Network Working Group J.L. Le Roux
Internet Draft France Telecom
Category: Standard Track
Created: December 27, 2008 J.P. Vasseur
Expires: June 27, 2009 Cisco System Inc.
Y. Lee
Huawei
Encoding of Objective Functions in the Path Computation Element
Communication Protocol (PCEP)
draft-ietf-pce-of-06.txt
Status of this Memo
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Abstract
The computation of one or a set of Traffic Engineering Label Switched
Paths (TE LSPs) in MultiProtocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) networks, is subject to a set of one or more
specific optimization criteria, referred to as objective functions
(e.g. minimum cost path, widest path, etc.).
In the Path Computation Element (PCE) architecture, a Path
Computation Client (PCC) may want a path to be computed for one or
more TE LSPs according to a specific objective function. Thus, the
PCC needs to instruct the PCE to use the correct objective function.
Furthermore, it is possible that not all PCEs support the same set of
objective functions, therefore it is useful for the PCC to be able to
automatically discover the set of objective functions supported by
each PCE.
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This document defines extensions to the PCE communication Protocol
(PCEP) to allow a PCE to indicate the set of objective functions it
supports. Extensions are also defined so that a PCC can indicate in
a path computation request the required objective function, and so
that a PCE can report in a path computation reply the objective
function that was used for path computation.
This document defines objective function code types for six
objective functions previously listed in the PCE requirments work,
and provides the definition of four new metric types that apply to a
set of synchronized requests.
Table of Contents
1. Introduction................................................3
1.1. Terminology.................................................4
1.2. Message Formats.............................................5
2. Discovery of PCE Objective Functions........................5
2.1. OF-List TLV.................................................5
2.2. Elements of procedure.......................................6
3. Objective Function in PCEP Path Computation Request and
Reply Messages............................................6
3.1. OF Object...................................................6
3.1.1. Elements of Procedure.......................................7
3.2. Carrying The OF Object In a PCEP Message....................8
3.3. New RP Object Flag.........................................10
3.3.1. Elements Of Procedure......................................10
4. Objective Functions Definition.............................11
5. New Metric Types...........................................12
6. IANA Considerations........................................13
6.1. PCE Objective Function Sub-registry........................13
6.2. PCEP Code Points...........................................14
6.2.1. OF Object..................................................14
6.2.2. OF-List TLV................................................14
6.2.3. PCEP Error values..........................................15
6.2.4. RP Object Flag.............................................15
6.2.5. Metric Types...............................................15
7. Security Considerations....................................16
8. Manageability Considerations...............................16
8.1. Control of Function and Policy.............................16
8.2. Information and Data Models................................16
8.3. Liveness Detection and Monitoring..........................16
8.4. Verify Correct Operations..................................17
8.5. Requirements On Other Protocols............................17
8.6. Impact On Network Operations...............................17
9. Acknowledgments............................................17
10. References.................................................17
10.1. Normative Feferences.......................................17
10.2. Informative References.....................................17
11. Authors' Addresses.........................................18
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1. Introduction
The Path Computation Element-based network architecture [RFC4655]
defines a Path Computation Element (PCE) as an entity capable of
computing the paths of Traffic Engineered Label Switched Paths (TE
LSPs) based on a network graph, and applying computational
constraints. A PCE services path computation requests sent by Path
Computation Clients (PCC).
The PCE communication Protocol (PCEP), defined in [PCEP], allows for
communication between a PCC and a PCE or between two PCEs, in
compliance with requirements and guidelines set forth in [RFC4657].
Such interactions include path computation requests and path
computation replies.
The computation of one or a set of TE LSPs is subject to a set of one
or more optimization criteria, called an objective function. An
objective function is used by the PCE, when it computes a path or a
set of paths, in order to select the "best" candidate paths. There is
a variety of objective functions: an objective function could apply
either to a set of non-synchronized path computation requests, or to
a set of synchronized path computation requests. In the former case,
the objective function refers to an individual path computation
request (e.g. computation of the shortest constrained path where the
metric is the IGP metric, computation of the least loaded constrained
path, etc.). Conversely in the latter case, the objective function
refers to a set of path computation requests the computation of which
is synchronized (e.g., minimize the aggregate bandwidth consumption
of all LSPs, minimize the sum of the delays for two diverse paths, or
the delta between those delays, etc.). Moreover, some objective
functions relate to the optimization of a single metric and others to
the optimization of a set of metrics (organized in a hierarchical
manner, using a weighted function, etc.).
