to a PCC for the same target LSP
exceeds the rate at which the PCC can signal LSPs into the network,
the PCC MAY perform state compression on its ingress queue. The
compression algorithm is based on the fact that each PCUpd request
contains the complete LSP state the PCE wishes to be set and works as
follows: when the PCC starts processing a PCUpd message at the head
of its ingress queue, it may search the queue forward for more recent
PCUpd messages pertaining to that particular LSP, prune all but the
latest one from the queue, and process only the last one as that
request contains the most up-to-date desired state for the LSP. The
PCC MUST NOT send PCRpt nor PCErr messages for requests that were
pruned from the queue in this way. This compression step may be
performed only while the LSP is not being signaled, e.g., if two
PCUpd arrive for the same LSP in quick succession and the PCC started
the signaling of the changes relevant to the first PCUpd, then it
MUST wait until the signaling finishes (and report the new state via
a PCRpt) before attempting to apply the changes indicated in the
second PCUpd.

Note also that it is up to the PCE to handle inter-LSP dependencies;
for example, if ordering of LSP setups is required, the PCE has to
wait for an LSP State Report for a previous LSP before starting the
update of the next LSP.

If the PCUpd cannot be satisfied (for example, due to an unsupported
object or a TLV), the PCC MUST respond with a PCErr message
indicating the failure (see Section 7.3.3).

6.3. The PCErr Message

If the stateful PCE capability has been advertised on the PCEP
session, the PCErr message MAY include the SRP object. If the error
reported is the result of an LSP Update Request, then the
SRP-ID-number MUST be the one from the PCUpd that triggered the
error. If the error is unsolicited, the SRP object MAY be omitted.
This is equivalent to including an SRP object with the SRP-ID-number
equal to the reserved value 0x00000000.

The format of a PCErr message from [RFC5440] is extended as follows:

<PCErr Message> ::= <Common Header>
( <error-obj-list> [<Open>] ) | <error>
[<error-list>]

<error-obj-list>::=<PCEP-ERROR>[<error-obj-list>]

<request-id-list>::=<RP>[<request-id-list>]

<stateful-request-id-list>::=<SRP>[<stateful-request-id-list>]

<error-list>::=<error>[<error-list>]

6.4. The PCReq Message

A PCC MAY include the LSP object in the PCReq message (see
Section 7.3) if the stateful PCE capability has been negotiated on a
PCEP session between the PCC and a PCE.

The definition of the PCReq message from [RFC5440] is extended to
optionally include the LSP object after the END-POINTS object. The
encoding from [RFC5440] will become:

<PCReq Message>::= <Common Header>
[<svec-list>]
<request-list>
Where:

<svec-list>::=<SVEC>[<svec-list>]
<request-list>::=<request>[<request-list>]

<request>::= <RP>
<END-POINTS>
[<LSP>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>[<BANDWIDTH>]]
[<IRO>]
[<LOAD-BALANCING>]

6.5. The PCRep Message

A PCE MAY include the LSP object in the PCRep message (see
Section 7.3) if the stateful PCE capability has been negotiated on a
PCEP session between the PCC, and the PCE and the LSP object were
included in the corresponding PCReq message from the PCC.

The definition of the PCRep message from [RFC5440] is extended to
optionally include the LSP object after the Request Parameter (RP)
object. The encoding from [RFC5440] will become:

Where:

<response-list>::=<response>[<response-list>]

<response>::=<RP>
[<LSP>]
[<NO-PATH>]
[<attribute-list>]
[<path-list>]

7. Object Formats

The PCEP objects defined in this document are compliant with the PCEP
object format defined in [RFC5440]. The P and I flags of the PCEP
objects defined in the current document MUST be set to 0 on
transmission and SHOULD be ignored on receipt since they are
exclusively related to path computation requests.

7.1. OPEN Object

This document defines one new optional TLV for use in the OPEN
Object.
object.

7.1.1. Stateful PCE Capability STATEFUL-PCE-CAPABILITY TLV

The STATEFUL-PCE-CAPABILITY TLV is an optional TLV for use in the
OPEN object for stateful PCE capability advertisement. Its format 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=16 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |U|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 9: STATEFUL-PCE-CAPABILITY TLV Format

The type (16 bits) of the TLV is 16. The length field is 16 bits
long and has a fixed value of 4.

The value comprises a single field -- Flags (32 bits):

U (LSP-UPDATE-CAPABILITY - 1 bit): if set to 1 by a PCC, the U Flag flag
indicates that the PCC allows modification of LSP parameters; if
set to 1 by a PCE, the U Flag flag indicates that the PCE is capable of
updating LSP parameters. The LSP-UPDATE-CAPABILITY Flag flag must be
advertised by both a PCC and a PCE for PCUpd messages to be
allowed on a PCEP session.

Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.

A PCEP speaker operating in passive stateful PCE mode advertises the
stateful PCE capability with the U flag set to 0. A PCEP speaker
operating in active stateful PCE mode advertises the stateful PCE
capability with the U Flag flag set to 1.

