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IETF RFC 5886
A Set of Monitoring Tools for Path Computation Element (PCE)-Based Architecture
Last modified on Monday, June 21st, 2010
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Internet Engineering Task Force (IETF) JP. Vasseur, Ed.
Request for Comments: 5886 Cisco Systems, Inc.
Category: Standards Track JL. Le Roux
ISSN: 2070-1721 France Telecom
Y. Ikejiri
NTT Communications Corporation
June 2010
A Set of Monitoring Tools for
Path Computation Element (PCE)-Based Architecture
 Abstract
A Path Computation Element (PCE)-based architecture has been
specified for the computation of Traffic Engineering (TE) Label
Switched Paths (LSPs) in Multiprotocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) networks in the context of single or
multiple domains (where a domain refers to a collection of network
elements within a common sphere of address management or path
computational responsibility such as Interior Gateway Protocol (IGP)
areas and Autonomous Systems). Path Computation Clients (PCCs) send
computation requests to PCEs, and these may forward the requests to
and cooperate with other PCEs forming a "path computation chain".
In PCE-based environments, it is thus critical to monitor the state
of the path computation chain for troubleshooting and performance
monitoring purposes: liveness of each element (PCE) involved in the
PCE chain and detection of potential resource contention states and
statistics in terms of path computation times are examples of such
metrics of interest. This document specifies procedures and
extensions to the Path Computation Element Protocol (PCEP) in order
to gather such information.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 5886.
Vasseur, et al. Standards Track PAGE 1 
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
Copyright Notice
Copyright (c) 2010 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Vasseur, et al. Standards Track PAGE 2
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
Table of Contents
1. Introduction ....................................................4
1.1. Requirements Language ......................................5
2. Terminology .....................................................5
3. Path Computation Monitoring Messages ............................6
3.1. Path Computation Monitoring Request (PCMonReq) Message .....6
3.2. Path Monitoring Reply (PCMonRep) Message ...................9
4. Path Computation Monitoring Objects ............................11
4.1. MONITORING Object .........................................11
4.2. PCC-ID-REQ Object .........................................13
4.3. PCE-ID Object .............................................14
4.4. PROC-TIME Object ..........................................15
4.5. OVERLOAD Object ...........................................17
5. Policy .........................................................18
6. Elements of Procedure ..........................................18
7. Manageability Considerations ...................................20
7.1. Control of Function and Policy ............................20
7.2. Information and Data Models ...............................20
7.3. Liveness Detection and Monitoring .........................20
7.4. Verify Correct Operations .................................20
7.5. Requirements on Other Protocols ...........................21
7.6. Impact on Network Operations ..............................21
8. Guidelines to Avoid Overload Thrashing .........................21
9. IANA Considerations ............................................22
9.1. New PCEP Message ..........................................22
9.2. New PCEP Objects ..........................................22
9.3. New Error-Values ..........................................23
9.4. MONITORING Object Flag Field ..............................23
9.5. PROC-TIME Object Flag Field ...............................24
9.6. OVERLOAD Object Flag Field ................................24
10. Security Considerations .......................................24
11. Acknowledgments ...............................................25
12. References ....................................................25
12.1. Normative References .....................................25
12.2. Informative References ...................................25
Vasseur, et al. Standards Track PAGE 3
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
1. Introduction
The Path Computation Element (PCE)-based architecture has been
specified in [RFC 4655] for the computation of Traffic Engineering
(TE) Label Switched Paths (LSPs) in Multiprotocol Label Switching
(MPLS) and Generalized MPLS (GMPLS) networks in the context of single
or multiple domains where a domain refers to a collection of network
elements within a common sphere of address management or path
computational responsibility such Interior Gateway Protocol (IGP)
areas and Autonomous Systems.
Path Computation Clients (PCCs) send computation requests to PCEs
using PCReq messages, and these may forward the requests to and
cooperate with other PCEs forming a "path computation chain". In the
case of successful path computation, the computed paths are then
provided to the requesting PCC using PCRep messages. The PCReq and
PCRep messages are defined in [RFC 5440].
In PCE-based environments, it is critical to monitor the state of the
path computation chain for troubleshooting and performance monitoring
purposes: liveness of each element (PCE) involved in the PCE chain
and detection of potential resource contention states and statistics
in terms of path computation times are examples of such metrics of
interest.
As defined in [RFC 4655], there are circumstances in which more than
one PCE is involved in the computation of a TE LSP. A typical
example is when the PCC requires the computation of a TE LSP where
the head-end and the tail-end of the TE LSP do not reside in adjacent
domains and there is no single PCE with the visibility of both the
head-end and tail-end domain. We call the set of PCEs involved in
the computation of a TE LSP a "path computation chain". As further
discussed in Section 3.1, the path computation chain may either be
static (pre-configured) or dynamically determined during the path
computation process.