As spelled out in [RFC4674], it may be useful for a PCC to discover
the set of objective functions supported by a PCE. Furthermore,
[RFC4657] requires the ability for a PCC to indicate in a path
computation request a required/desired objective function, as well as
optional function parameters.
For these purposes, this document extends the PCE communication
Protocol (PCEP). It defines PCEP extensions allowing a PCE to
advertise a list of supported objective functions, as well as
extensions to carry the objective function in PCEP request and reply
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messages. It complements the PCEP base specification [PCEP].
Note that IS-IS and OSPF-based PCE Discovery mechanisms are defined
in ([RFC5089], [RFC5088]). These mechanisms are dedicated to the
discovery of a few generic parameters while more detailed PCE
parameters should be discovered using the PCE communication Protocol.
Objective functions are in this second category; thus the Objective
Function discovery procedure is handled by PCEP.
A new PCEP TLV, named the OF-List TLV is defined in Section 2. The
OF-List TLV is carried in the PCEP OPEN object and allows a PCE to
list, during PCEP session setup phase, the objective functions that
it supports.
A new PCEP object, the OF object, is defined in Section 3. The OF
object is carried within a PCReq message to indicate the
required/desired objective function to be applied by a PCE, or in a
PCRep message to indicate the objective function that was used for
path computation.
Six mandatory objective functions that must be supported by PCEP are
listed in [RFC4657]. This document provides a definition of these six
mandatory objective functions. Additional objective functions may be
defined in other documents. Note that additional objective functions
are defined for PCE Global Concurrent Optimization (GCO) application,
in [PCE-GCO].
This document also provides the definition of four new metric types
that apply to a set of synchronized requests.
1.1. Terminology
LSR: Label Switching Router.
OF: Objective Function: A set of one or more optimization criteria
used for the computation of a single path (e.g. path cost
minimization), or the synchronized computation of a set of paths
(e.g., aggregate bandwidth consumption minimization, etc.).
PCC: Path Computation Client: Any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element: An entity (component, application, or
network node) that is capable of computing a network path or route
based on a network graph, and applying computational constraints.
PCEP: Path Computation Element communication Protocol.
TE LSP: Traffic Engineered Label Switched Path.
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1.2. Message Formats
Message formats in this document are expressed using Reduced BNF as
used in [PCEP] and defined in [RBNF].
2. Discovery of PCE Objective Functions
This section defines PCEP extensions (see [PCEP]) so as to support
the advertisement of the objective functions supported by a PCE.
A new PCEP OF-List (Objective Function list) TLV is defined. The PCEP
OF-List TLV is carried within an OPEN object, in order for a PCE to
advertise to a PCEP peer the list of objective functions it supports,
during PCEP session setup phase.
2.1. OF-List TLV
The PCEP OF-List TLV is optional. It MAY be carried within an OPEN
object sent by a PCE in an Open message to a PCEP peer, so as to
indicate the list of supported objective functions.
The OF-List TLV format is compliant with the PCEP TLV format defined
in [PCEP]. That is, the TLV is composed of 2 octets for the type, 2
octets specifying the TLV length, and a value field. The Length field
defines the length of the value portion in octets. The TLV is padded
to four-octet alignment and padding is not included in the Length
field (e.g. a three octet value would have a length of three, but the
total size of the TLV would be eight octets).
The PCEP OF-List TLV has the following format:
TYPE: To be assigned by IANA (suggested value = 4 )
LENGTH: N * 2 (where N is the number of objective functions)
VALUE: list of 2-bytes objective function code points, identifying
the objective functions supported by the sender of the Open message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OF Code #1 | OF Code #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OF Code #N | padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OF Code (2 bytes): Objective Function code point identifier.
IANA is requested to manage the PCE objective function code point
registry (see Section 6).
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2.2. Elements of procedure
A PCE MAY include an OF-List TLV within an OPEN object in an Open
message sent to a PCEP peer, to advertise a set of one or more
objective functions. The OF-List TLV MUST NOT appear more than once
in an OPEN object. If it appears more than once the PCEP session MUST
be rejected with error type 1 and error value 1 (PCEP session
establishment failure / Reception of an invalid Open message).
The absence of the OF-List TLV in an OPEN object MUST be interpreted
as an absence of information on the list of supported objective
functions by the PCE.
As specified in [PCEP], a PCEP peer that does not recognize the OF-
List TLV will silently ignore it.
