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IETF RFC 8408
Conveying Path Setup Type in PCE Communication Protocol (PCEP) Messages
Last modified on Wednesday, July 25th, 2018
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Internet Engineering Task Force (IETF) S. Sivabalan
Request for Comments: 8408 Cisco Systems, Inc.
Category: Standards Track J. Tantsura
ISSN: 2070-1721 Nuage Networks
I. Minei
Google, Inc.
R. Varga
Pantheon Technologies SRO
J. Hardwick
Metaswitch Networks
July 2018
Conveying Path Setup Type
in PCE Communication Protocol (PCEP) Messages
 Abstract
A Path Computation Element (PCE) can compute Traffic Engineering (TE)
paths through a network; these paths are subject to various
constraints. Currently, TE paths are Label Switched Paths (LSPs)
that are set up using the RSVP-TE signaling protocol. However, other
TE path setup methods are possible within the PCE architecture. This
document proposes an extension to the PCE Communication Protocol
(PCEP) to allow support for different path setup methods over a given
PCEP session.
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/RFC 8408.
Sivabalan, et al. Standards Track PAGE 1 
RFC 8408 PCE Path Setup Type July 2018
Copyright Notice
Copyright (c) 2018 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 Simplified BSD License text as described in Section 4.e of
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. Path Setup Type Capability TLV . . . . . . . . . . . . . . . 4
4. Path Setup Type TLV . . . . . . . . . . . . . . . . . . . . . 6
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Manageability Considerations . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8.1. Additions to PCEP TLV Type Indicators Registry . . . . . 9
8.2. New PCEP Path Setup Types Registry . . . . . . . . . . . 9
8.3. Additions to PCEP-ERROR Object Error Types and Values
Registry . . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
Sivabalan, et al. Standards Track PAGE 2
RFC 8408 PCE Path Setup Type July 2018
1. Introduction
[RFC 5440] describes the PCE Communication Protocol (PCEP) for
communication between a Path Computation Client (PCC) and a Path
Computation Element (PCE) or between a PCE and a PCE. A PCC
requests, from a PCE, a path subject to various constraints and
optimization criteria. The PCE responds to the PCC with a hop-by-hop
path in an Explicit Route Object (ERO). The PCC uses the ERO to set
up the path in the network.
[RFC 8231] specifies extensions to PCEP that allow a PCC to delegate
its LSPs to a PCE. The PCE can then update the state of LSPs
delegated to it. In particular, the PCE may modify the path of an
LSP by sending a new ERO. The PCC uses this ERO to reroute the LSP
in a make-before-break fashion. [RFC 8281] specifies a mechanism that
allows a PCE to dynamically instantiate an LSP on a PCC by sending
the ERO and the characteristics of the LSP. The PCC creates the LSP
using the ERO and other attributes sent by the PCE.
So far, PCEP and its extensions have assumed that the TE paths are
label switched and are established via the RSVP-TE signaling
protocol. However, other methods of LSP setup are possible in the
PCE architecture (see [RFC 4655] and [RFC 4657]). This document
generalizes PCEP to allow other LSP setup methods to be used. It
defines two new TLVs and specifies the base procedures to facilitate
this:
o The PATH-SETUP-TYPE-CAPABILITY TLV allows a PCEP speaker to
announce which LSP setup methods it supports when the PCEP session
is established.
o The PATH-SETUP-TYPE TLV allows a PCEP speaker to specify which
setup method should be used for a given LSP. When multiple path
setup types are deployed in a network, a given PCEP session may
have to simultaneously support more than one path setup type. A
PCEP speaker uses the PATH-SETUP-TYPE TLV to explicitly indicate
the intended path setup type in the appropriate PCEP messages,
unless the path setup type is RSVP-TE (which is assumed to be the
path setup type if no other setup type is indicated). This is so
that both the PCC and the PCE can take the necessary steps to set
up the path.
This document defines a path setup type code for RSVP-TE. When a new
path setup type (other than RSVP-TE) is introduced for setting up a
path, a path setup type code and, optionally, a sub-TLV pertaining to
the new path setup type will be defined by the document that
specifies the new path setup type.
Sivabalan, et al. Standards Track PAGE 3
RFC 8408 PCE Path Setup Type July 2018
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 [RFC 2119] [RFC 8174] when, and only when, they appear in all
capitals, as shown here.