Advertisement of the stateful PCE capability implies support of LSPs
that are signaled via RSVP, as well as the objects, TLVs, and
procedures defined in this document.

7.2. SRP Object

The SRP (Stateful PCE Request Parameters) object MUST be carried
within PCUpd messages and MAY be carried within PCRpt and PCErr
messages. The SRP object is used to correlate between update
requests sent by the PCE and the error reports and state reports sent
by the PCC.

SRP Object-Class is 33.

SRP Object-Type is 1.

The format of the SRP object body is shown in Figure 10:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRP-ID-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 10: The SRP Object Format

The SRP object body has a variable length and may contain additional
TLVs.

Flags (32 bits): None defined yet.

SRP-ID-number (32 bits): The SRP-ID-number value in the scope of the
current PCEP session uniquely identifies the operation that the PCE
has requested the PCC to perform on a given LSP. The SRP-ID-number
is incremented each time a new request is sent to the PCC, and it may
wrap around.

The values 0x00000000 and 0xFFFFFFFF are reserved.

Optional TLVs MAY be included within the SRP object body. The
specification of such TLVs is outside the scope of this document.

Every request to update an LSP receives a new SRP-ID-number. This
number is unique per PCEP session and is incremented each time an
operation is requested from the PCE. Thus, for a given LSP, there
may be more than one SRP-ID-number unacknowledged at a given time.
The value of the SRP-ID-number is echoed back by the PCC in PCErr and
PCRpt messages to allow for correlation between requests made by the
PCE and errors or state reports generated by the PCC. If the error
or report was not a result of a PCE operation (for example, in the
case of a link down event), the reserved value of 0x00000000 is used
for the SRP-ID-number. The absence of the SRP object is equivalent
to an SRP object with the reserved value of 0x00000000. An
SRP-ID-number is considered unacknowledged and cannot be reused until
a PCErr or PCRpt arrives with an SRP-ID-number equal or higher for
the same LSP. In case of SRP-ID-number wrapping, the last
SRP-ID-number before the wrapping MUST be explicitly acknowledged, to
avoid a situation where SRP-ID-numbers remain unacknowledged after
the wrap. This means that the PCC may need to issue two PCUpd
messages on detecting a wrap.

7.3. LSP Object

The LSP object MUST be present within PCRpt and PCUpd messages. The
LSP object MAY be carried within PCReq and PCRep messages if the
stateful PCE capability has been negotiated on the session. The LSP
object contains a set of fields used to specify the target LSP, the
operation to be performed on the LSP, and LSP Delegation. delegation. It also
contains a flag indicating to a PCE that the LSP state
synchronization State
Synchronization is in progress. This document focuses on LSPs that
are signaled with RSVP; many of the TLVs used with the LSP object
mirror RSVP state.

LSP Object-Class is 32.

LSP Object-Type is 1.

The format of the LSP object body is shown in Figure 11:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PLSP-ID | Flag | O |A|R|S|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 11: The LSP Object Format
PLSP-ID (20 bits): A PCEP-specific identifier for the LSP. A PCC
creates a unique PLSP-ID for each LSP that is constant for the
lifetime of a PCEP session. The PCC will advertise the same PLSP-ID
on all PCEP sessions it maintains at a given time. The mapping of
the symbolic path name to PLSP-ID is communicated to the PCE by
sending a PCRpt message containing the SYMBOLIC-PATH-NAME TLV. All
subsequent PCEP messages then address the LSP by the PLSP-ID. The
values of 0 and 0xFFFFF are reserved. Note that the PLSP-ID is a
value that is constant for the lifetime of the PCEP session, during
which time for an RSVP-signaled LSP there might be different RSVP
identifiers (LSP-id, tunnel-id) allocated to it.

Flags (12 bits), starting from the least significant bit:

D (Delegate - 1 bit): On a PCRpt message, the D Flag flag set to 1
indicates that the PCC is delegating the LSP to the PCE. On a
PCUpd message, the D flag set to 1 indicates that the PCE is
confirming the LSP Delegation. delegation. To keep an LSP delegated to the
PCE, the PCC must set the D flag to 1 on each PCRpt message for
the duration of the delegation -- the first PCRpt with the D flag
set to 0 revokes the delegation. To keep the delegation, the PCE
must set the D flag to 1 on each PCUpd message for the duration of
the delegation -- the first PCUpd with the D flag set to 0 returns
the delegation.

S (SYNC - 1 bit): The S Flag flag MUST be set to 1 on each PCRpt sent
from a PCC during State Synchronization. The S Flag flag MUST be set
to 0 in other messages sent from the PCC. When sending a PCUpd
message, the PCE MUST set the S Flag flag to 0.

R (Remove - 1 bit): On PCRpt messages, the R Flag flag indicates that the
LSP has been removed from the PCC and the PCE SHOULD remove all
state from its database. Upon receiving an LSP State Report with
the R Flag flag set to 1 for an RSVP-signaled LSP, the PCE SHOULD
remove all state for the path identified by the LSP-IDENTIFIERS
TLV from its database. When the all-zeros LSP-IDENTIFIERS TLV is
used, the PCE SHOULD remove all state for the PLSP-ID from its
database. When sending a PCUpd message, the PCE MUST set the R
Flag
flag to 0.

