PCE Working Group S. Sidor
Internet-Draft Z. Ali
Intended status: Standards Track Cisco Systems, Inc.
Expires: 4 September 2025 C. Li
Huawei Technologies
M. Koldychev
Ciena Corporation
3 March 2025
LSP State Reporting Extensions in Path Computation Element Communication
Protocol (PCEP)
draft-sidor-pce-lsp-state-reporting-extensions-02
Abstract
The Path Computation Element Communication Protocol (PCEP) is defined
in multiple RFCs for enabling communication between Path Computation
Elements (PCEs) and Path Computation Clients (PCCs).
Although PCEP defines various LSP identifiers, attributes, and
constraints, there are operational attributes available on the PCC
that can enhance path computation and improve the debugging
experience, which are not currently supported in PCEP.
This document proposes extensions to PCEP to include:
* Support for explicit or dynamic path types
* Mechanisms to mark LSPs as eligible for use as transit LSPs
* Allowing instantiation of LSP and optionally do fallback to
Binding label/Segment Identifier (SID) allocation by the PCC when
the binding value specified by the PCE is unavailable
These extensions aim to address the existing gaps, enhancing the
overall functionality and operational efficiency of PCEP.
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.
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Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 4 September 2025.
Copyright Notice
Copyright (c) 2025 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of Extensions to PCEP . . . . . . . . . . . . . . . 4
3.1. STATEFUL-PCE-CAPABILITY TLV Flag . . . . . . . . . . . . 4
3.2. LSP-EXTENDED-FLAG TLV Flags . . . . . . . . . . . . . . . 5
3.3. TE-PATH-BINDING TLV Flag . . . . . . . . . . . . . . . . 5
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Binding Label/SID Flags . . . . . . . . . . . . . . . . . 5
4.2. Explicit or Dynamic Path . . . . . . . . . . . . . . . . 6
4.3. Transit Eligible . . . . . . . . . . . . . . . . . . . . 7
5. Manageability Considerations . . . . . . . . . . . . . . . . 7
5.1. Control of Function and Policy . . . . . . . . . . . . . 7
5.2. Information and Data Models . . . . . . . . . . . . . . . 7
5.3. Verify Correct Operations . . . . . . . . . . . . . . . . 7
5.4. Impact On Network Operations . . . . . . . . . . . . . . 8
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6. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. STATEFUL-PCE-CAPABILITY TLV Flag . . . . . . . . . . . . 8
8.2. TE-PATH-BINDING TLV Flag . . . . . . . . . . . . . . . . 9
8.3. LSP-EXTENDED-FLAG TLV Flags . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
A Stateful Path Computation Element (PCE) maintains comprehensive
information on the current network state, including computed Label
Switched Paths (LSPs), reserved network resources, and the pending
path computation requests. This information is critical for
computing paths for traffic-engineering LSPs and any associated or
dependent LSPs.
[RFC9604] outlines the usage of Binding labels/ Segment Identifiers
(SID) usage for an RSVP-TE-signaled Label Switched Paths (LSPs) and
Segment-routing Traffic Engineering paths. It specifies the
possibility of a PCE explicitly requesting the allocation of a
specific binding value by a PCC. However, [RFC9604] only considers
the option of rejecting entire request if the specified binding value
is unavailable, but section 6.2 of [RFC9256] allows also fallback to
a dynamically allocated binding value. This document introduces the
possibility for a PCC to accept such request and include originally
specified binding value for which allocation failed, as well as a
binding value allocated from the dynamic range as a fallback.
This document specifies a set of extensions to Path Computation
Element Communication Protocol(PCEP) to enhance the accuracy of path
computations by considering whether the Binding label/SID of an LSP
can be utilized in the path computation for another LSP, based on LSP
transit eligibility, for example as described in case of LSP
stitching in [I-D.ietf-pce-stateful-interdomain].
Additionally, this document introduces the ability to encode
information regarding whether a path included in an Explicit Route
Object (ERO) was specified explicitly or it is the result of dynamic
path computation executed by a PCE or PCC. Such information can help
in debuggability and can be used by other PCEs in the network to
avoid triggering unnecessary path computations for LSPs where it is
not intended (e.g., PCE-initiated LSPs with explicit path).
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The mechanisms described in this document are applicable to all path
setup types.
2. Terminology
The following terminologies are used in this document:
BSID: Binding Segment Identifier.
ERO: Explicit Route Object.
IGP: Interior Gateway Protocol.
NAI: Node or Adjacency Identifier.
P2P: Point-to-Point.
PCE: Path Computation Element.
PCEP: Path Computation Element Protocol.
SID: Segment Identifier.
SR: Segment Routing.
SR-TE: Segment Routing Traffic Engineering.
LSP: Label Switched Path.
LSPA: Label Switched Path Attributes.
3. Overview of Extensions to PCEP
3.1. STATEFUL-PCE-CAPABILITY TLV Flag
New flags are proposed for the STATEFUL-PCE-CAPABILITY TLV,
originally defined in Section 5.4 of [RFC8231].
