Network Working Group JP. Vasseur, Ed.
Request for Comments: 5440 Cisco Systems
Category: Standards Track JL. Le Roux, Ed.
France Telecom
March 2009
Path Computation Element (PCE) 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.
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Vasseur & Le Roux Standards Track [Page 1]RFC 5440 PCEP March 2009
Abstract
This document specifies the Path Computation Element (PCE)
Communication Protocol (PCEP) for communications between a Path
Computation Client (PCC) and a PCE, or between two PCEs. Such
interactions include path computation requests and path computation
replies as well as notifications of specific states related to the
use of a PCE in the context of Multiprotocol Label Switching (MPLS)
and Generalized MPLS (GMPLS) Traffic Engineering. PCEP is designed
to be flexible and extensible so as to easily allow for the addition
of further messages and objects, should further requirements be
expressed in the future.
Vasseur & Le Roux Standards Track [Page 2]
RFC 5440 PCEP March 2009
Table of Contents
1. Introduction ....................................................5
1.1. Requirements Language ......................................5
2. Terminology .....................................................5
3. Assumptions .....................................................6
4. Architectural Protocol Overview (Model) .........................7
4.1. Problem ....................................................7
4.2. Architectural Protocol Overview ............................7
4.2.1. Initialization Phase ................................8
4.2.2. Session Keepalive ...................................9
4.2.3. Path Computation Request Sent by a PCC to a PCE ....10
4.2.4. Path Computation Reply Sent by The PCE to a PCC ....11
4.2.5. Notification .......................................12
4.2.6. Error ..............................................14
4.2.7. Termination of the PCEP Session ....................14
4.2.8. Intermittent versus Permanent PCEP Session .........15
5. Transport Protocol .............................................15
6. PCEP Messages ..................................................15
6.1. Common Header .............................................16
6.2. Open Message ..............................................16
6.3. Keepalive Message .........................................18
6.4. Path Computation Request (PCReq) Message ..................19
6.5. Path Computation Reply (PCRep) Message ....................20
6.6. Notification (PCNtf) Message ..............................21
6.7. Error (PCErr) Message .....................................22
6.8. Close Message .............................................23
6.9. Reception of Unknown Messages .............................23
7. Object Formats .................................................23
7.1. PCEP TLV Format ...........................................24
7.2. Common Object Header ......................................24
7.3. OPEN Object ...............................................25
7.4. RP Object .................................................27
7.4.1. Object Definition ..................................27
7.4.2. Handling of the RP Object ..........................30
7.5. NO-PATH Object ............................................31
7.6. END-POINTS Object .........................................34
7.7. BANDWIDTH Object ..........................................35
7.8. METRIC Object .............................................36
7.9. Explicit Route Object .....................................39
7.10. Reported Route Object ....................................39
7.11. LSPA Object ..............................................40
7.12. Include Route Object .....................................42
7.13. SVEC Object ..............................................42
7.13.1. Notion of Dependent and Synchronized Path
Computation Requests ..............................42
7.13.2. SVEC Object .......................................44
7.13.3. Handling of the SVEC Object .......................45
Vasseur & Le Roux Standards Track [Page 3]RFC 5440 PCEP March 2009
7.14. NOTIFICATION Object ......................................46
7.15. PCEP-ERROR Object ........................................49
7.16. LOAD-BALANCING Object ....................................54
7.17. CLOSE Object .............................................55
8. Manageability Considerations ...................................56
8.1. Control of Function and Policy ............................56
8.2. Information and Data Models ...............................57
8.3. Liveness Detection and Monitoring .........................57
8.4. Verifying Correct Operation ...............................58
8.5. Requirements on Other Protocols and Functional
Components ................................................58
8.6. Impact on Network Operation ...............................58
9. IANA Considerations ............................................59
9.1. TCP Port ..................................................59
9.2. PCEP Messages .............................................59
9.3. PCEP Object ...............................................59
9.4. PCEP Message Common Header ................................61
9.5. Open Object Flag Field ....................................61
9.6. RP Object .................................................61
9.7. NO-PATH Object Flag Field .................................62
9.8. METRIC Object .............................................63
9.9. LSPA Object Flag Field ....................................63
9.10. SVEC Object Flag Field ...................................64
9.11. NOTIFICATION Object ......................................64
9.12. PCEP-ERROR Object ........................................65
9.13. LOAD-BALANCING Object Flag Field .........................67
9.14. CLOSE Object .............................................67
9.15. PCEP TLV Type Indicators .................................68
9.16. NO-PATH-VECTOR TLV .......................................68
10. Security Considerations .......................................69
10.1. Vulnerability ............................................69
10.2. TCP Security Techniques ..................................70
10.3. PCEP Authentication and Integrity ........................70
10.4. PCEP Privacy .............................................71
10.5. Key Configuration and Exchange ...........................71
10.6. Access Policy ............................................73
10.7. Protection against Denial-of-Service Attacks .............73
10.7.1. Protection against TCP DoS Attacks ................73
10.7.2. Request Input Shaping/Policing ....................74
11. Acknowledgments ...............................................75
12. References ....................................................75
12.1. Normative References .....................................75
12.2. Informative References ...................................76
Appendix A. PCEP Finite State Machine (FSM) ......................79
Appendix B. PCEP Variables .......................................85
Appendix C. Contributors .........................................86
Vasseur & Le Roux Standards Track [Page 4]RFC 5440 PCEP March 2009
1. Introduction
[RFC4655] describes the motivations and architecture for a Path
Computation Element (PCE) based model for the computation of
Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
Traffic Engineering Label Switched Paths (TE LSPs). The model allows
for the separation of PCE from Path Computation Client (PCC), and
allows for the cooperation between PCEs. This necessitates a
communication protocol between PCC and PCE, and between PCEs.
[RFC4657] states the generic requirements for such a protocol
including that the same protocol be used between PCC and PCE, and
between PCEs. Additional application-specific requirements (for
scenarios such as inter-area, inter-AS, etc.) are not included in
[RFC4657], but there is a requirement that any solution protocol must
be easily extensible to handle other requirements as they are
introduced in application-specific requirements documents. Examples
of such application-specific requirements are [RFC4927], [RFC5376],
and [INTER-LAYER].
This document specifies the Path Computation Element Protocol (PCEP)
for communications between a PCC and a PCE, or between two PCEs, in
compliance with [RFC4657]. Such interactions include path
computation requests and path computation replies as well as
notifications of specific states related to the use of a PCE in the
context of MPLS and GMPLS Traffic Engineering.
PCEP is designed to be flexible and extensible so as to easily allow
for the addition of further messages and objects, should further
requirements be expressed in the future.
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 [RFC2119].
2. Terminology
The following terminology is used in this document.
AS: Autonomous System.
Explicit path: Full explicit path from start to destination; made of
a list of strict hops where a hop may be an abstract node such as
an AS.
IGP area: OSPF area or IS-IS level.
Vasseur & Le Roux Standards Track [Page 5]RFC 5440 PCEP March 2009
Inter-domain TE LSP: A TE LSP whose path transits at least two
different domains where a domain can be an IGP area, an Autonomous
System, or a sub-AS (BGP confederation).
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 Peer: An element involved in a PCEP session (i.e., a PCC or a
PCE).
TED: Traffic Engineering Database that contains the topology and
resource information of the domain. The TED may be fed by IGP
extensions or potentially by other means.
TE LSP: Traffic Engineering Label Switched Path.
Strict/loose path: A mix of strict and loose hops comprising at
least one loose hop representing the destination where a hop may
be an abstract node such as an AS.
Within this document, when describing PCE-PCE communications, the
requesting PCE fills the role of a PCC. This provides a saving in
documentation without loss of function.
The message formats in this document are specified using Backus-Naur
Format (BNF) encoding as specified in [RBNF].
3. Assumptions
[RFC4655] describes various types of PCE. PCEP does not make any
assumption about, and thus does not impose any constraint on, the
nature of the PCE.
Moreover, it is assumed that the PCE has the required information
(usually including network topology and resource information) so as
to perform the computation of a path for a TE LSP. Such information
can be gathered by routing protocols or by some other means. The way
in which the information is gathered is out of the scope of this
document.
Similarly, no assumption is made about the discovery method used by a
PCC to discover a set of PCEs (e.g., via static configuration or
dynamic discovery) and on the algorithm used to select a PCE. For
Vasseur & Le Roux Standards Track [Page 6]RFC 5440 PCEP March 2009
reference, [RFC4674] defines a list of requirements for dynamic PCE
discovery and IGP-based solutions for such PCE discovery are
specified in [RFC5088] and [RFC5089].
4. Architectural Protocol Overview (Model)
The aim of this section is to describe the PCEP model in the spirit
of [RFC4101]. An architectural protocol overview (the big picture of
the protocol) is provided in this section. Protocol details can be
found in further sections.
4.1. Problem
The PCE-based architecture used for the computation of paths for MPLS
and GMPLS TE LSPs is described in [RFC4655]. When the PCC and the
PCE are not collocated, a communication protocol between the PCC and
the PCE is needed. PCEP is such a protocol designed specifically for
communications between a PCC and a PCE or between two PCEs in
compliance with [RFC4657]: a PCC may use PCEP to send a path
computation request for one or more TE LSPs to a PCE, and the PCE may
reply with a set of computed paths if one or more paths can be found
that satisfies the set of constraints.
4.2. Architectural Protocol Overview
PCEP operates over TCP, which fulfills the requirements for reliable
messaging and flow control without further protocol work.
Several PCEP messages are defined:
o Open and Keepalive messages are used to initiate and maintain a
PCEP session, respectively.
o PCReq: a PCEP message sent by a PCC to a PCE to request a path
computation.
o PCRep: a PCEP message sent by a PCE to a PCC in reply to a path
computation request. A PCRep message can contain either a set of
computed paths if the request can be satisfied, or a negative
reply if not. The negative reply may indicate the reason why no
path could be found.
o PCNtf: a PCEP notification message either sent by a PCC to a PCE
or sent by a PCE to a PCC to notify of a specific event.
o PCErr: a PCEP message sent upon the occurrence of a protocol error
condition.
Vasseur & Le Roux Standards Track [Page 7]RFC 5440 PCEP March 2009
o Close message: a message used to close a PCEP session.
The set of available PCEs may be either statically configured on a
PCC or dynamically discovered. The mechanisms used to discover one
or more PCEs and to select a PCE are out of the scope of this
document.
A PCC may have PCEP sessions with more than one PCE, and similarly a
PCE may have PCEP sessions with multiple PCCs.
Each PCEP message is regarded as a single transmission unit and parts
of messages MUST NOT be interleaved. So, for example, a PCC sending
a PCReq and wishing to close the session, must complete sending the
request message before starting to send a Close message.
4.2.1. Initialization Phase
The initialization phase consists of two successive steps (described
in a schematic form in Figure 1):
1) Establishment of a TCP connection (3-way handshake) between the
PCC and the PCE.
2) Establishment of a PCEP session over the TCP connection.
Once the TCP connection is established, the PCC and the PCE (also
referred to as "PCEP peers") initiate PCEP session establishment
during which various session parameters are negotiated. These
parameters are carried within Open messages and include the Keepalive
timer, the DeadTimer, and potentially other detailed capabilities and
policy rules that specify the conditions under which path computation
requests may be sent to the PCE. If the PCEP session establishment
phase fails because the PCEP peers disagree on the session parameters
or one of the PCEP peers does not answer after the expiration of the
establishment timer, the TCP connection is immediately closed.
Successive retries are permitted but an implementation should make
use of an exponential back-off session establishment retry procedure.
Keepalive messages are used to acknowledge Open messages, and are
used once the PCEP session has been successfully established.
Only one PCEP session can exist between a pair of PCEP peers at any
one time. Only one TCP connection on the PCEP port can exist between
a pair of PCEP peers at any one time.
Details about the Open message and the Keepalive message can be found
in Sections 6.2 and 6.3, respectively.
Vasseur & Le Roux Standards Track [Page 8]RFC 5440 PCEP March 2009
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
| Open msg |
|-------- |
| \ Open msg |
| \ ---------|
| \/ |
| /\ |
| / -------->|
| / |
|<------ Keepalive|
| --------|
|Keepalive / |
|-------- / |
| \/ |
| /\ |
|<------ ---------->|
| |
Figure 1: PCEP Initialization Phase (Initiated by a PCC)
(Note that once the PCEP session is established, the exchange of
Keepalive messages is optional.)
4.2.2. Session Keepalive
Once a session has been established, a PCE or PCC may want to know
that its PCEP peer is still available for use.
It can rely on TCP for this information, but it is possible that the
remote PCEP function has failed without disturbing the TCP
connection. It is also possible to rely on the mechanisms built into
the TCP implementations, but these might not provide failure
notifications that are sufficiently timely. Lastly, a PCC could wait
until it has a path computation request to send and could use its
failed transmission or the failure to receive a response as evidence
that the session has failed, but this is clearly inefficient.
In order to handle this situation, PCEP includes a keepalive
mechanism based on a Keepalive timer, a DeadTimer, and a Keepalive
message.
Each end of a PCEP session runs a Keepalive timer. It restarts the
timer every time it sends a message on the session. When the timer
expires, it sends a Keepalive message. Other traffic may serve as
Keepalive (see Section 6.3).
Vasseur & Le Roux Standards Track [Page 9]RFC 5440 PCEP March 2009
The ends of the PCEP session also run DeadTimers, and they restart
the timers whenever a message is received on the session. If one end
of the session receives no message before the DeadTimer expires, it
declares the session dead.
Note that this means that the Keepalive message is unresponded and
does not form part of a two-way keepalive handshake as used in some
protocols. Also note that the mechanism is designed to reduce to a
minimum the amount of keepalive traffic on the session.
The keepalive traffic on the session may be unbalanced according to
the requirements of the session ends. Each end of the session can
specify (on an Open message) the Keepalive timer that it will use
(i.e., how often it will transmit a Keepalive message if there is no
other traffic) and a DeadTimer that it recommends its peer to use
(i.e., how long the peer should wait before declaring the session
dead if it receives no traffic). The session ends may use different
Keepalive timer values.
The minimum value of the Keepalive timer is 1 second, and it is
specified in units of 1 second. The recommended default value is 30
seconds. The timer may be disabled by setting it to zero.
The recommended default for the DeadTimer is 4 times the value of the
Keepalive timer used by the remote peer. This means that there is
never any risk of congesting TCP with excessive Keepalive messages.
4.2.3. Path Computation Request Sent by a PCC to a PCE
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1) Path computation | |
event | |
2) PCE Selection | |
3) Path computation |---- PCReq message--->|
request sent to | |
the selected PCE | |
Figure 2: Path Computation Request
Once a PCC has successfully established a PCEP session with one or
more PCEs, if an event is triggered that requires the computation of
a set of paths, the PCC first selects one or more PCEs. Note that
the PCE selection decision process may have taken place prior to the
PCEP session establishment.
Vasseur & Le Roux Standards Track [Page 10]RFC 5440 PCEP March 2009
Once the PCC has selected a PCE, it sends a path computation request
to the PCE (PCReq message) that contains a variety of objects that
specify the set of constraints and attributes for the path to be
computed. For example, "Compute a TE LSP path with source IP
address=x.y.z.t, destination IP address=x'.y'.z'.t', bandwidth=B
Mbit/s, Setup/Holding priority=P, ...". Additionally, the PCC may
desire to specify the urgency of such request by assigning a request
priority. Each request is uniquely identified by a request-id number
and the PCC-PCE address pair. The process is shown in a schematic
form in Figure 2.
Note that multiple path computation requests may be outstanding from
a PCC to a PCE at any time.
Details about the PCReq message can be found in Section 6.4.