A (Administrative - 1 bit): On PCRpt messages, the A Flag flag indicates
the PCC's target operational status for this LSP. On PCUpd
messages, the A Flag flag indicates the LSP status that the PCE desires
for this LSP. In both cases, a value of '1' means that the
desired operational state is active, and a value of '0' means that
the desired operational state is inactive. A PCC ignores the A
flag on a PCUpd message unless the operator's policy allows the
PCE to control the corresponding LSP's administrative state.

O (Operational - 3 bits): On PCRpt messages, the O field represents
the operational status of the LSP.

The following values are defined:

0 - DOWN: not active.

1 - UP: signaled.

2 - ACTIVE: up and carrying traffic.

3 - GOING-DOWN: LSP is being torn down, and resources are being
released.

4 - GOING-UP: LSP is being signaled.

5-7 - Reserved: these values are reserved for future use.

Unassigned bits are considered reserved. reserved for future uses. They MUST be set to 0
on transmission and MUST be ignored on receipt. When sending a PCUpd
message, the PCE MUST set the O field to 0.

TLVs that may be included in the LSP Object object are described in the
following sections. Other optional TLVs, that are not defined in
this document, MAY also be included within the LSP Object object body.

7.3.1. LSP-IDENTIFIERS TLVs

The LSP-IDENTIFIERS TLV MUST be included in the LSP object in PCRpt
messages for RSVP-signaled LSPs. If the TLV is missing, the PCE will
generate an error with error-type 6 Error-type=6 (Mandatory object Object missing) and
error-value 11 (LSP-IDENTIFIERS TLV missing) and close the session.
The LSP-IDENTIFIERS TLV MAY be included in the LSP object in PCUpd
messages for RSVP-signaled LSPs. The special value of all zeros for
this TLV is used to refer to all paths pertaining to a particular
PLSP-ID. There are two LSP-IDENTIFIERS TLVs, one for IPv4 and one
for IPv6.

It is the responsibility of the PCC to send to the PCE the
identifiers for each RSVP incarnation of the tunnel. For example, in
a make-before-break scenario, the PCC MUST send a separate PCRpt for
the old and reoptimized paths and explicitly report removal of any of
these paths using the R bit in the LSP object.

The format of the IPV4-LSP-IDENTIFIERS 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=18 | Length=16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Tunnel Sender Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP ID | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Tunnel Endpoint Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 12: IPV4-LSP-IDENTIFIERS TLV Format

The type (16 bits) of the TLV is 18. The length field is 16 bits
long and has a fixed value of 16. The value contains the following
fields:

IPv4 Tunnel Sender Address: contains the sender node's IPv4 address,
as defined in [RFC3209], Section 4.6.2.1, for the LSP_TUNNEL_IPv4
Sender Template Object.

LSP ID: contains the 16-bit 'LSP ID' identifier defined in
[RFC3209], Section 4.6.2.1 for the LSP_TUNNEL_IPv4 Sender Template
Object. A value of 0 MUST be used if the LSP is not yet signaled.

Tunnel ID: contains the 16-bit 'Tunnel ID' identifier defined in
[RFC3209], Section 4.6.1.1 for the LSP_TUNNEL_IPv4 Session Object.

Extended Tunnel ID: contains the 32-bit 'Extended Tunnel ID'
identifier defined in [RFC3209], Section 4.6.1.1 for the
LSP_TUNNEL_IPv4 Session Object.

IPv4 Tunnel Endpoint Address: contains the egress node's IPv4
address, as defined in [RFC3209], Section 4.6.1.1, for the
LSP_TUNNEL_IPv4 Sender Template Object.

The format of the IPV6-LSP-IDENTIFIERS 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=19 | Length=52 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| IPv6 Tunnel Sender Address |
+ (16 octets) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP ID | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Extended Tunnel ID |
+ (16 octets) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| IPv6 Tunnel Endpoint Address |
+ (16 octets) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 13: IPV6-LSP-IDENTIFIERS TLV Format

The type (16 bits) of the TLV is 19. The length field is 16 bits
long and has a fixed value of 52. The value contains the following
fields:

IPv6 Tunnel Sender Address: contains the sender node's IPv6 address,
as defined in [RFC3209], Section 4.6.2.2, for the LSP_TUNNEL_IPv6
Sender Template Object.

LSP ID: contains the 16-bit 'LSP ID' identifier defined in
[RFC3209], Section 4.6.2.2 for the LSP_TUNNEL_IPv6 Sender Template
Object. A value of 0 MUST be used if the LSP is not yet signaled.

Tunnel ID: contains the 16-bit 'Tunnel ID' identifier defined in
[RFC3209], Section 4.6.1.2 for the LSP_TUNNEL_IPv6 Session Object.