3. Objective Function in PCEP Path Computation Request and Reply
Messages
This section defines PCEP extensions ([PCEP]) so as to support the
communication of objective functions in PCEP path computation request
and reply messages. A new PCEP OF (Objective Function) object is
defined, to be carried within a PCReq message in order for the PCC to
indicate the required/desired objective function.
The PCEP OF Object may also be carried within a PCRep message in
order for the PCE to indicate the objective function that was used by
the PCE.
A new flag is defined in the RP object. The flag is used in a PCReq
message to indicate that the PCE MUST include an OF object in the
PCRep message to indicate the objective function that was used during
path computation.
Also, new PCEP error types and values are defined.
3.1. OF Object
The PCEP OF (Objective Function) object is optional. It MAY be
carried within a PCReq message so as to indicate the desired/required
objective function to be applied by the PCE during path computation,
or within a PCRep message so as to indicate the objective function
that was used by the PCE during path computation.
The OF object format is compliant with the PCEP object format defined
in [PCEP].
The OF Object-Class is to be assigned by IANA (recommended value=21).
The OF Object-Type is to be assigned by IANA (recommended value=1).
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The format of the OF object body is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Objective Function Code(IANA) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Objective Function Code (2 bytes): The identifier of the Objective
Function. IANA is requested to manage the PCE objective function code
point registry (see Section 6).
Reserved (2 bytes): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Optional TLVs may be defined in the future so as to encode objective
function parameters.
3.1.1. Elements of Procedure
To request the use of a specific objective function by the PCE, a PCC
includes an OF object in the PCReq message.
[PCEP] specifies a bit flag, referred to as the P bit, carried in the
common PCEP object header. The P bit is set by a PCC to mandate that
a PCE must take the information carried in the object into account
during the path computation.
If the P bit is set in the OF object, the objective function is
mandatory (required objective function) and the PCE MUST use the
objective function during path computation. If the P bit is clear
in the OF object, the objective function is optional (desired
objective function) and the PCE SHOULD apply the function if it is
supported, but MAY choose to apply a different objective function
according to local capabilities and policies.
On receipt of a PCReq message with an OF object, a PCE MUST proceed
as follows:
- If the OF object is unknown/unsupported, the PCE MUST follow
procedures defined in [PCEP], that is if the P bit is set, it sends
a PCErr message with error type 3 or 4 (Unknown / Not supported
object) and error value 1 or 2 (unknown / unsupported object class
/ object type), and the related path computation request MUST be
discarded. If the P bit is cleared it is free to ignore the object.
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- If the objective function is unknown / unsupported and the P bit is
set, the PCE MUST send a PCErr message with error type 3 or 4
(Unknown / Not supported Object) and error value 4 (Unrecognized /
Unsupported parameter), and the related path computation request
MUST be discarded.
- If the objective function is unknown / unsupported and the P bit is
cleared, the PCE SHOULD apply another (default) objective function.
- If the objective function is supported but policy does not permit
applying it, and the P bit is set, the PCE MUST send a PCErr
message with the PCEP error type "policy-violation" (type 5) and a
new error value "objective function not allowed" (defined in this
document).
- If the objective function is supported but policy does not allow
applying it, and the P bit is cleared, the PCE SHOULD apply another
(default) objective function.
- If the objective function is supported and policy allows applying
it, then if the P bit is set the PCE MUST apply the requested
objective function, else if the P bit is cleared the PCE is free to
apply any other objective function.
The default objective function may be locally configured.
3.2. Carrying The OF Object In a PCEP Message
The OF object MAY be carried within a PCReq message. If an objective
function is to be applied to a set of synchronized path computation
requests, the OF object MUST be carried just after the corresponding
SVEC object, and MUST NOT be repeated for each elementary request.
Similarly if a metric is to be applied to a set of synchronized
requests, the METRIC object MUST follow the SVEC object and MUST NOT
be repeated for each elementary request. Note that metrics applied to
a set of synchronized requests are defined in section 5.
An OF object specifying an objective function that applies to an
individual path computation request (non synchronized case) MUST
follow the RP object for which it applies.
The format of the PCReq message is updated as follows:
<PCReq Message> ::= <Common Header>
[<svec-list>]
<request-list>
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where:
<svec-list> ::= <SVEC>
[<OF>]
[<metric-list>]
[<svec-list>]
<request-list> ::= <request> [<request-list>]
<request> ::= <RP>
<END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<OF>]
[<RRO>[<BANDWIDTH>]]
[<IRO>]
[<LOAD-BALANCING>]
and where:
<metric-list> ::= <METRIC>[<metric-list>]
The OF object MAY be carried within a PCRep message to indicate the
objective function used by the PCE during path computation.
