Internet Engineering Task Force (IETF) Y. Lee

Internet Engineering Task Force (IETF) Y. Lee
Request for Comments: 9358 Samsung Electronics
Category: Standards Track H. Zheng
ISSN: 2070-1721 Huawei Technologies
D. Ceccarelli
Cisco Systems
February 2023

Path Computation Element Communication Protocol (PCEP) Extensions for
Establishing Relationships between Sets of Label Switched Paths and
Virtual Networks

Abstract

This document describes how to extend the Path Computation Element
Communication Protocol (PCEP) association mechanism introduced by RFC
8697 to further associate sets of Label Switched Paths (LSPs) with a
higher-level structure such as a Virtual Network (VN) requested by a
customer or application. This extended association mechanism can be
used to facilitate control of a VN using the PCE architecture.

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/rfc9358.

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
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Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.

Table of Contents

1. Introduction
2. Terminology
3. Operation Overview
4. Extensions to PCEP
5. Security Considerations
6. IANA Considerations
6.1. ASSOCIATION Object Type Indicator
6.2. PCEP TLV Type Indicator
6.3. PCEP Error
7. Manageability Considerations
7.1. Control of Function and Policy
7.2. Information and Data Models
7.3. Liveness Detection and Monitoring
7.4. Verification of Correct Operations
7.5. Requirements on Other Protocols
7.6. Impact on Network Operations
8. References
8.1. Normative References
8.2. Informative References
Contributors
Authors' Addresses

1. Introduction

The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to requests from Path Computation Clients
(PCCs) [RFC5440].

[RFC8051] describes general considerations for a stateful PCE
deployment and examines its applicability and benefits as well as its
challenges and limitations through a number of use cases. [RFC8231]
describes a set of extensions to PCEP to provide stateful control.
For its computations, a stateful PCE has access to not only the
information carried by the network's Interior Gateway Protocol (IGP)
but also the set of active paths and their reserved resources. The
additional state allows the PCE to compute constrained paths while
considering individual Label Switched Paths (LSPs) and their
interactions.

[RFC8281] describes the setup, maintenance, and teardown of PCE-
initiated LSPs under the stateful PCE model.

[RFC8697] introduces a generic mechanism to create a grouping of
LSPs. This grouping can then be used to define associations between
sets of LSPs or between a set of LSPs and a set of attributes.

[RFC8453] introduces a framework for Abstraction and Control of TE
Networks (ACTN) and describes various VN operations initiated by a
customer or application. A VN is a customer view of the TE network.
Depending on the agreement between client and provider, various VN
operations and VN views are possible.

[RFC8637] examines the PCE and ACTN architectures and describes how
the PCE architecture is applicable to ACTN. [RFC6805] and [RFC8751]
describe a hierarchy of stateful PCEs with the parent PCE
coordinating multi-domain path computation functions between child
PCEs, thus making it the base for PCE applicability for ACTN. As
[RFC8751] explains, in the context of ACTN, the child PCE is
identified with the Provisioning Network Controller (PNC), and the
parent PCE is identified with the Multi-Domain Service Coordinator
(MDSC).

In this context, there is a need to associate a set of LSPs with a VN
"construct" to facilitate VN operations in the PCE architecture.
This association allows a PCE to identify which LSPs belong to a
certain VN. The PCE could then use this association to optimize all
LSPs belonging to the VN at once. The PCE could further take VN-
specific actions on the LSPs, such as relaxing constraints, taking
policy actions, setting default behavior, etc.

This document specifies a PCEP extension to associate a set of LSPs
based on their VN.

2. Terminology

This document uses terminology from [RFC4655], [RFC5440], [RFC6805],
[RFC8231], and [RFC8453].

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.

3. Operation Overview

As per [RFC8697], LSPs are associated with other LSPs with which they
interact by adding them to a common association group.

