Internet Engineering Task Force (IETF) Y. Lee

Internet Engineering Task Force (IETF) Y. Lee
Request for Comments: 9504 Samsung
Category: Standards Track H. Zheng
ISSN: 2070-1721 Huawei Technologies
O. Gonzalez de Dios
Telefonica
V. Lopez
Nokia
Z. Ali
Cisco
December 2023

Path Computation Element Communication Protocol (PCEP) Extensions for
Stateful PCE Usage in GMPLS-Controlled Networks

Abstract

The Path Computation Element Communication Protocol (PCEP) has been
extended to support stateful PCE functions where the stateful PCE
maintains information about paths and resource usage within a
network; however, these extensions do not cover all requirements for
GMPLS networks.

This document provides the extensions required for PCEP so as to
enable the usage of a stateful PCE capability in GMPLS-controlled
networks.

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
https://www.rfc-editor.org/info/rfc9504.

Copyright Notice

Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.

Table of Contents

1. Introduction
1.1. Conventions Used in This Document
2. Terminology
3. General Context of Stateful PCE and PCEP for GMPLS
4. Main Requirements
5. Overview of Stateful PCEP Extensions for GMPLS Networks
5.1. Capability Advertisement for Stateful PCEP in GMPLS
5.2. LSP Synchronization
5.3. LSP Delegation and Cleanup
5.4. LSP Operations
6. PCEP Object Extensions
6.1. Existing Extensions Used for Stateful GMPLS
6.2. New Extensions
6.2.1. GMPLS-CAPABILITY TLV in OPEN Object
6.2.2. New LSP Exclusion Subobject in the XRO
6.2.3. New Flags in the LSP-EXTENDED-FLAG TLV in LSP Object
7. Update to Error Handling
7.1. Error Handling in PCEP Capabilities Advertisement
7.2. Error Handling in LSP Reoptimization
7.3. Error Handling in Route Exclusion
7.4. Error Handling for the Generalized END-POINTS Object
8. IANA Considerations
8.1. New Flags in the GMPLS-CAPABILITY TLV
8.2. New Subobject for the Exclude Route Object
8.3. Flags Field for the LSP Exclusion Subobject
8.4. New Flags in the LSP-EXTENDED-FLAGS TLV
8.5. New PCEP Error Codes
9. Manageability Considerations
9.1. Control of Function through Configuration and Policy
9.2. Information and Data Models
9.3. Liveness Detection and Monitoring
9.4. Verifying Correct Operation
9.5. Requirements on Other Protocols and Functional Components
9.6. Impact on Network Operation
10. Security Considerations
11. References
11.1. Normative References
11.2. Informative References
Appendix A. PCEP Messages
A.1. The PCRpt Message
A.2. The PCUpd Message
A.3. The PCInitiate Message
Acknowledgements
Contributors
Authors' Addresses

1. Introduction

[RFC4655] presents the architecture of a PCE-based model for
computing Multiprotocol Label Switching (MPLS) and Generalized MPLS
(GMPLS) Traffic Engineering Label Switched Paths (TE LSPs). To
perform such a constrained computation, a PCE stores the network
topology (i.e., TE links and nodes) and resource information (i.e.,
TE attributes) in its TE Database (TED). A PCE that only maintains a
TED is referred to as a "stateless PCE". [RFC5440] describes the
Path Computation Element Communication Protocol (PCEP) for
interaction between a Path Computation Client (PCC) and a PCE or
between two PCEs, enabling computation of TE LSPs. PCEP is further
extended to support GMPLS-controlled networks as per [RFC8779].

Stateful PCEs are shown to be helpful in many application scenarios,
in both MPLS and GMPLS networks, as illustrated in [RFC8051].
Further discussion of the concept of a stateful PCE can be found in
[RFC7399]. In order for these applications to be able to exploit the
capability of stateful PCEs, extensions to stateful PCEP for GMPLS
are required.

[RFC8051] describes how a stateful PCE can be applied to solve
various problems for MPLS-TE and GMPLS networks and the benefits it
brings to such deployments.

[RFC8231] specifies a set of extensions to PCEP to enable stateful
control of TE LSPs where they are configured on the PCC and control
over them could be delegated to the PCE. Furthermore, [RFC8281]
describes the setup and teardown of PCE-initiated LSPs under the
active stateful PCE model, without the need for local configuration
on the PCC. However, both documents omit the specification for
technology-specific objects and TLVs, and they do not cover GMPLS-
controlled networks (e.g., Wavelength Switched Optical Network
(WSON), Optical Transport Network (OTN), Synchronous Optical Network
(SONET) / Synchronous Digital Hierarchy (SDH)).

This document focuses on the extensions that are necessary in order
for the deployment of stateful PCEs and the requirements for PCE-
initiated LSPs in GMPLS-controlled networks. Section 3 provides a
general context of the usage of stateful PCEs and PCEP for GMPLS.
The various requirements for stateful GMPLS, including PCE initiation
for GMPLS LSPs, are provided in Section 4. An overview of the PCEP
extensions is specified in Section 5. A solution to address such
requirements with PCEP object extensions is specified in Section 6.