When the PCE wants to indicate to the PCC the objective function that
was used for the synchronized computation of a set of paths, the
PCRep message MUST include the corresponding SVEC object directly
followed by the OF object, which MUST NOT be repeated for each
elementary request. If a metric is applicable to the set of paths,
the METRIC object MUST directly follow the SVEC object and MUST NOT
be repeated for each elementary request.
An OF object specifying an objective function used for an individual
path computation (non synchronized case) MUST follow the RP object
for which it applies.
The format of the PCRep message is updated as follows:
<PCRep Message> ::= <Common Header>
[<svec-list>]
<response-list>
where:
<svec-list> ::= <SVEC>
[<OF>]
[<metric-list>]
[<svec-list>]
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<response-list> ::= <response> [<response-list>]
<response> ::= <RP>
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
<path-list> ::= <path> [<path-list>]
<path> ::= <ERO>
<attribute-list>
and where:
<attribute-list> ::= [<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
<metric-list> ::= <METRIC> [<metric-list>]
Note: The OF object MAY be associated to a negative reply, i.e., a
reply with a NO-PATH object.
3.3. New RP Object Flag
In some cases, where no objective function is specified in the
request, or an optional objective function is desired (P flag cleared
in the OF object common header) but the PCE does not follow the
request, the PCC may desire to know the objective function that was
used by the PCE during path computation. To that end, a new flag is
defined in the RP object, named the OF flag, allowing a PCC to
request for the inclusion in the path computation reply of the
objective function that was used by the PCE during path computation.
The following new bit flag of the RP object is defined:
Objective Function (OF) flag (bit number 24) (suggested value, to be
assigned by IANA). When set in a PCReq message, this indicates that
the PCE MUST provide the applied objective function (should a path
satisfying the constraints be found) in the PCRep message. When set
in a PCRep message this indicates that the Objective Function that
was used during path computation is included.
3.3.1. Elements Of Procedure
If the PCC wants to know the objective function used by the PCE
during path computation for a given request, it sets the OF flag in
the RP object.
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On receipt of a PCReq message with the OF flag in the RP object set,
the PCE proceeds as follows:
- If policy permits it MUST include in the PCRep message an OF object
indicating the objective function it used during path computation.
- If policy does not permit, it MUST send a PCErr message with the
PCEP error code "policy-violation" (type 5) and a new error value
"objective function indication not allowed" (defined in this
document).
Note that a legacy PCE might not recognize the OF flag in the RP
object. According to the definition of the RP object Flag Field in
Section 7.4.1 of [PCEP], the legacy PCE will ignore the unknown flag
resulting in it sending a PCRep that does not contain an OF object.
In this case, the PCC's beahvior is an implementation choice. The PCC
might:
- Discard the PCRep because it really wanted the OF object returned.
- Accept the PCRep without the knowledge of the OF that was applied.
Note also that these procedures can give rise to the situation where
a PCC receives a PCRep that contains an OF object with an Objective
Function identifier that the PCC does not recognize. In this
situation the PCC behavior is dependent on implementaiton and
configuration. The PCC could choose any of the following (or some
other action):
- Ignore the OF object and use the computed path.
- Add the Objective Function to its view of the PCE's repetoire for
inclusion in future computation requests.
- Discard the PCRep (i.e., the computed path) and send a PCReq to
another PCE.
- Discard the PCRep (i.e., the computed path) and send another PCReq
to the same PCE explicitly requiring the use of some other
Objective Function (i.e., by setting the P bit in the OF object).
4. Objective Functions Definition
Six objective functions that must be supported by PCEP are listed in
[RFC4657]. Objective function codes should be assigned by IANA and
are suggested below.
Objective functions are formulated using the following terminology:
- a network comprises a set of N links {Li, (i=1...N)}
- a path P is a list of K links {Lpi,(i=1...K)}
- metric of link L is denoted M(L), this can be the IGP metric the TE
metric, or any other metric.
- the cost of a path P is denoted C(P), where
C(P) = sum {M(Lpi), (i=1...K)}.
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- residual bandwidth on link L is denoted r(L)
- maximum reservable bandwidth on link L is denoted R(L).
There are three objective functions that apply to the computation of
a single path:
Objective Function Code: 1 (suggested value, to be assigned by IANA)
Name: Minimum Cost Path (MCP)
Description: Find a path P such that C(P) is minimized.
