draft-ietf-pce-pcep-11.txt   draft-ietf-pce-pcep-12.txt 
Networking Working Group JP. Vasseur, Ed.
Internet-Draft Cisco Systems
Intended status: Standards Track JL. Le Roux, Ed.
Created: March 15, 2008 France Telecom
Expires: September 15, 2008
Path Computation Element (PCE) Communication Protocol (PCEP)
draft-ietf-pce-pcep-11.txt
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Abstract
This document specifies the Path Computation Element Communication
Protocol (PCEP) for communications between a Path Computation Client
(PCC) and a Path Computation Element (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 (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.
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].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Architectural Protocol Overview (Model) . . . . . . . . . . . 6
4.1. Problem . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Architectural Protocol Overview . . . . . . . . . . . . . 6
4.2.1. Initialization Phase . . . . . . . . . . . . . . . . . 7
4.2.2. Path Computation Request Sent By a PCC to a PCE . . . 8
4.2.3. Path Computation Reply Sent By The PCE to a PCC . . . 9
4.2.4. Notification . . . . . . . . . . . . . . . . . . . . . 11
4.2.5. Error . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.6. Termination of the PCEP Session . . . . . . . . . . . 13
4.2.7. Intermitent versus Permanent PCEP Session . . . . . . 14
5. Transport Protocol . . . . . . . . . . . . . . . . . . . . . . 14
6. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Common header . . . . . . . . . . . . . . . . . . . . . . 15
6.2. Open Message . . . . . . . . . . . . . . . . . . . . . . . 15
6.3. Keepalive Message . . . . . . . . . . . . . . . . . . . . 16
6.4. Path Computation Request (PCReq) Message . . . . . . . . . 17
6.5. Path Computation Reply (PCRep) Message . . . . . . . . . . 18
6.6. Notification (PCNtf) Message . . . . . . . . . . . . . . . 20
6.7. Error (PCErr) Message . . . . . . . . . . . . . . . . . . 20
6.8. Close Message . . . . . . . . . . . . . . . . . . . . . . 21
7. Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1. PCE TLV Format . . . . . . . . . . . . . . . . . . . . . . 22
7.2. Common Object Header . . . . . . . . . . . . . . . . . . . 22
7.3. OPEN Object . . . . . . . . . . . . . . . . . . . . . . . 24
7.4. RP Object . . . . . . . . . . . . . . . . . . . . . . . . 25
7.4.1. Object Definition . . . . . . . . . . . . . . . . . . 26
7.4.2. Handling of the RP Object . . . . . . . . . . . . . . 28
7.5. NO-PATH Object . . . . . . . . . . . . . . . . . . . . . . 28
7.6. END-POINT Object . . . . . . . . . . . . . . . . . . . . . 31
7.7. BANDWIDTH Object . . . . . . . . . . . . . . . . . . . . . 32
7.8. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 33
7.9. Explicit Route Object . . . . . . . . . . . . . . . . . . 36
7.10. Reported Route Object . . . . . . . . . . . . . . . . . . 36
7.11. LSPA Object . . . . . . . . . . . . . . . . . . . . . . . 37
7.12. Include Route Object Object . . . . . . . . . . . . . . . 38
7.13. SVEC Object . . . . . . . . . . . . . . . . . . . . . . . 39
7.13.1. Notion of Dependent and Synchronized Path
Computation Requests . . . . . . . . . . . . . . . . . 39
7.13.2. SVEC Object . . . . . . . . . . . . . . . . . . . . . 41
7.13.3. Handling of the SVEC Object . . . . . . . . . . . . . 42
7.14. NOTIFICATION Object . . . . . . . . . . . . . . . . . . . 42
7.15. PCEP-ERROR Object . . . . . . . . . . . . . . . . . . . . 45
7.16. LOAD-BALANCING Object . . . . . . . . . . . . . . . . . . 49
7.17. CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 50
8. Manageability Considerations . . . . . . . . . . . . . . . . . 51
8.1. Control of Function and Policy . . . . . . . . . . . . . . 51
8.2. Information and Data Models . . . . . . . . . . . . . . . 53
8.3. Liveness Detection and Monitoring . . . . . . . . . . . . 53
8.4. Verifying Correct Operation . . . . . . . . . . . . . . . 53
8.5. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . . 54
8.6. Impact on Network Operation . . . . . . . . . . . . . . . 54
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 54
9.1. TCP Port . . . . . . . . . . . . . . . . . . . . . . . . . 54
9.2. PCEP Top-Level Registry . . . . . . . . . . . . . . . . . . 54
9.2.1. PCEP Messages . . . . . . . . . . . . . . . . . . . . 54
9.2.2. PCEP Object . . . . . . . . . . . . . . . . . . . . . 55
9.2.3. RP Object . . . . . . . . . . . . . . . . . . . . . . 56
9.2.4. Notification Object . . . . . . . . . . . . . . . . . 57
9.2.5. PCEP-ERROR Object . . . . . . . . . . . . . . . . . . 57