* F (BSID-FALLBACK-CAPABILITY): If set, indicates that the PCEP peer
supports LSP creation and fallback to dynamic binding value
allocation if the specific binding value is unavailable, as
detailed in Section 4.1 of this document.
* T (TRANSIT-ELIGIBLE-CAPABILITY): If set, indicates that the PCEP
peer supports the advertisement of the Transit Eligible flag in
the LSP-EXTENDED-FLAG as described in Section 4.3 of this
document.
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3.2. LSP-EXTENDED-FLAG TLV Flags
New flags are introduced in the LSP-EXTENDED-FLAG TLV, which was
initially defined in Section 3.1 of [RFC9357].
* E (Explicit): If set, indicates that the path encoded in the
Explicit Route Object (ERO) is explicitly specified and not
dynamically computed by the PCEP peer.
* T (Transit Eligible): If set, indicates that the binding value of
the LSP can be used in paths computed for other LSPs.
3.3. TE-PATH-BINDING TLV Flag
New flags proposed in the TE-PATH-BINDING TLV, which was originally
defined in Section 4 of [RFC9604].
* A (Allocated): If set, indicates that the binding value encoded in
the TLV represents an allocated binding value.
* D (Down on BSID Unavailability): If set, indicates that LSP can be
created even if specified binding value is unavailable, but LSP
will be in down state.
* F (Fallback): If set, indicates that binding value allocation from
the dynamic range will be performed if the specified binding value
is unavailable.
4. Operation
The PCEP protocol extensions defined in Section 3.3 of this draft
MUST NOT be used if one or both PCEP speakers have not indicated
support for the extensions using the F flag in the STATEFUL-PCE-
CAPABILITY TLV in their respective OPEN messages.
4.1. Binding Label/SID Flags
[RFC9604] specifies the possibility for a PCE to explicitly request
the allocation of a specific binding value by a PCC. If the
specified binding value is unavailable, the entire request MUST be
rejected. However, if either the D or F flag in the TE-PATH-BINDING
TLV is set and the specified binding value in the PCInitiate or PCUpd
message is unavailable, the PCC MUST NOT reject the request and MUST
proceed with the LSP operation as specified in the message. If the D
flag is set, LSP instantiation is allowed, but the LSP SHOULD remain
in an operational down state. If the F flag is set, the PCC MUST do
a fallback to binding value allocation from the dynamic range, as
described in Section 6.2 of [RFC9256].
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If the originally requested binding value and the allocated binding
value differ, two instances of the TE-PATH-BINDING TLV MUST be
included in the PCRpt message:
* A TLV instance with requested binding value with the A flag
cleared
* A TLV instance with allocated binding value with the A flag set
The A flag MUST NOT be set if TE-PATH-BINDING TLV is included in
PCInitiate and PCUpd messages as encoded value represents requested
Binding Label/SID.
The A, D and F flags MUST NOT be used if one or both PCEP speakers
have not set the BSID-FALLBACK-CAPABILITY in the STATEFUL-PCE-
CAPABILITY TLV in their respective OPEN messages.
4.2. Explicit or Dynamic Path
[RFC9256] describes various types of Segment Routing (SR) Policy
Candidate Paths and methods to identify them. Specifically, Sections
5.1 and 5.2 are describing explicit and dynamic candidate paths, but
there is currently no way to encode this information in PCEP. A
similar limitation applies to LSPs of other path setup types.
For instance, if an operator requests the creation of a PCE-Initiated
Candidate Path with an Explicit Path, then such path will be encoded
in the ERO object of the PCInitiate message sent to the PCC. If the
delegation of such LSP is transferred to another PCE, the new PCE
will not know whether the path of the LSP was computed dynamically or
explicitly specified by the operator.
Even if similar problem does not exist for LSPs originated on the
PCC, information about the type of path may be valuable for other
purposes, such as debuggability.
For LSPs initiated by PCC, the E flag value is initially set by the
PCC in the PCRpt message and the PCE MUST set the flag value in PCUpd
messages for such LSP based on the last reported state.
For PCE-initiated LSPs, the E flag value is initially set by the PCE
in PCInitiate message but MAY be modified in the PCUpd messages. The
PCC MUST set the flag value in PCRpt messages for such LSP based on
the value received from the last PCInitiate or PCUpd message.
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4.3. Transit Eligible
The T flag in the LSP-EXTENDED-FLAG TLV MUST NOT be set unless the
TRANSIT-ELIGIBLE-CAPABILITY is supported by both PCEP peers.
If the TRANSIT-ELIGIBLE-CAPABILITY is not advertised, the PCE
implementation MAY use a local policy to determine the value of the
Transit Eligible flag.
For PCC-initiated LSPs, the T flag value is initially set by the PCC
in the PCRpt message. The PCE MUST set the flag value in PCUpd
messages for these LSPs based on the last reported state.