1.1. Conventions Used in This Document

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

Terminology used in this document is the same as terminology used in
[RFC5440], [RFC8231], [RFC8281], and [RFC8779].

3. General Context of Stateful PCE and PCEP for GMPLS

This section is built on the basis of stateful PCEs specified in
[RFC8231] and PCEP for GMPLS specified in [RFC8779].

The operation of a stateful PCE on LSPs can be divided into two
types: active stateful PCE and passive stateful PCE (as described in
[RFC8051]).

* For active stateful PCEs, a Path Computation Update Request
(PCUpd) message is sent from the PCE to the PCC to update the LSP
state for the LSPs delegated to the PCE. Any changes to the
delegated LSPs generate a Path Computation State Report (PCRpt)
message from the PCC to the PCE to convey the changes of the LSPs.
Any modifications to the objects and TLVs that are identified in
this document to support GMPLS-specific attributes will be carried
in the PCRpt and PCUpd messages.

* For passive stateful PCEs, Path Computation Request (PCReq) and
Path Computation Reply (PCRep) messages are used to request path
computation. GMPLS-specific objects and TLVs are defined in
[RFC8779], which this document builds on and adds the stateful PCE
aspects where applicable. A passive stateful PCE makes use of
PCRpt messages when reporting LSP state changes sent by PCCs to
PCEs. Any modifications to the objects and TLVs that are
identified in this document to support GMPLS-specific attributes
will be carried in the PCRpt message.

Furthermore, the LSP Initiation function of PCEP is defined in
[RFC8281] to allow the PCE to initiate LSP establishment after the
path is computed. An LSP Initiate Request (PCInitiate) message is
used to trigger the end node to set up the LSP. Any modifications to
the objects and TLVs that are identified in this document to support
GMPLS-specific attributes will be carried in the PCInitiate messages.

[RFC8779] defines GMPLS-specific objects and TLVs in stateless PCEP;
this document makes use of these objects and TLVs without
modifications where applicable. Where these objects and TLVs require
modifications to incorporate stateful PCEs, they are described in
this document. PCE-initiated LSPs follow the principle specified in
[RFC8281], and the GMPLS-specific extensions are also included in
this document.

4. Main Requirements

This section notes the main functional requirements for PCEP
extensions to support stateful PCEs for use in GMPLS-controlled
networks, based on the description in [RFC8051]. Many requirements
are common across a variety of network types (e.g., MPLS-TE networks
and GMPLS networks) and the protocol extensions to meet the
requirements are already described in [RFC8231] (such as LSP update,
delegation, and state synchronization/report). Protection context
information that describes the GMPLS requirement can also follow the
description in [RFC8745]. This document does not repeat the
description of those protocol extensions. This document presents
protocol extensions for a set of requirements that are specific to
the use of a stateful PCE in a GMPLS-controlled network.

The requirements for GMPLS-specific stateful PCEs are as follows:

* Advertisement of the stateful PCE capability. This generic
requirement is covered in Section 5.4 of [RFC8231]. The GMPLS-
CAPABILITY TLV specified in Section 2.1 of [RFC8779] and its
extension in this document need to be advertised as well.

* All the PCEP messages need to be capable of indicating GMPLS-
specific switching capabilities. GMPLS LSP creation,
modification, and deletion require knowledge of LSP switching
capabilities (e.g., Time-Division Multiplex Capable (TDM), Layer 2
Switch Capable (L2SC), OTN-TDM, Lambda Switch Capable (LSC), etc.)
and the Generalized Payload Identifier (G-PID) to be used
according to [RFC3471] and [RFC3473]. It also requires that
traffic parameters that are both data flow and technology specific
be defined. These traffic parameters are also known as "Traffic
Specification" or "Tspec". Such information would need to be
included in various PCEP messages.

* In some technologies, path calculation is tightly coupled with
label selection along the route. For example, path calculation in
a Wavelength Division Multiplexing (WDM) network may include
lambda continuity and/or lambda feasibility constraints; hence, a
path computed by the PCE is associated with a specific lambda
(label). Thus, in such networks, the label information needs to
be provided to a PCC in order for a PCE to initiate GMPLS LSPs
under the active stateful PCE model, i.e., Explicit Label Control
(ELC) may be required.

* Stateful PCEP messages also need to indicate the protection
context information for the LSP specified by GMPLS, as defined in
[RFC4872] and [RFC4873].

5. Overview of Stateful PCEP Extensions for GMPLS Networks

5.1. Capability Advertisement for Stateful PCEP in GMPLS

Capability advertisement is specified in [RFC8231]; it can be
achieved by using the STATEFUL-PCE-CAPABILITY TLV in the Open
message. Another GMPLS-CAPABILITY TLV is defined in [RFC8779]. A
subregistry to manage the Flag field of the GMPLS-CAPABILITY TLV has
been created by IANA as requested by [RFC8779]. The following bits
are introduced by this document in the GMPLS-CAPABILITY TLV as flags
to indicate the capability for LSP report, update, and initiation in
GMPLS networks: LSP-REPORT-CAPABILITY (31), LSP-UPDATE-CAPABILITY
(30), and LSP-INSTANTIATION-CAPABILITY (29).