4.2.4. Path Computation Reply Sent by The PCE to a PCC
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---- PCReq message--->|
| |1) Path computation
| | request received
| |
| |2) Path successfully
| | computed
| |
| |3) Computed paths
| | sent to the PCC
| |
|<--- PCRep message ---|
| (Positive reply) |
Figure 3a: Path Computation Request With Successful
Path Computation
Vasseur & Le Roux Standards Track [Page 11]RFC 5440 PCEP March 2009
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
| |
|---- PCReq message--->|
| |1) Path computation
| | request received
| |
| |2) No Path found that
| | satisfies the request
| |
| |3) Negative reply sent to
| | the PCC (optionally with
| | various additional
| | information)
|<--- PCRep message ---|
| (Negative reply) |
Figure 3b: Path Computation Request With Unsuccessful
Path Computation
Upon receiving a path computation request from a PCC, the PCE
triggers a path computation, the result of which can be either:
o Positive (Figure 3a): the PCE manages to compute a path that
satisfies the set of required constraints. In this case, the PCE
returns the set of computed paths to the requesting PCC. Note
that PCEP supports the capability to send a single request that
requires the computation of more than one path (e.g., computation
of a set of link-diverse paths).
o Negative (Figure 3b): no path could be found that satisfies the
set of constraints. In this case, a PCE may provide the set of
constraints that led to the path computation failure. Upon
receiving a negative reply, a PCC may decide to resend a modified
request or take any other appropriate action.
Details about the PCRep message can be found in Section 6.5.
4.2.5. Notification
There are several circumstances in which a PCE may want to notify a
PCC of a specific event. For example, suppose that the PCE suddenly
gets overloaded, potentially leading to unacceptable response times.
The PCE may want to notify one or more PCCs that some of their
requests (listed in the notification) will not be satisfied or may
experience unacceptable delays. Upon receiving such notification,
Vasseur & Le Roux Standards Track [Page 12]RFC 5440 PCEP March 2009
the PCC may decide to redirect its path computation requests to
another PCE should an alternate PCE be available. Similarly, a PCC
may desire to notify a PCE of a particular event such as the
cancellation of pending requests.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1) Path computation | |
event | |
2) PCE Selection | |
3) Path computation |---- PCReq message--->|
request X sent to | |4) Path computation
the selected PCE | | request queued
| |
| |
5) Path computation | |
request X cancelled| |
|---- PCNtf message -->|
| |6) Path computation
| | request X cancelled
Figure 4: Example of PCC Notification (Cancellation Notification)
Sent to a PCE
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1) Path computation | |
event | |
2) PCE Selection | |
3) Path computation |---- PCReq message--->|
request X sent to | |4) Path computation
the selected PCE | | request queued
| |
| |
| |5) PCE gets overloaded
| |
| |
| |6) Path computation
| | request X cancelled
| |
|<--- PCNtf message----|
Figure 5: Example of PCE Notification (Cancellation Notification)
Sent to a PCC
Details about the PCNtf message can be found in Section 6.6.
Vasseur & Le Roux Standards Track [Page 13]RFC 5440 PCEP March 2009
4.2.6. Error
The PCEP Error message (also referred to as a PCErr message) is sent
in several situations: when a protocol error condition is met or when
the request is not compliant with the PCEP specification (e.g.,
capability not supported, reception of a message with a mandatory
missing object, policy violation, unexpected message, unknown request
reference).
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1) Path computation | |
event | |
2) PCE Selection | |
3) Path computation |---- PCReq message--->|
request X sent to | |4) Reception of a
the selected PCE | | malformed object
| |
| |5) Request discarded
| |
|<-- PCErr message ---|
| |
Figure 6: Example of Error Message Sent by a PCE to a PCC
in Reply to the Reception of a Malformed Object
Details about the PCErr message can be found in Section 6.7.
4.2.7. Termination of the PCEP Session
When one of the PCEP peers desires to terminate a PCEP session it
first sends a PCEP Close message and then closes the TCP connection.
If the PCEP session is terminated by the PCE, the PCC clears all the
states related to pending requests previously sent to the PCE.
Similarly, if the PCC terminates a PCEP session, the PCE clears all
pending path computation requests sent by the PCC in question as well
as the related states. A Close message can only be sent to terminate
a PCEP session if the PCEP session has previously been established.
In case of TCP connection failure, the PCEP session is immediately
terminated.
Details about the Close message can be found in Section 6.8.
Vasseur & Le Roux Standards Track [Page 14]RFC 5440 PCEP March 2009
4.2.8. Intermittent versus Permanent PCEP Session
An implementation may decide to keep the PCEP session alive (and thus
the corresponding TCP connection) for an unlimited time. (For
instance, this may be appropriate when path computation requests are
sent on a frequent basis so as to avoid opening a TCP connection each
time a path computation request is needed, which would incur
additional processing delays.) Conversely, in some other
circumstances, it may be desirable to systematically open and close a
PCEP session for each PCEP request (for instance, when sending a path
computation request is a rare event).
5. Transport Protocol
PCEP operates over TCP using a registered TCP port (4189). This
allows the requirements of reliable messaging and flow control to be
met without further protocol work. All PCEP messages MUST be sent
using the registered TCP port for the source and destination TCP
port.
6. PCEP Messages
A PCEP message consists of a common header followed by a variable-
length body made of a set of objects that can either be mandatory or
optional. In the context of this document, an object is said to be
mandatory in a PCEP message when the object MUST be included for the
message to be considered valid. A PCEP message with a missing
mandatory object MUST trigger an Error message (see Section 7.15).
Conversely, if an object is optional, the object may or may not be
present.
A flag referred to as the P flag is defined in the common header of
each PCEP object (see Section 7.2). When this flag is set in an
object in a PCReq, the PCE MUST take the information carried in the
object into account during the path computation. For example, the
METRIC object defined in Section 7.8 allows a PCC to specify a
bounded acceptable path cost. The METRIC object is optional, but a
PCC may set a flag to ensure that the constraint is taken into
account. In this case, if the constraint cannot be taken into
account by the PCE, the PCE MUST trigger an Error message.
For each PCEP message type, rules are defined that specify the set of
objects that the message can carry. We use the Backus-Naur Form
(BNF) (see [RBNF]) to specify such rules. Square brackets refer to
optional sub-sequences. An implementation MUST form the PCEP
messages using the object ordering specified in this document.
Vasseur & Le Roux Standards Track [Page 15]
RFC 5440 PCEP March 2009
6.1. Common Header
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Flags | Message-Type | Message-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: PCEP Message Common Header
Ver (Version - 3 bits): PCEP version number. Current version is
version 1.
Flags (5 bits): No flags are currently defined. Unassigned bits are
considered as reserved. They MUST be set to zero on transmission
and MUST be ignored on receipt.
Message-Type (8 bits): The following message types are currently
defined:
Value Meaning
1 Open
2 Keepalive
3 Path Computation Request
4 Path Computation Reply
5 Notification
6 Error
7 Close
Message-Length (16 bits): total length of the PCEP message including
the common header, expressed in bytes.
6.2. Open Message
The Open message is a PCEP message sent by a PCC to a PCE and by a
PCE to a PCC in order to establish a PCEP session. The Message-Type
field of the PCEP common header for the Open message is set to 1.
Once the TCP connection has been successfully established, the first
message sent by the PCC to the PCE or by the PCE to the PCC MUST be
an Open message as specified in Appendix A.
Any message received prior to an Open message MUST trigger a protocol
error condition causing a PCErr message to be sent with Error-Type
"PCEP session establishment failure" and Error-value "reception of an
invalid Open message or a non Open message" and the PCEP session
establishment attempt MUST be terminated by closing the TCP
connection.
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The Open message is used to establish a PCEP session between the PCEP
peers. During the establishment phase, the PCEP peers exchange
several session characteristics. If both parties agree on such
characteristics, the PCEP session is successfully established.
The format of an Open message is as follows:
<Open Message>::= <Common Header>
<OPEN>
The Open message MUST contain exactly one OPEN object (see
Section 7.3).
Various session characteristics are specified within the OPEN object.
Once the TCP connection has been successfully established, the sender
MUST start an initialization timer called OpenWait after the
expiration of which, if no Open message has been received, it sends a
PCErr message and releases the TCP connection (see Appendix A for
details).
Once an Open message has been sent to a PCEP peer, the sender MUST
start an initialization timer called KeepWait after the expiration of
which, if neither a Keepalive message has been received nor a PCErr
message in case of disagreement of the session characteristics, a
PCErr message MUST be sent and the TCP connection MUST be released
(see Appendix A for details).
The OpenWait and KeepWait timers have a fixed value of 1 minute.
Upon the receipt of an Open message, the receiving PCEP peer MUST
determine whether the suggested PCEP session characteristics are
acceptable. If at least one of the characteristics is not acceptable
to the receiving peer, it MUST send an Error message. The Error
message SHOULD also contain the related OPEN object and, for each
unacceptable session parameter, an acceptable parameter value SHOULD
be proposed in the appropriate field of the OPEN object in place of
the originally proposed value. The PCEP peer MAY decide to resend an
Open message with different session characteristics. If a second
Open message is received with the same set of parameters or with
parameters that are still unacceptable, the receiving peer MUST send
an Error message and it MUST immediately close the TCP connection.
Details about error messages can be found in Section 7.15.
Successive retries are permitted, but an implementation SHOULD make
use of an exponential back-off session establishment retry procedure.
If the PCEP session characteristics are acceptable, the receiving
PCEP peer MUST send a Keepalive message (defined in Section 6.3) that
serves as an acknowledgment.
Vasseur & Le Roux Standards Track [Page 17]RFC 5440 PCEP March 2009
The PCEP session is considered as established once both PCEP peers
have received a Keepalive message from their peer.
6.3. Keepalive Message
A Keepalive message is a PCEP message sent by a PCC or a PCE in order
to keep the session in active state. The Keepalive message is also
used in response to an Open message to acknowledge that an Open
message has been received and that the PCEP session characteristics
are acceptable. The Message-Type field of the PCEP common header for
the Keepalive message is set to 2. The Keepalive message does not
contain any object.
PCEP has its own keepalive mechanism used to ensure the liveness of
the PCEP session. This requires the determination of the frequency
at which each PCEP peer sends Keepalive messages. Asymmetric values
may be chosen; thus, there is no constraint mandating the use of
identical keepalive frequencies by both PCEP peers. The DeadTimer is
defined as the period of time after the expiration of which a PCEP
peer declares the session down if no PCEP message has been received
(Keepalive or any other PCEP message); thus, any PCEP message acts as
a Keepalive message. Similarly, there are no constraints mandating
the use of identical DeadTimers by both PCEP peers. The minimum
Keepalive timer value is 1 second. Deployments SHOULD consider
carefully the impact of using low values for the Keepalive timer as
these might not give rise to the expected results in periods of
temporary network instability.
Keepalive messages are sent at the frequency specified in the OPEN
object carried within an Open message according to the rules
specified in Section 7.3. Because any PCEP message may serve as
Keepalive, an implementation may either decide to send Keepalive
messages at fixed intervals regardless of whether other PCEP messages
might have been sent since the last sent Keepalive message, or may
decide to differ the sending of the next Keepalive message based on
the time at which the last PCEP message (other than Keepalive) was
sent.
Note that sending Keepalive messages to keep the session alive is
optional, and PCEP peers may decide not to send Keepalive messages
once the PCEP session is established; in which case, the peer that
does not receive Keepalive messages does not expect to receive them
and MUST NOT declare the session as inactive.
The format of a Keepalive message is as follows:
<Keepalive Message>::= <Common Header>
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RFC 5440 PCEP March 2009
6.4. Path Computation Request (PCReq) Message
A Path Computation Request message (also referred to as a PCReq
message) is a PCEP message sent by a PCC to a PCE to request a path
computation. A PCReq message may carry more than one path
computation request. The Message-Type field of the PCEP common
header for the PCReq message is set to 3.
There are two mandatory objects that MUST be included within a PCReq
message: the RP and the END-POINTS objects (see Section 7). If one
or both of these objects is missing, the receiving PCE MUST send an
error message to the requesting PCC. Other objects are optional.
The format of a PCReq message is as follows:
<PCReq Message>::= <Common Header>
[<svec-list>]
<request-list>
where:
<svec-list>::=<SVEC>[<svec-list>]
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<RRO>[<BANDWIDTH>]]
[<IRO>]
[<LOAD-BALANCING>]
where:
<metric-list>::=<METRIC>[<metric-list>]
The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, RRO, IRO, and
LOAD-BALANCING objects are defined in Section 7. The special case of
two BANDWIDTH objects is discussed in detail in Section 7.7.
A PCEP implementation is free to process received requests in any
order. For example, the requests may be processed in the order they
are received, reordered and assigned priority according to local
policy, reordered according to the priority encoded in the RP object
(Section 7.4.1), or processed in parallel.
Vasseur & Le Roux Standards Track [Page 19]RFC 5440 PCEP March 2009
6.5. Path Computation Reply (PCRep) Message
The PCEP Path Computation Reply message (also referred to as a PCRep
message) is a PCEP message sent by a PCE to a requesting PCC in
response to a previously received PCReq message. The Message-Type
field of the PCEP common header for the PCRep message is set to 4.
The bundling of multiple replies to a set of path computation
requests within a single PCRep message is supported by PCEP. If a
PCE receives non-synchronized path computation requests by means of
one or more PCReq messages from a requesting PCC, it MAY decide to
bundle the computed paths within a single PCRep message so as to
reduce the control plane load. Note that the counter side of such an
approach is the introduction of additional delays for some path
computation requests of the set. Conversely, a PCE that receives
multiple requests within the same PCReq message MAY decide to provide
each computed path in separate PCRep messages or within the same
PCRep message. A PCRep message may contain positive and negative
replies.
A PCRep message may contain a set of computed paths corresponding to
either a single path computation request with load-balancing (see
Section 7.16) or multiple path computation requests originated by a
requesting PCC. The PCRep message may also contain multiple
acceptable paths corresponding to the same request.
The PCRep message MUST contain at least one RP object. For each
reply that is bundled into a single PCReq message, an RP object MUST
be included that contains a Request-ID-number identical to the one
specified in the RP object carried in the corresponding PCReq message
(see Section 7.4 for the definition of the RP object).
If the path computation request can be satisfied (i.e., the PCE finds
a set of paths that satisfy the set of constraints), the set of
computed paths specified by means of Explicit Route Objects (EROs) is
inserted in the PCRep message. The ERO is defined in Section 7.9.
The situation where multiple computed paths are provided in a PCRep
message is discussed in detail in Section 7.13. Furthermore, when a
PCC requests the computation of a set of paths for a total amount of
bandwidth by means of a LOAD-BALANCING object carried within a PCReq
message, the ERO of each computed path may be followed by a BANDWIDTH
object as discussed in section Section 7.16.
If the path computation request cannot be satisfied, the PCRep
message MUST include a NO-PATH object. The NO-PATH object (described
in Section 7.5) may also contain other information (e.g, reasons for
the path computation failure).
Vasseur & Le Roux Standards Track [Page 20]
RFC 5440 PCEP March 2009
The format of a PCRep message is as follows:
<PCRep Message> ::= <Common Header>
<response-list>
where:
<response-list>::=<response>[<response-list>]
<response>::=<RP>
[<NO-PATH>]
[<attribute-list>]
[<path-list>]
<path-list>::=<path>[<path-list>]
<path>::= <ERO><attribute-list>
where:
<attribute-list>::=[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
<metric-list>::=<METRIC>[<metric-list>]
6.6. Notification (PCNtf) Message
The PCEP Notification message (also referred to as the PCNtf message)
can be sent either by a PCE to a PCC, or by a PCC to a PCE, to notify
of a specific event. The Message-Type field of the PCEP common
header for the PCNtf message is set to 5.
The PCNtf message MUST carry at least one NOTIFICATION object and MAY
contain several NOTIFICATION objects should the PCE or the PCC intend
to notify of multiple events. The NOTIFICATION object is defined in
Section 7.14. The PCNtf message MAY also contain RP objects (see
Section 7.4) when the notification refers to particular path
computation requests.
The PCNtf message may be sent by a PCC or a PCE in response to a
request or in an unsolicited manner.