As discussed in [RFC 4655], a TE LSP may be computed by one PCE
(referred to as single PCE path computation) or several PCEs
(referred to as multiple PCE path computation). In the former case,
the PCC may be able to use IGP extensions to check the liveness of
the PCE (see [RFC 5088] and [RFC 5089]) or PCEP using Keepalive
messages. In contrast, when multiple PCEs are involved in the path
computation chain, an example of which is the Backward Recursive PCE-
based Computation (BRPC) procedure defined in [RFC 5441], the PCC's
visibility may be limited to the first PCE involved in the path
computation chain. Thus, it is critical to define mechanisms in
order to monitor the state of the path computation chain.
Vasseur, et al. Standards Track PAGE 4
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
This document specifies PCEP extensions in order to gather various
state metrics along the path computation chain. In this document, we
call a "state metric" a metric that characterizes a PCE state. For
example, such a metric can have a form of a boolean (PCE is alive or
not, PCE is congested or not) or a performance metric (path
computation time at each PCE).
PCE state metrics can be gathered in two different contexts: in band
or out of band. By "in band" we refer to the situation whereby a PCC
requests to gather metrics in the context of a path computation
request. For example, a PCC may send a path computation request to a
PCE and may want to know the processing time of that request in
addition to the computed path. Conversely, if the request is "out of
band", PCE state metric collection is performed as a standalone
request (e.g., check the liveness of a specific path computation
chain, collect the average processing time computed over the last
5-minute period on one or more PCEs).
In this document, we define two monitoring request types: general and
specific. A general monitoring request relates to the collection of
a PCE state metrics that is not coupled to a particular path
computation request (e.g., average CPU load on a PCE). Conversely, a
specific monitoring request relates to a particular path computation
request (processing time to complete the path computation for a TE
LSP).
This document specifies procedures and extensions to the Path
Computation Element Protocol (PCEP) ([RFC 5440]), including new
objects and new PCEP messages, in order to monitor the path
computation chain and gather various performance metrics.
The message formats in this document are specified using Backus Naur
Format (BNF) encoding as specified in [RFC 5511].
1.1. Requirements Language
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 [RFC 2119].
2. Terminology
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.
Vasseur, et al. Standards Track PAGE 5
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
TE LSP: Traffic Engineering Label Switched Path.
3. Path Computation Monitoring Messages
As defined in [RFC 5440], a PCEP message consists of a common header
followed by a variable-length body made of a set of objects that can
be either mandatory or optional. As a reminder, an object is said to
be mandatory in a PCEP message when the object must be included for
the message to be considered valid. The P flag (defined in
[RFC 5440]) is located in the common header of each PCEP object and
can be set by a PCEP peer to require a PCE to take into account the
related information during the path computation. Because the P flag
exclusively relates to a path computation request, it MUST be cleared
in the two PCEP messages (PCMonReq and PCMonRep message) defined in
this document.
For each PCEP message type, a set of rules is defined that specify
the set of objects that the message can carry. An implementation
MUST form the PCEP messages using the object ordering specified in
this document.
In this document, we define two PCEP messages referred to as the Path
Computation Monitoring Request (PCMonReq) and Path Computation
Monitoring Reply (PCMonRep) messages so as to handle out-of-band
monitoring requests. The aim of the PCMonReq message sent by a PCC
to a PCE is to gather one or more PCE state metrics on a set of PCEs
involved in a path computation chain. The PCMonRep message sent by a
PCE to a PCC is used to provide such data.
3.1. Path Computation Monitoring Request (PCMonReq) Message
The Message-Type field of the PCEP common header for the PCMonReq
message is set to 8.
There is one mandatory object that MUST be included within a PCMonReq
message: the MONITORING object (see Section 4.1). If the MONITORING
object is missing, the receiving PCE MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value=4 (MONITORING
object missing). Other objects are optional.
Format of a PCMonReq message (out-of-band request):
<PCMonReq Message>::= <Common Header>
<MONITORING>
<PCC-ID-REQ>
[<pce-list>]
[<svec-list>]
[<request-list>]
Vasseur, et al. Standards Track PAGE 6
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
where:
<pce-list>::=<PCE-ID>[<pce-list>]
<svec-list>::=<SVEC>
[<OF>]
[<svec-list>]
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>]
[<IRO>]
[<LOAD-BALANCING>]
[<XRO>]
<metric-list>::=<METRIC>[<metric-list>]
Format of a PCReq message with monitoring data requested (in-band
request):
<PCReq Message>::= <Common Header>
<MONITORING>
<PCC-ID-REQ>
[<pce-list>]
[<svec-list>]
<request-list>
where:
<pce-list>::=<PCE-ID>[<pce-list>]
<svec-list>::=<SVEC>[<svec-list>]
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>[<BANDWIDTH>]]
[<IRO>]
[<LOAD-BALANCING>]
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RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
where:
<metric-list>::=<METRIC>[<metric-list>]
The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, RRO, IRO, and
LOAD-BALANCING objects are defined in [RFC 5440]. The XRO object is
defined in [RFC 5521] and the OF object is defined in [RFC 5541]. The
PCC-ID-REQ object is defined in Section 4.2.
