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IETF RFC 5541
Encoding of Objective Functions in the Path Computation Element Communication Protocol (PCEP)
Last modified on Wednesday, June 10th, 2009
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Network Working Group JL. Le Roux
Request for Comments: 5541 France Telecom
Category: Standards Track JP. Vasseur
Cisco System Inc.
Y. Lee
Huawei
June 2009
Encoding of Objective Functions in the
Path Computation Element Communication Protocol (PCEP)
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
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document authors. All rights reserved.
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Without obtaining an adequate license from the person(s) controlling
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than English.
Le Roux, et al. Standards Track PAGE 1 
RFC 5541 Objective Functions in PCEP June 2009
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.
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 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 requirements work, and
provides the definition of four new metric types that apply to a set
of synchronized requests.
Le Roux, et al. Standards Track PAGE 2
RFC 5541 Objective Functions in PCEP June 2009
Table of Contents
1. Introduction ....................................................3
1.1. Conventions Used in This Document ..........................5
1.2. Terminology ................................................5
1.3. Message Formats ............................................6
2. Discovery of PCE Objective Functions ............................6
2.1. OF-List TLV ................................................6
2.2. Elements of Procedure ......................................7
3. Objective Function in PCEP Path Computation Request and Reply
Messages ........................................................7
3.1. OF Object ..................................................7
3.1.1. Elements of Procedure ...............................8
3.2. Carrying The OF Object In a PCEP Message ...................9
3.3. New RP Object Flag ........................................12
3.3.1. Elements Of Procedure ..............................12
4. Objective Functions Definition .................................13
5. New Metric Types ...............................................14
6. IANA Considerations ............................................15
6.1. PCE Objective Function Sub-Registry .......................15
6.2. PCEP Code Points ..........................................16
6.2.1. OF Object ..........................................16
6.2.2. OF-List TLV ........................................16
6.2.3. PCEP Error Values ..................................16
6.2.4. RP Object Flag .....................................17
6.2.5. Metric Types .......................................17
7. Security Considerations ........................................17
8. Manageability Considerations ...................................18
8.1. Control of Function and Policy ............................18
8.2. Information and Data Models ...............................18
8.3. Liveness Detection and Monitoring .........................18
8.4. Verify Correct Operations .................................18
8.5. Requirements On Other Protocols ...........................19
8.6. Impact On Network Operations ..............................19
9. Acknowledgments ................................................19
10. References ....................................................19
10.1. Normative References .....................................19
10.2. Informative References ...................................19
Appendix A. RBNF Code Fragments ...................................21
1. Introduction
The Path Computation Element-based network architecture [RFC 4655]
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 of applying computational
constraints. A PCE services path computation requests that are sent
by Path Computation Clients (PCC).
Le Roux, et al. Standards Track PAGE 3
RFC 5541 Objective Functions in PCEP June 2009
The PCE communication Protocol (PCEP), defined in [RFC 5440], allows
for communication between a PCC and a PCE or between two PCEs, in
compliance with requirements and guidelines set forth in [RFC 4657].
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
of 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 [RFC 4674], it may be useful for a PCC to discover
the set of objective functions supported by a PCE. Furthermore,
[RFC 4657] 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 that allow a PCE to
advertise a list of supported objective functions, as well as
extensions to carry the objective function in PCEP request and reply
messages. It complements the PCEP base specification [RFC 5440].
Note that OSPF- and IS-IS-based PCE discovery mechanisms are defined
in [RFC 5088] and [RFC 5089]. 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.
Le Roux, et al. Standards Track PAGE 4
RFC 5541 Objective Functions in PCEP June 2009
A new PCEP object, the OF object, is defined in Section 3. The OF
object is carried within a PCReq (Path Computation Request) message
to indicate the required/desired objective function to be applied by
a PCE, or in a PCRep (Path Computation Reply) 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 [RFC 4657]. 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 the 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. 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 [RFC 2119].
1.2. 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 for 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 of applying
computational constraints.
PCEP: Path Computation Element communication Protocol.
TE LSP: Traffic Engineered Label Switched Path.
Le Roux, et al. Standards Track PAGE 5
RFC 5541 Objective Functions in PCEP June 2009
1.3. Message Formats
Message formats in this document are expressed using Reduced BNF as
used in [RFC 5440] and defined in [RFC 5511].
2. Discovery of PCE Objective Functions
This section defines PCEP extensions (see [RFC 5440]) 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. This way, during
PCEP session-setup phase, a PCE can advertise to a PCEP peer the list
of objective functions it supports.