An association group based on VN is useful for various optimizations
that should be applied by considering all the LSPs in the
association. This includes, but is not limited to, the following:

Path Computation: When computing a path for an LSP, it is useful to
analyze the impact of this LSP on the other LSPs belonging to the
same VN. The aim would be to optimize all LSPs belonging to the
VN rather than a single LSP. Also, the optimization criteria
(such as minimizing the load of the most loaded link (MLL)
[RFC5541]) could be applied for all the LSPs belonging to the VN
identified by the VN association.

Path Reoptimization: The PCE would like to use advanced path
computation algorithms and optimization techniques that consider
all the LSPs belonging to a VN and optimize them all together
during the path reoptimization.

In this document, we define a new association group called the "VN
Association Group (VNAG)". This grouping is used to define the
association between a set of LSPs and a VN.

The ASSOCIATION object contains a field to identify the type of
association, and this document defines a new Association Type value
of 7 to indicate that the association is a "VN Association". The
Association Identifier in the ASSOCIATION object is the VNAG
Identifier and is handled in the same way as the generic Association
Identifier defined in [RFC8697].

In this document, "VNAG object" refers to an ASSOCIATION object with
the Association Type set to "VN Association" (7).

Local policies on the PCE define the computational and optimization
behavior for the LSPs in the VN. An LSP MUST NOT belong to more than
one VNAG. If an implementation encounters more than one VNAG object
in a PCEP message, it MUST process the first occurrence, and it MUST
ignore the others.

[RFC8697] specifies the mechanism by which a PCEP speaker can
advertise which Association Types it supports. This is done using
the ASSOC-Type-List TLV carried within an OPEN object. A PCEP
speaker MUST include the VN Association Type (7) in the ASSOC-Type-
List TLV before using the VNAG object in a PCEP message. As per
[RFC8697], if the implementation does not support the VN Association
Type, it will return a PCErr message with Error-Type=26 (Association
Error) and Error-value=1 (Association Type is not supported).

The Association Identifiers (VNAG IDs) for this Association Type are
dynamic in nature and created by the parent PCE (MDSC) based on the
VN operations for the LSPs belonging to the same VN. Operator
configuration of VNAG IDs is not supported, so there is no need for
an Operator-configured Association Range to be set. Thus, the VN
Association Type (7) MUST NOT be present in the Operator-configured
Association Range TLV if that TLV is present in the OPEN object. If
an implementation encounters the VN Association Type (7) in an
Operator-configured Association Range TLV, it MUST ignore the
associated Start-Assoc-ID and Range values.

This association is useful in a PCEP session between a parent PCE
(MDSC) and a child PCE (PNC). When computing the path, the child PCE
(PNC) refers to the VN association in the request from the parent PCE
(MDSC) and maps the VN to the associated LSPs and network resources.
From the perspective of the parent PCE, it receives a VN creation
request from its customer, with the VN uniquely identified by the
association parameters (Section 6.1.4 of [RFC8697]) in the VNAG or
the Virtual Network Identifier encoded in the VIRTUAL-NETWORK-TLV.
This VN may comprise multiple LSPs in the network in a single domain
or across multiple domains. The parent PCE sends a PCInitiate
message with this association information in the VNAG object. This
in effect binds an LSP that is to be instantiated at the child PCE
with the VN. The VN association information MUST be included as a
part of the first PCRpt message. Figure 1 shows an example of a
typical VN operation using PCEP. It is worth noting that in a multi-
domain scenario, the different domains are controlled by different
child PCEs. In order to set up the cross-domain tunnel, multiple
segments need to be stitched by the border nodes in each domain that
receive the instruction from their child PCE (PNC).

******
..........*MDSC*..............................
. ****** .. MPI .
. . . .
. . . PCInitiate LSPx .
. . . with VNAG .
. . . .
. . . .
. . . .
v v v .
****** ****** ****** .
*PNC1* *PNC2* *PNC4* .
****** ****** ****** .
+---------------+ +---------------+ +---------------+ .
| |----| |----| C| .
| | | | | | .
|DOMAIN 1 |----|DOMAIN 2 |----|DOMAIN 4 | .
+---------------+ +---------------+ +---------------+ .
/ .
****** / .
*PNC3*<............/......................
****** /
+---------------+/
| |
| |
|DOMAIN 3 |
+---------------+

MDSC -> parent PCE
PNC -> child PCE
MPI -> PCEP

Figure 1: Example of VN Operations in H-PCE (Hierarchical PCE)
Architecture

Whenever changes occur with the instantiated LSP in a domain network,
the domain child PCE reports the changes using a PCRpt message in
which the VNAG object indicates the relationship between the LSP and
the VN.