The PCMonReq message is used to gather various PCE state metrics
along a path computation chain. The path computation chain may be
determined by the PCC (in the form of a series of a series of PCE-ID
objects defined in Section 4.3) according to policy specified on the
PCC or alternatively may be determined by the path computation
procedure. For example, if the BRPC procedure ([RFC 5441]) is used to
compute an inter-domain TE LSP, the path computation chain may be
determined dynamically. In that case, the PCC sends a PCMonReq
message that contains the PCEP objects that characterize the TE LSP
attributes along with the MONITORING object (see Section 4.1) that
lists the set of metrics of interest. If a list of PCEs is present
in the monitoring request, it takes precedence over mechanisms used
to dynamically determine the path computation chain. If a PCE
receives a monitoring request that specifies a next-hop PCE in the
PCE list that is unreachable, the request MUST be silently discarded.
Several PCE state metrics may be requested that are specified by a
set of objects defined in Section 4. Note that this set of objects
may be extended in the future.
As pointed out in [RFC 5440], several situations can arise in the form
of:
o a bundle of a set of independent and non-synchronized path
computation requests,
o a bundle of a set of independent and synchronized path computation
requests (SVEC object defined below required), or
o a bundle of a set of dependent and synchronized path computation
requests (SVEC object defined below required).
In the case of a bundle of a set of requests, the MONITORING object
SHOULD only be present in the first PCReq or PCMonReq message, and
the monitoring request applies to all the requests of the bundle,
even in the case of dependent and/or synchronized requests sent using
more than one PCReq or PCMonReq message.
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RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
Examples of requests. For the sake of illustration, consider the
three following examples:
Example 1 (out-of-band request): PCC1 makes a request to check the
path computation chain that would be used should it request a path
computation for a specific TE LSP named T1. A PCMonReq message is
sent that contains a MONITORING object specifying a path computation
check, along with the appropriate set of objects (e.g., RP, END-
POINTS, etc.) that would be included in a PCReq message for T1.
Example 2 (in-band request): PCC1 requests a path computation for a
TE LSP and also makes a request to gather the processing time along
the path computation chain selected for the computation of T1. A
PCReq message is sent that also contains a MONITORING object that
specifies the performance metrics of interest.
Example 3 (out-of-band request): PCC2 requests to gather performance
metrics along the specific path computation chain <pce1, pce2, pce3,
pce7>. A PCMonReq message is sent to PCE1 that contains a MONITORING
object and a sequence of PCE-ID objects that identify PCE1, PCE2,
PCE3, and PCE7, respectively.
In all of the examples above, a PCRep message (in-band request) or
PCMonReq message (out-of-band request) is sent in response to the
request that reports the computed metrics.
3.2. Path Monitoring Reply (PCMonRep) Message
The PCMonRep message is used to provide PCE state metrics back to the
requester for out-of-band monitoring requests. The Message-Type
field of the PCEP common header for the PCMonRep message is set to 9.
There is one mandatory object that MUST be included within a PCMonRep
message: the MONITORING object (see Section 4.1). If the MONITORING
object is missing, the receiving PCE MUST send a PCErr message with
Error-type=6 (Mandatory Object missing) and Error-value=4 (MONITORING
object missing).
Other objects are optional.
Format of a PCMonRep (out-of-band request):
<PCMonRep Message>::= <Common Header>
<MONITORING>
<PCC-ID-REQ>
[<RP>]
[<metric-pce-list>]
Vasseur, et al. Standards Track PAGE 9
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
where:
<metric-pce-list>::=<metric-pce>[<metric-pce-list>]
<metric-pce>::=<PCE-ID>
[<PROC-TIME>]
[<OVERLOAD>]
Format of a PCRep message with monitoring data (in band):
<PCRep Message> ::= <Common Header>
<response-list>
where:
<response-list>::=<response>[<response-list>]
<response>::=<RP>
<MONITORING>
<PCC-ID-REQ>
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
[<metric-pce-list>]
<path-list>::=<path>[<path-list>]
<path>::= <ERO><attribute-list>
where:
<attribute-list>::=[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
<metric-list>::=<METRIC>[<metric-list>]
<metric-pce-list>::=<metric-pce>[<metric-pce-list>]
<metric-pce>::=<PCE-ID>
[<PROC-TIME>]
[<OVERLOAD>]
The RP and the NO-PATH objects are defined in [RFC 5440]. The PCC-ID-
REQ object is defined in Section 4.2.