9.2.6. CLOSE Object . . . . . . . . . . . . . . . . . . . . . 59
9.2.7. NO-PATH Object . . . . . . . . . . . . . . . . . . . . 59
9.2.7.1. No-Path Nature of Issue . . . . . . . . . . . . . . 59
9.2.7.2. No-Path Bit Flags . . . . . . . . . . . . . . . . . 60
9.2.8. METRIC Object . . . . . . . . . . . . . . . . . . . . 60
9.2.8.1. Metric Type . . . . . . . . . . . . . . . . . . . . 60
9.2.8.2. Metric Control Flags . . . . . . . . . . . . . . . 60
9.2.9. PCEP TLV Type Indicators . . . . . . . . . . . . . . . 61
9.2.10. NO-PATH-VECTOR TLV . . . . . . . . . . . . . . . . . . 61
10. Security Considerations . . . . . . . . . . . . . . . . . . . 62
10.1. PCEP Authentication and Integrity . . . . . . . . . . . . 62
10.2. PCEP Privacy . . . . . . . . . . . . . . . . . . . . . . . 62
10.3. Protection Against Denial of Service Attacks . . . . . . . 63
10.3.1. Protection Against TCP DoS Attacks . . . . . . . . . . 63
10.3.2. Request Input Shaping/Policing . . . . . . . . . . . . 63
11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 63
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 64
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 65
13.1. Normative References . . . . . . . . . . . . . . . . . . . 65
13.2. Informative References . . . . . . . . . . . . . . . . . . 65
Appendix A. PCEP Finite State Machine (FSM) . . . . . . . . . . . 68
Appendix B. PCEP Variables . . . . . . . . . . . . . . . . . . . 74
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 75
Intellectual Property and Copyright Statements . . . . . . . . . . 76
1. Introduction
[RFC4655] describes the motivations and architecture for a Path
Compuation Element (PCE) based model for the computation of
Multiprotocol Label Switching (MPLS) and Generalized (GMPLS) Traffic
Engineering Label Swtich 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 the requirement
for using the same protocol 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],
[I-D.ietf-pce-interas-pcecp-reqs] and [I-D.ietf-pce-inter-layer-req].
This document specifies the Path Computation Element Communication
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.
2. Terminology
Terminology 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.
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 confederations).
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: 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.
3. Assumptions
[RFC4655] describes various types of PCE. PCEP does not make any
assumption 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
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 architecture 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 path 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 fulfils the requirements for reliable
messaging and flow control without further protocol work.
Several PCEP messages are defined:
- Open and Keepalive messages are used to initiate and maintain a
PCEP session respectively.
- PCReq: a PCEP message sent by a PCC to a PCE to request a path
computation.
- PCRep: a PCEP message sent by a PCE to a PCC in reply to a path
computation request. A PCRep message can either contain 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.
- PCNtf: a PCEP notification message either sent by a PCC to a PCE or
a PCE to a PCC to notify of a specific event.
- PCErr: a PCEP message sent upon the occurrence of a protocol error
condition.
- 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.
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 once
the PCEP session has been successfully established, Keepalive
messages may be exchanged between PCEP peers to ensure the liveness
of the PCEP session.
Only one PCEP session can exist between a pair a PCEP peers at any
one time.
Details about the Open message and the Keepalive message can be found
inSection 6.2 and Section 6.3 respectively.
+---+ +---+
|PCC| |PCE|
+-+-+ +-+-+
| |
| Open msg |
|-------- |
| \ Open msg |
| \ ---------|
| \/ |
| /\ |
| / -------->|
| / |
|<------ Keepalive|
| --------|
|Keeplaive / |
|-------- / |
| \/ |
| /\ |
|<------ ---------->|
| |
: :
: :
| |
|---- 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. Path Computation Request Sent By a PCC to a PCE
+---+ +---+
|PCC| |PCE|
+-+-+ +-+-+
1)Path computation | |
event | |
| |
2)PCE Selection | |
| |
3)Path computation | |
request sent to | |
the selected PCE | |
|---- PCReq message -->|
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 PCE. Note that the
PCE selection decision process may have taken place prior to the PCEP
session establishment.