Whenever an update occurs with VNs in the parent PCE (due to the
customer's request), the parent PCE sends a PCUpd message to inform
each affected child PCE of this change.

4. Extensions to PCEP

The VNAG uses the generic ASSOCIATION object [RFC8697].

This document defines one new mandatory TLV called the "VIRTUAL-
NETWORK-TLV". Optionally, the new TLV can be jointly used with the
existing VENDOR-INFORMATION-TLV specified in [RFC7470] as described
below:

VIRTUAL-NETWORK-TLV: Used to communicate the Virtual Network
Identifier.

VENDOR-INFORMATION-TLV: Used to communicate arbitrary vendor-
specific behavioral information, as described in [RFC7470].

The format of the VIRTUAL-NETWORK-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=65 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Virtual Network Identifier //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Format of the VIRTUAL-NETWORK-TLV

Type (16 bits): 65

Length (16 bits): Indicates the length of the value portion 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.

Virtual Network Identifier (variable): A symbolic name for the VN
that uniquely identifies the VN. It SHOULD be a string of
printable ASCII [RFC0020] characters (i.e., 0x20 to 0x7E), without
a NULL terminator. The Virtual Network Identifier is a human-
readable string that identifies a VN. It can be specified with
the association information, which may be conveyed in a VENDOR-
INFORMATION-TLV. An implementation uses the Virtual Network
Identifier to maintain a mapping to the VNAG and the LSPs
associated with the VN. The Virtual Network Identifier MAY be
specified by the customer, set via an operator policy, or auto-
generated by the PCEP speaker.

The VIRTUAL-NETWORK-TLV MUST be included in VNAG object. If a PCEP
speaker receives the VNAG object without the VIRTUAL-NETWORK-TLV, it
MUST send a PCErr message with Error-Type=6 (Mandatory Object
missing) and Error-value=18 (VIRTUAL-NETWORK-TLV missing) and close
the session.

The format of VENDOR-INFORMATION-TLV is defined in [RFC7470].

If a PCEP speaker receives a VNAG object with a TLV that violates the
rules specified in this document, the PCEP speaker MUST send a PCErr
message with Error-Type=10 (Reception of an invalid object) and
Error-value=11 (Malformed object) and MUST close the PCEP session.

5. Security Considerations

The security considerations described in [RFC5440], [RFC8231], and
[RFC8281] apply to the extensions defined in this document as well.

This document introduces the VN Association Type (7) for the
ASSOCIATION object. Additional security considerations related to
LSP associations due to a malicious PCEP speaker are described in
[RFC8697] and apply to the VN Association Type. Hence, securing the
PCEP session using Transport Layer Security (TLS) [RFC8253] is
RECOMMENDED.

6. IANA Considerations

6.1. ASSOCIATION Object Type Indicator

IANA has assigned the following new value in the "ASSOCIATION Type
Field" subregistry within the "Path Computation Element Protocol
(PCEP) Numbers" registry:

+=======+================+===========+
| Value | Name | Reference |
+=======+================+===========+
| 7 | VN Association | RFC 9358 |
+-------+----------------+-----------+

Table 1

6.2. PCEP TLV Type Indicator

IANA has assigned the following new value in the "PCEP TLV Type
Indicators" subregistry within the "Path Computation Element Protocol
(PCEP) Numbers" registry:

+=======+=====================+===========+
| Value | Name | Reference |
+=======+=====================+===========+
| 65 | VIRTUAL-NETWORK-TLV | RFC 9358 |
+-------+---------------------+-----------+