Vasseur, et al. Standards Track PAGE 10
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
If the path computation chain has been statically specified in the
corresponding monitoring request using the series of a series of PCE-
ID objects defined in Section 4.3, the monitoring request MUST use
the same path computation chain (using the PCE list but in the
reverse order).
4. Path Computation Monitoring Objects
The PCEP objects defined in the document are compliant with the PCEP
object format defined in [RFC 5440]. The P flag and the I flag of the
PCEP objects defined in this document SHOULD always be set to 0 on
transmission and MUST be ignored on receipt since these flags are
exclusively related to path computation requests.
Several objects are defined in this section that can be carried
within the PCEP PCReq or PCRep messages defined in [RFC 5440] in the
case of in-band monitoring requests (the PCC requests the computation
of the TE LSP in addition to gathering PCE state metrics). In the
case of out-of-band monitoring requests, the objects defined in this
section are carried within PCMonReq and PCMonRep messages.
All TLVs carried in objects defined in this document have the TLV
format defined in [RFC 5440]:
o Type: 2 bytes
o Length: 2 bytes
o Value: variable
A PCEP object TLV is comprised of 2 bytes for the type, 2 bytes
specifying the TLV length, and a value field. The Length field
defines the length of the value portion in bytes. The TLV is padded
to 4-byte alignment; padding is not included in the Length field (so
a 3-byte value would have a length of 3, but the total size of the
TLV would be 8 bytes). Unrecognized TLVs MUST be ignored.
4.1. MONITORING Object
The MONITORING object MUST be present within PCMonReq and PCMonRep
messages (out-of-band monitoring requests) and MAY be carried within
PCRep and PCReq messages (in-band monitoring requests). There SHOULD
NOT be more than one instance of the MONITORING object in a PCMonReq
or PCMonRep message: if more than one instance of the MONITORING
object is present, the recipient MUST process the first instance and
MUST ignore other instances.
Vasseur, et al. Standards Track PAGE 11
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
The MONITORING object is used to specify the set of requested PCE
state metrics.
The MONITORING Object-Class (19) has been assigned by IANA.
The MONITORING Object-Type (1) has been assigned by IANA.
The format of the MONITORING object body 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |I|C|P|G|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Monitoring-id-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: 24 bits
The following flags are currently defined:
L (Liveness) - 1 bit: when set, this indicates that the state metric
of interest is the PCE's liveness and thus the PCE MUST include a
PCE-ID object in the corresponding reply. The L bit MUST always be
ignored in a PCMonRep or PCRep message.
G (General) - 1 bit: when set, this indicates that the monitoring
request is a general monitoring request. When the requested
performance metric is specific, the G bit MUST be cleared. The G bit
MUST always be ignored in a PCMonRep or PCRep message.
P (Processing Time) - 1 bit: the P bit of the MONITORING object
carried in a PCMonReq or a PCReq message is set to indicate that the
processing times is a metric of interest. If allowed by policy, a
PROC-TIME object MUST be inserted in the corresponding PCMonRep or
PCRep message. The P bit MUST always be ignored in a PCMonRep or
PCRep message.
C (Overload) - 1 bit: The C bit of the MONITORING object carried in a
PCMonReq or a PCReq message is set to indicate that the overload
status is a metric of interest, in which case an OVERLOAD object MUST
be inserted in the corresponding PCMonRep or PCRep message. The C
bit MUST always be ignored in a PCMonRep or PCRep message.
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RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
I (Incomplete) - 1 bit: If a PCE supports a received PCMonReq message
and that message does not trigger any policy violation, but the PCE
cannot provide any of the set of requested performance metrics for
unspecified reasons, the PCE MUST set the I bit. The I bit has no
meaning in a request and SHOULD be ignored on receipt.
Monitoring-id-number (32 bits): The monitoring-id-number value
combined with the PCC-REQ-ID identifying the requesting PCC uniquely
identifies the monitoring request context. The monitoring-id-number
MUST start at a non-zero value and MUST be incremented each time a
new monitoring request is sent to a PCE. Each increment SHOULD have
a value of 1 and may cause a wrap back to zero. If no reply to a
monitoring request is received from the PCE, and the PCC wishes to
resend its path computation monitoring request, the same monitoring-
id-number MUST be used. Conversely, a different monitoring-id-number
MUST be used for different requests sent to a PCE. A PCEP
implementation SHOULD checkpoint the Monitoring-id-number of pending
monitoring requests in case of restart thus avoiding the reuse of a
Monitoring-id-number of an in-process monitoring request.