Once the PCC has selected a PCE, it sends the PCE 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/Hold 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.
Details about the PCReq message can be found in Section 6.4
4.2.3. 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
+---+ +---+
|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 either be:
o Positive (Figure 3-a): the PCE manages to compute a path that
satisfies the set of required constraints, in which 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 3-b): 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.
4.2.4. 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,
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 | |
request X sent to | |
the selected PCE | |
|---- PCReq message -->|
| |4) Path computation
| |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 | |
request X sent to | |
the selected PCE | |
|---- PCReq message -->|
| |4) Path computation
| |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.
4.2.5. 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.,
reception of a malformed message, 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 | |
request X sent to | |
the selected PCE | |
|---- PCReq message--->|
| |4) Reception of a
| |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.
4.2.6. 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.
4.2.7. Intermitent versus Permanent PCEP Session
An implementation may decide to keep the PCEP session alive (and thus
the corresponding TCP connection) for an unlimited time (this may for
instance be appropriate when path computation requests are sent on a
frequent basis so as to avoid to open 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 well-known TCP port (to be assigned by
IANA). This allows the requirements of reliable messaging and flow
control to be met without further protocol work.
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 as 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) 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.
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 and MUST be set to zero on transmission.
Message-Type (8 bits):
The following message types are currently defined (to be confirmed by
IANA).
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 expressed
in bytes including the common header.
6.2. Open Message
The Open message is a PCEP message sent by a PCC to a PCE and 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 (To
be confirmed by IANA).
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 and
the PCEP session MUST be terminated. 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. TOTO
Open message
<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 KeepWait timer has 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 by the receiving peer, it MUST send an Error message. The
Error message SHOULD also contain the related Open object: 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 message can be found in Section 7.15.
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.
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 (To be confirmed by IANA). The
Keepalive message does not contain any object.
PCEP has its own keepalive mechanism used to ensure of 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 is
no constraints mandating the use of identical DeadTimers by both PCEP
peers. The minimum KeepAlive timer value is 1 second.
Keepalive messages are sent at the frequency specified in the OPEN
object carried within an Open message according to the rules
speciifed 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 on 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 to not 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.
Keepalive message
<Keepalive Message>::= <Common Header>
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 (To be confirmed by IANA).
There are two mandatory objects that MUST be included within a PCReq
message: the RP and the END-POINTS objects (see section 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.
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 is set to 4 (To be confirmed by
IANA).
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 (the PCE finds a set
of paths that satisfy the set of constraints), the set of computed
paths specified by means of ERO objects 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).
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 is set to 5 (To be confirmed by IANA).
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.
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 is set to 6 (To be confirmed by IANA).
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 later 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 Section 7.15.
The format of a PCErr message is as follows:
<PCErr Message> ::= <Common Header>
( <error-object-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>]
<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 (To be confirmed by IANA).
Close message
<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 vlaid 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.
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.
7.1. PCE 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 three byte value would have a length of three,
but the total size of the TLV would be eight 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 which 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.
Res flags (2 bits). Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt. Unassigned bits are
considered as reserved. They MUST be set to zero on transmission and
MUST be ignored on receipt.
o 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.
o 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, 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.
OPEN Object-Class is to be assigned by IANA (recommended value=1)
OPEN Object-Type is to be assigned by IANA (recommended value=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 and MUST be set to zero on transmission.
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 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=30 seconds. This means that A sends Keepalive messages (or
ay 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 30 second period.
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 and is used for logging and
troubleshooting purposes. 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 PCReq messages
and MUST be cleared in PCNtf and PCErr messages. If the RP objet is
received with the P flag set incorrectely according to the rules
states 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 to be assigned by IANA (recommended value=2)
RP Object-Type is to be assigned by IANA (recommended value=1)
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 of a local matter and 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
the handling of request priorities: in other words, the path
computation request has been honoured 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 in which case, in addition to the TE LSP
attributes, the current path of the existing TE LSP to be
reoptimized MUST be provided in the PCReq (except for 0-bandwidth
TE LSPs) message by means of an RRO object defined in Section 7.10
and (again except in the case of 0-bandwidth TE LSPs) the existing
bandwidth of the LSP to be reoptimized MUST be supplied in an
additional BANDWIDTH object as described in Section 7.7.
o B (Bi-directional - 1 bit): when set, the PCC specifies that the
path computation request relates to a bidirectional 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 (the O bit is cleared), the returned path is made of
strict hops.