Vasseur & Le Roux Standards Track [Page 21]RFC 5440 PCEP March 2009
The format of a PCNtf message is as follows:
<PCNtf Message>::=<Common Header>
<notify-list>
<notify-list>::=<notify> [<notify-list>]
<notify>::= [<request-id-list>]
<notification-list>
<request-id-list>::=<RP>[<request-id-list>]
<notification-list>::=<NOTIFICATION>[<notification-list>]
6.7. Error (PCErr) Message
The PCEP Error message (also referred to as a PCErr message) is sent
in several situations: when a protocol error condition is met or when
the request is not compliant with the PCEP specification (e.g.,
reception of a malformed message, reception of a message with a
mandatory missing object, policy violation, unexpected message,
unknown request reference). The Message-Type field of the PCEP
common header for the PCErr message is set to 6.
The PCErr message is sent by a PCC or a PCE in response to a request
or in an unsolicited manner. If the PCErr message is sent in
response to a request, the PCErr message MUST include the set of RP
objects related to the pending path computation requests that
triggered the error condition. In the latter case (unsolicited), no
RP object is inserted in the PCErr message. For example, no RP
object is inserted in a PCErr when the error condition occurred
during the initialization phase. A PCErr message MUST contain a
PCEP-ERROR object specifying the PCEP error condition. The PCEP-
ERROR object is defined in Section 7.15.
The format of a PCErr message is as follows:
<PCErr Message> ::= <Common Header>
( <error-obj-list> [<Open>] ) | <error>
[<error-list>]
<error-obj-list>::=<PCEP-ERROR>[<error-obj-list>]
<error>::=[<request-id-list>]
<error-obj-list>
<request-id-list>::=<RP>[<request-id-list>]
Vasseur & Le Roux Standards Track [Page 22]RFC 5440 PCEP March 2009
<error-list>::=<error>[<error-list>]
The procedure upon the receipt of a PCErr message is defined in
Section 7.15.
6.8. Close Message
The Close message is a PCEP message that is either sent by a PCC to a
PCE or by a PCE to a PCC in order to close an established PCEP
session. The Message-Type field of the PCEP common header for the
Close message is set to 7.
The format of a Close message is as follows:
<Close Message>::= <Common Header>
<CLOSE>
The Close message MUST contain exactly one CLOSE object (see
Section 6.8). If more than one CLOSE object is present, the first
MUST be processed and subsequent objects ignored.
Upon the receipt of a valid Close message, the receiving PCEP peer
MUST cancel all pending requests, it MUST close the TCP connection
and MUST NOT send any further PCEP messages on the PCEP session.
6.9. Reception of Unknown Messages
A PCEP implementation that receives an unrecognized PCEP message MUST
send a PCErr message with Error-value=2 (capability not supported).
If a PCC/PCE receives unrecognized messages at a rate equal or
greater than MAX-UNKNOWN-MESSAGES unknown message requests per
minute, the PCC/PCE MUST send a PCEP CLOSE message with close
value="Reception of an unacceptable number of unknown PCEP message".
A RECOMMENDED value for MAX-UNKNOWN-MESSAGES is 5. The PCC/PCE MUST
close the TCP session and MUST NOT send any further PCEP messages on
the PCEP session.
7. Object Formats
PCEP objects have a common format. They begin with a common object
header (see Section 7.2). This is followed by object-specific fields
defined for each different object. The object may also include one
or more type-length-value (TLV) encoded data sets. Each TLV has the
same structure as described in Section 7.1.
Vasseur & Le Roux Standards Track [Page 23]RFC 5440 PCEP March 2009
7.1. PCEP TLV Format
A PCEP object may include a set of one or more optional TLVs.
All PCEP TLVs have the following format:
Type: 2 bytes
Length: 2 bytes
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-bytes 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.
IANA management of the PCEP Object TLV type identifier codespace is
described in Section 9.
7.2. Common Object Header
A PCEP object carried within a PCEP message consists of one or more
32-bit words with a common header that has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object-Class | OT |Res|P|I| Object Length (bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Object body) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: PCEP Common Object Header
Object-Class (8 bits): identifies the PCEP object class.
OT (Object-Type - 4 bits): identifies the PCEP object type.
The Object-Class and Object-Type fields are managed by IANA.
The Object-Class and Object-Type fields uniquely identify each
PCEP object.
Vasseur & Le Roux Standards Track [Page 24]RFC 5440 PCEP March 2009
Res flags (2 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
P flag (Processing-Rule - 1-bit): the P flag allows a PCC to specify
in a PCReq message sent to a PCE whether the object must be taken
into account by the PCE during path computation or is just
optional. When the P flag is set, the object MUST be taken into
account by the PCE. Conversely, when the P flag is cleared, the
object is optional and the PCE is free to ignore it.
I flag (Ignore - 1 bit): the I flag is used by a PCE in a PCRep
message to indicate to a PCC whether or not an optional object was
processed. The PCE MAY include the ignored optional object in its
reply and set the I flag to indicate that the optional object was
ignored during path computation. When the I flag is cleared, the
PCE indicates that the optional object was processed during the
path computation. The setting of the I flag for optional objects
is purely indicative and optional. The I flag has no meaning in a
PCRep message when the P flag has been set in the corresponding
PCReq message.
If the PCE does not understand an object with the P flag set or
understands the object but decides to ignore the object, the entire
PCEP message MUST be rejected and the PCE MUST send a PCErr message
with Error-Type="Unknown Object" or "Not supported Object" along with
the corresponding RP object. Note that if a PCReq includes multiple
requests, only requests for which an object with the P flag set is
unknown/unrecognized MUST be rejected.
Object Length (16 bits): Specifies the total object length including
the header, in bytes. The Object Length field MUST always be a
multiple of 4, and at least 4. The maximum object content length
is 65528 bytes.
7.3. OPEN Object
The OPEN object MUST be present in each Open message and MAY be
present in a PCErr message. There MUST be only one OPEN object per
Open or PCErr message.
The OPEN object contains a set of fields used to specify the PCEP
version, Keepalive frequency, DeadTimer, and PCEP session ID, along
with various flags. The OPEN object may also contain a set of TLVs
used to convey various session characteristics such as the detailed
PCE capabilities, policy rules, and so on. No TLVs are currently
defined.
Vasseur & Le Roux Standards Track [Page 25]RFC 5440 PCEP March 2009
OPEN Object-Class is 1.
OPEN Object-Type is 1.
The format of the OPEN 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Flags | Keepalive | DeadTimer | SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: OPEN Object Format
Ver (3 bits): PCEP version. Current version is 1.
Flags (5 bits): No flags are currently defined. Unassigned bits are
considered as reserved. They MUST be set to zero on transmission
and MUST be ignored on receipt.
Keepalive (8 bits): maximum period of time (in seconds) between two
consecutive PCEP messages sent by the sender of this message. The
minimum value for the Keepalive is 1 second. When set to 0, once
the session is established, no further Keepalive messages are sent
to the remote peer. A RECOMMENDED value for the keepalive
frequency is 30 seconds.
DeadTimer (8 bits): specifies the amount of time after the
expiration of which the PCEP peer can declare the session with the
sender of the Open message to be down if no PCEP message has been
received. The DeadTimer SHOULD be set to 0 and MUST be ignored if
the Keepalive is set to 0. A RECOMMENDED value for the DeadTimer
is 4 times the value of the Keepalive.
Example:
A sends an Open message to B with Keepalive=10 seconds and
DeadTimer=40 seconds. This means that A sends Keepalive messages (or
any other PCEP message) to B every 10 seconds and B can declare the
PCEP session with A down if no PCEP message has been received from A
within any 40-second period.
Vasseur & Le Roux Standards Track [Page 26]RFC 5440 PCEP March 2009
SID (PCEP session ID - 8 bits): unsigned PCEP session number that
identifies the current session. The SID MUST be incremented each
time a new PCEP session is established. It is used for logging
and troubleshooting purposes. Each increment SHOULD have a value
of 1 and may cause a wrap back to zero.
The SID is used to disambiguate instances of sessions to the same
peer. A PCEP implementation could use a single source of SIDs
across all peers, or one source for each peer. The former might
constrain the implementation to only 256 concurrent sessions. The
latter potentially requires more states. There is one SID number
in each direction.
Optional TLVs may be included within the OPEN object body to specify
PCC or PCE characteristics. The specification of such TLVs is
outside the scope of this document.
When present in an Open message, the OPEN object specifies the
proposed PCEP session characteristics. Upon receiving unacceptable
PCEP session characteristics during the PCEP session initialization
phase, the receiving PCEP peer (PCE) MAY include an OPEN object
within the PCErr message so as to propose alternative acceptable
session characteristic values.
7.4. RP Object
The RP (Request Parameters) object MUST be carried within each PCReq
and PCRep messages and MAY be carried within PCNtf and PCErr
messages. The RP object is used to specify various characteristics
of the path computation request.
The P flag of the RP object MUST be set in PCReq and PCRep messages
and MUST be cleared in PCNtf and PCErr messages. If the RP object is
received with the P flag set incorrectly according to the rules
stated above, the receiving peer MUST send a PCErr message with
Error-Type=10 and Error-value=1. The corresponding path computation
request MUST be cancelled by the PCE without further notification.
7.4.1. Object Definition
RP Object-Class is 2.
RP Object-Type is 1.
Vasseur & Le Roux Standards Track [Page 27]RFC 5440 PCEP March 2009
The format of the RP 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 |O|B|R| Pri |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request-ID-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: RP Object Body Format
The RP object body has a variable length and may contain additional
TLVs. No TLVs are currently defined.
Flags (32 bits)
The following flags are currently defined:
o Pri (Priority - 3 bits): the Priority field may be used by the
requesting PCC to specify to the PCE the request's priority from 1
to 7. The decision of which priority should be used for a
specific request is a local matter; it MUST be set to 0 when
unused. Furthermore, the use of the path computation request
priority by the PCE's scheduler is implementation specific and out
of the scope of this document. Note that it is not required for a
PCE to support the priority field: in this case, it is RECOMMENDED
that the PCC set the priority field to 0 in the RP object. If the
PCE does not take into account the request priority, it is
RECOMMENDED to set the priority field to 0 in the RP object
carried within the corresponding PCRep message, regardless of the
priority value contained in the RP object carried within the
corresponding PCReq message. A higher numerical value of the
priority field reflects a higher priority. Note that it is the
responsibility of the network administrator to make use of the
priority values in a consistent manner across the various PCCs.
The ability of a PCE to support request prioritization MAY be
dynamically discovered by the PCCs by means of PCE capability
discovery. If not advertised by the PCE, a PCC may decide to set
the request priority and will learn the ability of the PCE to
support request prioritization by observing the Priority field of
the RP object received in the PCRep message. If the value of the
Pri field is set to 0, this means that the PCE does not support
Vasseur & Le Roux Standards Track [Page 28]RFC 5440 PCEP March 2009
the handling of request priorities: in other words, the path
computation request has been honored but without taking the
request priority into account.
o R (Reoptimization - 1 bit): when set, the requesting PCC specifies
that the PCReq message relates to the reoptimization of an
existing TE LSP. For all TE LSPs except zero-bandwidth LSPs, when
the R bit is set, an RRO (see Section 7.10) MUST be included in
the PCReq message to show the path of the existing TE LSP. Also,
for all TE LSPs except zero-bandwidth LSPs, when the R bit is set,
the existing bandwidth of the TE LSP to be reoptimized MUST be
supplied in a BANDWIDTH object (see Section 7.7). This BANDWIDTH
object is in addition to the instance of that object used to
describe the desired bandwidth of the reoptimized LSP. For zero-
bandwidth LSPs, the RRO and BANDWIDTH objects that report the
characteristics of the existing TE LSP are optional.
o B (Bi-directional - 1 bit): when set, the PCC specifies that the
path computation request relates to a bi-directional TE LSP that
has the same traffic engineering requirements including fate
sharing, protection and restoration, LSRs, TE links, and resource
requirements (e.g., latency and jitter) in each direction. When
cleared, the TE LSP is unidirectional.
o O (strict/loose - 1 bit): when set, in a PCReq message, this
indicates that a loose path is acceptable. Otherwise, when
cleared, this indicates to the PCE that a path exclusively made of
strict hops is required. In a PCRep message, when the O bit is
set this indicates that the returned path is a loose path;
otherwise (when the O bit is cleared), the returned path is made
of strict hops.
Unassigned bits are considered reserved. They MUST be set to zero on
transmission and MUST be ignored on receipt.
Request-ID-number (32 bits): The Request-ID-number value combined
with the source IP address of the PCC and the PCE address uniquely
identify the path computation request context. The Request-ID-
number is used for disambiguation between pending requests, and
thus it MUST be changed (such as by incrementing it) each time a
new request is sent to the PCE, and may wrap.
The value 0x00000000 is considered invalid.
If no path computation reply is received from the PCE (e.g., the
request is dropped by the PCE because of memory overflow), and the
PCC wishes to resend its request, the same Request-ID-number MUST
be used. Upon receiving a path computation request from a PCC
Vasseur & Le Roux Standards Track [Page 29]RFC 5440 PCEP March 2009
with the same Request-ID-number, the PCE SHOULD treat the request
as a new request. An implementation MAY choose to cache path
computation replies in order to quickly handle retransmission
without having to process a path computation request twice (in the
case that the first request was dropped or lost). Upon receiving
a path computation reply from a PCE with the same Request-ID-
number, the PCC SHOULD silently discard the path computation
reply.
Conversely, different Request-ID-numbers MUST be used for
different requests sent to a PCE.
The same Request-ID-number MAY be used for path computation
requests sent to different PCEs. The path computation reply is
unambiguously identified by the IP source address of the replying
PCE.
7.4.2. Handling of the RP Object
If a PCReq message is received that does not contain an RP object,
the PCE MUST send a PCErr message to the requesting PCC with Error-
Type="Required Object missing" and Error-value="RP Object missing".
If the O bit of the RP message carried within a PCReq message is
cleared and local policy has been configured on the PCE to not
provide explicit paths (for instance, for confidentiality reasons), a
PCErr message MUST be sent by the PCE to the requesting PCC and the
pending path computation request MUST be discarded. The Error-Type
is "Policy Violation" and Error-value is "O bit cleared".
When the R bit of the RP object is set in a PCReq message, this
indicates that the path computation request relates to the
reoptimization of an existing TE LSP. In this case, the PCC MUST
also provide the strict/loose path by including an RRO object in the
PCReq message so as to avoid/limit double-bandwidth counting if and
only if the TE LSP is a non-zero-bandwidth TE LSP. If the PCC has
not requested a strict path (O bit set), a reoptimization can still
be requested by the PCC, but this requires that the PCE either be
stateful (keep track of the previously computed path with the
associated list of strict hops), or have the ability to retrieve the
complete required path segment. Alternatively, the PCC MUST inform
the PCE about the working path and the associated list of strict hops
in PCReq. The absence of an RRO in the PCReq message for a non-zero-
bandwidth TE LSP (when the R bit of the RP object is set) MUST
trigger the sending of a PCErr message with Error-Type="Required
Object Missing" and Error-value="RRO Object missing for
reoptimization".
Vasseur & Le Roux Standards Track [Page 30]RFC 5440 PCEP March 2009
If a PCC/PCE receives a PCRep/PCReq message that contains an RP
object referring to an unknown Request-ID-number, the PCC/PCE MUST
send a PCErr message with Error-Type="Unknown request reference".
This is used for debugging purposes. If a PCC/PCE receives PCRep/
PCReq messages with unknown requests at a rate equal or greater than
MAX-UNKNOWN-REQUESTS unknown requests per minute, the PCC/PCE MUST
send a PCEP CLOSE message with close value="Reception of an
unacceptable number of unknown requests/replies". A RECOMMENDED
value for MAX-UNKNOWN-REQUESTS is 5. The PCC/PCE MUST close the TCP
session and MUST NOT send any further PCEP messages on the PCEP
session.
The reception of a PCEP message that contains an RP object referring
to a Request-ID-number=0x00000000 MUST be treated in similar manner
as an unknown request.
7.5. NO-PATH Object
The NO-PATH object is used in PCRep messages in response to an
unsuccessful path computation request (the PCE could not find a path
satisfying the set of constraints). When a PCE cannot find a path
satisfying a set of constraints, it MUST include a NO-PATH object in
the PCRep message.