Extended Tunnel ID: contains the 128-bit 'Extended Tunnel ID'
identifier defined in [RFC3209], Section 4.6.1.2 for the
LSP_TUNNEL_IPv6 Session Object.

IPv6 Tunnel Endpoint Address: contains the egress node's IPv6
address, as defined in [RFC3209], Section 4.6.1.2, for the
LSP_TUNNEL_IPv6 Session Object.

The Tunnel ID remains constant over the lifetime of a tunnel.

7.3.2. Symbolic Path Name TLV

Each LSP MUST have a symbolic path name that is unique in the PCC.
The symbolic path name is a human-readable string that identifies an
LSP in the network. The symbolic path name MUST remain constant
throughout an LSP's lifetime, which may span across multiple
consecutive PCEP sessions and/or PCC restarts. The symbolic path
name MAY be specified by an operator in a PCC's configuration. If
the operator does not specify a unique symbolic name for an LSP, then
the PCC MUST auto-generate one.

The PCE uses the symbolic path name as a stable identifier for the
LSP. If the PCEP session restarts, or the PCC restarts, or the PCC
re-delegates the LSP to a different PCE, the symbolic path name for
the LSP remains constant and can be used to correlate across the PCEP
session instances.

The other protocol identifiers for the LSP cannot reliably be used to
identify the LSP across multiple PCEP sessions, for the following
reasons.

o The PLSP-ID is unique only within the scope of a single PCEP
session.

o The LSP-IDENTIFIERS TLV is only guaranteed to be present for LSPs
that are signaled with RSVP-TE, and it may change during the
lifetime of the LSP.

The SYMBOLIC-PATH-NAME TLV MUST be included in the LSP object in the
LSP State Report (PCRpt) message when during a given PCEP session an
LSP is first reported to a PCE. A PCC sends to a PCE the first LSP
State Report either during State Synchronization or when a new LSP is
configured at the PCC.

The initial PCRpt creates a binding between the symbolic path name
and the PLSP-ID for the LSP that lasts for the duration of the PCEP
session. The PCC MAY omit the symbolic path name from subsequent LSP
State Reports for that LSP on that PCEP session, and just use the
PLSP-ID.

The format of the SYMBOLIC-PATH-NAME 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=17 | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Symbolic Path Name //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 14: SYMBOLIC-PATH-NAME TLV Format

Type (16 bits): the type is 17.

Length (16 bits): indicates the total length of the TLV in octets and
MUST be greater than 0. The TLV MUST be zero-padded so that the TLV
is 4-octet aligned.

Symbolic Path Name (variable): symbolic name for the LSP, unique in
the PCC. It SHOULD be a string of printable ASCII characters,
without a NULL terminator.

7.3.3. LSP Error Code TLV

The LSP Error Code TLV is an optional TLV for use in the LSP object
to convey error information. When an LSP Update Request fails, an
LSP State Report MUST be sent to report the current state of the LSP,
and it SHOULD contain the LSP-ERROR-CODE TLV indicating the reason
for the failure. Similarly, when a PCRpt is sent as a result of an
LSP transitioning to non-operational state, the LSP-ERROR-CODE TLV
SHOULD be included to indicate the reason for the transition.

The format of the LSP-ERROR-CODE 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=20 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 15: LSP-ERROR-CODE TLV Format

The type (16 bits) of the TLV is 20. The length field is 16 bits
long and has a fixed value of 4. The value contains an error code
that indicates the cause of the failure.

The following LSP Error Codes are currently defined:

Value Description
----- -------------------------------------
1 Unknown reason
2 Limit reached for PCE-controlled LSPs
3 Too many pending LSP Update Requests
4 Unacceptable parameters
5 Internal error
6 LSP administratively brought down
7 LSP preempted
8 RSVP signaling error

7.3.4. RSVP Error Spec TLV

The RSVP-ERROR-SPEC TLV is an optional TLV for use in the LSP object
to carry RSVP error information. It includes the RSVP ERROR_SPEC or
USER_ERROR_SPEC Object object ([RFC2205] and [RFC5284]), which were returned
to the PCC from a downstream node. If the setup of an LSP fails at a
downstream node that returned an ERROR_SPEC to the PCC, the PCC
SHOULD include in the PCRpt for this LSP the LSP-ERROR-CODE TLV with
LSP Error Code = "RSVP signaling error" and the RSVP-ERROR-SPEC TLV
with the relevant RSVP ERROR-SPEC or USER_ERROR_SPEC Object. object.

The format of the RSVP-ERROR-SPEC 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=21 | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ RSVP ERROR_SPEC or USER_ERROR_SPEC Object +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 16: RSVP-ERROR-SPEC TLV Format

Type (16 bits): the type is 21.

Length (16 bits): indicates the total length of the TLV in octets.
The TLV MUST be zero-padded so that the TLV is 4-octet aligned.

Value (variable): contains the RSVP ERROR_SPEC or USER_ERROR_SPEC
Object,
object, as specified in [RFC2205] and [RFC5284], including the object
header.