Unassigned bits are considered as reserved and MUST be set to zero on
transmission.
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
MUST be incremented each time a new request is sent to the PCE. The
value 0x0000000 is considered as invalid. If no path computation
reply is received from the PCE, and the PCC wishes to resend its
request, the same Request-ID-number MUST be used. Conversely,
different Request-ID-number 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".
R bit: 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-0-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 of the working path with the associated list of strict hops
in PCReq. The absence of an RRO in the PCReq message for a non-0-
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".
If the PCC receives a PCRep message that contains a RP object
referring to an unknown Request-ID-Number, the PCC MUST send a PCErr
message with Error-Type="Unknown request reference".
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 to be assigned by IANA (recommended value=3)
NO-PATH Object-Type is to be assigned by IANA (recommended value=1)
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:
0x00: No path satisfying the set of constraints could be found
0x01: PCE chain broken
IANA management of the NI field codespace is described in Section 9.
Flags (16 bits).
The following flag is currently defined:
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.
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 MBits/s. Suppose that PCE cannot
find a path for X MBits/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
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 value field of 32-bit flags field.
TYPE: To be assigned by IANA (suggested value=1)
LENGTH: 1
VALUE: 32-bit flags field
IANA is requested to manage the space of flags carried in the NO-
PATH-VECTOR TLV (see Section 9).
The following flags are currently defined:
o Bit number: 1 - PCE currently unavailable
o Bit number: 2 - Unknown destination
o Bit number: 3 - Unknown source
7.6. END-POINT 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-POINT
object MUST be set. If the END-POINT objet 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 or may not correspond to the source and destination
IP address of the TE LSP but rather to a path segment. Two END-
POINTS objects (for IPv4 and IPv6) are defined.
END-POINTS Object-Class is to be assigned by IANA (recommended
value=4).
END-POINTS Object-Type is to be assigned by IANA (recommended value=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
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.
If the requested bandwidth is equal to 0, the BANDWIDTH object is
optional. Conversely, if the requested bandwidth is non 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 to be assigned by IANA (recommended
value=5)
Two Object-Type values are defined for the BANDWIDTH object:
o Requested bandwidth: BANDWIDTH Object-Type is to be assigned by
IANA (recommended value=1)
o Bandwidth of an existing TE LSP for which a reoptimization is
requested. BANDWIDTH Object-Type is to be assigned by IANA
(recommended value=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, 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 of 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.
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 to be assigned by IANA (recommended value=6)
METRIC Object-Type is to be assigned by IANA (recommended value=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:
o T=1: IGP metric
o T=2: TE metric
o T=3: Hop Counts
Flags (8 bits): Two flags are currently defined:
o 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.
o 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.
Multiple METRIC Objects MAY be inserted in a PCRep or the PCReq
message. There MUST be at most one instance of the METRIC object for
each metric type with the same B flag value. If 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.
The presence of two METRIC objects of the same type with a different
value of the B-Flag in a PCEReq message is allowed. Furthermore, it
is also allowed to insert in a PCReq message two METRIC objects with
the same type that have both their B-Flag cleared: in this case, an
objective function must be used by the PCE to solve a multi-parameter
constraint 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 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, 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 bit 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.
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 object 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 should the path computation have been 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 to be assigned by IANA (recommended value=7)
ERO Object-Type is to be assigned by IANA (recommended value=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-
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 to be assigned by IANA (recommended value=8)
RRO Object-Type is to be assigned by IANA (recommended value=1)
7.11. LSPA Object
The LSPA object is optional and specifies various TE LSP attributes
to be taken into account by the PCE during path computation. The
LSPA (LSP Attributes) 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 (C-Type = 7) object 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.
LSPA Object-Class is to be assigned by IANA (recommended value=9)
LSPA Object-Types is to be assigned by IANA (recommended value=1)
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)
The flag L corresponds to the "Local protection desired" bit
([RFC3209]) of the SESSION-ATTRIBUTE Object.
L Flag (Local protection desired). 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 [RFC4420].
7.12. Include Route Object 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 de PCE to fail to find a
path.