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 [RFC 5440]. 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 4-octet alignment, and padding is not included in the
Length field (e.g., a 3-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: 4
LENGTH: N * 2 (where N is the number of objective functions)
VALUE: list of 2-byte 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Le Roux, et al. Standards Track PAGE 6
RFC 5541 Objective Functions in PCEP June 2009
OF Code (2 bytes): Objective Function code point identifier. IANA
manages the "PCE Objective Function" code point registry (see Section
6).
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 in order 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 [RFC 5440], 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 [RFC 5440] 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 (Request Parameters) 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.
Le Roux, et al. Standards Track PAGE 7
RFC 5541 Objective Functions in PCEP June 2009
The OF object format is compliant with the PCEP object format defined
in [RFC 5440].
The OF Object-Class is 21.
The OF Object-Type is 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OF Code | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OF Code (2 bytes): The identifier of the objective function. IANA
manages 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.
[RFC 5440] 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.
Le Roux, et al. Standards Track PAGE 8
RFC 5541 Objective Functions in PCEP June 2009
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 [RFC 5440]. That is, if the P bit is set, the
PCE 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, the PCE is
free to ignore the object.
- 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 if 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", which is defined
in this document.
- If the objective function is supported but policy does not allow
applying it and if the P bit is cleared, the PCE SHOULD apply
another (default) objective function.
- If the objective function is supported and policy allows applying
it and if the P bit is set, the PCE MUST apply the requested
objective function. Otherwise, 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 (Synchronization VECtor) object and MUST NOT be repeated for
each elementary request.
Le Roux, et al. Standards Track PAGE 9
RFC 5541 Objective Functions in PCEP June 2009
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. Please see
Appendix A for a full set of RBNF fragments defined in this document
and the necessary code license.
<PCReq Message> ::= <Common Header>
[<svec-list>]
<request-list>
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.
Le Roux, et al. Standards Track PAGE 10
RFC 5541 Objective Functions in PCEP June 2009
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. Please see
Appendix A for a full set of RBNF fragments defined in this document
and the necessary code license.
<PCRep Message> ::= <Common Header>
[<svec-list>]
<response-list>
where:
<svec-list> ::= <SVEC>
[<OF>]
[<metric-list>]
[<svec-list>]
<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.
Le Roux, et al. Standards Track PAGE 11
RFC 5541 Objective Functions in PCEP June 2009
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:
The Supply OF on response flag (bit number 24). 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.
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", which is 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 Flags field for the RP
object (Section 7.4.1 of [RFC 5440]), 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 behavior 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.
Le Roux, et al. Standards Track PAGE 12
RFC 5541 Objective Functions in PCEP June 2009
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 implementation 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 repertoire 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
[RFC 4657]. Objective function codes have been assigned by IANA and
are described 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)}.
- 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
Name: Minimum Cost Path (MCP)
Description: Find a path P such that C(P) is minimized.
Le Roux, et al. Standards Track PAGE 13
RFC 5541 Objective Functions in PCEP June 2009
Objective Function Code: 2
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
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
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
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
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: Aggregate bandwidth consumption.
Type 5: Load of the most loaded link.
Type 6: Cumulative IGP cost.
Type 7: Cumulative TE cost.
Le Roux, et al. Standards Track PAGE 14
RFC 5541 Objective Functions in PCEP June 2009
These metrics may be used in a PCReq to indicate a bound (B bit set
in the METRIC object) or to request the computation of a metric (C
bit set in the METRIC object), or in a PCRep to indicate a computed
metric.
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, and also defines the PCEP OF-
List TLV.
IANA created and now manages 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
that are defined in this document.
The guidelines (using terms defined in [RFC 5226]) 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 assigned as follows:
o Function code values 1 through 1023 are assigned by IANA using
the "IETF Review" policy.
o Function code values 1024 through 32767 are assigned by IANA,
using the "First Come First Served" policy.
o Function code values in the range 32768-65535 are for "Private
Use".
Le Roux, et al. Standards Track PAGE 15
RFC 5541 Objective Functions in PCEP June 2009
Six objective functions are defined in Section 4 of this document and
have been assigned by IANA:
Code Point Name Reference
-------------------------------------------------------
1 MCP RFC 5541
2 MLP RFC 5541
3 MBP RFC 5541
4 MBC RFC 5541
5 MLL RFC 5541
6 MCC RFC 5541
6.2. PCEP Code Points
6.2.1. OF Object
IANA manages the PCEP Objects code point registry (see [RFC 5440]).