5.2. LSP Synchronization

After the session between the PCC and a stateful PCE is initialized,
the PCE must learn the state of a PCC's LSPs (including its
attributes) before it can perform path computations or update LSP
attributes in a PCC. This process is known as "LSP state
synchronization". The LSP attributes, including bandwidth,
associated route, and protection information etc., are stored by the
PCE in the LSP database (LSP-DB). Note that, as described in
[RFC8231], the LSP state synchronization covers both the bulk
reporting of LSPs at initialization as well as the reporting of new
or modified LSPs during normal operation. Incremental LSP-DB
synchronization may be desired in a GMPLS-controlled network; it is
specified in [RFC8232].

The format of the PCRpt message is specified in [RFC8231] and
extended in [RFC8623] to include the END-POINTS object. The END-
POINTS object is extended for GMPLS in [RFC8779]. The END-POINTS
object can be carried in the PCRpt message as specified in [RFC8623].
The END-POINTS object type for GMPLS is included in the PCRpt message
as per the same.

The following objects are extended for GMPLS in [RFC8779] and are
also used in the PCRpt in the same manner: BANDWIDTH, LSP Attributes
(LSPA), Include Route Object (IRO), and Exclude Route Object (XRO).
These objects are carried in the PCRpt message as specified in
[RFC8231] (as the attribute-list defined in Section 6.5 of [RFC5440]
and extended by many other documents that define PCEP extensions for
specific scenarios).

The SWITCH-LAYER object is defined in [RFC8282]. This object is
carried in the PCRpt message as specified in Section 3.2 of
[RFC8282].

5.3. LSP Delegation and Cleanup

The LSP delegation and cleanup procedure specified in [RFC8281] are
equally applicable to GMPLS LSPs and this document does not modify
the associated usage.

5.4. LSP Operations

Both passive and active stateful PCE mechanisms in [RFC8231] are
applicable in GMPLS-controlled networks. Remote LSP Initiation in
[RFC8281] is also applicable in GMPLS-controlled networks.

6. PCEP Object Extensions

6.1. Existing Extensions Used for Stateful GMPLS

Existing extensions defined in [RFC8779] can be used in stateful PCEP
with no or slight changes for GMPLS network control, including the
following:

END-POINTS: The END-POINTS object was specified in [RFC8779] to
include GMPLS capabilities. All stateful PCEP messages MUST
include the END-POINTS object with Generalized Endpoint object
type, containing the LABEL-REQUEST TLV. Further note that:

* As per [RFC8779], for stateless GMPLS path computation, the
Generalized END-POINTS object may contain a LABEL-REQUEST and/
or LABEL-SET TLV. In this document, only the LABEL-REQUEST TLV
is used to specify the switching type, encoding type, and G-PID
of the LSP.

* If unnumbered endpoint addresses are used for the LSP, the
UNNUMBERED-ENDPOINT TLV [RFC8779] MUST be used to specify the
unnumbered endpoint addresses.

* The Generalized END-POINTS object MAY contain other TLVs
defined in [RFC8779].

RP: The Request Parameter (RP) object extension (together with the
Routing Granularity (RG) flag defined in [RFC8779]) is applicable
in stateful PCEP for GMPLS networks.

BANDWIDTH: Generalized BANDWIDTH is specified in [RFC8779] to
represent GMPLS features, including asymmetric bandwidth and G-PID
information.

LSPA: LSPA Extensions in Section 2.8 of [RFC8779] are applicable in
stateful PCEP for GMPLS networks.

IRO: IRO Extensions in Section 2.6 of [RFC8779] are applicable in
stateful PCEP for GMPLS networks.

XRO: XRO Extensions in Section 2.7 of [RFC8779] are applicable in
stateful PCEP for GMPLS networks. A new flag is defined in
Section 6.2.3 of this document.

ERO: The Explicit Route Object (ERO) is not extended in [RFC8779],
nor is it in this document.

SWITCH-LAYER: The SWITCH-LAYER definition in Section 3.2 of
[RFC8282] is applicable in stateful PCEP messages for GMPLS
networks.

6.2. New Extensions

6.2.1. GMPLS-CAPABILITY TLV in OPEN Object

In [RFC8779], IANA allocates value 45 (GMPLS-CAPABILITY) from the
"PCEP TLV Type Indicators" subregistry. This specification adds
three flags to the Flag field of this TLV to indicate the Report,
Update, and Initiation capabilities.

R (LSP-REPORT-CAPABILITY (31) -- 1 bit):
If set to 1 by a PCC, the R flag indicates that the PCC is capable
of reporting the current state of a GMPLS LSP whenever there's a
change to the parameters or operational status of the GMPLS LSP.
If set to 1 by a PCE, the R flag indicates that the PCE is
interested in receiving GMPLS LSP State Reports whenever there is
a parameter or operational status change to the LSP. The LSP-
REPORT-CAPABILITY flag must be advertised by both a PCC and a PCE
for PCRpt messages to be allowed on a PCEP session for GMPLS LSP.