Unassigned bits are considered as reserved and MUST be set to zero on
transmission and ignored on reception.
No optional TLVs are currently defined.
4.2. PCC-ID-REQ Object
The PCC-ID-REQ object is used to specify the IP address of the
requesting PCC.
The PCC-ID-REQ MUST be inserted within a PCReq or a PCMonReq message
to specify the IP address of the requesting PCC.
Two PCC-ID-REQ objects (for IPv4 and IPv6) are defined. PCC-ID-REQ
Object-Class (20) has been assigned by IANA. PCC-ID-REQ Object-Type
(1 for IPv4 and 2 for IPv6) has been assigned by IANA.
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RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
The format of the PCC-ID-REQ object body for IPv4 and IPv6 are 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The PCC-ID-REQ object body has a fixed length of 4 octets for IPv4
and 16 octets for IPv6.
4.3. PCE-ID Object
The PCE-ID object is used to specify a PCE's IP address. The PCE-ID
object can either be used to specify the list of PCEs for which
monitoring data is requested and to specify the IP address of the
requesting PCC.
A set of PCE-ID objects may be inserted within a PCReq or a PCMonReq
message to specify the PCE for which PCE state metrics are requested
and in a PCMonRep or a PCRep message to record the IP address of the
PCE reporting PCE state metrics or that was involved in the path
computation chain.
Two PCE-ID objects (for IPv4 and IPv6) are defined. PCE-ID Object-
Class (25) has been assigned by IANA. PCE-ID Object-Type (1 for IPv4
and 2 for IPv6) has been assigned by IANA.
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RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
The format of the PCE-ID object body for IPv4 and IPv6 are 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The PCE-ID object body has a fixed length of 4 octets for IPv4 and 16
octets for IPv6.
When a dynamic discovery mechanism is used for PCE discovery, a PCE
advertises its PCE address in the PCE-ADDRESS sub-TLV defined in
[RFC 5088] and [RFC 5089]. A PCC MUST use this address in PCReq and
PCMonReq messages and a PCE MUST also use this address in PCRep and
PCMonRep messages.
4.4. PROC-TIME Object
If allowed by policy, the PCE includes a PROC-TIME object within a
PCMonRep or a PCRep message if the P bit of the MONITORING object
carried within the corresponding PCMonReq or PCReq message is set.
The PROC-TIME object is used to report various processing time
related metrics.
1) Case of general monitoring requests
A PCC may request processing time metrics for general monitoring
requests (e.g., the PCC may want to know the minimum, maximum, and
average processing times on a particular PCE). In this case,
general requests can only be made by using PCMonReq/PCMonRep
messages. The Current-processing-time field (as explained below)
is exclusively used for specific monitoring requests and MUST be
cleared for general monitoring requests. The algorithms used by a
PCE to compute the minimum, maximum, average, and variance of the
processing times are out of the scope of this document (a PCE may
decide to compute the minimum processing time over a period of
time, for the last N path computation requests, etc.).
Vasseur, et al. Standards Track PAGE 15
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
2) Case of specific monitoring requests
In the case of a specific request, the algorithms used by a PCE to
compute the Processing-time metrics are out of the scope of this
document, but a flag is specified that is used to indicate to the
requester whether the processing time value was estimated or
computed. The PCE may either (1) estimate the processing time
without performing an actual path computation or (2) effectively
perform the computation to report the processing time. In the
former case, the E bit of the PROC-TIME object MUST be set. The G
bit MUST be cleared and the Min-processing-time, Max-processing-
time, Average-processing-time, and Variance-processing-time MUST
be set to 0x00000000.
When the processing time is requested in addition to a path
computation (case where the MONITORING object is carried within a
PCReq message), the PROC-TIME object always reports the actual
processing time for that request and thus the E bit MUST be
cleared.
The PROC-TIME Object-Class (26) has been assigned by IANA.
The PROC-TIME Object-Type (1) has been assigned by IANA.
The format of the PROC-TIME object body 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Current-processing-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min-processing-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max-processing-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Average-processing time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variance-processing-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: 16 bits - one flag is currently defined:
E (Estimated) - 1 bit: when set, this indicates that the reported
metric value is based on estimated processing time as opposed to
actual computations.
Vasseur, et al. Standards Track PAGE 16
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Unassigned bits are considered as reserved and MUST be set to zero on
transmission.
Current-processing-time: This field indicates, in milliseconds, the
processing time for the path computation of interest characterized in
the corresponding PCMonReq message.
Min-processing-time: This field indicates, in milliseconds, the
minimum processing time.
Max-processing-time: This field indicates, in milliseconds, the
maximum processing time.
Average-processing-time: This field indicates, in milliseconds, the
average processing time.
