Internet DRAFT - draft-ietf-pce-lsp-setup-type
draft-ietf-pce-lsp-setup-type
PCE Working Group S. Sivabalan
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track J. Tantsura
Expires: November 5, 2018 Nuage Networks
I. Minei
Google, Inc.
R. Varga
Pantheon Technologies SRO
J. Hardwick
Metaswitch Networks
May 4, 2018
Conveying path setup type in PCEP messages
draft-ietf-pce-lsp-setup-type-10
Abstract
A Path Computation Element (PCE) can compute Traffic Engineering (TE)
paths through a network that are subject to various constraints.
Currently, TE paths are Label Switched Paths (LSPs) which 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 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 November 5, 2018.
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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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Path Setup Type Capability TLV . . . . . . . . . . . . . . . 4
4. Path Setup Type TLV . . . . . . . . . . . . . . . . . . . . . 6
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Manageability Considerations . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8.1. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 9
8.2. New Path Setup Type Registry . . . . . . . . . . . . . . 9
8.3. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 10
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
[RFC5440] describes the Path Computation Element 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 a path subject to various constraints and
optimization criteria from a PCE. 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.
[RFC8231] specifies extensions to PCEP that allow a PCC to delegate
its LSPs to a PCE. The PCE can then update the state of LSPs
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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 re-route the LSP
in a make-before-break fashion. [RFC8281] specifies a mechanism
allowing 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 protocol.
However, other methods of LSP setup are possible in the PCE
architecture (see [RFC4655] and [RFC4657]). 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, as follows.
o The PATH-SETUP-TYPE-CAPABILITY TLV, which allows a PCEP speaker to
announce which LSP setup methods it supports when the PCEP session
is established.
o The PATH-SETUP-TYPE TLV, which 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.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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2. Terminology
The following terminologies are used in this document:
ERO: Explicit Route Object.
LSR: Label Switching Router.
PCC: Path Computation Client.
PCE: Path Computation Element.
PCEP: Path Computation Element 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, as follows. 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 (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Num of PSTs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PST#1 | ... | PST#N | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional sub-TLVs (variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PATH-SETUP-TYPE-CAPABILITY TLV
The TLV type is TBD1 (to be assigned by IANA). 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.
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Number 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 muliple of four bytes in length. This
document defines the following PST value:
* PST = 0: Path is setup 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 ([RFC5440]).
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 can be
found in [I-D.ietf-pce-segment-routing].
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 Number of PSTs field MUST be greater than zero.
If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV which
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.
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 of 0 (RSVP-TE signaling protocol) and no sub-TLVs. A PCEP
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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 [RFC5440].
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. That means, 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
PATH-SETUP-TYPE TLV is an optional TLV associated with the RP
([RFC5440]) and the SRP ([RFC8231]) objects. Its format is shown in
the above figure. The TLV type is 28. Its reserved field MUST be
set to zero. The one byte value 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 (RSVP-TE). 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.
If a PCEP speaker does not recognize the PATH-SETUP-TYPE TLV, it will
ignore the TLV in accordance with [RFC5440], and will 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
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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 ([RFC5440]), 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 ([RFC5440]), 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 ([RFC8231]) or a PCInitiate
message ([RFC8281]) 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.
When a PCC sends a PCRpt message to a stateful PCE ([RFC8231]), 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
MUST match the PST that the stateful PCE intended in the PCUpd or
PCInitiate. If it does not, then the PCE MUST send a PCErr message
with Error-Type = 21 (Invalid traffic engineering path setup type)
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and Error-Value = 2 (Mismatched path setup type) and close the PCEP
session.
6. Manageability Considerations
This document generalises 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 Path Setup
Type Registry (Section 8.2) must include a manageability section.
The manageability 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?
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 [RFC5706] for further guidance on how to write manageability
sections in standards-track documents.
7. Security Considerations
The security considerations described in [RFC5440] and [RFC8281] are
applicable to this specification. No additional security measure is
required.
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Note that, if the security mechanisms of [RFC5440] and [RFC8281] are
not used, then the protocol described by this draft 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. By doing so, the attacker could
potentially force the use of a specific PST, which may allow them to
subsequently attack a weakness in that PST.
8. IANA Considerations
8.1. PCEP TLV Type Indicators
IANA is requested to confirm the early allocation of the following
code point in the PCEP TLV Type Indicators registry.
Value Description Reference
28 PATH-SETUP-TYPE This document
IANA is requested to allocate a new code point for the following TLV
in the PCEP TLV Type Indicators registry.
Value Description Reference
TBD1 PATH-SETUP-TYPE-CAPABILITY This document
Note to IANA: The above TLV type was not part of the early code point
allocation that was done for this draft. It was added to the draft
after the early code point allocation had taken place. Please assign
a code point from the indicated registry and replace each instance of
"TBD1" in this document with the allocated code point.
8.2. New Path Setup Type Registry
IANA is requested to create 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
should be by IETF Review. The new registry should contain the
following value:
Value Description Reference
0 Path is setup using the RSVP- This document
TE signaling protocol.
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8.3. PCEP-Error Object
IANA is requested to confirm the early allocation of the following
code-points in the PCEP-ERROR Object Error Types and Values registry.
Error-Type Meaning
10 Reception of an invalid object
Error-value=11: Malformed object
Error-Type Meaning
21 Invalid traffic engineering path setup type
Error-value=0: Unassigned
Error-value=1: Unsupported path setup type
Error-value=2: Mismatched path setup type
Note to IANA: the early allocation for Error-Type=10, Error-value=11
was originally done by draft-ietf-pce-segment-routing. However, we
have since moved its definition into this document. Therefore,
please update the reference for this Error-value in the indicated
registry to point to RFC.ietf-pce-lsp-setup-type.
9. Contributors
The following people contributed to this document:
- Jan Medved
- Edward Crabbe
10. Acknowledgements
We like to thank Marek Zavodsky for valuable comments.
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>.
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[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>.
[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>.
11.2. Informative References
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-11 (work in progress),
November 2017.
[RFC4655] Farrel, A., Vasseur, J., 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. 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>.
[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC5706, November 2009,
<https://www.rfc-editor.org/info/rfc5706>.
Authors' Addresses
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: msiva@cisco.com
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Jeff Tantsura
Nuage Networks
755 Ravendale Drive
Mountain View, CA 94043
USA
Email: jefftant.ietf@gmail.com
Ina Minei
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
USA
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
UK
Email: jonathan.hardwick@metaswitch.com
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