U (LSP-UPDATE-CAPABILITY (30) -- 1 bit):
If set to 1 by a PCC, the U flag indicates that the PCC allows
modification of GMPLS LSP parameters. If set to 1 by a PCE, the U
flag indicates that the PCE is capable of updating GMPLS LSP
parameters. The LSP-UPDATE-CAPABILITY flag must be advertised by
both a PCC and a PCE for PCUpd messages to be allowed on a PCEP
session for GMPLS LSP.

I (LSP-INSTANTIATION-CAPABILITY (29) -- 1 bit):
If set to 1 by a PCC, the I flag indicates that the PCC allows
instantiation of a GMPLS LSP by a PCE. If set to 1 by a PCE, the
I flag indicates that the PCE supports instantiating GMPLS LSPs.
The LSP-INSTANTIATION-CAPABILITY flag must be set by both the PCC
and PCE in order to enable PCE-initiated LSP instantiation.

6.2.2. New LSP Exclusion Subobject in the XRO

[RFC5521] defines a mechanism for a PCC to request or demand that
specific nodes, links, or other network resources be excluded from
paths computed by a PCE. A PCC may wish to request the computation
of a path that avoids all links and nodes traversed by some other
LSP.

To this end, this document defines a new subobject for use with route
exclusion defined in [RFC5521]. The LSP Exclusion subobject is as
follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X|Type (11) | Length | Reserved | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Symbolic Path Name //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: New LSP Exclusion Subobject Format

X: This field is the same as the X-bit defined in the XRO subobjects
in Section 2.1.1 of [RFC5521] where it says:

The X-bit indicates whether the exclusion is mandatory or
desired. 0 indicates that the resource specified MUST be
excluded from the path computed by the PCE. 1 indicates that
the resource specified SHOULD be excluded from the path
computed by the PCE, but MAY be included subject to PCE policy
and the absence of a viable path that meets the other
constraints and excludes the resource.

Type: The subobject type for an LSP Exclusion subobject. Value of
11.

Length: The Length contains the total length of the subobject in
bytes, including the Type and Length fields.

Reserved: Reserved MUST be set to zero on transmission and ignored
on receipt.

Flags: This field may be used to further specify the exclusion
constraint with regard to the LSP. Currently, no flags are
defined.

Symbolic Path Name: This is the identifier given to an LSP. Its
syntax and semantics are identical to those of the Symbolic Path
Name field defined in Section 7.3.2 of [RFC8231] where it says:
"symbolic name for the LSP, unique in the PCC. It SHOULD be a
string of printable ASCII characters, without a NULL terminator."
The symbolic path name in the LSP Exclusion subobject MUST only
vary from being a string of printable ASCII characters without a
NULL terminator when it is matching the value contained in another
subobject. It is worth noting that given that the symbolic path
name is unique in the context of the headnode, only LSPs that
share the same headnode or PCC could be excluded.

This subobject MAY be present multiple times in the XRO to exclude
resources from multiple LSPs. When a stateful PCE receives a
PCReq message carrying this subobject, it MUST search for the
identified LSP in its LSP-DB and then exclude from the new path
computation all resources used by the identified LSP.

Note that this XRO subobject could also be used by non-GMPLS LSPs.
The usage of the XRO subobject for any non-GMPLS LSPs is not in
the scope of this document.

6.2.3. New Flags in the LSP-EXTENDED-FLAG TLV in LSP Object

The LSP object is defined in Section 7.3 of [RFC8231], and the new
extended flags TLV is defined in [RFC9357]. This TLV is used in
PCUpd, PCRpt and PCInitiate messages for GMPLS, with the following
flags defined in this document:

G (GMPLS LSP (0) -- 1 bit):
If set to 1, it indicates the LSP is a GMPLS LSP.

B (Bidirectional LSP (1) -- 1 bit):
If set to 0, it indicates a request to create a unidirectional
LSP. If set to 1, it indicates a request to create a
bidirectional co-routed LSP.

RG (Routing Granularity (2-3) -- 2 bits):
The RG flag for GMPLS is also defined in the LSP-EXTENDED-FLAG
TLV. The values are defined as per [RFC8779]:

00: reserved
01: node
10: link
11: label

7. Update to Error Handling

A PCEP-ERROR object is used to report a PCEP error and is
characterized by an Error-Type that specifies the type of error and
an Error-value that provides additional information about the error.
This section adds additional error handling procedures to those
specified in Section 3 of [RFC8779]. Please note that all error
handling specified in Section 3 of [RFC8779] is applicable and MUST
be supported for a stateful PCE in GMPLS networks.

7.1. Error Handling in PCEP Capabilities Advertisement

The PCEP extensions described in this document for stateful PCEs with
GMPLS capabilities MUST NOT be used if the PCE has not advertised its
capabilities with GMPLS as per Section 6.2.1.