IRO Object-Class is to be assigned by IANA (recommended value=10)
IRO Object-Type is to be assigned by IANA (recommended value=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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Subobjects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: IRO Body Format
Subobjects: The IRO is made of subobjects identical to the ones
defined in [RFC3209], [RFC3473] and [RFC3477] where the IRO subobject
type is identical to the subobject type defined in the related
documents.
The following subobject types are supported.
Type Subobject
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).
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 MBits/s and N2 MBits/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
set up failure probability compared to the serialized computation of
independent requests.
Dependent path computation 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
probability of not being able to satisfy all requests (sometimes also
referred to as the well-know "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 (SVEC object defined below required),
o Bundle of a set of dependent and synchronized path computation
requests (SVEC object defined below required).
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 to be assigned by IANA (recommended value=11)
SVEC Object-Type is to be assigned by IANA (recommended value=1)
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.
o 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.
o 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.
o 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 later case, it is
RECOMMENDED for the PCE to implement a local timer 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 (this timer is
called the SyncTimer). 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 message may also contain non-synchronized path
computation requests. For example, the PCReq message may comprise N
synchronized path computation requests related to RP 1, ... , RP N
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 to be assigned by IANA (recommended
value=12)
NOTIFICATION Object-Type is to be assigned by IANA (recommended
value=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.
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 should be 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-
value=1 indicates to the PCCs 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.
Optionally, a TLV named OVERLOADED-DURATION may be included in
the NOTIFICATION object that specifies the period of time
during whichno further request should be sent to the PCE. Once
this period of time has elapsed, the PCE should no longer be
considered in 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 fix length value field of
32-bits flags field.
TYPE: To be assigned by IANA (suggested value=2)
LENGTH: 4
VALUE: 32-bits 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 congested 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
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-thresholds mechanism
triggering 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 path computation requests oscillation.
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 to be assigned by IANA (recommended
value=13)
PCEP-ERROR Object-Type is to be assigned by IANA (recommended
value=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
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 should be 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 TLV so as to
provide further information about the encountered error.
A single PCErr message may contain multiple PCEP-ERROR objects.
For each PCEP error, an Error-type and an Error-value are defined.
Error- Meaning
Type
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.
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.
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 identifies 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 fix length value field of 4 bytes.
TYPE: To be assigned by IANA (suggested value=3)
LENGTH: 4
VALUE: 4 bytes that indicates 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.
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 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 MBits/s, with
potentially some constraints on the number of TE LSPs and the minimum
bandwidth of each of these TE LSPs. Such 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 to be assigned by IANA (recommended
value=14)
LOAD-BALANCING Object-Type is to be assigned by IANA (recommended
value=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 Flag 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, expressed in bytes per second.
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 LSP 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 to be assigned by IANA (recommended value=15)
CLOSE Object-Type is to be assigned by IANA (recommended value=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 is requested to manage
the codespace of the Reason field. The following values are
currently defined (To be confirmed by IANA).
Reasons
Value Meaning
1 No explanation provided
2 DeadTimer expired
3 Reception of a malformed PCEP message
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
[I-D.ietf-pce-manageability-requirements].
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 Negotiation 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 setup,
o Request timer: amount of time a PCC waits for a reply before
resending its path computation requests (potentially to an
alternate PCE).
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 a specific group of sessions 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 [I-D.kkoushik-pce-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
congestion 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
[I-D.ietf-pce-monitoring].
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 a
returned path fit in with the requested TE parameters.
A PCEP implementation SHOULD log error events (e.g. corrupted
messages, unrecognized objects, etc.).
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 Discovery/
Disappearance trigger high frequency of PCEP session setup/deletion,
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
session 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.
9. IANA Considerations
9.1. TCP Port
PCEP uses a well-known TCP port. IANA is requested to assign a port
number from the "System" sub-registry of the "Port Numbers" registry.
9.2. PCEP Top-Level Registry
IANA is requested to establish a new top-level registry to contain
all PCEP codepoints and sub-registries. The registry should be called
"Path Computation Element Protocol (PCEP)".
The allocation policy for each sub-registry defined in this document
is "IETF Consensus" (see [RFC2434]). 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).
9.2.1. PCEP Messages
IANA is requested to create a sub-registry for PCEP messages type
values. Each PCEP message has a message type value. The sub-registry
should be called "PCEP Message Types".
New PCEP Message Types may be allocated only by an IETF Consensus
action.