Table 2

6.3. PCEP Error

IANA has allocated the following new error value in the "PCEP-ERROR
Object Error Types and Values" subregistry within the "Path
Computation Element Protocol (PCEP) Numbers" registry:

+============+================+=====================+===========+
| Error-Type | Meaning | Error-value | Reference |
+============+================+=====================+===========+
| 6 | Mandatory | 18: VIRTUAL- | RFC 9358 |
| | Object missing | NETWORK-TLV missing | |
+------------+----------------+---------------------+-----------+

Table 3

7. Manageability Considerations

7.1. Control of Function and Policy

An operator MUST be allowed to mark LSPs that belong to the same VN.
This could also be done automatically based on the VN configuration.

7.2. Information and Data Models

The PCEP YANG module [PCE-PCEP-YANG] should support the association
between LSPs including VN association.

7.3. Liveness Detection and Monitoring

Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].

7.4. Verification of Correct Operations

Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440].

7.5. Requirements on Other Protocols

Mechanisms defined in this document do not imply any new requirements
on other protocols.

7.6. Impact on Network Operations

[RFC8637] describes the network operations when PCE is used for VN
operations. Section 3 further specifies the operations when VN
associations are used.

8. References

8.1. Normative References

[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>.

[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>.

[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>.

[RFC8697] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
Dhody, D., and Y. Tanaka, "Path Computation Element
Communication Protocol (PCEP) Extensions for Establishing
Relationships between Sets of Label Switched Paths
(LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
<https://www.rfc-editor.org/info/rfc8697>.

8.2. Informative References

[PCE-PCEP-YANG]
Dhody, D., Ed., Beeram, V., 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-20, 23 October
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-yang-20>.

[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>.

[RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC 5541,
DOI 10.17487/RFC5541, June 2009,
<https://www.rfc-editor.org/info/rfc5541>.

[RFC6805] King, D., Ed. and A. Farrel, Ed., "The Application of the
Path Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
DOI 10.17487/RFC6805, November 2012,
<https://www.rfc-editor.org/info/rfc6805>.

[RFC7470] Zhang, F. and A. Farrel, "Conveying Vendor-Specific
Constraints in the Path Computation Element Communication
Protocol", RFC 7470, DOI 10.17487/RFC7470, March 2015,
<https://www.rfc-editor.org/info/rfc7470>.

[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>.

[RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for
Abstraction and Control of TE Networks (ACTN)", RFC 8453,
DOI 10.17487/RFC8453, August 2018,
<https://www.rfc-editor.org/info/rfc8453>.

[RFC8637] Dhody, D., Lee, Y., and D. Ceccarelli, "Applicability of
the Path Computation Element (PCE) to the Abstraction and
Control of TE Networks (ACTN)", RFC 8637,
DOI 10.17487/RFC8637, July 2019,
<https://www.rfc-editor.org/info/rfc8637>.

[RFC8751] Dhody, D., Lee, Y., Ceccarelli, D., Shin, J., and D. King,
"Hierarchical Stateful Path Computation Element (PCE)",
RFC 8751, DOI 10.17487/RFC8751, March 2020,
<https://www.rfc-editor.org/info/rfc8751>.

Contributors

Dhruv Dhody
Huawei Technologies
Divyashree Technopark, Whitefield
Bangalore 560066
Karnataka
India
Email: [email protected]

Qin Wu
Huawei Technologies
China
Email: [email protected]

Xian Zhang
Huawei Technologies
China
Email: [email protected]

Adrian Farrel
Old Dog Consulting
Email: [email protected]

Authors' Addresses

Young Lee
Samsung Electronics
Seoul
Republic of Korea
Email: [email protected]

Haomian Zheng
Huawei Technologies
H1, Huawei Xiliu Beipo Village Songshan Lake
Dongguan
Guangdong, 523808
China
Email: [email protected]

Daniele Ceccarelli
Cisco Systems
Torshamnsgatan,48
Stockholm
Sweden
Email: [email protected]