There are several categories of issue that can lead to a negative
reply. For example, the PCE chain might be broken (should there be
more than one PCE involved in the path computation) or no path
obeying the set constraints could be found. The "NI (Nature of
Issue)" field in the NO-PATH object is used to report the error
category.
Optionally, if the PCE supports such capability, the NO-PATH object
MAY contain an optional NO-PATH-VECTOR TLV defined below and used to
provide more information on the reasons that led to a negative reply.
The PCRep message MAY also contain a list of objects that specify the
set of constraints that could not be satisfied. The PCE MAY just
replicate the set of objects that was received that was the cause of
the unsuccessful computation or MAY optionally report a suggested
value for which a path could have been found (in which case, the
value differs from the value in the original request).
NO-PATH Object-Class is 3.
NO-PATH Object-Type is 1.
Vasseur & Le Roux Standards Track [Page 31]
RFC 5440 PCEP March 2009
The format of the NO-PATH 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Nature of Issue|C| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: NO-PATH Object Format
NI - Nature of Issue (8 bits): The NI field is used to report the
nature of the issue that led to a negative reply. Two values are
currently defined:
0: No path satisfying the set of constraints could be found
1: PCE chain broken
The Nature of Issue field value can be used by the PCC for various
purposes:
* Constraint adjustment before reissuing a new path computation
request,
* Explicit selection of a new PCE chain,
* Logging of the error type for further action by the network
administrator.
IANA management of the NI field codespace is described in
Section 9.
Flags (16 bits).
The following flag is currently defined:
o C flag (1 bit): when set, the PCE indicates the set of unsatisfied
constraints (reasons why a path could not be found) in the PCRep
message by including the relevant PCEP objects. When cleared, no
failing constraints are specified. The C flag has no meaning and
is ignored unless the NI field is set to 0x00.
Unassigned bits are considered as reserved. They MUST be set to zero
on transmission and MUST be ignored on receipt.
Vasseur & Le Roux Standards Track [Page 32]RFC 5440 PCEP March 2009
Reserved (8 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
The NO-PATH object body has a variable length and may contain
additional TLVs. The only TLV currently defined is the NO-PATH-
VECTOR TLV defined below.
Example: consider the case of a PCC that sends a path computation
request to a PCE for a TE LSP of X Mbit/s. Suppose that PCE cannot
find a path for X Mbit/s. In this case, the PCE must include in the
PCRep message a NO-PATH object. Optionally, the PCE may also include
the original BANDWIDTH object so as to indicate that the reason for
the unsuccessful computation is the bandwidth constraint (in this
case, the NI field value is 0x00 and C flag is set). If the PCE
supports such capability, it may alternatively include the BANDWIDTH
object and report a value of Y in the bandwidth field of the
BANDWIDTH object (in this case, the C flag is set) where Y refers to
the bandwidth for which a TE LSP with the same other characteristics
(such as Setup/Holding priorities, TE LSP attribute, local
protection, etc.) could have been computed.
When the NO-PATH object is absent from a PCRep message, the path
computation request has been fully satisfied and the corresponding
paths are provided in the PCRep message.
An optional TLV named NO-PATH-VECTOR MAY be included in the NO-PATH
object in order to provide more information on the reasons that led
to a negative reply.
The NO-PATH-VECTOR TLV is compliant with the PCEP TLV format defined
in Section 7.1 and is comprised of 2 bytes for the type, 2 bytes
specifying the TLV length (length of the value portion in bytes)
followed by a fixed-length 32-bit flags field.
Type: 1
Length: 4 bytes
Value: 32-bit flags field
IANA manages the space of flags carried in the NO-PATH-VECTOR TLV
(see Section 9).
The following flags are currently defined:
o Bit number: 31 - PCE currently unavailable
o Bit number: 30 - Unknown destination
o Bit number: 29 - Unknown source
Vasseur & Le Roux Standards Track [Page 33]RFC 5440 PCEP March 2009
7.6. END-POINTS Object
The END-POINTS object is used in a PCReq message to specify the
source IP address and the destination IP address of the path for
which a path computation is requested. The P flag of the END-POINTS
object MUST be set. If the END-POINTS object is received with the P
flag cleared, the receiving peer MUST send a PCErr message with
Error-Type=10 and Error-value=1. The corresponding path computation
request MUST be cancelled by the PCE without further notification.
Note that the source and destination addresses specified in the END-
POINTS object may correspond to the source and destination IP address
of the TE LSP or to those of a path segment. Two END-POINTS objects
(for IPv4 and IPv6) are defined.
END-POINTS Object-Class is 4.
END-POINTS Object-Type is 1 for IPv4 and 2 for IPv6.
The format of the END-POINTS object body for IPv4 (Object-Type=1) 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: END-POINTS Object Body Format for IPv4
Vasseur & Le Roux Standards Track [Page 34]RFC 5440 PCEP March 2009
The format of the END-POINTS object for IPv6 (Object-Type=2) 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source IPv6 address (16 bytes) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination IPv6 address (16 bytes) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: END-POINTS Object Body Format for IPv6
The END-POINTS object body has a fixed length of 8 bytes for IPv4 and
32 bytes for IPv6.
If more than one END-POINTS object is present, the first MUST be
processed and subsequent objects ignored.
7.7. BANDWIDTH Object
The BANDWIDTH object is used to specify the requested bandwidth for a
TE LSP. The notion of bandwidth is similar to the one used for RSVP
signaling in [RFC2205], [RFC3209], and [RFC3473].
If the requested bandwidth is equal to 0, the BANDWIDTH object is
optional. Conversely, if the requested bandwidth is not equal to 0,
the PCReq message MUST contain a BANDWIDTH object.
In the case of the reoptimization of a TE LSP, the bandwidth of the
existing TE LSP MUST also be included in addition to the requested
bandwidth if and only if the two values differ. Consequently, two
Object-Type values are defined that refer to the requested bandwidth
and the bandwidth of the TE LSP for which a reoptimization is being
performed.
The BANDWIDTH object may be carried within PCReq and PCRep messages.
BANDWIDTH Object-Class is 5.
Vasseur & Le Roux Standards Track [Page 35]RFC 5440 PCEP March 2009
Two Object-Type values are defined for the BANDWIDTH object:
o Requested bandwidth: BANDWIDTH Object-Type is 1.
o Bandwidth of an existing TE LSP for which a reoptimization is
requested. BANDWIDTH Object-Type is 2.
The format of the BANDWIDTH 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: BANDWIDTH Object Body Format
Bandwidth (32 bits): The requested bandwidth is encoded in 32 bits
in IEEE floating point format (see [IEEE.754.1985]), expressed in
bytes per second. Refer to Section 3.1.2 of [RFC3471] for a table
of commonly used values.
The BANDWIDTH object body has a fixed length of 4 bytes.
7.8. METRIC Object
The METRIC object is optional and can be used for several purposes.
In a PCReq message, a PCC MAY insert one or more METRIC objects:
o To indicate the metric that MUST be optimized by the path
computation algorithm (IGP metric, TE metric, hop counts).
Currently, three metrics are defined: the IGP cost, the TE metric
(see [RFC3785]), and the number of hops traversed by a TE LSP.
o To indicate a bound on the path cost that MUST NOT be exceeded for
the path to be considered as acceptable by the PCC.
In a PCRep message, the METRIC object MAY be inserted so as to
provide the cost for the computed path. It MAY also be inserted
within a PCRep with the NO-PATH object to indicate that the metric
constraint could not be satisfied.
The path computation algorithmic aspects used by the PCE to optimize
a path with respect to a specific metric are outside the scope of
this document.
Vasseur & Le Roux Standards Track [Page 36]RFC 5440 PCEP March 2009
It must be understood that such path metrics are only meaningful if
used consistently: for instance, if the delay of a computed path
segment is exchanged between two PCEs residing in different domains,
consistent ways of defining the delay must be used.
The absence of the METRIC object MUST be interpreted by the PCE as a
path computation request for which no constraints need be applied to
any of the metrics.
METRIC Object-Class is 6.
METRIC Object-Type is 1.
The format of the METRIC 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 |C|B| T |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| metric-value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: METRIC Object Body Format
The METRIC object body has a fixed length of 8 bytes.
Reserved (16 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
T (Type - 8 bits): Specifies the metric type.
Three values are currently defined:
* T=1: IGP metric
* T=2: TE metric
* T=3: Hop Counts
Flags (8 bits): Two flags are currently defined:
* B (Bound - 1 bit): When set in a PCReq message, the metric-
value indicates a bound (a maximum) for the path metric that
must not be exceeded for the PCC to consider the computed path
as acceptable. The path metric must be less than or equal to
the value specified in the metric-value field. When the B flag
is cleared, the metric-value field is not used to reflect a
bound constraint.
Vasseur & Le Roux Standards Track [Page 37]RFC 5440 PCEP March 2009
* C (Computed Metric - 1 bit): When set in a PCReq message, this
indicates that the PCE MUST provide the computed path metric
value (should a path satisfying the constraints be found) in
the PCRep message for the corresponding metric.
Unassigned flags MUST be set to zero on transmission and MUST be
ignored on receipt.
Metric-value (32 bits): metric value encoded in 32 bits in IEEE
floating point format (see [IEEE.754.1985]).
Multiple METRIC objects MAY be inserted in a PCRep or a PCReq message
for a given request (i.e., for a given RP). For a given request,
there MUST be at most one instance of the METRIC object for each
metric type with the same B flag value. If, for a given request, two
or more instances of a METRIC object with the same B flag value are
present for a metric type, only the first instance MUST be considered
and other instances MUST be ignored.
For a given request, the presence of two METRIC objects of the same
type with a different value of the B flag is allowed. Furthermore,
it is also allowed to insert, for a given request, two METRIC objects
with different types that have both their B flag cleared: in this
case, an objective function must be used by the PCE to solve a multi-
parameter optimization problem.
A METRIC object used to indicate the metric to optimize during the
path computation MUST have the B flag cleared and the C flag set to
the appropriate value. When the path computation relates to the
reoptimization of an exiting TE LSP (in which case, the R flag of the
RP object is set), an implementation MAY decide to set the metric-
value field to the computed value of the metric of the TE LSP to be
reoptimized with regards to a specific metric type.
A METRIC object used to reflect a bound MUST have the B flag set, and
the C flag and metric-value field set to the appropriate values.
In a PCRep message, unless not allowed by PCE policy, at least one
METRIC object MUST be present that reports the computed path metric
if the C flag of the METRIC object was set in the corresponding path
computation request (the B flag MUST be cleared). The C flag has no
meaning in a PCRep message. Optionally, the PCRep message MAY
contain additional METRIC objects that correspond to bound
constraints; in which case, the metric-value MUST be equal to the
corresponding computed path metric (the B flag MUST be set). If no
path satisfying the constraints could be found by the PCE, the METRIC
objects MAY also be present in the PCRep message with the NO-PATH
object to indicate the constraint metric that could be satisfied.
Vasseur & Le Roux Standards Track [Page 38]RFC 5440 PCEP March 2009
Example: if a PCC sends a path computation request to a PCE where the
metric to optimize is the IGP metric and the TE metric must not
exceed the value of M, two METRIC objects are inserted in the PCReq
message:
o First METRIC object with B=0, T=1, C=1, metric-value=0x0000
o Second METRIC object with B=1, T=2, metric-value=M
If a path satisfying the set of constraints can be found by the PCE
and there is no policy that prevents the return of the computed
metric, the PCE inserts one METRIC object with B=0, T=1, metric-
value= computed IGP path cost. Additionally, the PCE may insert a
second METRIC object with B=1, T=2, metric-value= computed TE path
cost.
7.9. Explicit Route Object
The ERO is used to encode the path of a TE LSP through the network.
The ERO is carried within a PCRep message to provide the computed TE
LSP if the path computation was successful.
The contents of this object are identical in encoding to the contents
of the Resource Reservation Protocol Traffic Engineering Extensions
(RSVP-TE) Explicit Route Object (ERO) defined in [RFC3209],
[RFC3473], and [RFC3477]. That is, the object is constructed from a
series of sub-objects. Any RSVP-TE ERO sub-object already defined or
that could be defined in the future for use in the RSVP-TE ERO is
acceptable in this object.
PCEP ERO sub-object types correspond to RSVP-TE ERO sub-object types.
Since the explicit path is available for immediate signaling by the
MPLS or GMPLS control plane, the meanings of all of the sub-objects
and fields in this object are identical to those defined for the ERO.
ERO Object-Class is 7.
ERO Object-Type is 1.
7.10. Reported Route Object
The RRO is exclusively carried within a PCReq message so as to report
the route followed by a TE LSP for which a reoptimization is desired.
The contents of this object are identical in encoding to the contents
of the Route Record Object defined in [RFC3209], [RFC3473], and
[RFC3477]. That is, the object is constructed from a series of sub-
Vasseur & Le Roux Standards Track [Page 39]
RFC 5440 PCEP March 2009
objects. Any RSVP-TE RRO sub-object already defined or that could be
defined in the future for use in the RSVP-TE RRO is acceptable in
this object.
The meanings of all of the sub-objects and fields in this object are
identical to those defined for the RSVP-TE RRO.
PCEP RRO sub-object types correspond to RSVP-TE RRO sub-object types.
RRO Object-Class is 8.
RRO Object-Type is 1.
7.11. LSPA Object
The LSPA (LSP Attributes) object is optional and specifies various TE
LSP attributes to be taken into account by the PCE during path
computation. The LSPA object can be carried within a PCReq message,
or a PCRep message in case of unsuccessful path computation (in this
case, the PCRep message also contains a NO-PATH object, and the LSPA
object is used to indicate the set of constraints that could not be
satisfied). Most of the fields of the LSPA object are identical to
the fields of the SESSION-ATTRIBUTE object (C-Type = 7) defined in
[RFC3209] and [RFC4090]. When absent from the PCReq message, this
means that the Setup and Holding priorities are equal to 0, and there
are no affinity constraints. See Section 4.7.4 of [RFC3209] for a
detailed description of the use of resource affinities.
LSPA Object-Class is 9.
LSPA Object-Types is 1.
Vasseur & Le Roux Standards Track [Page 40]
RFC 5440 PCEP March 2009
The format of the LSPA 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Exclude-any |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-any |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-all |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Setup Prio | Holding Prio | Flags |L| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: LSPA Object Body Format
Setup Prio (Setup Priority - 8 bits): The priority of the TE LSP
with respect to taking resources, in the range of 0 to 7. The
value 0 is the highest priority. The Setup Priority is used in
deciding whether this session can preempt another session.
Holding Prio (Holding Priority - 8 bits): The priority of the TE LSP
with respect to holding resources, in the range of 0 to 7. The
value 0 is the highest priority. Holding Priority is used in
deciding whether this session can be preempted by another session.
Flags (8 bits)
L flag: Corresponds to the "Local Protection Desired" bit
([RFC3209]) of the SESSION-ATTRIBUTE Object. When set, this
means that the computed path must include links protected with
Fast Reroute as defined in [RFC4090].
Unassigned flags MUST be set to zero on transmission and MUST be
ignored on receipt.
Reserved (8 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Note that optional TLVs may be defined in the future to carry
additional TE LSP attributes such as those defined in [RFC5420].
Vasseur & Le Roux Standards Track [Page 41]RFC 5440 PCEP March 2009
7.12. Include Route Object
The IRO (Include Route Object) is optional and can be used to specify
that the computed path MUST traverse a set of specified network
elements. The IRO MAY be carried within PCReq and PCRep messages.
When carried within a PCRep message with the NO-PATH object, the IRO
indicates the set of elements that cause the PCE to fail to find a
path.
IRO Object-Class is 10.
IRO Object-Type is 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Sub-objects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: IRO Body Format
Sub-objects: The IRO is made of sub-objects identical to the ones
defined in [RFC3209], [RFC3473], and [RFC3477], where the IRO sub-
object type is identical to the sub-object type defined in the
related documents.
The following sub-object types are supported.
Type Sub-object
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number
The L bit of such sub-object has no meaning within an IRO.