Objective Function Code: 2 (suggested value, to be assigned by IANA)
Name: Minimum Load Path (MLP)
Description: Find a path P such that
( Max {(R(Lpi) - r(Lpi) / R(Lpi), i=1...K } ) is minimized.
Objective Function Code: 3 (suggested value, to be assigned by IANA)
Name: Maximum residual Bandwidth Path (MBP)
Description: Find a path P such that ( Min { r(Lpi), i=1...K } ) is
maximized.
There are three objective functions that apply to a set of path
computation requests the computation of which is synchronized:
Objective Function Code: 4 (suggested value, to be assigned by IANA)
Name: Minimize aggregate Bandwidth Consumption (MBC)
Description: Find a set of paths such that ( Sum {R(Li) - r(Li),
i=1...N} ) is minimized.
Objective Function Code: 5 (suggested value, to be assigned by IANA)
Name: Minimize the Load of the most loaded Link (MLL)
Description: Find a set of paths such that ( Max { (R(Li) - r(Li)) /
R(Li), i=1...N}) is minimized.
Objective Function Code: 6 (suggested value, to be assigned by IANA)
Name: Minimize the Cumulative Cost of a set of paths (MCC)
Description: Find a set of paths {P1...Pm} such that (Sum { C(Pi),
i=1...m}) is minimized.
Other objective functions may be defined in separate documents.
5. New Metric Types
Three metric types are defined in PCEP for the METRIC object: TE
metric, IGP metric and hop count. These metric types apply to an
individual request. Here we define four new metric types that apply
to a set of synchronized requests:
Type 4 (suggested value to be assigned by IANA) : Aggregate
bandwidth consumption.
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Type 5 (suggested value to be assigned by IANA) : Load of the most
loaded link.
Type 6 (suggested value to be assigned by IANA) : Cumulative IGP
cost.
Type 7 (suggested value to be assigned by IANA) : Cumulative TE
cost.
These metrics may be used to indicate a bound (B bit set in the
METRIC object) or a computed metric (C bit set in the METRIC
object).
A METRIC object with one of these four types follows the SVEC object
for which it applies.
6. IANA Considerations
6.1. PCE Objective Function Sub-registry
This document defines a 16-bit PCE Objective Function identifier to
be carried within the PCEP OF object, as well as the PCEP OF-List
TLV.
IANA is requested to create and manage the 16-bit "PCE Objective
Function" code point registry, starting from 1 and continuing through
32767, as follows:
- Objective Function code point value
- Objective Function name
- Defining RFC
The same registry is applicable to the OF object and the OF-List TLV
defined in this document.
The guidelines (using terms defined in [RFC5226]) for the
assignment of objective function code point values are as follows:
- Function code value 0 is reserved.
- Function code values in the range 1-32767 are to be assigned as
follows:
- Function code values 1 through 1023 are to be assigned by IANA
using the "IETF Consensus" policy.
- Function code values 1024 through 32767 are to be assigned by
IANA, using the "First Come First Served" policy.
- Function code values in the range 32768-65535 are for "Private
Use".
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Six objective functions are defined in Section 4 of this document and
should be assigned by IANA:
Code Point Name Defining RFC
1 MCP this doc
2 MLP this doc
3 MBP this doc
4 MBC this doc
5 MLL this doc
6 MCC this doc
6.2. PCEP Code Points
6.2.1. OF Object
IANA manages the PCEP Objects code point registry (see [PCEP]). This
is maintained as the "PCEP Objects" sub-registry of the "Path
Computation Element Protocol (PCEP) Numbers" registry.
This document defines a new PCEP object, the OF object, to be carried
in PCReq and PCRep messages. IANA is requested to make the following
allocation (suggested value):
Object Name Object Name Reference
Class Type
21 OF 1 Objective Function (this document)
6.2.2. OF-List TLV
IANA manages the PCEP TLV code point registry (see [PCEP]). This is
maintained as the "PCEP TLV Type Indicators" sub-registry of the
"Path Computation Element Protocol (PCEP) Numbers" registry.
This document defines a new PCEP TLV, the OF-List TLV, to be carried
in the OPEN object. IANA is requested to make the following
allocation (suggested value):
Type TLV name References
----- -------- ----------
4 OF-List (This document)
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6.2.3. PCEP Error values
IANA maintains a registry of Error-types and Error-values for use in
PCEP messages. This is maintained as the "PCEP-ERROR Object Error
Types and Values" sub-registry of the "Path Computation Element
Protocol (PCEP) Numbers" registry.