8. IANA Considerations

The code points described below have been allocated for the protocol
elements defined in this document.

8.1. PCE Capabilities in IGP Advertisements

The following bits have been reigstered in the "Path Computation
Element (PCE) Capability Flags" subregistry of the "Open Shortest
Path First (OSPF) Parameters" registry:

Bit Description Reference
--- ------------------------------- -------------
11 Active Stateful stateful PCE capability This document
12 Passive Stateful stateful PCE capability This document

8.2. PCEP Messages

The following message types have been allocated within the "PCEP
Messages" subregistry of the "Path Computation Element Protocol
(PCEP) Numbers" registry:

Value Description Reference
----- ------------ -------------
10 Report This document
11 Update This document

8.3. PCEP Objects

The following object-class values and object types have been
allocated within the "PCEP Objects" subregistry of the "Path
Computation Element Protocol (PCEP) Numbers" registry:

Object-Class Value Name Reference
------------------ ---------------- -------------
32 LSP This document
Object-Type
0: Reserved
1: LSP

33 SRP This document
Object-Type
0: Reserved
1: SRP

8.4. LSP Object

A new subregistry, named "LSP Object Flag Field", has been created
within the "Path Computation Element Protocol (PCEP) Numbers"
registry to manage the Flag field of the LSP object. New values are
assigned by Standards Action [RFC8126]. Each bit should be tracked
with the following qualities:

o Bit number (counting from bit 0 as the most significant bit)

o Capability description

o Defining RFC

The following values are defined in this document:

Bit Description Reference
--- -------------------- -------------
0-4 Reserved Unassigned This document
5-7 Operational (3 bits) This document
8 Administrative This document
9 Remove This document
10 SYNC This document
11 Delegate This document

8.5. PCEP-Error Object

The following error types and error values have been registered
within the "PCEP-ERROR Object Error Types and Values" subregistry of
the "Path Computation Element Protocol (PCEP) Numbers" registry:

Error-Type Meaning
---------- -------------------------------------------------------
6 Mandatory Object missing

Error-value
8: LSP Object object missing
9: ERO Object object missing
10: SRP Object object missing
11: LSP-IDENTIFIERS TLV missing

19 Invalid Operation

Error-value
1: Attempted LSP Update Request for a non-delegated
LSP. The PCEP-ERROR Object object is followed by the LSP
Object
object that identifies the LSP.
2: Attempted LSP Update Request if the stateful PCE
capability was not advertised.
3: Attempted LSP Update Request for an LSP identified
by an unknown PLSP-ID.
5: Attempted LSP State Report if stateful PCE
capability was not advertised.

20 LSP State synchronization error Synchronization Error

Error-value
1: A PCE indicates to a PCC that it cannot process
(an otherwise valid) LSP State Report. The PCEP-
ERROR Object object is followed by the LSP Object object that
identifies the LSP.
5: A PCC indicates to a PCE that it cannot complete
the state synchronization. State Synchronization.

8.6. Notification Object

The following Notification Types and Notification Values have been
allocated within the "Notification Object" subregistry of the PCEP
Numbers registry, and to update the reference in the "Path
Computation Element Protocol (PCEP) Numbers" registry:

Notification-Type Name
4 Stateful PCE resource limit exceeded

Notification-value
1: Entering resource limit exceeded state
2: Deprecated
Note that the early allocation included an additional Notification
Value 2 for "Exiting resource limit exceeded state". This
Notification Value is no longer required and has been marked as
"Deprecated".

8.7. PCEP TLV Type Indicators

The following TLV Type Indicator values have been regisered within
the "PCEP TLV Type Indicators" subregistry of the "Path Computation
Element Protocol (PCEP) Numbers" registry. registry:

Value Description Reference
----- ----------------------- -------------
16 STATEFUL-PCE-CAPABILITY This document
17 SYMBOLIC-PATH-NAME This document
18 IPV4-LSP-IDENTIFIERS This document
19 IPV6-LSP-IDENTIFIERS This document
20 LSP-ERROR-CODE This document
21 RSVP-ERROR-SPEC This document

8.8. STATEFUL-PCE-CAPABILITY TLV

A new subregistry, named "STATEFUL-PCE-CAPABILITY TLV Flag Field",
has been created within the "Path Computation Element Protocol (PCEP)
Numbers" registry to manage the Flag field in the STATEFUL-PCE-
CAPABILITY TLV of the PCEP OPEN object (class = 1). New values are
assigned by Standards Action [RFC8126]. Each bit should be tracked
with the following qualities:

o Bit number (counting from bit 0 as the most significant bit)

o Capability description

o Defining RFC

The following values are defined in this document:

Value Description Reference
----- --------------------- -------------
31 LSP-UPDATE-CAPABILITY This document

8.9. LSP-ERROR-CODE TLV

A new sub-registry, subregistry, named "LSP-ERROR-CODE TLV Error Code Field", has
been created within the "Path Computation Element Protocol (PCEP)
Numbers" registry to manage the LSP Error Code field of the LSP-
ERROR-CODE TLV. This field specifies the reason for failure to
update the LSP.