If the PCC understands the U flag that indicates the stateful LSP-
UPDATE-CAPABILITY, but did not advertise this capability, then upon
receipt of a PCUpd message for GMPLS LSP from the PCE, it SHOULD
generate a PCErr with Error-Type 19 ("Invalid Operation") Error-value
25 ("Attempted LSP update request for GMPLS if stateful PCE
capability not advertised") and terminate the PCEP session. Such a
PCC MAY decide to utilize the capability even though it did not
advertise support for it.

If the PCE understands the R flag that indicates the stateful LSP-
REPORT-CAPABILITY, but did not advertise this capability, then upon
receipt of a PCRpt message for GMPLS LSP from the PCC, it SHOULD
generate a PCErr with Error-Type 19 ("Invalid Operation") Error-value
26 ("Attempted LSP State Report for GMPLS if stateful PCE capability
not advertised") and terminate the PCEP session. Such a PCE MAY
decide to utilize the capability even though it did not advertise
support for it.

If the PCC understands the I flag that indicates LSP-INSTANTIATION-
CAPABILITY, but did not advertise this capability, then upon receipt
of a PCInitiate message for GMPLS LSP from the PCE, it SHOULD
generate a PCErr with Error-Type 19 ("Invalid Operation") Error-value
27 ("Attempted LSP instantiation request for GMPLS if stateful PCE
instantiation capability for not advertised") and terminate the PCEP
session. Such a PCC MAY decide to utilize the capability even though
it did not advertise support for it.

7.2. Error Handling in LSP Reoptimization

A stateful PCE is expected to perform an LSP reoptimization when
receiving a message with the R bit set in the RP object. If no LSP
state information is available to carry out reoptimization, the
stateful PCE SHOULD report Error-Type 19 ("Invalid Operation") Error-
value 23 ("LSP state info unavailable for reoptimization"), although
such a PCE MAY consider the reoptimization to have successfully
completed. Note that this error message could also be used by non-
GMPLS LSPs.

7.3. Error Handling in Route Exclusion

The LSP Exclusion subobject in XRO, as defined in Section 6.2.2 of
this document, MAY be present multiple times. When a stateful PCE
receives a PCEP message carrying this subobject, it searches for the
identified LSP in its LSP-DB. It then excludes from the new path
computation all the resources used by the identified LSP. If the
stateful PCE cannot recognize the symbolic path name of the
identified LSP, it SHOULD send an error message PCErr reporting
Error-Type 19 ("Invalid Operation") Error-value 24 ("LSP state info
for route exclusion not found"). Along with the unrecognized
symbolic path name, it MAY also provide information to the requesting
PCC using the error-reporting techniques described in [RFC5440]. An
implementation MAY choose to ignore the requested exclusion when the
LSP cannot be found because it could claim that it has avoided using
all resources associated with an LSP that doesn't exist.

7.4. Error Handling for the Generalized END-POINTS Object

Note that the END-POINTS object in stateful PCEP messages was
introduced for Point-to-Multipoint (P2MP) [RFC8623]. Similarly, the
END-POINTS object MUST be carried for the GMPLS LSP. If the END-
POINTS object is missing and the GMPLS flag in LSP-EXTENDED-FLAG is
set, the receiving PCE or PCC MUST send a PCErr message with Error-
Type 6 ("Mandatory Object missing") and Error-value 3 ("END-POINTS
object missing") (defined in [RFC5440]). Similarly, if the END-
POINTS object with the Generalized Endpoint object type is received
but the LSP-EXTENDED-FLAG TLV is missing in the LSP object or the G
flag in the LSP-EXTENDED-FLAG TLV is not set, the receiving PCE or
PCC MUST send a PCErr message with Error-Type 19 ("Invalid
Operation") Error-value 28 ("Use of the Generalized Endpoint object
type for non-GMPLS LSPs").

If the END-POINTS object with Generalized Endpoint object type is
missing the LABEL-REQUEST TLV, the receiving PCE or PCC MUST send a
PCErr message with Error-Type 6 ("Mandatory Object missing") Error-
value 20 ("LABEL-REQUEST TLV missing").

8. IANA Considerations

8.1. New Flags in the GMPLS-CAPABILITY TLV

[RFC8779] defines the GMPLS-CAPABILITY TLV; per that RFC, IANA
created the "GMPLS-CAPABILITY TLV Flag Field" registry to manage the
values of the GMPLS-CAPABILITY TLV's Flag field. This document
registers new bits in this registry as follows:

+=====+==================================+===========+
| Bit | Capability Description | Reference |
+=====+==================================+===========+
| 31 | LSP-REPORT-CAPABILITY (R) | RFC 9504 |
+-----+----------------------------------+-----------+
| 30 | LSP-UPDATE-CAPABILITY (U) | RFC 9504 |
+-----+----------------------------------+-----------+
| 29 | LSP-INSTANTIATION-CAPABILITY (I) | RFC 9504 |
+-----+----------------------------------+-----------+