Message Message Reference
Type
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
9.2.2. PCEP Object
IANA is requested to create a sub-registry for objects carried in
PCEP messages. Each PCEP object has an Object-Class and an
Object-Type. The sub-registry should be called "PCEP Objects".
New Object-Classes and new Object-Types of existing Object-Classes
may be allocated only by an IETF Consensus action.
Object Name Reference
Class
1 OPEN This document
Object-Type
1: Open This document
2 RP This document
Object-Type
1: Request Parameters This document
3 NO-PATH This document
Object-Type
1: No Path This document
4 END-POINTS This document
Object-Type
1: IPv4 addresses This document
2: IPv6 addresses This document
5 BANDWIDTH This document
Object-Type
1: Requested bandwidth This document
2: Bandwidth of an existing TE LSP for This document
which a reoptimization is performed.
6 METRIC This document
Object-Type
1: Metric This document
7 ERO This document
Object-Type
1: Explicit Route This document
8 RRO This document
Object-Type
1: Record Route This document
9 LSPA This document
Object-Type
1: LSP Attributes This document
10 IRO This document
Object-Type
1: Include Route This document
11 SVEC This document
Object-Type
1: Synchronization Vector This document
12 NOTIFICATION This document
Object-Type
1: Notification This document
13 PCEP-ERROR This document
Object-Type
1: Error This document
14 LOAD-BALANCING This document
Object-Type
1: Load Balancing This document
15 CLOSE This document
Object-Type
1: Close This document
9.2.3. RP Object
IANA is requested to create a new sub-registry for the bits in the
Flags field of the RP Object. The sub-registry should be called
"Request Parameters Bit Flags".
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
- Bit number
- Bit name
- Description
- Defining RFC
The field contains 32 bits numbered from 1 as the least significant
bit.
Bit Name Description Reference
1-3 Pri Priority This document
4 R-bit Reoptimization This document
5 B-bit Bi-directional This document
6 O-bit Strict/Loose This document
9.2.4. Notification Object
IANA is requested to create a sub-registry for the Notification-type
and Notification-value of the Notification Object and manage the code
space. The sub-registry should be called "Notification Types and
Values".
New Notification-Types and new Notification-Values of existing
Notification-Types may be allocated only by an IETF Consensus action.
Notification
Type Name Reference
1 Pending Request cancelled This document
Notification-value:
1: PCC cancels a set of pending requests This document
2: PCE cancels a set of pending requests This document
2 PCE Congestion This document
Notification-value
1: PCE in congested state This document
2: PCE no longer in congested state This document
9.2.5. PCEP-ERROR Object
IANA is requested to create a sub-registry for the Error-type and
Error-value of the PCEP Error Object and manage the code space. The
sub-registry should be called "Error Types and Values".
New Error-Types and new Error-Values of existing Error-Types may be
allocated only by an IETF Consensus action.
For each PCEP error, an Error-type and an Error-value are defined.
Error
Type Meaning Reference
1 PCEP session establishment failure This document
Error-value=1: This document
Reception of an invalid Open message or a
non-Open message.
Error-value=2: This document
No Open message received before the expiration
of the OpenWait timer.
Error-value=3:
Unacceptable and non negotiable session This document
characteristics.
Error-value=4:
Unacceptable but negotiable session This document
characteristics.
Error-value=5: This document
Reception of a second Open message with still
unacceptable session characteristics.
Error-value=6: This document
Reception of a PCErr message proposing
unacceptable session characteristics.
Error-value=7: This document
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: This document
Unrecognized object class
Error-value=2: This document
Unrecognized object Type
4 Not supported object This document
Error-value=1:
Unsupported object class. This document
Error-value=2:
Unsupported object Type. This document
5 Policy violation This document
Error-value=1: This document
C bit of the METRIC object set (request
rejected).
Error-value=2: This document
O bit of the RP object cleared (request
rejected).
6 Mandatory Object missing. This document
Error-value=1:
RP object missing.
Error-value=2: This document
RRO missing for a reoptimization request
(R bit of the RP object set).
Error-value=3: This document
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: This document
Reception of an object with P flag not set
although the P-flag must be set according
to this specification.
9.2.6. CLOSE Object
IANA is requested to create a sub-registry for the Reason field of
the PCEP Close Object and manage the code space. The sub-registry
should be called "Close Reasons".
New Close Reasons may be allocated only by an IETF Consensus action.