New values are assigned by Standards Action [RFC8126]. Each value
should be tracked with the following qualities: value, meaning, and
defining RFC. The following values are defined in this document:

Value Meaning
--- -------------------------------------
0 Reserved
1 Unknown reason
2 Limit reached for PCE-controlled LSPs
3 Too many pending LSP Update Requests
4 Unacceptable parameters
5 Internal error
6 LSP administratively brought down
7 LSP preempted
8 RSVP signaling error

9. Manageability Considerations

All manageability requirements and considerations listed in [RFC5440]
apply to the PCEP extensions defined in this document. In addition,
requirements and considerations listed in this section apply.

9.1. Control Function and Policy

In addition to configuring specific PCEP session parameters, as
specified in [RFC5440], Section 8.1, a PCE or PCC implementation MUST
allow configuring the stateful PCEP capability and the LSP Update
capability. A PCC implementation SHOULD allow the operator to
specify multiple candidate PCEs for and a delegation preference for
each candidate PCE. A PCC SHOULD allow the operator to specify an
LSP delegation policy where LSPs are delegated to the most-preferred
online PCE. A PCC MAY allow the operator to specify different LSP
delegation policies.

A PCC implementation that allows concurrent connections to multiple
PCEs SHOULD allow the operator to group the PCEs by administrative
domains, and it MUST NOT advertise LSP existence and state to a PCE
if the LSP is delegated to a PCE in a different group.

A PCC implementation SHOULD allow the operator to specify whether the
PCC will advertise LSP existence and state for LSPs that are not
controlled by any PCE (for example, LSPs that are statically
configured at the PCC).

A PCC implementation SHOULD allow the operator to specify both the
Redelegation Timeout Interval and the State Timeout Interval. The
default value of the Redelegation Timeout Interval SHOULD be set to
30 seconds. An operator MAY also configure a policy that will
dynamically adjust the Redelegation Timeout Interval, for example
setting it to zero when the PCC has an established session to a
backup PCE. The default value for the State Timeout Interval SHOULD
be set to 60 seconds.

After the expiration of the State Timeout Interval, the LSP reverts
to operator-defined default parameters. A PCC implementation MUST
allow the operator to specify the default LSP parameters. To achieve
a behavior where the LSP retains the parameters set by the PCE until
such time that the PCC makes a change to them, a State Timeout
Interval of infinity SHOULD be used. Any changes to LSP parameters
SHOULD be done in a make-before-break fashion.

LSP Delegation delegation is controlled by operator-defined policies on a PCC.
LSPs are delegated individually -- different LSPs may be delegated to
different PCEs. An LSP is delegated to at most one PCE at any given
point in time. A PCC implementation SHOULD support the delegation
policy, when all PCC's LSPs are delegated to a single PCE at any
given time. Conversely, the policy revoking the delegation for all
PCC's LSPs SHOULD also be supported.

A PCC implementation SHOULD allow the operator to specify delegation
priority for PCEs. This effectively defines the primary PCE and one
or more backup PCEs to which a primary PCE's LSPs can be delegated
when the primary PCE fails.

Policies defined for stateful PCEs and PCCs should eventually fit in
the policy-enabled path computation framework defined in [RFC5394],
and the framework should be extended to support stateful PCEs.

9.2. Information and Data Models

The PCEP YANG module [PCEP-YANG] should include:

o advertised stateful capabilities and synchronization status per
PCEP session.

o the delegation status of each configured LSP.

The PCEP MIB [RFC7420] could also be updated to include this
information.

9.3. Liveness Detection and Monitoring

PCEP extensions defined in this document do not require any new
mechanisms beyond those already defined in [RFC5440], Section 8.3.

9.4. Verifying Correct Operation

Mechanisms defined in [RFC5440], Section 8.4 also apply to PCEP
extensions defined in this document. In addition to monitoring
parameters defined in [RFC5440], a stateful PCC-side PCEP
implementation SHOULD provide the following parameters:

o Total number of LSP updates Updates

o Number of successful LSP updates Updates

o Number of dropped LSP updates Updates

o Number of LSP updates Updates where LSP setup failed

A PCC implementation SHOULD provide a command to show for each LSP
whether it is delegated, and if so, to which PCE.

A PCC implementation SHOULD allow the operator to manually revoke LSP
delegation.

9.5. Requirements on Other Protocols and Functional Components

PCEP extensions defined in this document do not put new requirements
on other protocols.

9.6. Impact on Network Operation

Mechanisms defined in [RFC5440], Section 8.6 also apply to PCEP
extensions defined in this document.

Additionally, a PCEP implementation SHOULD allow a limit to be placed
on the number of LSPs delegated to the PCE and on the rate of PCUpd
and PCRpt messages sent by a PCEP speaker and processed from a peer.
It SHOULD also allow sending a notification when a rate threshold is
reached.