Table 1

8.2. New Subobject for the Exclude Route Object

IANA maintains the various XRO subobject types within the "XRO
Subobjects" subregistry of the "Path Computation Element Protocol
(PCEP) Numbers" registry. IANA has allocated a codepoint for another
XRO subobject as follows:

+=======+=============+===========+
| Value | Description | Reference |
+=======+=============+===========+
| 11 | LSP | RFC 9504 |
+-------+-------------+-----------+

Table 2

8.3. Flags Field for the LSP Exclusion Subobject

IANA has created a registry named "LSP Exclusion Subobject Flag
Field", within the "Path Computation Element Protocol (PCEP) Numbers"
group, to manage the Flag field of the LSP Exclusion subobject in the
XRO. No flag is currently defined for this Flag field in this
document.

Codespace of the Flag field (LSP Exclusion Subobject)

+=====+========================+===========+
| Bit | Capability Description | Reference |
+=====+========================+===========+
| 0-7 | Unassigned | RFC 9504 |
+-----+------------------------+-----------+

Table 3

New values are to be assigned by Standards Action [RFC8126]. Each
bit should be registered with the following entries:

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

* Capability description

* Reference to defining RFC

8.4. New Flags in the LSP-EXTENDED-FLAGS TLV

[RFC9357] requested IANA to create a subregistry, named the "LSP-
EXTENDED-FLAG TLV Flag Field", within the "Path Computation Element
Protocol (PCEP) Numbers" registry, to manage the Flag field of the
LSP-EXTENDED-FLAG TLV.

IANA has made assignments from this registry as follows:

+=====+=================================+===========+
| Bit | Capability Description | Reference |
+=====+=================================+===========+
| 0 | GMPLS LSP (G) | RFC 9504 |
+-----+---------------------------------+-----------+
| 1 | Bidirectional Co-routed LSP (B) | RFC 9504 |
+-----+---------------------------------+-----------+
| 2-3 | Routing Granularity (RG) | RFC 9504 |
+-----+---------------------------------+-----------+

Table 4

8.5. New PCEP Error Codes

IANA has made the following allocations in the "PCEP-ERROR Object
Error Types and Values" registry.

+============+===========+===========================+===========+
| Error-Type | Meaning | Error-value | Reference |
+============+===========+===========================+===========+
| 6 | Mandatory | 20: LABEL-REQUEST TLV | RFC 9504 |
| | Object | missing | |
| | missing | | |
+------------+-----------+---------------------------+-----------+
| 19 | Invalid | 23: LSP state info | RFC 9504 |
| | Operation | unavailable for | |
| | | reoptimization | |
| | +---------------------------+-----------+
| | | 24: LSP state info for | RFC 9504 |
| | | route exclusion not found | |
| | +---------------------------+-----------+
| | | 25: Attempted LSP update | RFC 9504 |
| | | request for GMPLS if | |
| | | stateful PCE capability | |
| | | not advertised | |
| | +---------------------------+-----------+
| | | 26: Attempted LSP State | RFC 9504 |
| | | Report for GMPLS if | |
| | | stateful PCE capability | |
| | | not advertised | |
| | +---------------------------+-----------+
| | | 27: Attempted LSP | RFC 9504 |
| | | instantiation request for | |
| | | GMPLS if stateful PCE | |
| | | instantiation capability | |
| | | not advertised | |
| | +---------------------------+-----------+
| | | 28: Use of the | RFC 9504 |
| | | Generalized Endpoint | |
| | | object type for non-GMPLS | |
| | | LSPs | |
+------------+-----------+---------------------------+-----------+

Table 5

9. Manageability Considerations

General PCE management considerations are discussed in [RFC4655] and
[RFC5440], and GMPLS-specific PCEP management considerations are
described in [RFC8779]. In this document, the management
considerations for stateful PCEP extension in GMPLS are described.

This section follows the guidance of [RFC6123].

9.1. Control of Function through Configuration and Policy

In addition to the parameters already listed in Section 8.1 of
[RFC5440], a PCEP implementation SHOULD allow configuration of the
following PCEP session parameters on a PCC. However, an
implementation MAY choose to make these features available on all
PCEP sessions:

* The ability to send stateful PCEP messages for GMPLS LSPs.

* The ability to use path computation constraints (e.g., XRO).

In addition to the parameters already listed in Section 8.1 of
[RFC5440], a PCEP implementation SHOULD allow configuration of the
following PCEP session parameters on a PCE:

* The ability to compute paths in a stateful manner in GMPLS
networks.

* A set of GMPLS-specific constraints.

These parameters may be configured as default parameters for any PCEP
session the PCEP speaker participates in or they may apply to a
specific session with a given PCEP peer or a specific group of
sessions with a specific group of PCEP peers.

9.2. Information and Data Models

The YANG module in [PCE-PCEP-YANG] can be used to configure and
monitor PCEP states and messages. To make sure that the YANG module
is useful for the extensions as described in this document, it would
need to include advertised GMPLS stateful capabilities etc. A future
version of [PCE-PCEP-YANG] will include this.