Reasons
Value Meaning
1 No explanation provided
2 DeadTimer expired
3 Reception of a malformed PCEP message
9.2.7. NO-PATH Object
9.2.7.1. No-Path Nature of Issue
IANA is requested to create a sub-registry to manage the Nature of
Issue (NI) field present in the NO-PATH Object. The sub-registry
should be called "No-Path Nature of Issue".
New Nature of Issue values may be allocated only by an IETF Consensus
action.
Value Meaning Reference
0 No path satisfying the set of constraints This document
could be found
1 PCE chain broken This document
9.2.7.2. No-Path Bit Flags
IANA is requested to created a sub-registry of bits carried in the
Flags field of the PCEP NO-PATH object. The sub-registry should be
called "No-Path Flags".
New assignments from this sub-registry are by IETF Consensus action.
The field contains 16 bits numbered from 1 as the least significant
bit.
Bit Name Description Reference
16 C-bit Unsatisfied constraints included This document
9.2.8. METRIC Object
9.2.8.1. Metric Type
IANA is requested to create a sub-registry to manage the Metric Type
carried in the T field of the PCEP METRIC object. The sub-registry
should be called "Metric Types".
New assignments from this sub-registry are by IETF Consensus action.
Value Meaning Reference
1 IGP metric This document
2 TE metric This document
3 Hop Counts This document
9.2.8.2. Metric Control Flags
IANA is requested to create a sub-registry to manage the Flags field
carried in the PCEP METRIC object. The sub-registry should be called
"Metric Control Flags".
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
- Bit number
- Bit name
- Description
- Defining RFC
The field contains 8 bits numbered from 1 as the least significant
bit.
Bit Name Description Reference
1 B-bit Bound This document
2 C-bit Computed metric This document
9.2.9. PCEP TLV Type Indicators
PCEP TLV type values are allocated from a common TLV type codepoint
space. IANA is requested to create a sub-registry for the PCEP TLV
types. The sub-registry should be called "PCEP TLV Types"
New assignments from this sub-registry are by IETF Consensus action.
TLV Type Meaning Reference
1 NO-PATH-VECTOR TLV This document
2 OVERLOAD-DURATION TLV This document
3 REQ-MISSING TLV This document
9.2.10. NO-PATH-VECTOR TLV
IANA is requested to manage the space of flags carried in the NO-
PATH-VECTOR TLV. The sub-registry should be called "No-Path Reasons".
New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities:
- Bit number
- Name
- Reference
The field carries 32 bits numbered from zer as the most significant
bit to 31 as the least significant bit.
Bit
Number Name Reference
1 PCE currently Unavailable This document
2 Unknown Destination This document
3 Unknown Source This document
10. Security Considerations
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
A PCEP attack may have significant impact, particularly in an
inter-AS context as PCEP facilitates inter-AS path establishment.
Several mechanisms are proposed below, so as to ensure
authentication, integrity and privacy of PCEP Communications, and
also to protect against DoS attacks.
10.1. PCEP Authentication and Integrity
It is RECOMMENDED to use TCP-MD5 [RFC1321] signature option to
provide for the authenticity and integrity of PCEP messages. This
will allow protecting against PCE or PCC impersonation and also
against message content falsification.
This requires the maintenance, exchange and configuration of MD-5
keys on PCCs and PCEs. Note that such maintenance may be especially
onerous to the operators as pointed out in
[I-D.ietf-rpsec-bgpsecrec]. Hence it is important to limit the
number of keys while ensuring the required level of security.
MD-5 signature faces some limitations, as explained in [RFC2385].
Note that when a digest technique stronger than MD5 is specified and
implemented, PCEP could be easily upgraded to use it.
10.2. 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 intercept a PCE message
could obtain sensitive information related to computed paths and
resources. Privacy can be ensured thanks to encryption. To ensure
privacy of PCEP communication, IPsec [RFC4303] tunnels MAY be used
between PCC and PCEs or between PCEs. Note that this could also be
used to ensure Authentication and Integrity, in which case, TCP MD-5
option would not be required.
10.3. Protection Against Denial of Service Attacks
10.3.1. Protection Against TCP DoS Attacks
PCEP can be the target of TCP DoS attacks, such as for instance SYN
attacks, as all protocols running on top of TCP. PCEP can use the
same mechanisms as defined in [RFC5036] to mitigate the threat of
such attacks:
o A PCE should avoid promiscuous TCP listens for PCEP TCP connection
establishment. It should use only listens that are specific to
authorized PCCs.
o The use of the MD5 option helps somewhat since it prevents a SYN
from being accepted unless the MD5 segment checksum is valid.