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 has made the following allocation:
Object Name Object Name Reference
Class Type
------------------------------------------------------------
21 OF 1 Objective Function RFC 5541
6.2.2. OF-List TLV
IANA manages the PCEP TLV code point registry (see [RFC 5440]). 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 has made the following allocation:
Type TLV name References
-----------------------------------------------
4 OF-List RFC 5541
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.
Le Roux, et al. Standards Track PAGE 16
RFC 5541 Objective Functions in PCEP June 2009
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 RFC 5541
allowed (request rejected)
Error-value=4: OF bit of the RP object RFC 5541
set (request rejected)
6.2.4. RP Object Flag
A new flag of the RP object (specified in [RFC 5440]) 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 has made the following allocation:
Bit Description Reference
-------------------------------------------
24 Supply OF on response RFC 5541
6.2.5. Metric Types
Four new metric types are defined in this document for the METRIC
object (specified in [RFC 5440]). 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 has made the following allocations:
- Type 4: Aggregate bandwidth consumption
- Type 5: Load of the most loaded link
- Type 6: Cumulative IGP cost
- Type 7: Cumulative TE cost
7. Security Considerations
PCEP security mechanisms are described in [RFC 5440] 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 [RFC 5440] continue to be applicable.
Le Roux, et al. Standards Track PAGE 17
RFC 5541 Objective Functions in PCEP June 2009
This document introduces a single new object that may optionally be
carried on PCEP messages and will be automatically secured using the
mechanisms described in [RFC 5440].
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
[RFC 5440], a PCEP implementation SHOULD allow configuring a list of
authorized objective functions on a PCE. 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 [RFC 5440].
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
[RFC 5440].
Le Roux, et al. Standards Track PAGE 18
RFC 5541 Objective Functions in PCEP June 2009
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 [RFC 5440].
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 [RFC 5440].
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
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
[RFC 5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
10.2. Informative References
[RFC 4657] Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, September 2006.
[RFC 4674] Le Roux, J., Ed., "Requirements for Path Computation
Element (PCE) Discovery", RFC 4674, October 2006.
[RFC 5088] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5088, January 2008.
[RFC 5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, January 2008.
Le Roux, et al. Standards Track PAGE 19
RFC 5541 Objective Functions in PCEP June 2009
[RFC 5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[PCE-GCO] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
Computation Element Communication Protocol (PCEP)
Requirements and Protocol Extensions in Support of Global
Concurrent Optimization", Work in Progress, March 2009.
[PCEP-MIB] Koushik, K., and E. Stephan, "PCE Communication Protocol
(PCEP) Management Information Base", Work in Progress,
January 2009.
[RFC 5511] Farrel, A., "Routing Backus-Naur Form (RBNF) - A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, April 2009.
Le Roux, et al. Standards Track PAGE 20
RFC 5541 Objective Functions in PCEP June 2009
Appendix A. RBNF Code Fragments
This appendix contains the full set of code fragments defined in this
document.
Copyright (c) 2009 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
o Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
o Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the
distribution.
o Neither the name of Internet Society, IETF or IETF Trust, nor the
names of specific contributors, may be used to endorse or promote
products derived from this software without specific prior written
permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
<PCReq Message> ::= <Common Header>
[<svec-list>]
<request-list>
<PCRep Message> ::= <Common Header>
[<svec-list>]
<response-list>
Le Roux, et al. Standards Track PAGE 21
RFC 5541 Objective Functions in PCEP June 2009
<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>]
<metric-list> ::= <METRIC>[<metric-list>]
<response-list> ::= <response> [<response-list>]
<response> ::= <RP>
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
<path-list> ::= <path> [<path-list>]
<path> ::= <ERO>
<attribute-list>
<attribute-list> ::= [<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
Le Roux, et al. Standards Track PAGE 22
RFC 5541 Objective Functions in PCEP June 2009
Authors' Addresses
JL Le Roux
France Telecom
2, Avenue Pierre-Marzin
Lannion 22307
France
EMail: jeanlouis.leroux@orange-ftgroup.com
Jean-Philippe Vasseur
Cisco Systems, Inc
11, Rue Camille Desmoulins
L'Atlantis
92782 Issy Les Moulineaux
France
EMail: jpv@cisco.com
Young Lee
Huawei Technologies, LTD.
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
EMail: ylee@huawei.com
Le Roux, et al. Standards Track PAGE 23
Encoding of Objective Functions in the Path Computation Element Communication Protocol (PCEP)
RFC TOTAL SIZE: 45589 bytes
PUBLICATION DATE: Wednesday, June 10th, 2009
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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