7.13. SVEC Object
7.13.1. Notion of Dependent and Synchronized Path Computation Requests
Independent versus dependent path computation requests: path
computation requests are said to be independent if they are not
related to each other. Conversely, a set of dependent path
computation requests is such that their computations cannot be
performed independently of each other (a typical example of dependent
requests is the computation of a set of diverse paths).
Vasseur & Le Roux Standards Track [Page 42]RFC 5440 PCEP March 2009
Synchronized versus non-synchronized path computation requests: a set
of path computation requests is said to be non-synchronized if their
respective treatment (path computations) can be performed by a PCE in
a serialized and independent fashion.
There are various circumstances where the synchronization of a set of
path computations may be beneficial or required.
Consider the case of a set of N TE LSPs for which a PCC needs to send
path computation requests to a PCE. The first solution consists of
sending N separate PCReq messages to the selected PCE. In this case,
the path computation requests are non-synchronized. Note that the
PCC may chose to distribute the set of N requests across K PCEs for
load balancing purposes. Considering that M (with M<N) requests are
sent to a particular PCEi, as described above, such M requests can be
sent in the form of successive PCReq messages destined to PCEi or
bundled within a single PCReq message (since PCEP allows for the
bundling of multiple path computation requests within a single PCReq
message). That said, even in the case of independent requests, it
can be desirable to request from the PCE the computation of their
paths in a synchronized fashion that is likely to lead to more
optimal path computations and/or reduced blocking probability if the
PCE is a stateless PCE. In other words, the PCE should not compute
the corresponding paths in a serialized and independent manner, but
it should rather "simultaneously" compute their paths. For example,
trying to "simultaneously" compute the paths of M TE LSPs may allow
the PCE to improve the likelihood to meet multiple constraints.
Consider the case of two TE LSPs requesting N1 Mbit/s and N2 Mbit/s,
respectively, and a maximum tolerable end-to-end delay for each TE
LSP of X ms. There may be circumstances where the computation of the
first TE LSP, irrespectively of the second TE LSP, may lead to the
impossibility to meet the delay constraint for the second TE LSP.
A second example is related to the bandwidth constraint. It is quite
straightforward to provide examples where a serialized independent
path computation approach would lead to the impossibility to satisfy
both requests (due to bandwidth fragmentation), while a synchronized
path computation would successfully satisfy both requests.
A last example relates to the ability to avoid the allocation of the
same resource to multiple requests, thus helping to reduce the call
setup failure probability compared to the serialized computation of
independent requests.
Dependent path computations are usually synchronized. For example,
in the case of the computation of M diverse paths, if such paths are
computed in a non-synchronized fashion, this seriously increases the
Vasseur & Le Roux Standards Track [Page 43]
RFC 5440 PCEP March 2009
probability of not being able to satisfy all requests (sometimes also
referred to as the well-known "trapping problem").
Furthermore, this would not allow a PCE to implement objective
functions such as trying to minimize the sum of the TE LSP costs. In
such a case, the path computation requests must be synchronized: they
cannot be computed independently of each other.
Conversely, a set of independent path computation requests may or may
not be synchronized.
The synchronization of a set of path computation requests is achieved
by using the SVEC object that specifies the list of synchronized
requests that can either be dependent or independent.
PCEP supports the following three modes:
o Bundle of a set of independent and non-synchronized path
computation requests,
o Bundle of a set of independent and synchronized path computation
requests (requires the SVEC object defined below),
o Bundle of a set of dependent and synchronized path computation
requests (requires the SVEC object defined below).
7.13.2. SVEC Object
Section 7.13.1 details the circumstances under which it may be
desirable and/or required to synchronize a set of path computation
requests. The SVEC (Synchronization VECtor) object allows a PCC to
request the synchronization of a set of dependent or independent path
computation requests. The SVEC object is optional and may be carried
within a PCReq message.
The aim of the SVEC object carried within a PCReq message is to
request the synchronization of M path computation requests. The SVEC
object is a variable-length object that lists the set of M path
computation requests that must be synchronized. Each path
computation request is uniquely identified by the Request-ID-number
carried within the respective RP object. The SVEC object also
contains a set of flags that specify the synchronization type.
SVEC Object-Class is 11.
SVEC Object-Type is 1.
Vasseur & Le Roux Standards Track [Page 44]RFC 5440 PCEP March 2009
The format of the SVEC 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 |S|N|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request-ID-number #1 |
// //
| Request-ID-number #M |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: SVEC Body Object Format
Reserved (8 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Flags (24 bits): Defines the potential dependency between the set of
path computation requests.
* L (Link diverse) bit: when set, this indicates that the
computed paths corresponding to the requests specified by the
following RP objects MUST NOT have any link in common.
* N (Node diverse) bit: when set, this indicates that the
computed paths corresponding to the requests specified by the
following RP objects MUST NOT have any node in common.
* S (SRLG diverse) bit: when set, this indicates that the
computed paths corresponding to the requests specified by the
following RP objects MUST NOT share any SRLG (Shared Risk Link
Group).
In case of a set of M synchronized independent path computation
requests, the bits L, N, and S are cleared.
Unassigned flags MUST be set to zero on transmission and MUST be
ignored on receipt.
The flags defined above are not exclusive.
7.13.3. Handling of the SVEC Object
The SVEC object allows a PCC to specify a list of M path computation
requests that MUST be synchronized along with a potential dependency.
The set of M path computation requests may be sent within a single
PCReq message or multiple PCReq messages. In the latter case, it is
RECOMMENDED for the PCE to implement a local timer (called the
Vasseur & Le Roux Standards Track [Page 45]RFC 5440 PCEP March 2009
SyncTimer) activated upon the receipt of the first PCReq message that
contains the SVEC object after the expiration of which, if all the M
path computation requests have not been received, a protocol error is
triggered. When a PCE receives a path computation request that
cannot be satisfied (for example, because the PCReq message contains
an object with the P bit set that is not supported), the PCE sends a
PCErr message for this request (see Section 7.2), the PCE MUST cancel
the whole set of related path computation requests and MUST send a
PCErr message with Error-Type="Synchronized path computation request
missing".
Note that such PCReq messages may also contain non-synchronized path
computation requests. For example, the PCReq message may comprise N
synchronized path computation requests that are related to RP 1, ...,
RP N and are listed in the SVEC object along with any other path
computation requests that are processed as normal.
7.14. NOTIFICATION Object
The NOTIFICATION object is exclusively carried within a PCNtf message
and can either be used in a message sent by a PCC to a PCE or by a
PCE to a PCC so as to notify of an event.
NOTIFICATION Object-Class is 12.
NOTIFICATION Object-Type is 1.
The format of the NOTIFICATION body object 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 | NT | NV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: NOTIFICATION Body Object Format
Reserved (8 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Flags (8 bits): No flags are currently defined. Unassigned flags
MUST be set to zero on transmission and MUST be ignored on
receipt.
Vasseur & Le Roux Standards Track [Page 46]RFC 5440 PCEP March 2009
NT (Notification Type - 8 bits): The Notification-type specifies the
class of notification.
NV (Notification Value - 8 bits): The Notification-value provides
addition information related to the nature of the notification.
Both the Notification-type and Notification-value are managed by
IANA.
The following Notification-type and Notification-value values are
currently defined:
o Notification-type=1: Pending Request cancelled
* Notification-value=1: PCC cancels a set of pending requests. A
Notification-type=1, Notification-value=1 indicates that the
PCC wants to inform a PCE of the cancellation of a set of
pending requests. Such an event could be triggered because of
external conditions such as the receipt of a positive reply
from another PCE (should the PCC have sent multiple requests to
a set of PCEs for the same path computation request), a network
event such as a network failure rendering the request obsolete,
or any other events local to the PCC. A NOTIFICATION object
with Notification-type=1, Notification-value=1 is carried
within a PCNtf message sent by the PCC to the PCE. The RP
object corresponding to the cancelled request MUST also be
present in the PCNtf message. Multiple RP objects may be
carried within the PCNtf message; in which case, the
notification applies to all of them. If such a notification is
received by a PCC from a PCE, the PCC MUST silently ignore the
notification and no errors should be generated.
* Notification-value=2: PCE cancels a set of pending requests. A
Notification-type=1, Notification-value=2 indicates that the
PCE wants to inform a PCC of the cancellation of a set of
pending requests. A NOTIFICATION object with Notification-
type=1, Notification-value=2 is carried within a PCNtf message
sent by a PCE to a PCC. The RP object corresponding to the
cancelled request MUST also be present in the PCNtf message.
Multiple RP objects may be carried within the PCNtf message; in
which case, the notification applies to all of them. If such
notification is received by a PCE from a PCC, the PCE MUST
silently ignore the notification and no errors should be
generated.
o Notification-type=2: Overloaded PCE
* Notification-value=1: A Notification-type=2, Notification-
Vasseur & Le Roux Standards Track [Page 47]RFC 5440 PCEP March 2009
value=1 indicates to the PCC that the PCE is currently in an
overloaded state. If no RP objects are included in the PCNtf
message, this indicates that no other requests SHOULD be sent
to that PCE until the overloaded state is cleared: the pending
requests are not affected and will be served. If some pending
requests cannot be served due to the overloaded state, the PCE
MUST also include a set of RP objects that identifies the set
of pending requests that are cancelled by the PCE and will not
be honored. In this case, the PCE does not have to send an
additional PCNtf message with Notification-type=1 and
Notification-value=2 since the list of cancelled requests is
specified by including the corresponding set of RP objects. If
such notification is received by a PCE from a PCC, the PCE MUST
silently ignore the notification and no errors should be
generated.
* A PCE implementation SHOULD use a dual-threshold mechanism used
to determine whether it is in a congestion state with regards
to specific resource monitoring (e.g. CPU, memory). The use
of such thresholds is to avoid oscillations between overloaded/
non-overloaded state that may result in oscillations of request
targets by the PCCs.
* Optionally, a TLV named OVERLOADED-DURATION may be included in
the NOTIFICATION object that specifies the period of time
during which no further request should be sent to the PCE.
Once this period of time has elapsed, the PCE should no longer
be considered in a congested state.
The OVERLOADED-DURATION TLV is compliant with the PCEP TLV
format defined in Section 7.1 and is comprised of 2 bytes for
the type, 2 bytes specifying the TLV length (length of the
value portion in bytes), followed by a fixed-length value field
of a 32-bit flags field.
Type: 2
Length: 4 bytes
Value: 32-bit flags field indicates the estimated PCE
congestion duration in seconds.
* Notification-value=2: A Notification-type=2, Notification-
value=2 indicates that the PCE is no longer in an overloaded
state and is available to process new path computation
requests. An implementation SHOULD make sure that a PCE sends
such notification to every PCC to which a Notification message
(with Notification-type=2, Notification-value=1) has been sent
unless an OVERLOADED-DURATION TLV has been included in the
corresponding message and the PCE wishes to wait for the
Vasseur & Le Roux Standards Track [Page 48]RFC 5440 PCEP March 2009
expiration of that period of time before receiving new
requests. If such notification is received by a PCE from a
PCC, the PCE MUST silently ignore the notification and no
errors should be generated. It is RECOMMENDED to support some
dampening notification procedure on the PCE so as to avoid too
frequent congestion state and congestion state release
notifications. For example, an implementation could make use
of an hysteresis approach using a dual-threshold mechanism that
triggers the sending of congestion state notifications.
Furthermore, in case of high instabilities of the PCE
resources, an additional dampening mechanism SHOULD be used
(linear or exponential) to pace the notification frequency and
avoid oscillation of path computation requests.
When a PCC receives an overload indication from a PCE, it should
consider the impact on the entire network. It must be remembered
that other PCCs may also receive the notification, and so many path
computation requests could be redirected to other PCEs. This may, in
turn, cause further overloading at PCEs in the network. Therefore,
an application at a PCC receiving an overload notification should
consider applying some form of back-off (e.g., exponential) to the
rate at which it generates path computation requests into the
network. This is especially the case as the number of PCEs reporting
overload grows.
7.15. PCEP-ERROR Object
The PCEP-ERROR object is exclusively carried within a PCErr message
to notify of a PCEP error.
PCEP-ERROR Object-Class is 13.
PCEP-ERROR Object-Type is 1.
The format of the PCEP-ERROR 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 | Error-Type | Error-value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: PCEP-ERROR Object Body Format
Vasseur & Le Roux Standards Track [Page 49]RFC 5440 PCEP March 2009
A PCEP-ERROR object is used to report a PCEP error and is
characterized by an Error-Type that specifies the type of error and
an Error-value that provides additional information about the error
type. Both the Error-Type and the Error-value are managed by IANA
(see the IANA section).
Reserved (8 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Flags (8 bits): no flag is currently defined. This flag MUST be set
to zero on transmission and MUST be ignored on receipt.
Error-Type (8 bits): defines the class of error.
Error-value (8 bits): provides additional details about the error.
Optionally, the PCEP-ERROR object may contain additional TLVs so as
to provide further information about the encountered error.
A single PCErr message may contain multiple PCEP-ERROR objects.
Vasseur & Le Roux Standards Track [Page 50]RFC 5440 PCEP March 2009
For each PCEP error, an Error-Type and an Error-value are defined.
Error-Type Meaning
1 PCEP session establishment failure
Error-value=1: reception of an invalid Open message or
a non Open message.
Error-value=2: no Open message received before the
expiration of the OpenWait timer
Error-value=3: unacceptable and non-negotiable session
characteristics
Error-value=4: unacceptable but negotiable session
characteristics
Error-value=5: reception of a second Open message with
still unacceptable session
characteristics
Error-value=6: reception of a PCErr message proposing
unacceptable session characteristics
Error-value=7: No Keepalive or PCErr message received
before the expiration of the KeepWait
timer
2 Capability not supported
3 Unknown Object
Error-value=1: Unrecognized object class
Error-value=2: Unrecognized object Type
4 Not supported object
Error-value=1: Not supported object class
Error-value=2: Not supported object Type
5 Policy violation
Error-value=1: C bit of the METRIC object set
(request rejected)
Error-value=2: O bit of the RP object set
(request rejected)
6 Mandatory Object missing
Error-value=1: RP object missing
Error-value=2: RRO object missing for a reoptimization
request (R bit of the RP object set)
when bandwidth is not equal to 0.
Error-value=3: END-POINTS object missing
7 Synchronized path computation request missing
8 Unknown request reference
9 Attempt to establish a second PCEP session
10 Reception of an invalid object
Error-value=1: reception of an object with P flag not
set although the P flag must be set according to this
specification.
Vasseur & Le Roux Standards Track [Page 51]RFC 5440 PCEP March 2009
The error types listed above are described below.
Error-Type=1: PCEP session establishment failure.
If a malformed message is received, the receiving PCEP peer MUST
send a PCErr message with Error-Type=1, Error-value=1.
If no Open message is received before the expiration of the
OpenWait timer, the receiving PCEP peer MUST send a PCErr message
with Error-Type=1, Error-value=2 (see Appendix A for details).
If one or more PCEP session characteristics are unacceptable by
the receiving peer and are not negotiable, it MUST send a PCErr
message with Error-Type=1, Error-value=3.
If an Open message is received with unacceptable session
characteristics but these characteristics are negotiable, the
receiving PCEP peer MUST send a PCErr message with Error-Type-1,
Error-value=4 (see Section 6.2 for details).
If a second Open message is received during the PCEP session
establishment phase and the session characteristics are still
unacceptable, the receiving PCEP peer MUST send a PCErr message
with Error-Type-1, Error-value=5 (see Section 6.2 for details).
If a PCErr message is received during the PCEP session
establishment phase that contains an Open message proposing
unacceptable session characteristics, the receiving PCEP peer MUST
send a PCErr message with Error-Type=1, Error-value=6.
If neither a Keepalive message nor a PCErr message is received
before the expiration of the KeepWait timer during the PCEP
session establishment phase, the receiving PCEP peer MUST send a
PCErr message with Error-Type=1, Error-value=7.
Error-Type=2: the PCE indicates that the path computation request
cannot be honored because it does not support one or more required
capability. The corresponding path computation request MUST be
cancelled.