A PCC implementation SHOULD allow a limit to be placed on the rate of
LSP Updates to the same LSP to avoid signaling overload discussed in
Section 10.3.

10. Security Considerations

10.1. Vulnerability

This document defines extensions to PCEP to enable stateful PCEs.
The nature of these extensions and the delegation of path control to
PCEs results in more information being available for a hypothetical
adversary and a number of additional attack surfaces that must be
protected.

The security provisions described in [RFC5440] remain applicable to
these extensions. However, because the protocol modifications
outlined in this document allow the PCE to control path computation
timing and sequence, the PCE defense mechanisms described in
[RFC5440], Section 7.2 are also now applicable to PCC security.

As a general precaution, it is RECOMMENDED that these PCEP extensions
only be activated on authenticated and encrypted sessions across PCEs
and PCCs belonging to the same administrative authority, using
Transport Layer Security (TLS) [PCEPS], as per the recommendations
and best current practices in [RFC7525].

The following sections identify specific security concerns that may
result from the PCEP extensions outlined in this document along with
recommended mechanisms to protect PCEP infrastructure against related
attacks.

10.2. LSP State Snooping

The stateful nature of this extension explicitly requires LSP status
updates to be sent from PCC to PCE. While this gives the PCE the
ability to provide more optimal computations to the PCC, it also
provides an adversary with the opportunity to eavesdrop on decisions
made by network systems external to PCE. This is especially true if
the PCC delegates LSPs to multiple PCEs simultaneously.

Adversaries may gain access to this information by eavesdropping on
unsecured PCEP sessions and might then use this information in
various ways to target or optimize attacks on network infrastructure,
for example, by flexibly countering anti-DDoS measures being taken to
protect the network or by determining choke points in the network
where the greatest harm might be caused.

PCC implementations that allow concurrent connections to multiple
PCEs SHOULD allow the operator to group the PCEs by administrative
domains, and they MUST NOT advertise LSP existence and state to a PCE
if the LSP is delegated to a PCE in a different group.

10.3. Malicious PCE

The LSP delegation mechanism described in this document allows a PCC
to grant effective control of an LSP to the PCE for the duration of a
PCEP session. While this enables PCE control of the timing and
sequence of path computations within and across PCEP sessions, it
also introduces a new attack vector: an attacker may flood the PCC
with PCUpd messages at a rate that exceeds either the PCC's ability
to process them or the network's ability to signal the changes, by
either spoofing messages or compromising the PCE itself.

A PCC is free to revoke an LSP delegation at any time without needing
any justification. A defending PCC can do this by enqueueing the
appropriate PCRpt message. As soon as that message is enqueued in
the session, the PCC is free to drop any incoming PCUpd messages
without additional processing.

10.4. Malicious PCC

A stateful session also results in an increased attack surface by
placing a requirement for the PCE to keep an LSP state replica for
each PCC. It is RECOMMENDED that PCE implementations provide a limit
on resources a single PCC can occupy. A PCE implementing such a
limit MUST send a PCNtf message with notification-type 4 (Stateful
PCE resource limit exceeded) and notification-value 1 (Entering
resource limit exceeded state) upon receiving an LSP State Report
causing it to exceed this threshold.

Delegation of LSPs can create further strain on PCE resources and a
PCE implementation MAY preemptively give back delegations if it finds
itself lacking the resources needed to effectively manage the
delegation. Since the delegation state is ultimately controlled by
the PCC, PCE implementations SHOULD provide throttling mechanisms to
prevent strain created by flaps of either a PCEP session or an LSP
delegation.

11. References

11.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <http://www.rfc-editor.org/info/rfc2205>. <https://www.rfc-editor.org/info/rfc2205>.

[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,
<http://www.rfc-editor.org/info/rfc3209>.
<https://www.rfc-editor.org/info/rfc3209>.

[RFC5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
January 2008, <http://www.rfc-editor.org/info/rfc5088>. <https://www.rfc-editor.org/info/rfc5088>.

[RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
January 2008, <http://www.rfc-editor.org/info/rfc5089>. <https://www.rfc-editor.org/info/rfc5089>.

[RFC5284] Swallow, G. and A. Farrel, "User-Defined Errors for RSVP",
RFC 5284, DOI 10.17487/RFC5284, August 2008,
<http://www.rfc-editor.org/info/rfc5284>.
<https://www.rfc-editor.org/info/rfc5284>.

[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<http://www.rfc-editor.org/info/rfc5440>.
<https://www.rfc-editor.org/info/rfc5440>.

[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, DOI 10.17487/RFC5511, April
2009, <http://www.rfc-editor.org/info/rfc5511>. <https://www.rfc-editor.org/info/rfc5511>.

[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<http://www.rfc-editor.org/info/rfc8051>.
<https://www.rfc-editor.org/info/rfc8051>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <http://www.rfc-editor.org/info/rfc8174>. <https://www.rfc-editor.org/info/rfc8174>.