Variance-processing-time: This field indicates, in milliseconds, the
variance of the processing times.
Since the PCC may potentially use monitoring metrics as input to
their PCE selection, it MAY be required to normalize how time metrics
(along with others metrics described in further revision of this
document) are computed to ensure consistency between the monitoring
metrics computed by a set of PCEs.
4.5. OVERLOAD Object
The OVERLOAD object is used to report a PCE processing congestion
state. Note that "overload" as indicated by this object refers to
the processing state of the PCE and its ability to handle new PCEP
requests. A PCE is overloaded when it has a backlog of PCEP requests
such that it cannot immediately start to process a new request thus
leading to waiting times. The overload duration is quantified as
being the (estimated) time until the PCE expects to be able to
immediately process a new PCEP request.
The OVERLOAD object MUST be present within a PCMonRep or a PCRep
message if the C bit of the MONITORING object carried within the
corresponding PCMonReq or PCReq message is set and the PCE is
experiencing a congested state. The OVERLOAD Object-Class (27) has
been assigned by IANA. The overload Object-Type (1) has been
assigned by IANA.
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The format of the CONGESTION object body 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | Overload Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: 8 bits - No flag is currently defined.
Overload duration - 16 bits: This field indicates the amount of time,
in seconds, that the responding PCE expects that it may continue to
be overloaded from the time that the response message was generated.
The receiver MAY use this value to decide whether or not to send
further requests to the same PCE.
It is worth noting that a PCE along a path computation chain involved
in the monitoring request may decide to learn from the overload
information received by one of downstream PCEs in the chain.
5. Policy
The receipt of a PCMonReq message may trigger a policy violation on
some PCE; in which case, the PCE MUST send a PCErr message with
Error-type=5 and Error-value=6.
6. Elements of Procedure
I bit processing: as indicated in Section 4.1, if a PCE supports a
received PCMonReq message and that message does not trigger any
policy violation, but the PCE cannot provide any of the set of
requested performance metrics for unspecified reasons, the PCE MUST
set the I bit. Once set, the I bit MUST NOT be changed by a
receiving PCE.
Upon receiving a PCMonReq message:
1) As specified in [RFC 5440], if the PCE does not support the
PCMonReq message, the PCE peer MUST send a PCErr message with
Error-value=2 (capability not supported). According to the
procedure defined in Section 6.9 of [RFC 5440], if a PCC/PCE
receives unrecognized messages at a rate equal of greater than
specified rate, the PCC/PCE must send a PCEP CLOSE message with
close value=5 "Reception of an unacceptable number of unrecognized
PCEP messages". In this case, the PCC/PCE must also close the TCP
session and must not send any further PCEP messages on the PCEP
session.
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2) If the PCE supports the PCMonReq message but the monitoring
request is prohibited by policy, the PCE must follow the procedure
specified in Section 5. As pointed out in Section 4.3, a PCE may
still partially satisfy a request, leaving out some of the
required data if not allowed by policy.
3) If the PCE supports the PCMonReq and the monitoring request is not
prohibited by policy, the receiving PCE MUST first determine
whether it is the last PCE of the path computation chain. If the
PCE is not the last element of the path computation chain, the
PCMonReq message is relayed to the next-hop PCE: such a next hop
may be either specified by means of a PCE-ID object present in the
PCMonReq message or dynamically determined by means of a procedure
outside of the scope of this document. Conversely, if the PCE is
the last PCE of the path computation chain, the PCE originates a
PCMonRep message that contains the requested objects according to
the set of requested PCE states metrics listed in the MONITORING
object carried in the corresponding PCMonReq message.
Upon receiving a PCReq message that carries a MONITORING and
potentially other monitoring objects (e.g., PCE-ID object):
1) As specified in [RFC 5440], if the PCE does not support (in-band)
monitoring, the PCE peer MUST send a PCErr message with Error-
value=2 (capability not supported). According to the procedure
defined in Section 6.9 of [RFC 5440], if a PCC/PCE receives
unrecognized messages at a rate equal or greater than a specified
rate, the PCC/PCE must send a PCEP CLOSE message with close
value=5 "Reception of an unacceptable number of unrecognized PCEP
messages". In this case, the PCC/PCE must also close the TCP
session and must not send any further PCEP messages on the PCEP
session.
2) If the PCE supports the monitoring request but the monitoring
request is prohibited by policy, the PCE must follow the procedure
specified in Section 5. As pointed out in Section 4.3, a PCE may
still partially satisfy a request, leaving out some of the
required data if not allowed by policy.
3) If the PCE supports the monitoring request and that request is not
prohibited by policy, the receiving PCE MUST first determine
whether it is the last PCE of the path computation chain. If the
PCE is not the last element of the path computation chain, the
PCReq message (with the MONITORING object and potentially other
monitoring objects such as the PCE-ID) is relayed to the next-hop
PCE: such a next hop may be either specified by means of a PCE-ID
object present in the PCReq message or dynamically determined by
means of a procedure outside of the scope of this document.