Error-Type=3 or Error-Type=4: if a PCEP message is received that
carries a PCEP object (with the P flag set) not recognized by the
PCE or recognized but not supported, then the PCE MUST send a
PCErr message with a PCEP-ERROR object (Error-Type=3 and 4,
respectively). In addition, the PCE MAY include in the PCErr
message the unknown or not supported object. The corresponding
path computation request MUST be cancelled by the PCE without
further notification.
Vasseur & Le Roux Standards Track [Page 52]RFC 5440 PCEP March 2009
Error-Type=5: if a path computation request is received that is not
compliant with an agreed policy between the PCC and the PCE, the
PCE MUST send a PCErr message with a PCEP-ERROR object (Error-
Type=5). The corresponding path computation MUST be cancelled.
Policy-specific TLVs carried within the PCEP-ERROR object may be
defined in other documents to specify the nature of the policy
violation.
Error-Type=6: if a path computation request is received that does
not contain a mandatory object, the PCE MUST send a PCErr message
with a PCEP-ERROR object (Error-Type=6). If there are multiple
mandatory objects missing, the PCErr message MUST contain one
PCEP-ERROR object per missing object. The corresponding path
computation MUST be cancelled.
Error-Type=7: if a PCC sends a synchronized path computation request
to a PCE and the PCE does not receive all the synchronized path
computation requests listed within the corresponding SVEC object
after the expiration of the timer SyncTimer defined in
Section 7.13.3, the PCE MUST send a PCErr message with a PCEP-
ERROR object (Error-Type=7). The corresponding synchronized path
computation MUST be cancelled. It is RECOMMENDED for the PCE to
include the REQ-MISSING TLVs (defined below) that identify the
missing requests.
The REQ-MISSING TLV is compliant with the PCEP TLV format defined
in section 7.1 and is comprised of 2 bytes for the type, 2 bytes
specifying the TLV length (length of the value portion in bytes),
followed by a fixed-length value field of 4 bytes.
Type: 3
Length: 4 bytes
Value: 4 bytes that indicate the Request-ID-number that
corresponds to the missing request.
Error-Type=8: if a PCC receives a PCRep message related to an
unknown path computation request, the PCC MUST send a PCErr
message with a PCEP-ERROR object (Error-Type=8). In addition, the
PCC MUST include in the PCErr message the unknown RP object.
Error-Type=9: if a PCEP peer detects an attempt from another PCEP
peer to establish a second PCEP session, it MUST send a PCErr
message with Error-Type=9, Error-value=1. The existing PCEP
session MUST be preserved and all subsequent messages related to
the tentative establishment of the second PCEP session MUST be
silently ignored.
Vasseur & Le Roux Standards Track [Page 53]RFC 5440 PCEP March 2009
Error-Type=10: if a PCEP peers receives an object with the P flag
not set although the P flag must be set according to this
specification, it MUST send a PCErr message with Error-Type=10,
Error-value=1.
7.16. LOAD-BALANCING Object
There are situations where no TE LSP with a bandwidth of X could be
found by a PCE although such a bandwidth requirement could be
satisfied by a set of TE LSPs such that the sum of their bandwidths
is equal to X. Thus, it might be useful for a PCC to request a set
of TE LSPs so that the sum of their bandwidth is equal to X Mbit/s,
with potentially some constraints on the number of TE LSPs and the
minimum bandwidth of each of these TE LSPs. Such a request is made
by inserting a LOAD-BALANCING object in a PCReq message sent to a
PCE.
The LOAD-BALANCING object is optional.
LOAD-BALANCING Object-Class is 14.
LOAD-BALANCING Object-Type is 1.
The format of the LOAD-BALANCING 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 | Max-LSP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min-Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: LOAD-BALANCING Object Body Format
Reserved (16 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Flags (8 bits): No flag is currently defined. The Flags field MUST
be set to zero on transmission and MUST be ignored on receipt.
Max-LSP (8 bits): maximum number of TE LSPs in the set.
Min-Bandwidth (32 bits): Specifies the minimum bandwidth of each
element of the set of TE LSPs. The bandwidth is encoded in 32
bits in IEEE floating point format (see [IEEE.754.1985]),
expressed in bytes per second.
Vasseur & Le Roux Standards Track [Page 54]RFC 5440 PCEP March 2009
The LOAD-BALANCING object body has a fixed length of 8 bytes.
If a PCC requests the computation of a set of TE LSPs so that the sum
of their bandwidth is X, the maximum number of TE LSPs is N, and each
TE LSP must at least have a bandwidth of B, it inserts a BANDWIDTH
object specifying X as the required bandwidth and a LOAD-BALANCING
object with the Max-LSP and Min-Bandwidth fields set to N and B,
respectively.
7.17. CLOSE Object
The CLOSE object MUST be present in each Close message. There MUST
be only one CLOSE object per Close message. If a Close message is
received that contains more than one CLOSE object, the first CLOSE
object is the one that must be processed. Other CLOSE objects MUST
be silently ignored.
CLOSE Object-Class is 15.
CLOSE Object-Type is 1.
The format of the CLOSE 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 | Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: CLOSE Object Format
Reserved (16 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Flags (8 bits): No flags are currently defined. The Flag field MUST
be set to zero on transmission and MUST be ignored on receipt.
Reason (8 bits): specifies the reason for closing the PCEP session.
The setting of this field is optional. IANA manages the codespace
of the Reason field. The following values are currently defined:
Vasseur & Le Roux Standards Track [Page 55]RFC 5440 PCEP March 2009
Reasons
Value Meaning
1 No explanation provided
2 DeadTimer expired
3 Reception of a malformed PCEP message
4 Reception of an unacceptable number of unknown
requests/replies
5 Reception of an unacceptable number of unrecognized
PCEP messages
Optional TLVs may be included within the CLOSE object body. The
specification of such TLVs is outside the scope of this document.
8. Manageability Considerations
This section follows the guidance of [PCE-MANAGE].
8.1. Control of Function and Policy
A PCEP implementation SHOULD allow configuring the following PCEP
session parameters on the implementation:
o The local Keepalive and DeadTimer (i.e., parameters sent by the
PCEP peer in an Open message),
o The maximum acceptable remote Keepalive and DeadTimer (i.e.,
parameters received from a peer in an Open message),
o Whether negotiation is enabled or disabled,
o If negotiation is allowed, the minimum acceptable Keepalive and
DeadTimer timers received from a PCEP peer,
o The SyncTimer,
o The maximum number of sessions that can be set up,
o The request timer, the amount of time a PCC waits for a reply
before resending its path computation requests (potentially to an
alternate PCE),
o The MAX-UNKNOWN-REQUESTS,
o The MAX-UNKNOWN-MESSAGES.
These parameters may be configured as default parameters for any PCEP
session the PCEP speaker participates in, or may apply to a specific
session with a given PCEP peer or to a specific group of sessions
Vasseur & Le Roux Standards Track [Page 56]RFC 5440 PCEP March 2009
with a specific group of PCEP peers. A PCEP implementation SHOULD
allow configuring the initiation of a PCEP session with a selected
subset of discovered PCEs. Note that PCE selection is a local
implementation issue. A PCEP implementation SHOULD allow configuring
a specific PCEP session with a given PCEP peer. This includes the
configuration of the following parameters:
o The IP address of the PCEP peer,
o The PCEP speaker role: PCC, PCE, or both,
o Whether the PCEP speaker should initiate the PCEP session or wait
for initiation by the peer,
o The PCEP session parameters, as listed above, if they differ from
the default parameters,
o A set of PCEP policies including the type of operations allowed
for the PCEP peer (e.g., diverse path computation,
synchronization, etc.).
A PCEP implementation MUST allow restricting the set of PCEP peers
that can initiate a PCEP session with the PCEP speaker (e.g., list of
authorized PCEP peers, all PCEP peers in the area, all PCEP peers in
the AS).
8.2. Information and Data Models
A PCEP MIB module is defined in [PCEP-MIB] that describes managed
objects for modeling of PCEP communication including:
o PCEP client configuration and status,
o PCEP peer configuration and information,
o PCEP session configuration and information,
o Notifications to indicate PCEP session changes.
8.3. Liveness Detection and Monitoring
PCEP includes a keepalive mechanism to check the liveliness of a PCEP
peer and a notification procedure allowing a PCE to advertise its
overloaded state to a PCC. Also, procedures in order to monitor the
liveliness and performances of a given PCE chain (in case of
multiple-PCE path computation) are defined in [PCE-MONITOR].
Vasseur & Le Roux Standards Track [Page 57]RFC 5440 PCEP March 2009
8.4. Verifying Correct Operation
Verifying the correct operation of a PCEP communication can be
performed by monitoring various parameters. A PCEP implementation
SHOULD provide the following parameters:
o Response time (minimum, average, and maximum), on a per-PCE-peer
basis,
o PCEP session failures,
o Amount of time the session has been in active state,
o Number of corrupted messages,
o Number of failed computations,
o Number of requests for which no reply has been received after the
expiration of a configurable timer and by verifying that at least
one path exists that satisfies the set of constraints.
A PCEP implementation SHOULD log error events (e.g., corrupted
messages, unrecognized objects).
8.5. Requirements on Other Protocols and Functional Components
PCEP does not put any new requirements on other protocols. As PCEP
relies on the TCP transport protocol, PCEP management can make use of
TCP management mechanisms (such as the TCP MIB defined in [RFC4022]).
The PCE Discovery mechanisms ([RFC5088], [RFC5089]) may have an
impact on PCEP. To avoid that a high frequency of PCE Discoveries/
Disappearances triggers a high frequency of PCEP session setups/
deletions, it is RECOMMENDED to introduce some dampening for
establishment of PCEP sessions.
8.6. Impact on Network Operation
In order to avoid any unacceptable impact on network operations, an
implementation SHOULD allow a limit to be placed on the number of
sessions that can be set up on a PCEP speaker, and MAY allow a limit
to be placed on the rate of messages sent by a PCEP speaker and
received from a peer. It MAY also allow sending a notification when
a rate threshold is reached.
Vasseur & Le Roux Standards Track [Page 58]RFC 5440 PCEP March 2009
9. IANA Considerations
IANA assigns values to the PCEP protocol parameters (messages,
objects, TLVs).
IANA established a new top-level registry to contain all PCEP
codepoints and sub-registries.
The allocation policy for each new registry is by IETF Consensus: new
values are assigned through the IETF consensus process (see
[RFC5226]). Specifically, new assignments are made via RFCs approved
by the IESG. Typically, the IESG will seek input on prospective
assignments from appropriate persons (e.g., a relevant Working Group
if one exists).
9.1. TCP Port
PCEP has been registered as TCP port 4189.
9.2. PCEP Messages
IANA created a registry for PCEP messages. Each PCEP message has a
message type value.
Value Meaning Reference
1 Open This document
2 Keepalive This document
3 Path Computation Request This document
4 Path Computation Reply This document
5 Notification This document
6 Error This document
7 Close This document
9.3. PCEP Object
IANA created a registry for PCEP objects. Each PCEP object has an
Object-Class and an Object-Type.
Object-Class Value Name Reference
1 OPEN This document
Object-Type
1
2 RP This document
Object-Type
1
Vasseur & Le Roux Standards Track [Page 59]RFC 5440 PCEP March 2009
3 NO-PATH This document
Object-Type
1
4 END-POINTS This document
Object-Type
1: IPv4 addresses
2: IPv6 addresses
5 BANDWIDTH This document
Object-Type
1: Requested bandwidth
2: Bandwidth of an existing TE LSP
for which a reoptimization is performed.
6 METRIC This document
Object-Type
1
7 ERO This document
Object-Type
1
8 RRO This document
Object-Type
1
9 LSPA This document
Object-Type
1
10 IRO This document
Object-Type
1
11 SVEC This document
Object-Type
1
12 NOTIFICATION This document
Object-Type
1
13 PCEP-ERROR This document
Object-Type
1
Vasseur & Le Roux Standards Track [Page 60]RFC 5440 PCEP March 2009
14 LOAD-BALANCING This document
Object-Type
1
15 CLOSE This document
Object-Type
1
9.4. PCEP Message Common Header
IANA created a registry to manage the Flag field of the PCEP Message
Common Header.
New bit numbers may be allocated only by an IETF Consensus action.
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 bits are currently defined for the PCEP message common header.
9.5. Open Object Flag Field
IANA created a registry to manage the Flag field of the OPEN object.
New bit numbers may be allocated only by an IETF Consensus action.
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 bits are currently for the OPEN Object flag field.
9.6. RP Object
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability description
Vasseur & Le Roux Standards Track [Page 61]RFC 5440 PCEP March 2009
o Defining RFC
Several bits are defined for the RP Object flag field in this
document. The following values have been assigned:
Codespace of the Flag field (RP Object)
Bit Description Reference
26 Strict/Loose This document
27 Bi-directional This document
28 Reoptimization This document
29-31 Priority This document
9.7. NO-PATH Object Flag Field
IANA created a registry to manage the codespace of the NI field and
the Flag field of the NO-PATH object.
Value Meaning Reference
0 No path satisfying the set This document
of constraints could be found
1 PCE chain broken This document
New bit numbers may be allocated only by an IETF Consensus action.
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 NO-PATH Object flag field in this
document:
Codespace of the Flag field (NO-PATH Object)
Bit Description Reference
0 Unsatisfied constraint indicated This document
Vasseur & Le Roux Standards Track [Page 62]RFC 5440 PCEP March 2009
9.8. METRIC Object
IANA created a registry to manage the codespace of the T field and
the Flag field of the METRIC Object.
Codespace of the T field (Metric Object)
Value Meaning Reference
1 IGP metric This document
2 TE metric This document
3 Hop Counts This document
New bit numbers may be allocated only by an IETF Consensus action.
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 in this document. The following values have
been assigned:
Codespace of the Flag field (Metric Object)
Bit Description Reference
6 Computed metric This document
7 Bound This document
9.9. LSPA Object Flag Field
IANA created a registry to manage the Flag field of the LSPA object.
New bit numbers may be allocated only by an IETF Consensus action.
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 LSPA Object flag field in this document:
Vasseur & Le Roux Standards Track [Page 63]RFC 5440 PCEP March 2009
Codespace of the Flag field (LSPA Object)
Bit Description Reference
7 Local Protection Desired This document
9.10. SVEC Object Flag Field
IANA created a registry to manage the Flag field of the SVEC object.
New bit numbers may be allocated only by an IETF Consensus action.
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
Three bits are defined for the SVEC Object flag field in this
document:
Codespace of the Flag field (SVEC Object)
Bit Description Reference
21 SRLG Diverse This document
22 Node Diverse This document
23 Link Diverse This document
9.11. NOTIFICATION Object
IANA created a registry for the Notification-type and Notification-
value of the NOTIFICATION object and manages the code space.
Notification-type Name Reference
1 Pending Request cancelled This document
Notification-value
1: PCC cancels a set of pending requests
2: PCE cancels a set of pending requests
2 Overloaded PCE This document
Notification-value
1: PCE in congested state
2: PCE no longer in congested state
Vasseur & Le Roux Standards Track [Page 64]RFC 5440 PCEP March 2009
IANA created a registry to manage the Flag field of the NOTIFICATION
object.
New bit numbers may be allocated only by an IETF Consensus action.
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 bits are currently for the Flag Field of the NOTIFICATION object.
9.12. PCEP-ERROR Object
IANA created a registry for the Error-Type and Error-value of the
PCEP Error Object and manages the code space.
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RFC 5440 PCEP March 2009
For each PCEP error, an Error-Type and an Error-value are defined.
Error- Meaning Reference
Type
1 PCEP session establishment failure This document
Error-value=1: reception of an invalid Open message or
a non Open message.