However, the receiver must compute the checksum before it can
decide to discard an otherwise acceptable SYN segment.
o The use of access-list on the PCE so as to restrict access to
authorized PCCs.
10.3.2. Request Input Shaping/Policing
A PCEP implementation may be subject to Denial Of Service attacks
consisting of sending a very large number of PCEP messages (e.g.
PCReq messages). Thus, especially in multi-Service Provider
environments, a PCE implementation should implement request input
shaping/policing so as to throttle the amount of received PCEP
messages without compromising the implementation behavior.
11. Authors' Addresses
The content of this document was contributed by the editors and the
co-authors listed below:
Arthi Ayyangar
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
USA
Email: arthi@juniper.net
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
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
12. Acknowledgements
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. Special thank to Adrian Farrel for his very valuable
suggestions. The authors would also like to thank Fabien Verhaeghe
for the very fruitful discussions and useful suggestions.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 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.
13.2. Informative References
[I-D.ietf-pce-inter-layer-req]
Oki, E., "PCC-PCE Communication and PCE Discovery
Requirements for Inter-Layer Traffic Engineering",
draft-ietf-pce-inter-layer-req (work in progress).
[I-D.ietf-pce-interas-pcecp-reqs]
Bitar, N., "Inter-AS Requirements for the Path Computation
Element Communication Protocol (PCECP)",
draft-ietf-pce-interas-pcecp-reqs (work in progress).
[I-D.ietf-pce-manageability-requirements]
Farrel, A., "Inclusion of Manageability Sections in PCE
Working Group Drafts",
draft-ietf-pce-manageability-requirements (work in
progress.
[I-D.ietf-pce-monitoring]
Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
monitoring tools for Path Computation Element based
Architecture", draft-ietf-pce-monitoring (work in
progress).
[I-D.ietf-pce-monitoring]
Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
monitoring tools for Path Computation Element based
Architecture", draft-ietf-pce-monitoring (work in
progress).
[I-D.ietf-rpsec-bgpsecrec]
Christian, B. and T. Tauber, "BGP Security Requirements",
draft-ietf-rpsec-bgpsecrec (work in progress).
[I-D.kkoushik-pce-pcep-mib]
Stephan, E. and K. Koushik, "PCE communication
protocol(PCEP) Management Information Base",
draft-kkoushik-pce-pcep-mib (work in progress).
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, August 1998.
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[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.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4420] Farrel, A., Papadimitriou, D., Vasseur, J., and A.
Ayyangar, "Encoding of Attributes for Multiprotocol Label
Switching (MPLS) Label Switched Path (LSP) Establishment
Using Resource ReserVation Protocol-Traffic Engineering
(RSVP-TE)", RFC 4420, February 2006.
[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.
[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.
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: timer (in seconds) started after having initialized a TCP
connection using the PCEP well-known TCP port. The value of the
TCPConnect timer is 60 seconds.
ConnectRetry: specifies the number of times the system has tried to
establish a TCP connection with a PCEP peer without success.
ConnectMaxRetry: Maximum number of times the system tries to
establish a TCP connection using the PCEP well-known TCP port before
going back to the Idle state. The value of the ConnectMaxRetry is 5.
OpenWait: 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 go back
to the Idle state. The OpenWait timer has a fixed value of 60
seconds.
KeepWait: 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 go back to the Idle state. The KeepWait timer has a
fixed value of 60 seconds.
OpenRetry: specifies the number of times the system has received an
Open message with unacceptable PCEP session characteristics.
The following two states variable are defined:
RemoteOK: the RemoteOK variable is a Boolean set to 1 if the system
has received an acceptable Open message.
LocalOK: the LocalOK variable is a Boolean 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 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, ...) but no PCEP messages are
accepted from any PCEP peer. The system listens the well-known PCEP
TCP port.
The following set of variable are initialized:
TCPRetry=0,
LocalOK=0,
RemoteOK=0,
OpenRetry=0.
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 of 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 well-known PCEP 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
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 TPCPending 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, ...).
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.
If no errors are detected, PCEP increments the OpenRetry variable.
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, 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, 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.
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, start 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, 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.
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 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 setup 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
declared the session down if no PCEP message has been received.
SyncTimer: the SYNC timer is 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 SYNC timer 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. A RECOMMENDED value for the SYNC timer is 60 seconds.
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
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