As described in [YANG-PATH-COMPUTATION], a YANG-based interface can
be used in some cases to request GMPLS path computations, instead of
PCEP. Refer to [YANG-PATH-COMPUTATION] for details.

9.3. Liveness Detection and Monitoring

This document makes no change to the basic operation of PCEP, so
there are no changes to the requirements for liveness detection and
monitoring in [RFC4657] and Section 8.3 of [RFC5440].

9.4. Verifying Correct Operation

This document makes no change to the basic operations of PCEP and the
considerations described in Section 8.4 of [RFC5440]. New errors
defined by this document should satisfy the requirement to log error
events.

9.5. Requirements on Other Protocols and Functional Components

When the detailed route information is included for LSP state
synchronization (either at the initial stage or during the LSP State
Report process), this requires the ingress node of an LSP to carry
the Record Route Object (RRO) object in order to enable the
collection of such information.

9.6. Impact on Network Operation

The management considerations concerning the impact on network
operations described in Section 4.6 of [RFC8779] apply here.

10. Security Considerations

The security considerations elaborated in [RFC5440] apply to this
document. The PCEP extensions to support GMPLS-controlled networks
should be considered under the same security as for MPLS networks, as
noted in [RFC7025]. Therefore, the PCEP extension to support GMPLS
specified in [RFC8779] is used as the foundation of this document;
the security considerations in [RFC8779] should also be applicable to
this document. The secure transport of PCEP specified in [RFC8253]
allows the usage of Transport Layer Security (TLS). The same can
also be used by the PCEP extension defined in this document.

This document provides additional extensions to PCEP so as to
facilitate stateful PCE usage in GMPLS-controlled networks, on top of
[RFC8231] and [RFC8281]. Security issues caused by the extension in
[RFC8231] and [RFC8281] are not altered by the additions in this
document. The security considerations in [RFC8231] and [RFC8281],
including both issues and solutions, apply to this document as well.

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,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<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, <https://www.rfc-editor.org/info/rfc5511>.

[RFC5521] Oki, E., Takeda, T., and A. Farrel, "Extensions to the
Path Computation Element Communication Protocol (PCEP) for
Route Exclusions", RFC 5521, DOI 10.17487/RFC5521, April
2009, <https://www.rfc-editor.org/info/rfc5521>.

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

[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.

[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.

[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.

[RFC8779] Margaria, C., Ed., Gonzalez de Dios, O., Ed., and F.
Zhang, Ed., "Path Computation Element Communication
Protocol (PCEP) Extensions for GMPLS", RFC 8779,
DOI 10.17487/RFC8779, July 2020,
<https://www.rfc-editor.org/info/rfc8779>.

[RFC9357] Xiong, Q., "Label Switched Path (LSP) Object Flag
Extension for Stateful PCE", RFC 9357,
DOI 10.17487/RFC9357, February 2023,
<https://www.rfc-editor.org/info/rfc9357>.

11.2. Informative References

[PCE-PCEP-YANG]
Dhody, D., Ed., Beeram, V. P., Hardwick, J., and J.
Tantsura, "A YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", Work in Progress,
Internet-Draft, draft-ietf-pce-pcep-yang-22, 11 September
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-yang-22>.

[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description",
RFC 3471, DOI 10.17487/RFC3471, January 2003,
<https://www.rfc-editor.org/info/rfc3471>.

[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003,
<https://www.rfc-editor.org/info/rfc3473>.

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

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

[RFC4872] Lang, J.P., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
Ed., "RSVP-TE Extensions in Support of End-to-End
Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC 4872, DOI 10.17487/RFC4872, May 2007,
<https://www.rfc-editor.org/info/rfc4872>.

[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
"GMPLS Segment Recovery", RFC 4873, DOI 10.17487/RFC4873,
May 2007, <https://www.rfc-editor.org/info/rfc4873>.

[RFC6123] Farrel, A., "Inclusion of Manageability Sections in Path
Computation Element (PCE) Working Group Drafts", RFC 6123,
DOI 10.17487/RFC6123, February 2011,
<https://www.rfc-editor.org/info/rfc6123>.

[RFC7025] Otani, T., Ogaki, K., Caviglia, D., Zhang, F., and C.
Margaria, "Requirements for GMPLS Applications of PCE",
RFC 7025, DOI 10.17487/RFC7025, September 2013,
<https://www.rfc-editor.org/info/rfc7025>.

[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path
Computation Element Architecture", RFC 7399,
DOI 10.17487/RFC7399, October 2014,
<https://www.rfc-editor.org/info/rfc7399>.

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

[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,
<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, September 2017,
<https://www.rfc-editor.org/info/rfc8232>.

[RFC8282] Oki, E., Takeda, T., Farrel, A., and F. Zhang, "Extensions
to the Path Computation Element Communication Protocol
(PCEP) for Inter-Layer MPLS and GMPLS Traffic
Engineering", RFC 8282, DOI 10.17487/RFC8282, December
2017, <https://www.rfc-editor.org/info/rfc8282>.