Error-value=2: no Open message received before the expiration
of the OpenWait timer
Error-value=3: unacceptable and non-negotiable session
characteristics
Error-value=4: unacceptable but negotiable session
characteristics
Error-value=5: reception of a second Open message with
still unacceptable session characteristics
Error-value=6: reception of a PCErr message proposing
unacceptable session characteristics
Error-value=7: No Keepalive or PCErr message received
before the expiration of the KeepWait timer
Error-value=8: PCEP version not supported
2 Capability not supported This document
3 Unknown Object This document
Error-value=1: Unrecognized object class
Error-value=2: Unrecognized object Type
4 Not supported object This document
Error-value=1: Not supported object class
Error-value=2: Not supported object Type
5 Policy violation This document
Error-value=1: C bit of the METRIC object set
(request rejected)
Error-value=2: O bit of the RP object cleared
(request rejected)
6 Mandatory Object missing This document
Error-value=1: RP object missing
Error-value=2: RRO missing for a reoptimization
request (R bit of the RP object set)
Error-value=3: END-POINTS object missing
7 Synchronized path computation request missing This document
8 Unknown request reference This document
9 Attempt to establish a second PCEP session This document
10 Reception of an invalid object This document
Error-value=1: reception of an object with P flag
not set although the P flag must be
set according to this specification.
IANA created a registry to manage the Flag field of the PCEP-ERROR
object.
Vasseur & Le Roux Standards Track [Page 66]RFC 5440 PCEP March 2009
New bit numbers may be allocated only by an IETF Consensus action.
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 bits are currently for the Flag Field of the PCEP-ERROR Object.
9.13. LOAD-BALANCING Object Flag Field
IANA created a registry to manage the Flag field of the LOAD-
BALANCING object.
New bit numbers may be allocated only by an IETF Consensus action.
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 bits are currently for the Flag Field of the LOAD-BALANCING
Object.
9.14. CLOSE Object
The CLOSE object MUST be present in each Close message in order to
close a PCEP session. The reason field of the CLOSE object specifies
the reason for closing the PCEP session. The reason field of the
CLOSE object is managed by IANA.
Reasons
Value Meaning
1 No explanation provided
2 DeadTimer expired
3 Reception of a malformed PCEP message
4 Reception of an unacceptable number of unknown
requests/replies
5 Reception of an unacceptable number of unrecognized
PCEP messages
IANA created a registry to manage the flag field of the CLOSE object.
Vasseur & Le Roux Standards Track [Page 67]RFC 5440 PCEP March 2009
New bit numbers may be allocated only by an IETF Consensus action.
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 bits are currently for the Flag Field of the CLOSE Object.
9.15. PCEP TLV Type Indicators
IANA created a registry for the PCEP TLVs.
Value Meaning Reference
1 NO-PATH-VECTOR TLV This document
2 OVERLOAD-DURATION TLV This document
3 REQ-MISSING TLV This document
9.16. NO-PATH-VECTOR TLV
IANA manages the space of flags carried in the NO-PATH-VECTOR TLV
defined in this document, numbering them from 0 as the least
significant bit.
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Name flag
o Reference
Bit Number Name Reference
31 PCE currently unavailable This document
30 Unknown destination This document
29 Unknown source This document
Vasseur & Le Roux Standards Track [Page 68]RFC 5440 PCEP March 2009
10. Security Considerations
10.1. Vulnerability
Attacks on PCEP may result in damage to active networks. If path
computation responses are changed, the PCC may be encouraged to set
up inappropriate LSPs. Such LSPs might deviate to parts of the
network susceptible to snooping, or might transit congested or
reserved links. Path computation responses may be attacked by
modification of the PCRep message, by impersonation of the PCE, or by
modification of the PCReq to cause the PCE to perform a different
computation from that which was originally requested.
It is also possible to damage the operation of a PCE through a
variety of denial-of-service attacks. Such attacks can cause the PCE
to become congested with the result that path computations are
supplied too slowly to be of value for PCCs. This could lead to
slower-than-acceptable recovery times or delayed LSP establishment.
In extreme cases, it may be that service requests are not satisfied.
PCEP could be the target of the following attacks:
o Spoofing (PCC or PCE impersonation)
o Snooping (message interception)
o Falsification
o Denial of Service
In inter-AS scenarios when PCE-to-PCE communication is required,
attacks may be particularly significant with commercial as well as
service-level implications.
Additionally, snooping of PCEP requests and responses may give an
attacker information about the operation of the network. Simply by
viewing the PCEP messages someone can determine the pattern of
service establishment in the network and can know where traffic is
being routed, thereby making the network susceptible to targeted
attacks and the data within specific LSPs vulnerable.
The following sections identify mechanisms to protect PCEP against
security attacks.
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RFC 5440 PCEP March 2009
10.2. TCP Security Techniques
At the time of writing, TCP-MD5 [RFC2385] is the only available
security mechanism for securing the TCP connections that underly PCEP
sessions.
As explained in [RFC2385], the use of MD5 faces some limitations and
does not provide as high a level of security as was once believed. A
PCEP implementation supporting TCP-MD5 SHOULD be designed so that
stronger security keying techniques or algorithms that may be
specified for TCP can be easily integrated in future releases.
The TCP Authentication Option [TCP-AUTH] (TCP-AO) specifies new
security procedures for TCP, but is not yet complete. Since it is
believed that [TCP-AUTH] will offer significantly improved security
for applications using TCP, implementers should expect to update
their implementation as soon as the TCP Authentication Option is
published as an RFC.
Implementations MUST support TCP-MD5 and should make the security
function available as a configuration option.
Operators will need to observe that some deployed PCEP
implementations may pre-date the completion of [TCP-AUTH], and it
will be necessary to configure policy for secure communication
between PCEP speakers that support the TCP Authentication Option, and
those that don't.
An alternative approach for security over TCP transport is to use the
Transport Layer Security (TLS) protocol [RFC5246]. This provides
protection against eavesdropping, tampering, and message forgery.
But TLS doesn't protect the TCP connection itself, because it does
not authenticate the TCP header. Thus, it is vulnerable to attacks
such as TCP reset attacks (something against which TCP-MD5 does
protect). The use of TLS would, however, require the specification
of how PCEP initiates TLS handshaking and how it interprets the
certificates exchanged in TLS. That specification is out of the
scope of this document, but could be the subject of future work.
10.3. PCEP Authentication and Integrity
Authentication and integrity checks allow the receiver of a PCEP
message to know that the message genuinely comes from the node that
purports to have sent it and to know whether the message has been
modified.
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RFC 5440 PCEP March 2009
The TCP-MD5 mechanism [RFC2385] described in the previous section
provides such a mechanism subject to the concerns listed in [RFC2385]
and [RFC4278]. These issues will be addressed and resolved by
[TCP-AUTH].
10.4. PCEP Privacy
Ensuring PCEP communication privacy is of key importance, especially
in an inter-AS context, where PCEP communication end-points do not
reside in the same AS, as an attacker that intercepts a PCE message
could obtain sensitive information related to computed paths and
resources.
PCEP privacy can be ensured by encryption. TCP MAY be run over IPsec
[RFC4303] tunnels to provide the required encryption. Note that
IPsec can also ensure authentication and integrity; in which case,
TCP-MD5 or TCP-AO would not be required. However, there is some
concern that IPsec on this scale would be hard to configure and
operate. Use of IPSec with PCEP is out of the scope of this document
and may be addressed in a separate document.
10.5. Key Configuration and Exchange
Authentication, tamper protection, and encryption all require the use
of keys by sender and receiver.
Although key configuration per session is possible, it may be
particularly onerous to operators (in the same way as for the Border
Gateway Protocol (BGP) as discussed in [BGP-SEC]). If there is a
relatively small number of PCCs and PCEs in the network, manual key
configuration MAY be considered a valid choice by the operator,
although it is important to be aware of the vulnerabilities
introduced by such mechanisms (i.e., configuration errors, social
engineering, and carelessness could all give rise to security
breaches). Furthermore, manually configured keys are less likely to
be regularly updated which also increases the security risk. Where
there is a large number of PCCs and PCEs, the operator could find
that key configuration and maintenance is a significant burden as
each PCC needs to be configured to the PCE.
An alternative to individual keys is the use of a group key. A group
key is common knowledge among all members of a trust domain. Thus,
since the routers in an IGP area or an AS are part of a common trust
domain [MPLS-SEC], a PCEP group key MAY be shared among all PCCs and
PCEs in an IGP area or AS. The use of a group key will considerably
simplify the operator's configuration task while continuing to secure
Vasseur & Le Roux Standards Track [Page 71]
RFC 5440 PCEP March 2009
PCEP against attack from outside the network. However, it must be
noted that the more entities that have access to a key, the greater
the risk of that key becoming public.
With the use of a group key, separate keys would need to be
configured for the PCE-to-PCE communications that cross trust domain
(e.g., AS) boundaries, but the number of these relationships is
likely to be very small.
PCE discovery ([RFC5088] and [RFC5089]) is a significant feature for
the successful deployment of PCEP in large networks. This mechanism
allows a PCC to discover the existence of suitable PCEs within the
network without the necessity of configuration. It should be obvious
that, where PCEs are discovered and not configured, the PCC cannot
know the correct key to use. There are three possible approaches to
this problem that retain some aspect of security:
o The PCCs may use a group key as previously discussed.
o The PCCs may use some form of secure key exchange protocol with
the PCE (such as the Internet Key Exchange protocol v2 (IKE)
[RFC4306]). The drawback to this is that IKE implementations on
routers are not common and this may be a barrier to the deployment
of PCEP. Details are out of the scope of this document and may be
addressed in a separate document.
o The PCCs may make use of a key server to determine the key to use
when talking to the PCE. To some extent, this is just moving the
problem, since the PCC's communications with the key server must
also be secure (for example, using Kerberos [RFC4120]), but there
may some (minor) benefit in scaling if the PCC is to learn about
several PCEs and only needs to know one key server. Note that key
servers currently have very limited implementation. Details are
out of the scope of this document and may be addressed in a
separate document.
PCEP relationships are likely to be long-lived even if the PCEP
sessions are repeatedly closed and re-established. Where protocol
relationships persist for a large number of protocol interactions or
over a long period of time, changes in the keys used by the protocol
peers is RECOMMENDED [RFC4107]. Note that TCP-MD5 does not allow the
key to be changed without closing and reopening the TCP connection
which would result in the PCEP session being terminated and needing
to be restarted. That might not be a significant issue for PCEP.
Note also that the plans for the TCP Authentication Option [TCP-AUTH]
will allow dynamic key change (roll-over) for an active TCP
connection.
Vasseur & Le Roux Standards Track [Page 72]RFC 5440 PCEP March 2009
If key exchange is used (for example, through IKE), then it is
relatively simple to support dynamic key updates and apply these to
PCEP.
Note that in-band key management for the TCP Authentication Option
[TCP-AUTH] is currently unresolved.
[RFC3562] sets out some of the issues for the key management of
secure TCP connections.
10.6. Access Policy
Unauthorized access to PCE function represents a variety of potential
attacks. Not only may this be a simple denial-of-service attack (see
Section 10.7), but it would be a mechanism for an intruder to
determine important information about the network and operational
network policies simply by inserting bogus computation requests.
Furthermore, false computation requests could be used to predict
where traffic will be placed in the network when real requests are
made, allowing the attacker to target specific network resources.
PCEs SHOULD be configurable for access policy. Where authentication
is used, access policy can be achieved through the exchange or
configuration of keys as described in Section 10.5. More simple
policies MAY be configured on PCEs in the form of access lists where
the IP addresses of the legitimate PCCs are listed. Policies SHOULD
also be configurable to limit the type of computation requests that
are supported from different PCCs.
It is RECOMMENDED that access policy violations are logged by the PCE
and are available for inspection by the operator to determine whether
attempts have been made to attack the PCE. Such mechanisms MUST be
lightweight to prevent them from being used to support denial-of-
service attacks (see Section 10.7).
10.7. Protection against Denial-of-Service Attacks
Denial-of-service (DoS) attacks could be mounted at the TCP level or
at the PCEP level. That is, the PCE could be attacked through
attacks on TCP or through attacks within established PCEP sessions.
10.7.1. Protection against TCP DoS Attacks
PCEP can be the target of TCP DoS attacks, such as for instance SYN
attacks, as is the case for all protocols that run over TCP. Other
protocol specifications have investigated this problem and PCEP can
share their experience. The reader is referred to the specification
Vasseur & Le Roux Standards Track [Page 73]
RFC 5440 PCEP March 2009
of the Label Distribution Protocol (LDP) [RFC5036] for example. In
order to protect against TCP DoS attacks, PCEP implementations can
support the following techniques.
o PCEP uses a single registered port for all communications. The
PCE SHOULD listen for TCP connections only on ports where
communication is expected.
o The PCE MAY implement an access list to immediately reject (or
discard) TCP connection attempts from unauthorized PCCs.
o The PCE SHOULD NOT allow parallel TCP connections from the same
PCC on the PCEP-registered port.
o The PCE MAY require the use of the MD5 option on all TCP
connections, and MAY reject (or discard) any connection setup
attempt that does not use MD5. A PCE MUST NOT accept any SYN
packet for which the MD5 segment checksum is invalid. Note,
however, that the use of MD5 requires that the receiver use CPU
resources to compute the checksum before it can decide to discard
an otherwise acceptable SYN segment.
10.7.2. Request Input Shaping/Policing
A PCEP implementation may be subject to DoS attacks within a
legitimate PCEP session. For example, a PCC might send a very large
number of PCReq messages causing the PCE to become congested or
causing requests from other PCCs to be queued.
Note that the direct use of the Priority field on the RP object to
prioritize received requests does not provide any protection since
the attacker could set all requests to be of the highest priority.
Therefore, it is RECOMMENDED that PCE implementations include input
shaping/policing mechanisms that either throttle the requests
received from any one PCC, or apply queuing or priority-degradation
techniques to over-communicative PCCs.
Such mechanisms MAY be set by default, but SHOULD be available for
configuration. Such techniques may be considered particularly
important in multi-service-provider environments to protect the
resources of one service provider from unwarranted, over-zealous, or
malicious use by PCEs in another service provider.
Vasseur & Le Roux Standards Track [Page 74]RFC 5440 PCEP March 2009
11. Acknowledgments
The authors would like to thank Dave Oran, Dean Cheng, Jerry Ash,
Igor Bryskin, Carol Iturrade, Siva Sivabalan, Rich Bradford, Richard
Douville, Jon Parker, Martin German, and Dennis Aristow for their
very valuable input. The authors would also like to thank Fabien
Verhaeghe for the very fruitful discussions and useful suggestions.
David McGrew and Brian Weis provided valuable input to the Security
Considerations section.
Ross Callon, Magnus Westerlund, Lars Eggert, Pasi Eronen, Tim Polk,
Chris Newman, and Russ Housley provided important input during IESG
review.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and
S. Jamin, "Resource ReSerVation Protocol (RSVP) --
Version 1 Functional Specification", RFC 2205,
September 1997.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the
TCP MD5 Signature Option", RFC 2385, August 1998.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T.,
Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions
to RSVP for LSP Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
RFC 3473, January 2003.
[RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered
Links in Resource ReSerVation Protocol - Traffic
Engineering (RSVP-TE)", RFC 3477, January 2003.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
Vasseur & Le Roux Standards Track [Page 75]RFC 5440 PCEP March 2009
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs",
BCP 26, RFC 5226, May 2008.
12.2. Informative References
[BGP-SEC] Christian, B. and T. Tauber, "BGP Security
Requirements", Work in Progress, November 2008.
[IEEE.754.1985] IEEE Standard 754, "Standard for Binary Floating-
Point Arithmetic", August 1985.
[INTER-LAYER] Oki, E., Roux, J., Kumaki, K., Farrel, A., and T.
Takeda, "PCC-PCE Communication and PCE Discovery
Requirements for Inter-Layer Traffic Engineering",
Work in Progress, January 2009.
[MPLS-SEC] Fang, L. and M. Behringer, "Security Framework for
MPLS and GMPLS Networks", Work in Progress,
November 2008.
[PCE-MANAGE] Farrel, A., "Inclusion of Manageability Sections in
PCE Working Group Drafts", Work in Progress,
January 2009.
[PCE-MONITOR] Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
monitoring tools for Path Computation Element based
Architecture", Work in Progress, November 2008.