Two new Error-values are defined for the Error-type "policy
violation" (type 5):
Error-type Meaning and error values Reference
5 Policy violation
Error-value=3: objective function not (this doc)
allowed (request rejected)
Error-value=4: OF bit of the RP object (this doc)
set (request rejected)
6.2.4. RP Object Flag
A new flag of the RP object (specified in [PCEP]) is defined in this
document. IANA maintains a registry of RP object flags in the "RP
Object Flag Field" sub-registry of the "Path Computation Element
Protocol (PCEP) Numbers" registry.
IANA is requested to make the following allocation (suggested value):
Bit Description Reference
24 Supply OF on response This document
6.2.5. Metric Types
Four new metric types are defined in this document for the METRIC
object (specified in [PCEP]). IANA maintains a registry of metric
types in the "METRIC Object T Field" sub-registry of the "Path
Computation Element Protocol (PCEP) Numbers" registry.
IANA is requested to make the following allocation (suggested
values):
- Type 4 : Aggregate bandwidth consumption
- Type 5 : Load of the most loaded link
- Type 6 : Cumulative IGP cost
- Type 7 : Cumulative TE cost
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7. Security Considerations
PCEP security mechanisms are described in [PCEP] and are used to
secure entire PCEP messages. Nothing in this document changes the
message flows or introduces any new messages, so the security
mechanisms set out in [PCEP] continue to be applicable.
This document introduces a single new object that may optionally be
carried on PCEP messages and will be automatically secured using the
mechanims described in [PCEP].
If a PCEP message is vulnerable to attack, for example because the
security mechanisms are not used, then the OF object could be used as
part of an attack, however, it is likely that other objects will
provide far more significant ways of attacking a PCE or PCC in this
case.
8. Manageability Considerations
8.1. Control of Function and Policy
It MUST be possible to configure the activation/deactivation of
Objective Function Discovery in PCEP.
In addition to the parameters already listed in section 8.1 of
[PCEP], a PCEP implementation SHOULD allow configuring on a PCE a
list of authorized objective functions. This may apply to any session
the PCEP speaker participates in, to a specific session with a given
PCEP peer or to a specific group of sessions with a specific group of
PCEP peers.
Note that it is not mandatory for an implementation to support all
objective functions defined in Section 4.
It MUST be possible to configure a default objective function used
for path computation when a path request is received that requests to
use an optional objective function.
8.2. Information and Data Models
The PCEP MIB Module defined in [PCEP-MIB] could be extended to
include Objective Functions.
8.3. 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 [PCEP].
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8.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[PCEP].
8.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any requirements on
other protocols in addition to those already listed in [PCEP].
8.6. Impact On Network Operations
Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in [PCEP].
9. Acknowledgments
The authors would like to thank Jerry Ash, Fabien Verhaeghe,
Robert Sparks, and Adrian Farrel for their useful comments.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE)-based Architecture", RFC4655, august 2006.
[PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE)
communication Protocol (PCEP)", draft-ietf-pce-pcep, work
in progress.
10.2. Informative References
[RFC4657] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", RFC4657, September 2006.
[RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery",
RFC4674, October 2006.
[RFC5088] Le Roux, Vasseur, et al. "OSPF protocol extensions for
Path Computation Element (PCE) Discovery", RFC5088, January
2008.
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[RFC5089] Le Roux, Vasseur, et al. "IS-IS protocol extensions for
Path Computation Element (PCE) Discovery", RFC5089, January
2008.
[RFC5226] Narten, T. and Alverstrand, H., "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
2008.
[PCE-GCO] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path
Computation Element Communication Protocol (PCECP)
Requirements and Protocol Extensions In Support of Global
Concurrent Optimization", draft-ietf-pce-global-concurrent-
optimization, work in progress.
[PCEP-MIB] Koushik, K., and Stephan, E., "PCE communication protocol
(PCEP) Management Information Base", draft-kkoushik-pce-
pcep-mib, work in progress.
[RBNF] A. Farrel, "Reduced Backus-Naur Form (RBNF) - A Syntax Used
in Various Protocol Specifications", draft-farrel-rtg-
common-bnf, work in progress.
11. Authors' Addresses
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@orange-ftgroup.com
Jean-Philippe Vasseur
Cisco Systems, Inc.
1414 Massachusetts avenue
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
Young Lee
Huawei Technologies, LTD.
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
Email: ylee@huawei.com
Full Copyright Statement
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