2. Terminology
The following terminology is used in this document:
ERO: Explicit Route Object
PCC: Path Computation Client
PCE: Path Computation Element
PCEP: PCE Communication Protocol
PST: Path Setup Type
TLV: Type, Length, and Value
3. Path Setup Type Capability TLV
A PCEP speaker indicates which PSTs it supports during the PCEP
initialization phase using the following process. When the PCEP
session is created, it sends an Open message with an OPEN object
containing the PATH-SETUP-TYPE-CAPABILITY TLV. The format of this
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 (34) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Num of PSTs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PST#1 | ... | PST#N | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional sub-TLVs (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PATH-SETUP-TYPE-CAPABILITY TLV
Sivabalan, et al. Standards Track PAGE 4
RFC 8408 PCE Path Setup Type July 2018
The TLV Type is 34. Its Reserved field MUST be set to zero by the
sender and MUST be ignored by the receiver. The other fields in the
TLV are as follows.
Length: The total length in bytes of the remainder of the TLV, that
is, excluding the Type and Length fields.
Num of PSTs: The number of PSTs in the following list, excluding
padding.
List of PSTs: A list of the PSTs that the PCEP speaker supports.
Each PST is a single byte in length. Duplicate entries in this
list MUST be ignored. The PCEP speaker MUST pad the list with
zeros so that it is a multiple of four bytes in length. This
document defines the following PST value:
* PST = 0: Path is set up using the RSVP-TE signaling protocol
Optional sub-TLVs: A list of sub-TLVs associated with the supported
PSTs. Each PST has zero or one sub-TLVs associated with it, and
each sub-TLV is associated with exactly one PST. Each sub-TLV
MUST obey the rules for TLV formatting defined in [RFC 5440]. That
is, each sub-TLV is padded to a four-byte alignment, and the
Length field of each sub-TLV does not include the padding bytes.
This document does not define any sub-TLVs; an example sub-TLV can
be found in [PCEP-EXTENSIONS].
A PCEP speaker MUST check that this TLV is correctly formatted, as
follows.
o If there are no sub-TLVs, then the TLV Length field MUST be equal
to four bytes plus the size of the PST list, excluding any padding
bytes.
o If there are sub-TLVs, then the TLV Length field MUST be equal to
four bytes plus the size of the PST list (rounded up to the
nearest multiple of four) plus the size of the appended sub-TLVs,
excluding any padding bytes in the final sub-TLV.
o The Num of PSTs field MUST be greater than zero.
If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV that
violates these rules, then 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. The PCEP
speaker MAY include the malformed OPEN object in the PCErr message as
well.
Sivabalan, et al. Standards Track PAGE 5
RFC 8408 PCE Path Setup Type July 2018
If a PCEP speaker receives an OPEN object with more than one PATH-
SETUP-TYPE-CAPABILITY TLV, then it MUST ignore all but the first
instance of this TLV.
The absence of the PATH-SETUP-TYPE-CAPABILITY TLV from the OPEN
object is equivalent to a PATH-SETUP-TYPE-CAPABILITY TLV containing a
single PST value of 0 (Path is set up using the RSVP-TE signaling
protocol) and no sub-TLVs. A PCEP speaker MAY omit the PATH-SETUP-
TYPE-CAPABILITY TLV if the only PST it supports is RSVP-TE. If a
PCEP speaker supports other PSTs besides RSVP-TE, then it SHOULD
include the PATH-SETUP-TYPE-CAPABILITY TLV in its OPEN object.
If a PCEP speaker does not recognize the PATH-SETUP-TYPE-CAPABILITY
TLV, it will ignore the TLV in accordance with [RFC 5440].
4. Path Setup Type TLV
When a PCEP session is used to set up TE paths using different
methods, the corresponding PCE and PCC must be aware of the path
setup method used. This means that a PCE must be able to specify
paths in the correct format, and a PCC must be able to take control-
plane and forwarding-plane actions appropriate to the PST.
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 (28) | Length (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | PST |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PATH-SETUP-TYPE TLV
The PATH-SETUP-TYPE TLV is an optional TLV associated with the
Request Parameters (RP) [RFC 5440] and the Stateful PCE Request
Parameters (SRP) [RFC 8231] objects. Its format is shown in Figure 2.
The TLV type is 28. Its Reserved field MUST be set to zero. The
one-byte PST field contains the PST as defined for the PATH-SETUP-
TYPE-CAPABILITY TLV.
The absence of the PATH-SETUP-TYPE TLV is equivalent to a PATH-SETUP-
TYPE TLV with a PST value of 0 (Path is set up using the RSVP-TE
signaling protocol). A PCEP speaker MAY omit the TLV if the PST is
RSVP-TE. If the RP or SRP object contains more than one PATH-SETUP-
TYPE TLV, only the first TLV MUST be processed, and the rest MUST be
ignored.