[PCEP-MIB] Stephan, E. and K. Koushik, "PCE communication
protocol (PCEP) Management Information Base",
Work in Progress, November 2008.
[RBNF] Farrel, A., "Reduced Backus-Naur Form (RBNF) A
Syntax Used in Various Protocol Specifications",
Work in Progress, November 2008.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm",
RFC 1321, April 1992.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description",
RFC 3471, January 2003.
[RFC3562] Leech, M., "Key Management Considerations for the
TCP MD5 Signature Option", RFC 3562, July 2003.
Vasseur & Le Roux Standards Track [Page 76]RFC 5440 PCEP March 2009
[RFC3785] Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx,
P., and T. Telkamp, "Use of Interior Gateway
Protocol (IGP) Metric as a second MPLS Traffic
Engineering (TE) Metric", BCP 87, RFC 3785,
May 2004.
[RFC4022] Raghunarayan, R., "Management Information Base for
the Transmission Control Protocol (TCP)", RFC 4022,
March 2005.
[RFC4101] Rescorla, E. and IAB, "Writing Protocol Models",
RFC 4101, June 2005.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for
Cryptographic Key Management", BCP 107, RFC 4107,
June 2005.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn,
"The Kerberos Network Authentication Service (V5)",
RFC 4120, July 2005.
[RFC4278] Bellovin, S. and A. Zinin, "Standards Maturity
Variance Regarding the TCP MD5 Signature Option (RFC
2385) and the BGP-4 Specification", RFC 4278,
January 2006.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005.
[RFC5420] Farrel, A., Ed., Papadimitriou, D., Vasseur, JP.,
and A. Ayyangarps, "Encoding of Attributes for MPLS
LSP Establishment Using Resource Reservation
Protocol Traffic Engineering (RSVP-TE)", RFC 5420,
February 2009.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture",
RFC 4655, August 2006.
[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element
(PCE) Communication Protocol Generic Requirements",
RFC 4657, September 2006.
[RFC4674] Le Roux, J., "Requirements for Path Computation
Element (PCE) Discovery", RFC 4674, October 2006.
Vasseur & Le Roux Standards Track [Page 77]RFC 5440 PCEP March 2009
[RFC4927] Le Roux, J., "Path Computation Element Communication
Protocol (PCECP) Specific Requirements for Inter-
Area MPLS and GMPLS Traffic Engineering", RFC 4927,
June 2007.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R.
Zhang, "OSPF Protocol Extensions for Path
Computation Element (PCE) Discovery", RFC 5088,
January 2008.
[RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path
Computation Element (PCE) Discovery", RFC 5089,
January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
[RFC5376] Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS
Requirements for the Path Computation Element
Communication Protocol (PCECP)", RFC 5376,
November 2008.
[TCP-AUTH] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", Work in Progress,
November 2008.
Vasseur & Le Roux Standards Track [Page 78]RFC 5440 PCEP March 2009
Appendix A. PCEP Finite State Machine (FSM)
The section describes the PCEP finite state machine (FSM). PCEP
Finite State Machine
+-+-+-+-+-+-+<------+
+------| SessionUP |<---+ |
| +-+-+-+-+-+-+ | |
| | |
| +->+-+-+-+-+-+-+ | |
| | | KeepWait |----+ |
| +--| |<---+ |
|+-----+-+-+-+-+-+-+ | |
|| | | |
|| | | |
|| V | |
|| +->+-+-+-+-+-+-+----+ |
|| | | OpenWait |-------+
|| +--| |<------+
||+----+-+-+-+-+-+-+<---+ |
||| | | |
||| | | |
||| V | |
||| +->+-+-+-+-+-+-+ | |
||| | |TCPPending |----+ |
||| +--| | |
|||+---+-+-+-+-+-+-+<---+ |
|||| | | |
|||| | | |
|||| V | |
|||+--->+-+-+-+-+ | |
||+---->| Idle |-------+ |
|+----->| |----------+
+------>+-+-+-+-+
Figure 23: PCEP Finite State Machine for the PCC
PCEP defines the following set of variables:
Connect: the timer (in seconds) started after having initialized a
TCP connection using the PCEP-registered TCP port. The value of
the Connect timer is 60 seconds.
ConnectRetry: the number of times the system has tried to establish
a TCP connection with a PCEP peer without success.
Vasseur & Le Roux Standards Track [Page 79]RFC 5440 PCEP March 2009
ConnectMaxRetry: the maximum number of times the system tries to
establish a TCP connection using the PCEP-registered TCP port
before going back to the Idle state. The value of the
ConnectMaxRetry is 5.
OpenWait: the timer that corresponds to the amount of time a PCEP
peer will wait to receive an Open message from the PCEP peer after
the expiration of which the system releases the PCEP resource and
goes back to the Idle state. The OpenWait timer has a fixed value
of 60 seconds.
KeepWait: the timer that corresponds to the amount of time a PCEP
peer will wait to receive a Keepalive or a PCErr message from the
PCEP peer after the expiration of which the system releases the
PCEP resource and goes back to the Idle state. The KeepWait timer
has a fixed value of 60 seconds.
OpenRetry: the number of times the system has received an Open
message with unacceptable PCEP session characteristics.
The following two state variables are defined:
RemoteOK: a boolean that is set to 1 if the system has received an
acceptable Open message.
LocalOK: a boolean that is set to 1 if the system has received a
Keepalive message acknowledging that the Open message sent to the
peer was valid.
Idle State:
The idle state is the initial PCEP state where the PCEP (also
referred to as "the system") waits for an initialization event that
can either be manually triggered by the user (configuration) or
automatically triggered by various events. In Idle state, PCEP
resources are allocated (memory, potential process, etc.) but no PCEP
messages are accepted from any PCEP peer. The system listens to the
PCEP-registered TCP port.
The following set of variables are initialized:
TCPRetry=0,
LocalOK=0,
RemoteOK=0,
OpenRetry=0.
Vasseur & Le Roux Standards Track [Page 80]RFC 5440 PCEP March 2009
Upon detection of a local initialization event (e.g., user
configuration to establish a PCEP session with a particular PCEP
peer, local event triggering the establishment of a PCEP session with
a PCEP peer such as the automatic detection of a PCEP peer), the
system:
o Initiates a TCP connection with the PCEP peer,
o Starts the Connect timer,
o Moves to the TCPPending state.
Upon receiving a TCP connection on the PCEP-registered TCP port, if
the TCP connection establishment succeeds, the system:
o Sends an Open message,
o Starts the OpenWait timer,
o Moves to the OpenWait state.
If the connection establishment fails, the system remains in the Idle
state. Any other event received in the Idle state is ignored.
It is expected that an implementation will use an exponentially
increasing timer between automatically generated Initialization
events and between retries of TCP connection establishment.
TCPPending State:
If the TCP connection establishment succeeds, the system:
o Sends an Open message,
o Starts the OpenWait timer,
o Moves to the OpenWait state.
If the TCP connection establishment fails (an error is detected
during the TCP connection establishment) or the Connect timer
expires:
o If ConnectRetry = ConnectMaxRetry, the system moves to the Idle
State.
Vasseur & Le Roux Standards Track [Page 81]RFC 5440 PCEP March 2009
o If ConnectRetry < ConnectMaxRetry, the system:
1. Initiates of a TCP connection with the PCEP peer,
2. Increments the ConnectRetry variable,
3. Restarts the Connect timer,
4. Stays in the TCPPending state.
In response to any other event, the system releases the PCEP
resources for that peer and moves back to the Idle state.
OpenWait State:
In the OpenWait state, the system waits for an Open message from its
PCEP peer.
If the system receives an Open message from the PCEP peer before the
expiration of the OpenWait timer, the system first examines all of
its sessions that are in the OpenWait or KeepWait state. If another
session with the same PCEP peer already exists (same IP address),
then the system performs the following collision-resolution
procedure:
o If the system has initiated the current session and it has a lower
IP address than the PCEP peer, the system closes the TCP
connection, releases the PCEP resources for the pending session,
and moves back to the Idle state.
o If the session was initiated by the PCEP peer and the system has a
higher IP address that the PCEP peer, the system closes the TCP
connection, releases the PCEP resources for the pending session,
and moves back to the Idle state.
o Otherwise, the system checks the PCEP session attributes
(Keepalive frequency, DeadTimer, etc.).
If an error is detected (e.g., malformed Open message, reception of a
message that is not an Open message, presence of two OPEN objects),
PCEP generates an error notification, the PCEP peer sends a PCErr
message with Error-Type=1 and Error-value=1. The system releases the
PCEP resources for the PCEP peer, closes the TCP connection, and
moves to the Idle state.
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If no errors are detected, OpenRetry=1, and the session
characteristics are unacceptable, the PCEP peer sends a PCErr with
Error-Type=1 and Error-value=5, and the system releases the PCEP
resources for that peer and moves back to the Idle state.
If no errors are detected, and the session characteristics are
acceptable to the local system, the system:
o Sends a Keepalive message to the PCEP peer,
o Starts the Keepalive timer,
o Sets the RemoteOK variable to 1.
If LocalOK=1, the system clears the OpenWait timer and moves to the
UP state.
If LocalOK=0, the system clears the OpenWait timer, starts the
KeepWait timer, and moves to the KeepWait state.
If no errors are detected, but the session characteristics are
unacceptable and non-negotiable, the PCEP peer sends a PCErr with
Error-Type=1 and Error-value=3, and the system releases the PCEP
resources for that peer and moves back to the Idle state.
If no errors are detected, and OpenRetry is 0, and the session
characteristics are unacceptable but negotiable (such as, the
Keepalive period or the DeadTimer), then the system:
o Increments the OpenRetry variable,
o Sends a PCErr message with Error-Type=1 and Error-value=4 that
contains proposed acceptable session characteristics,
o If LocalOK=1, the system restarts the OpenWait timer and stays in
the OpenWait state.
o If LocalOK=0, the system clears the OpenWait timer, starts the
KeepWait timer, and moves to the KeepWait state.
If no Open message is received before the expiration of the OpenWait
timer, the PCEP peer sends a PCErr message with Error-Type=1 and
Error-value=2, the system releases the PCEP resources for the PCEP
peer, closes the TCP connection, and moves to the Idle state.
In response to any other event, the system releases the PCEP
resources for that peer and moves back to the Idle state.
Vasseur & Le Roux Standards Track [Page 83]RFC 5440 PCEP March 2009
KeepWait State:
In the Keepwait state, the system waits for the receipt of a
Keepalive from its PCEP peer acknowledging its Open message or a
PCErr message in response to unacceptable PCEP session
characteristics proposed in the Open message.
If an error is detected (e.g., malformed Keepalive message), PCEP
generates an error notification, the PCEP peer sends a PCErr message
with Error-Type=1 and Error-value=1. The system releases the PCEP
resources for the PCEP peer, closes the TCP connection, and moves to
the Idle state.
If a Keepalive message is received before the expiration of the
KeepWait timer, then the system sets LocalOK=1 and:
o If RemoteOK=1, the system clears the KeepWait timer and moves to
the UP state.
o If RemoteOK=0, the system clears the KeepWait timer, starts the
OpenWait timer, and moves to the OpenWait State.
If a PCErr message is received before the expiration of the KeepWait
timer:
1. If the proposed values are unacceptable, the PCEP peer sends a
PCErr message with Error-Type=1 and Error-value=6, and the system
releases the PCEP resources for that PCEP peer, closes the TCP
connection, and moves to the Idle state.
2. If the proposed values are acceptable, the system adjusts its
PCEP session characteristics according to the proposed values
received in the PCErr message, restarts the KeepWait timer, and
sends a new Open message. If RemoteOK=1, the system restarts the
KeepWait timer and stays in the KeepWait state. If RemoteOK=0,
the system clears the KeepWait timer, starts the OpenWait timer,
and moves to the OpenWait state.
If neither a Keepalive nor a PCErr is received after the expiration
of the KeepWait timer, the PCEP peer sends a PCErr message with
Error-Type=1 and Error-value=7, and the system releases the PCEP
resources for that PCEP peer, closes the TCP connection, and moves to
the Idle State.
In response to any other event, the system releases the PCEP
resources for that peer and moves back to the Idle state.
Vasseur & Le Roux Standards Track [Page 84]RFC 5440 PCEP March 2009
UP State:
In the UP state, the PCEP peer starts exchanging PCEP messages
according to the session characteristics.
If the Keepalive timer expires, the system restarts the Keepalive
timer and sends a Keepalive message.
If no PCEP message (Keepalive, PCReq, PCRep, PCNtf) is received from
the PCEP peer before the expiration of the DeadTimer, the system
terminates the PCEP session according to the procedure defined in
Section 6.8, releases the PCEP resources for that PCEP peer, closes
the TCP connection, and moves to the Idle State.
If a malformed message is received, the system terminates the PCEP
session according to the procedure defined in Section 6.8, releases
the PCEP resources for that PCEP peer, closes the TCP connection and
moves to the Idle State.
If the system detects that the PCEP peer tries to set up a second TCP
connection, it stops the TCP connection establishment and sends a
PCErr with Error-Type=9.
If the TCP connection fails, the system releases the PCEP resources
for that PCEP peer, closes the TCP connection, and moves to the Idle
State.
Appendix B. PCEP Variables
PCEP defines the following configurable variables:
Keepalive timer: minimum period of time between the sending of PCEP
messages (Keepalive, PCReq, PCRep, PCNtf) to a PCEP peer. A
suggested value for the Keepalive timer is 30 seconds.
DeadTimer: period of timer after the expiration of which a PCEP peer
declares the session down if no PCEP message has been received.
SyncTimer: timer used in the case of synchronized path computation
request using the SVEC object defined in Section 7.13.3. Consider
the case where a PCReq message is received by a PCE that contains
the SVEC object referring to M synchronized path computation
requests. If after the expiration of the SyncTimer all the M path
computation requests have not been received, a protocol error is
triggered and the PCE MUST cancel the whole set of path
computation requests. The aim of the SyncTimer is to avoid the
storage of unused synchronized requests should one of them get
lost for some reason (e.g., a misbehaving PCC). Thus, the value
Vasseur & Le Roux Standards Track [Page 85]RFC 5440 PCEP March 2009
of the SyncTimer must be large enough to avoid the expiration of
the timer under normal circumstances. A RECOMMENDED value for the
SyncTimer is 60 seconds.
MAX-UNKNOWN-REQUESTS: A RECOMMENDED value is 5.
MAX-UNKNOWN-MESSAGES: A RECOMMENDED value is 5.
Appendix C. Contributors
The content of this document was contributed by those listed below
and the editors listed at the end of the document.
Arthi Ayyangar
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
USA
EMail: arthi@juniper.net
Adrian Farrel
Old Dog Consulting
Phone: +44 (0) 1978 860944
EMail: adrian@olddog.co.uk
Eiji Oki
NTT
Midori 3-9-11
Musashino, Tokyo, 180-8585
JAPAN
EMail: oki.eiji@lab.ntt.co.jp
Alia Atlas
British Telecom
EMail: akatlas@alum.mit.edu
Vasseur & Le Roux Standards Track [Page 86]RFC 5440 PCEP March 2009
Andrew Dolganow
Alcatel
600 March Road
Ottawa, ON K2K 2E6
CANADA
EMail: andrew.dolganow@alcatel.com
Yuichi Ikejiri
NTT Communications Corporation
1-1-6 Uchisaiwai-cho, Chiyoda-ku
Tokyo, 100-819
JAPAN
EMail: y.ikejiri@ntt.com
Kenji Kumaki
KDDI Corporation
Garden Air Tower Iidabashi, Chiyoda-ku,
Tokyo, 102-8460
JAPAN
EMail: ke-kumaki@kddi.com
Authors' Addresses
JP Vasseur (editor)
Cisco Systems
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
EMail: jpv@cisco.com
JL Le Roux (editor)
France Telecom
2, Avenue Pierre-Marzin
Lannion 22307
FRANCE
EMail: jeanlouis.leroux@orange-ftgroup.com
Vasseur & Le Roux Standards Track [Page 87]