For PCE-initiated LSPs, the T flag value is initially set by the PCE
in the PCInitiate message but MAY be modified in subsequent PCUpd
messages. The PCC MUST set the flag value in PCRpt messages for
these LSPs based on the value received from the latest PCInitiate or
PCUpd message.
5. Manageability Considerations
All manageability requirements and considerations listed in
[RFC5440], [RFC8231] and [RFC8281] apply to PCEP protocol extensions
defined in this document. In addition, requirements and
considerations listed in this section apply.
5.1. Control of Function and Policy
A PCE or PCC implementation MAY allow the capability of supporting
PCEP extensions introduced in this document to be enabled/disabled as
part of the global configuration.
5.2. Information and Data Models
An implementation SHOULD allow the operator to view the capability
defined in this document. Sections 4.1 and 4.1.1 of
[I-D.ietf-pce-pcep-yang] should be extended to include the capability
introduced in Section 3.1 for the PCEP peer.
5.3. Verify Correct Operations
Operation verification requirements already listed in [RFC5440],
[RFC8231], [RFC8281] and [RFC8664] are applicable to mechanisms
defined in this document.
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5.4. Impact On Network Operations
The mechanisms defined in [RFC5440], [RFC8231], and [RFC8281] also
apply to the PCEP extensions defined in this document.
6. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to RFC 7942.]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
7. Security Considerations
The security considerations described in [RFC5440], [RFC8231],
[RFC8253], [RFC8281], [RFC8664].
8. IANA Considerations
8.1. STATEFUL-PCE-CAPABILITY TLV Flag
IANA maintains a registry, named "STATEFUL-PCE-CAPABILITY TLV Flag
Field", within the "Path Computation Element Protocol (PCEP) Numbers"
registry group to manage the Flags field of the STATEFUL-PCE-
CAPABILITY TLV. IANA is requested to make the following assignments:
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+======+=================================+===============+
| Bit | Description | Reference |
+======+=================================+===============+
+------+---------------------------------+---------------+
| TBA1 | F (BSID-FALLBACK-CAPABILITY) | This document |
+------+---------------------------------+---------------+
| TBA2 | T (TRANSIT-ELIGIBLE-CAPABILITY) | This document |
+------+---------------------------------+---------------+
Table 1
8.2. TE-PATH-BINDING TLV Flag
IANA maintains a registry, named "TE-PATH-BINDING TLV Flag Field",
within the "Path Computation Element Protocol (PCEP) Numbers"
registry group to manage the Flags field of the TE-PATH-BINDING TLV.
IANA is requested to make the following assignments:
+======+=================================+===============+
| Bit | Description | Reference |
+======+=================================+===============+
+------+---------------------------------+---------------+
| TBA3 | A (Allocated) | This document |
+------+---------------------------------+---------------+
| TBA4 | D (Down on BSID Unavailability) | This document |
+------+---------------------------------+---------------+
| TBA5 | F (Fallback) | This document |
+------+---------------------------------+---------------+
Table 2
8.3. LSP-EXTENDED-FLAG TLV Flags
IANA maintains a registry, named "LSP-EXTENDED-FLAG TLV Flag Field",
within the "Path Computation Element Protocol (PCEP) Numbers"
registry group to manage the Flags field of the LSP-EXTENDED-FLAG
TLV. IANA is requested to make the following assignments:
+======+======================+===============+
| Bit | Description | Reference |
+======+======================+===============+
+------+----------------------+---------------+
| TBA6 | E (Explicit) | This document |
+------+----------------------+---------------+
| TBA7 | T (Transit Eligible) | This document |
+------+----------------------+---------------+
Table 3
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9. References
9.1. Normative References
[I-D.ietf-pce-pcep-yang]
Dhody, D., 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-30, 26 January
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-yang-30>.
[I-D.ietf-pce-stateful-interdomain]
Dugeon, O., Meuric, J., Lee, Y., and D. Ceccarelli, "PCEP
Extension for Stateful Inter-Domain Tunnels", Work in
Progress, Internet-Draft, draft-ietf-pce-stateful-
interdomain-06, 6 January 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
stateful-interdomain-06>.
[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>.
[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>.
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[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[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>.
[RFC9604] Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
and C. Li, Ed., "Carrying Binding Label/SID in PCE-Based
Networks", RFC 9604, DOI 10.17487/RFC9604, August 2024,
<https://www.rfc-editor.org/info/rfc9604>.
9.2. Informative References
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
Appendix A. Contributors
Rajesh Melarcode Venkateswaran
Cisco Systems, Inc.
Email: rmelarco@cisco.com
Andrew Stone
Nokia
Email: andrew.stone@nokia.com
Authors' Addresses
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Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
Pribinova 10
811 09 Bratislava
Slovakia
Email: ssidor@cisco.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: c.l@huawei.com
Mike Koldychev
Ciena Corporation
385 Terry Fox Dr.
Kanata Ontario K2K 0L1
Canada
Email: mkoldych@proton.me
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