Sivabalan, et al. Standards Track PAGE 6
RFC 8408 PCE Path Setup Type July 2018
If a PCEP speaker does not recognize the PATH-SETUP-TYPE TLV, it will
ignore the TLV in accordance with [RFC 5440] and use RSVP-TE to set up
the path.
5. Operation
During the PCEP initialization phase, if a PCEP speaker receives a
PATH-SETUP-TYPE-CAPABILITY TLV from its peer, it MUST assume that the
peer supports only the PSTs listed in the TLV. If the PCEP speaker
and its peer have no PSTs in common, then the PCEP speaker MUST send
a PCErr message with Error-Type = 21 (Invalid traffic engineering
path setup type) and Error-value = 2 (Mismatched path setup type) and
close the PCEP session.
If the peer has sent no PATH-SETUP-TYPE-CAPABILITY TLV, then the PCEP
speaker MUST infer that the peer supports path setup using at least
RSVP-TE. The PCEP speaker MAY also infer that the peer supports
other path setup types, but the means of inference are outside the
scope of this document.
When a PCC sends a PCReq message to a PCE [RFC 5440], it MUST include
the PATH-SETUP-TYPE TLV in the RP object, unless the intended PST is
RSVP-TE (in which case it MAY omit the PATH-SETUP-TYPE TLV). If the
PCE is capable of expressing the path in a format appropriate to the
intended PST, it MUST use the appropriate ERO format in the PCRep
message.
When a PCE sends a PCRep message to a PCC [RFC 5440], it MUST include
the PATH-SETUP-TYPE TLV in the RP object, unless the PST is RSVP-TE
(in which case it MAY omit the PATH-SETUP-TYPE TLV). If the PCE does
not support the intended PST, it MUST send a PCErr message with
Error-Type = 21 (Invalid traffic engineering path setup type) and
Error-value = 1 (Unsupported path setup type) and close the PCEP
session. If the PSTs corresponding to the PCReq and PCRep messages
do not match, the PCC MUST send a PCErr message with Error-Type = 21
(Invalid traffic engineering path setup type) and Error-value = 2
(Mismatched path setup type) and close the PCEP session.
When a stateful PCE sends a PCUpd message [RFC 8231] or a PCInitiate
message [RFC 8281] to a PCC, it MUST include the PATH-SETUP-TYPE TLV
in the SRP object, unless the intended PST is RSVP-TE (in which case
it MAY omit the PATH-SETUP-TYPE TLV). If the PCC does not support
the PST associated with the PCUpd or PCInitiate message, it MUST send
a PCErr message with Error-Type = 21 (Invalid traffic engineering
path setup type) and Error-value = 1 (Unsupported path setup type)
and close the PCEP session.
Sivabalan, et al. Standards Track PAGE 7
RFC 8408 PCE Path Setup Type July 2018
When a PCC sends a PCRpt message to a stateful PCE [RFC 8231], it MUST
include the PATH-SETUP-TYPE TLV in the SRP object, unless the PST is
RSVP-TE (in which case it MAY omit the PATH-SETUP-TYPE TLV). The PCC
MUST include the SRP object in the PCRpt message if the PST is not
RSVP-TE, even when the SRP-ID-number is the reserved value of
0x00000000. If the PCRpt message is triggered by a PCUpd or
PCInitiate message, then the PST that the PCC indicates in the PCRpt
message MUST match the PST that the stateful PCE intended in the
PCUpd or PCInitiate message. If it does not match, then the PCE MUST
send a PCErr message with Error-Type = 21 (Invalid traffic
engineering path setup type) and Error-value = 2 (Mismatched path
setup type) and close the PCEP session.
6. Manageability Considerations
This document generalizes PCEP to allow path setup methods other than
RSVP-TE to be used by the network (but does not define any new path
setup types besides RSVP-TE). It is possible that, in a given
network, multiple path setup methods will be used. It is also
possible that not all devices will support the same set of path setup
methods. Managing networks that combine multiple path setup methods
may therefore raise some challenges from a configuration and
observability point of view.
Each document that defines a new path setup type in the "PCEP Path
Setup Types" registry (Section 8.2) must include a Manageability
Considerations section. The Manageability Considerations section
must explain how operators can manage PCEP with the new path setup
type. It must address the following questions, which are generally
applicable when working with multiple path setup types in PCEP.
o What are the criteria for when devices will use the new path setup
type in PCEP, and how can the operator control this?
o How can the network be migrated to the new path setup type, and
are there any backwards-compatibility issues that operators need
to be aware of?
o Are paths set up using the new path setup type intended to coexist
with other paths over the long term, and if so, how is this
situation managed with PCEP?
o How can operators verify the correct operation of PCEP in the
network with respect to the new path setup type? Which fault
conditions must be reported to the operators?