Vasseur, et al. Standards Track PAGE 19
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Conversely, if the PCE is the last PCE of the path computation
chain, the PCE originates a PCRep message that contains the
requested objects according to the set of requested PCE states
metrics listed in the MONITORING and potentially other monitoring
objects carried in the corresponding PCReq message.
Upon receiving a PCMonRep message, the PCE processes the request,
adds the relevant objects to the PCMonRep message and forwards the
PCMonRep message to the upstream requesting PCE or PCC.
Upon receiving a PCRep message that carries monitoring data, the
message is processed, additional monitoring data is added according
to this specification, and the message is forwarded upstream to the
requesting PCE or PCC.
7. Manageability Considerations
7.1. Control of Function and Policy
It MUST be possible to configure the activation/deactivation of PCEP
monitoring on a PCEP speaker. In addition to the parameters already
listed in Section 8.1 of [RFC 5440], a PCEP implementation SHOULD
allow configuring on a PCE whether or not specific, generic, in-band
and out-of-band monitoring requests are allowed. Also, a PCEP
implementation SHOULD allow configuring on a PCE a list of authorized
state metrics (aliveness, overload, processing time, etc.). This may
apply to any session in which the PCEP speaker participates, to a
specific session with a given PCEP peer or to a specific group of
sessions with a specific group of PCEP peers, for instance, the PCEP
peers of a neighbor AS.
7.2. Information and Data Models
A new MIB Module may be defined that provides local PCE state
metrics, as well as state metrics of other PCEs gathered using
mechanisms defined in this document.
7.3. Liveness Detection and Monitoring
This document provides mechanisms to monitor the liveliness and
performances of a given path computation chain.
7.4. 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].
Vasseur, et al. Standards Track PAGE 20
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7.5. 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].
7.6. Impact on Network Operations
The frequency of PCMonReq messages may impact the operations of PCEs.
An implementation SHOULD allow a limit to be placed on the rate of
PCMonReq messages sent by a PCEP speaker and processed from a peer.
It SHOULD also allow sending a notification when a rate threshold is
reached. An implementation SHOULD allow handling PCReq messages with
a higher priority than PCMonReq messages. An implementation SHOULD
allow the configuration of a second limit for the PCReq message
requesting monitoring data.
8. Guidelines to Avoid Overload Thrashing
An important concern while processing overload information is to
prevent the overload condition on one PCE simply being moved to
another PCE. Indeed, there is a risk that the reaction to an
indication of overload will act to increase the amount of overload
within the network. Furthermore, this may lead to oscillations
between PCEs if the overload information is not handled properly.
This section presents some brief guidance on how a PCC (which term
includes a PCE making requests of another PCE) should react when it
receives an indication that a PCE is overloaded.
When an overload indication is received (on a PCRep message or on a
PCMonRep message), it identifies that new PCReq messages sent to the
PCE might be subject to a delay equal to the value in the Overload
Duration field (when present).
It also indicates that PCReq messages already queued at the PCE might
be subject to a delay. The PCC must decide how to handle new PCReq
messages and what to do about PCReq messages already queued at the
PCE.
It is RECOMMENDED that a PCC does not cancel a queued PCReq and
reissue it to another PCE because of the PCE being overloaded.
Such behavior is likely to result in overload thrashing as multiple
PCCs move the PCE queue to another PCE. This would simply introduce
additional delay in the processing of all requests. A PCC MAY choose
to cancel a queued PCE request if it is willing to sacrifice the
request, maybe reissuing it later (after the overload condition has
been determined to have cleared by use of a PCMonReq/Rep exchange).
Vasseur, et al. Standards Track PAGE 21
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It is then RECOMMENDED to send the cancellation request with a higher
priority in order for the overloaded PCE to detect the request
cancellation before processing the related request.
A PCC that is aware of PCE overload at one PCE MAY select a different
PCE to service its next PCReq message. In doing so, it is
RECOMMENDED that the PCC consider whether the other PCE is overloaded
or might be likely to become overloaded by other PCCs similarly
directing new PCReq messages.
Furthermore, should the second PCE be also overloaded, it is
RECOMMENDED not to make any attempt to switch back to the other PCE
without knowing that the first PCE is no longer overloaded.
9. IANA Considerations
9.1. New PCEP Message
Each PCEP message has a message type value.