[RFC8623] Palle, U., Dhody, D., Tanaka, Y., and V. Beeram, "Stateful
Path Computation Element (PCE) Protocol Extensions for
Usage with Point-to-Multipoint TE Label Switched Paths
(LSPs)", RFC 8623, DOI 10.17487/RFC8623, June 2019,
<https://www.rfc-editor.org/info/rfc8623>.

[RFC8745] Ananthakrishnan, H., Sivabalan, S., Barth, C., Minei, I.,
and M. Negi, "Path Computation Element Communication
Protocol (PCEP) Extensions for Associating Working and
Protection Label Switched Paths (LSPs) with Stateful PCE",
RFC 8745, DOI 10.17487/RFC8745, March 2020,
<https://www.rfc-editor.org/info/rfc8745>.

[YANG-PATH-COMPUTATION]
Busi, I., Ed., Belotti, S., Ed., de Dios, O. G., Sharma,
A., and Y. Shi, "A YANG Data Model for requesting path
computation", Work in Progress, Internet-Draft, draft-
ietf-teas-yang-path-computation-21, 7 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
yang-path-computation-21>.

Appendix A. PCEP Messages

This section uses the Routing Backus-Naur Form (RBNF) [RFC5511] to
illustrate the PCEP messages. The RBNF in this section is reproduced
for informative purposes. It is also expanded to show the GMPLS-
specific objects.

A.1. The PCRpt Message

According to [RFC8231], the PCRpt message is used to report the
current state of an LSP. This document extends the message in
reporting the status of LSPs with GMPLS characteristics.

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>
[<END-POINTS>]
<path>

Where:

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

Where:

* The END-POINTS object MUST be carried in a PCRpt message when the
G flag is set in the LSP-EXTENDED-FLAG TLV in the LSP object for a
GMPLS LSP.

* <intended-path> is represented by the ERO object defined in
Section 7.9 of [RFC5440] and augmented in [RFC8779] with ELC.

* <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 many other documents that
define PCEP extensions for specific scenarios as shown below:

<attribute-list> ::= [<of-list>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>][<XRO>]
[<INTER-LAYER>]
[<SWITCH-LAYER>]
[<REQ-ADAP-CAP>]
[<SERVER-INDICATION>]

A.2. The PCUpd Message

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>
[<END-POINTS>]
<path>

Where:

<path> ::= <intended-path><intended-attribute-list>

Where:

* The END-POINTS object MUST be carried in a PCUpd message for the
GMPLS LSP.

* <intended-path> is represented by the ERO object defined in
Section 7.9 of [RFC5440], augmented in [RFC8779] with ELC.

* <intended-attribute-list> is the attribute-list defined in
[RFC5440] and extended by many other documents that define PCEP
extensions for specific scenarios and as shown for PCRpt above.

A.3. The PCInitiate Message

According to [RFC8281], the PCInitiate message is used allow LSP
Initiation. This document extends the message in initiating LSPs
with GMPLS characteristics. The format of a PCInitiate message is as
follows:

<PCInitiate Message> ::= <Common Header>
<PCE-initiated-lsp-list>

Where:

<Common Header> is defined in <xref target="RFC5440" />.
<PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
[<PCE-initiated-lsp-list>]
<PCE-initiated-lsp-request> ::= (<PCE-initiated-lsp-instantiation>|
<PCE-initiated-lsp-deletion>)
<PCE-initiated-lsp-instantiation> ::= <SRP>
<LSP>
[<END-POINTS>]
<ERO>
[<attribute-list>]
<PCE-initiated-lsp-deletion> ::= <SRP>
<LSP>

The format of the PCInitiate message is unchanged from Section 5.1 of
[RFC8281]. All fields are similar to the PCRpt and the PCUpd
messages.

Acknowledgements

We would like to thank Adrian Farrel, Cyril Margaria, George Swallow,
Jan Medved, Sue Hares, and John Scudder for the useful comments and
discussions.

Thanks to Dhruv Dhody for Shepherding this document and providing
useful comments.

Contributors

Xian Zhang
Huawei Technologies
Email: [email protected]

Dhruv Dhody
Huawei Technology
India
Email: [email protected]

Yi Lin
Huawei Technologies
Email: [email protected]

Fatai Zhang
Huawei Technologies
Email: [email protected]

Ramon Casellas
CTTC
Av. Carl Friedrich Gauss n7
08860 Barcelona Castelldefels
Spain
Email: [email protected]

Siva Sivabalan
Cisco Systems
Email: [email protected]

Clarence Filsfils
Cisco Systems
Email: [email protected]

Robert Varga
Pantheon Technologies
Email: [email protected]

Authors' Addresses

Young Lee
Samsung
Email: [email protected]

Haomian Zheng
Huawei Technologies
Email: [email protected]

Oscar Gonzalez de Dios
Telefonica
Email: [email protected]

Victor Lopez
Nokia
Email: [email protected]

Zafar Ali
Cisco
Email: [email protected]