Sivabalan, et al. Standards Track PAGE 8
RFC 8408 PCE Path Setup Type July 2018
o Are there any existing management interfaces (such as YANG models)
that must be extended to model the operation of PCEP in the
network with respect to the new path setup type?
See [RFC 5706] for further guidance on how to write Manageability
Considerations sections in Standards Track documents.
7. Security Considerations
The security considerations described in [RFC 5440] and [RFC 8281] are
applicable to this specification. No additional security measure is
required.
Note that if the security mechanisms of [RFC 5440] and [RFC 8281] are
not used, then the protocol described in this document could be
attacked in the following new way. An attacker, using a TCP man-in-
the-middle attack, could inject error messages into the PCEP session
when a particular PST is (or is not) used. Doing this could
potentially force the use of a specific PST, which may allow the
attacker to subsequently attack a weakness in that PST.
8. IANA Considerations
8.1. Additions to PCEP TLV Type Indicators Registry
IANA has allocated the following code points in the "PCEP TLV Type
Indicators" registry.
Value Description Reference
----- -------------------------- ---------
28 PATH-SETUP-TYPE RFC 8408
34 PATH-SETUP-TYPE-CAPABILITY RFC 8408
8.2. New PCEP Path Setup Types Registry
IANA has created a new sub-registry within the "Path Computation
Element Protocol (PCEP) Numbers" registry called "PCEP Path Setup
Types". The allocation policy for this new registry is IETF Review
[RFC 8126]. This new registry contains the following value:
Value Description Reference
----- -------------------------- ---------
0 Path is set up using the RFC 8408
RSVP-TE signaling protocol
Sivabalan, et al. Standards Track PAGE 9
RFC 8408 PCE Path Setup Type July 2018
8.3. Additions to PCEP-ERROR Object Error Types and Values Registry
IANA has allocated the following code points in the "PCEP-ERROR
Object Error Types and Values" registry.
Error-Type Meaning Reference
---------- ------------------------------------------- ---------
10 Reception of an invalid object RFC 5440
Error-value = 11: Malformed object RFC 8408
21 Invalid traffic engineering path setup type RFC 8408
Error-value = 0: Unassigned RFC 8408
Error-value = 1: Unsupported path setup type RFC 8408
Error-value = 2: Mismatched path setup type RFC 8408
9. References
9.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC 5440, March 2009,
<https://www.rfc-editor.org/info/RFC 5440>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[RFC 8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC 8231, September 2017,
<https://www.rfc-editor.org/info/RFC 8231>.
[RFC 8281] 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/RFC 8281, December 2017,
<https://www.rfc-editor.org/info/RFC 8281>.
Sivabalan, et al. Standards Track PAGE 10
RFC 8408 PCE Path Setup Type July 2018
9.2. Informative References
[PCEP-EXTENSIONS]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
Work in Progress, draft-ietf-pce-segment-routing-12, June
2018.
[RFC 4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC 4655, August 2006,
<https://www.rfc-editor.org/info/RFC 4655>.
[RFC 4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC 4657, September
2006, <https://www.rfc-editor.org/info/RFC 4657>.
[RFC 5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC 5706, November 2009,
<https://www.rfc-editor.org/info/RFC 5706>.
[RFC 8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC 8126, June 2017,
<https://www.rfc-editor.org/info/RFC 8126>.
Acknowledgements
We would like to thank Marek Zavodsky for valuable comments.
Contributors
The following people contributed to this document:
- Jan Medved
- Edward Crabbe
Sivabalan, et al. Standards Track PAGE 11
RFC 8408 PCE Path Setup Type July 2018
Authors' Addresses
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: msiva@cisco.com
Jeff Tantsura
Nuage Networks
755 Ravendale Drive
Mountain View, CA 94043
United States of America
Email: jefftant.ietf@gmail.com
Ina Minei
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America
Email: inaminei@google.com
Robert Varga
Pantheon Technologies SRO
Mlynske Nivy 56
Bratislava, 821 05
Slovakia
Email: nite@hq.sk
Jon Hardwick
Metaswitch Networks
100 Church Street
Enfield, Middlesex
United Kingdom
Email: jonathan.hardwick@metaswitch.com
Sivabalan, et al. Standards Track PAGE 12
Conveying Path Setup Type in PCE Communication Protocol (PCEP) Messages
RFC TOTAL SIZE: 26276 bytes
PUBLICATION DATE: Wednesday, July 25th, 2018
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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