11.2. Informative References

[MPLS-PC] Chaieb, I., Le Roux, JL., and B. Cousin, "Improved MPLS-TE
LSP Path Computation using Preemption", Global
Information Infrastructure Symposium,
DOI 10.1109/GIIS.2007.4404195, July 2007.

[MXMN-TE] Danna, E., Mandal, S., and A. Singh, "A practical
algorithm for balancing the max-min fairness and
throughput objectives in traffic engineering", INFOCOM,
2012 Proceedings IEEE, pp. 846-854,
DOI 10.1109/INFCOM.2012.6195833, March 2012.

[PCE-Init-LSP]
Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", Work in Progress, draft-ietf-pce-pce-initiated-
lsp-10, June 2017.

[PCEP-GMPLS]
Margaria, C., de Dios, O., and F. Zhang, "PCEP extensions
for GMPLS", Work in Progress, draft-ietf-pce-gmpls-pcep-
extensions-11, October 2015.

[PCEP-YANG]
Dhody, D., Hardwick, J., Beeram, V., and j.
jefftant@gmail.com, "A YANG Data Model for Path
Computation Element Communications Protocol (PCEP)", Work
in Progress, draft-ietf-pce-pcep-yang-05, June 2017.

[PCEPS] Lopez, D., de Dios, O., Wu, Q., and D. Dhody, "Secure
Transport for PCEP", Work in Progress, draft-ietf-pce-
pceps-14, July
pceps-18, September 2017.

[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, DOI 10.17487/RFC2702, September 1999,
<http://www.rfc-editor.org/info/rfc2702>.
<https://www.rfc-editor.org/info/rfc2702>.

[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<http://www.rfc-editor.org/info/rfc3031>.
<https://www.rfc-editor.org/info/rfc3031>.

[RFC3346] Boyle, J., Gill, V., Hannan, A., Cooper, D., Awduche, D.,
Christian, B., and W. Lai, "Applicability Statement for
Traffic Engineering with MPLS", RFC 3346,
DOI 10.17487/RFC3346, August 2002,
<http://www.rfc-editor.org/info/rfc3346>.
<https://www.rfc-editor.org/info/rfc3346>.

[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<http://www.rfc-editor.org/info/rfc3630>.
<https://www.rfc-editor.org/info/rfc3630>.

[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<http://www.rfc-editor.org/info/rfc4655>.
<https://www.rfc-editor.org/info/rfc4655>.

[RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <http://www.rfc-editor.org/info/rfc4657>. <https://www.rfc-editor.org/info/rfc4657>.

[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <http://www.rfc-editor.org/info/rfc5305>. <https://www.rfc-editor.org/info/rfc5305>.

[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
"Policy-Enabled Path Computation Framework", RFC 5394,
DOI 10.17487/RFC5394, December 2008,
<http://www.rfc-editor.org/info/rfc5394>.
<https://www.rfc-editor.org/info/rfc5394>.

[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP) Management Information Base (MIB) Module",
RFC 7420, DOI 10.17487/RFC7420, December 2014,
<http://www.rfc-editor.org/info/rfc7420>.
<https://www.rfc-editor.org/info/rfc7420>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>. <https://www.rfc-editor.org/info/rfc7525>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<http://www.rfc-editor.org/info/rfc8126>.
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
and D. Dhody, "Optimizations of Label Switched Path State
Synchronization Procedures for a Stateful PCE", RFC 8232,
DOI 10.17487/RFC8232, August September 2017,
<http://www.rfc-editor.org/info/rfc8232>.

Acknowledgements

We would like to thank Adrian Farrel, Cyril Margaria, and Ramon
Casellas for their contributions to this document.

We would like to thank Shane Amante, Julien Meuric, Kohei Shiomoto,
Paul Schultz, and Raveendra Torvi for their comments and suggestions.
Thanks also to Jon Hardwick, Oscar Gonzales de Dios, Tomas Janciga,
Stefan Kobza, Kexin Tang, Matej Spanik, Jon Parker, Marek Zavodsky,
Ambrose Kwong, Ashwin Sampath, Calvin Ying, Mustapha Aissaoui,
Stephane Litkowski, and Olivier Dugeon for helpful comments and
discussions.

Contributors

The following people contributed substantially to the content of this
document and should be considered co-authors:

Xian Zhang
Huawei Technology
F3-5-B R&D Center
Huawei Industrial Base, Bantian, Longgang District
Shenzhen, Guangdong 518129
China
Email: zhang.xian@huawei.com

Dhruv Dhody
Huawei Technology
Leela Palace
Bangalore, Karnataka 560008
INDIA
Email: dhruv.dhody@huawei.com

Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: msiva@cisco.com

Authors' Addresses

Edward Crabbe
Oracle
1501 4th Ave, suite 1800
Seattle, WA 98101
United States of America

Email: edward.crabbe@oracle.com

Ina Minei
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America

Email: inaminei@google.com
Jan Medved
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134
United States of America

Email: jmedved@cisco.com

Robert Varga
Pantheon Technologies SRO
Mlynske Nivy 56
Bratislava 821 05
Slovakia

Email: robert.varga@pantheon.tech