Two new PCEP (specified in [RFC 5440]) messages are defined in this
document:
Value Description Reference
8 Path Computation Monitoring Request (PCMonReq) This document
9 Path Computation Monitoring Reply (PCMonRep) This document
9.2. New PCEP Objects
Each PCEP object has an Object-Class and an Object-Type. The
following new PCEP objects are defined in this document:
Object-Class Value Name Object-Type Reference
19 MONITORING 1 This document
20 PCC-REQ-ID 1: IPv4 addresses This document
2: IPv6 addresses
25 PCE-ID 1: IPv4 addresses This document
2: IPv6 addresses This document
26 PROC-TIME 1 This document
27 OVERLOAD 1: overload This document
Vasseur, et al. Standards Track PAGE 22
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9.3. New Error-Values
A registry was created for the Error-type and Error-value of the PCEP
Error Object.
A new Error-value for the PCErr message Error-type=5 (Policy
Violation) (see [RFC 5440]) is defined in this document.
Error-type Meaning Error-value Reference
5 Policy violation 6: Monitoring message This document
supported but rejected
due to policy violation
A new Error-value for the PCErr message Error-type=6 (Mandatory
object missing) (see [RFC 5440]) is defined in this document.
Error-type Meaning Error-value Reference
6 Mandatory Object 4: MONITORING object This document
missing missing
9.4. MONITORING Object Flag Field
IANA has created a registry to manage the Flag field of
the MONITORING object.
New bit numbers may be allocated only by an IETF Review. Each bit
should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability Description
o Defining RFC
Several bits are defined for the MONITORING Object flag field in this
document:
Codespace of the Flag field (MONITORING Object)
Bit Description Reference
0-18 Unassigned
19 Incomplete This document
20 Overload This document
21 Processing Time This document
22 General This document
23 Liveness This document
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9.5. PROC-TIME Object Flag Field
IANA has created a registry to manage the Flag field of the PROC-TIME
object.
New bit numbers may be allocated only by an IETF Review. Each bit
should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability Description
o Defining RFC
One bit is defined for the PROC-TIME Object flag field in this
document:
Codespace of the Flag field (PROC-TIME Object)
Bit Description Reference
0-14 Unassigned
15 Estimated This document
9.6. OVERLOAD Object Flag Field
IANA has created a registry to manage the Flag field of the OVERLOAD
object.
New bit numbers may be allocated only by an IETF Review. Each bit
should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability Description
o Defining RFC
No Flag is currently defined for the OVERLOAD Object flag field in
this document.
Codespace of the Flag field (OVERLOAD Object)
Bit Description Reference
0-7 Unassigned
10. Security Considerations
The use of monitoring data can be used for various attacks such as
denial-of-service (DoS) attacks (for example, by setting the C bit
and overload duration field of the OVERLOAD object to stop PCCs from
Vasseur, et al. Standards Track PAGE 24
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
using a PCE). Thus, it is recommended to make use of the security
mechanisms discussed in [RFC 5440] to secure a PCEP session
(authenticity, integrity, privacy, and DoS protection, etc.) to
secure the PCMonReq and PCMonRep messages and PCE state metric
objects defined in this document. An implementation SHOULD allow
limiting the rate at which PCMonReq or PCReq messages carrying
monitoring requests received from a specific peer are processed
(input shaping) as discussed in Section 10.7.2 of [RFC 5440], or from
another domain (see also Section 7.6).
11. Acknowledgments
The authors would like to thank Eiji Oki, Mach Chen, Fabien
Verhaeghe, Dimitri Papadimitriou, and Francis Dupont for their useful
comments. Special thanks to Adrian Farrel for his detailed review.
12. References
12.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 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.
[RFC 5521] Oki, E., Takeda, T., and A. Farrel, "Extensions to the
Path Computation Element Communication Protocol (PCEP) for
Route Exclusions", RFC 5521, April 2009.
[RFC 5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC 5541, June 2009.
12.2. Informative References
[RFC 4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 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.
Vasseur, et al. Standards Track PAGE 25
RFC 5886 Monitoring Tools for PCE-Based Architecture June 2010
[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.
[RFC 5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
"A Backward-Recursive PCE-Based Computation (BRPC)
Procedure to Compute Shortest Constrained Inter-Domain
Traffic Engineering Label Switched Paths", RFC 5441, April
2009.
Authors' Addresses
JP. Vasseur (editor)
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
EMail: jpv@cisco.com
JL. Le Roux
France Telecom
2, Avenue Pierre-Marzin
Lannion 22307
France
EMail: jeanlouis.leroux@orange-ftgroup.com
Yuichi Ikejiri
NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
Japan
EMail: y.ikejiri@ntt.com
Vasseur, et al. Standards Track PAGE 26
A Set of Monitoring Tools for Path Computation Element (PCE)-Based Architecture
RFC TOTAL SIZE: 56554 bytes
PUBLICATION DATE: Monday, June 21st, 2010
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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