Networking Working Group JP. Vasseur, Ed.
Internet-Draft Cisco Systems, Inc
Expires: December 24, 2006 JL. Le Roux
France Telecom
A. Ayyangar
Juniper Networks
E. Oki
NTT
A. Atlas
Google
A. Dolganow
Alcatel
Y. Ikejiri
NTT Communications Corporation
K. Kumaki
KDDI Corporation
June 22, 2006
Path Computation Element (PCE) communication Protocol (PCEP) - Version 1
draft-ietf-pce-pcep-02.txt
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Copyright Notice
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Copyright (C) The Internet Society (2006).
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 MPLS and GMPLS Traffic
Engineering. The PCEP protocol 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].
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Transport protocol . . . . . . . . . . . . . . . . . . . . . . 6
5. Architectural Protocol Overview (Model) . . . . . . . . . . . 7
5.1. Problem . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Architectural Protocol Overview . . . . . . . . . . . . . 7
5.2.1. Initialization Phase . . . . . . . . . . . . . . . . . 8
5.2.2. Path computation request sent by a PCC to a PCE . . . 9
5.2.3. Path computation reply sent by the PCE to a PCC . . . 10
5.2.4. Notification . . . . . . . . . . . . . . . . . . . . . 12
5.2.5. Termination of the PCEP Session . . . . . . . . . . . 13
6. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Common header . . . . . . . . . . . . . . . . . . . . . . 14
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 . . . . . . . . . . . . . . . 19
6.7. Error (PCErr) Message . . . . . . . . . . . . . . . . . . 20
6.8. Close message . . . . . . . . . . . . . . . . . . . . . . 21
7. Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1. Common object header . . . . . . . . . . . . . . . . . . . 21
7.2. OPEN object . . . . . . . . . . . . . . . . . . . . . . . 23
7.3. RP Object . . . . . . . . . . . . . . . . . . . . . . . . 24
7.3.1. Object definition . . . . . . . . . . . . . . . . . . 24
7.3.2. Handling of the RP object . . . . . . . . . . . . . . 26
7.4. NO-PATH Object . . . . . . . . . . . . . . . . . . . . . . 27
7.5. END-POINT Object . . . . . . . . . . . . . . . . . . . . . 28
7.6. BANDWIDTH Object . . . . . . . . . . . . . . . . . . . . . 29
7.7. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 30
7.8. ERO Object . . . . . . . . . . . . . . . . . . . . . . . . 32
7.9. RRO Object . . . . . . . . . . . . . . . . . . . . . . . . 33
7.10. LSPA Object . . . . . . . . . . . . . . . . . . . . . . . 33
7.11. IRO Object . . . . . . . . . . . . . . . . . . . . . . . . 35
7.12. SVEC Object . . . . . . . . . . . . . . . . . . . . . . . 36
7.12.1. Independent versus synchronized path computation
requests . . . . . . . . . . . . . . . . . . . . . . . 36
7.12.2. SVEC Object . . . . . . . . . . . . . . . . . . . . . 37
7.12.3. Handling of the SVEC Object . . . . . . . . . . . . . 38
7.13. NOTIFICATION Object . . . . . . . . . . . . . . . . . . . 39
7.14. PCEP-ERROR Object . . . . . . . . . . . . . . . . . . . . 42
7.15. CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 44
8. Manageability Considerations . . . . . . . . . . . . . . . . . 45
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
9.1. TCP Port . . . . . . . . . . . . . . . . . . . . . . . . . 45
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9.2. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 45
9.3. PCEP Object . . . . . . . . . . . . . . . . . . . . . . . 46
9.4. Notification . . . . . . . . . . . . . . . . . . . . . . . 47
9.5. PCEP Error . . . . . . . . . . . . . . . . . . . . . . . . 48
10. PCEP Finite State Machine (FSM) . . . . . . . . . . . . . . . 49
11. Security Considerations . . . . . . . . . . . . . . . . . . . 54
11.1. PCEP Authentication and Integrity . . . . . . . . . . . . 55
11.2. PCEP Privacy . . . . . . . . . . . . . . . . . . . . . . . 55
11.3. Protection against Denial of Service attacks . . . . . . . 55
11.4. Request input shaping/policing . . . . . . . . . . . . . . 56
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 56
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 56
13.1. Normative References . . . . . . . . . . . . . . . . . . . 56
13.2. Informative References . . . . . . . . . . . . . . . . . . 57
Appendix A. Proposed Status and Discussion [To Be Removed
Upon Publication] . . . . . . . . . . . . . . . . . . 58
Appendix B. Compliance with the PCECP Requirement Document . . . 58
Appendix C. PCEP Variables . . . . . . . . . . . . . . . . . . . 59
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 60
Intellectual Property and Copyright Statements . . . . . . . . . . 62
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1. Terminology
Terminology used in this document
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 across at least two
different domains where a domain can either 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 the
PCE).
TED: Traffic Engineering Database which 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 of at
least one loose hop representing the destination where a hop may be
an abstract node such as an AS.
Within this document, when PCE-PCE communications are being
described, the requesting PCE fills the role of a PCC. This provides
a saving in documentation without loss of function.
2. Introduction
[I-D.ietf-pce-architecture]describes the motivations and architecture
for a PCE-based model for the computation of MPLS and GMPLS TE LSPs.
The model allows the separation of PCE from PCC, and allows
cooperation between PCEs. This necessitates a communication protocol
between PCC and PCE, and between PCEs.
[I-D.ietf-pce-comm-protocol-gen-reqs] states the generic requirements
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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 [I-D.ietf-pce-comm-protocol-gen-
reqs], 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 [I-D.ietf-pce-pcecp-interarea-
reqs]and [I-D.ietf-pce-inter-layer-req].
This document specifies the Path Computation Element communication
Protocol (PCEP) for communications between 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 MPLS and GMPLS Traffic Engineering.
The PCEP protocol 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.
3. Assumptions
[I-D.ietf-pce-architecture] 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 gets the required information so
as to perform TE LSP path computation which usually requires network
topology and resource information that can be gathered by routing
protocols or by some other means. The retrieval of such information
is out of the scope of this document.
Similarly, no assumption is made on the discovery method used by a
PCC to discover a set of PCEs (e.g. via static configuration or
dynamic discovery) and on the PCE decision selection process. For
the sake of reference [I-D.ietf-pce-discovery-reqs] defines a list of
requirements for dynamic PCE discovery and IGP-based solution for
such PCE discovery are specified in [I-D.ietf-pce-disco-proto-igp].
4. 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.
An implementation may decide to keep the TCP session alive for an
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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 session each time a path computation request is needed).
Conversely, in some other circumstances, it may be desirable to
systematically open and close the TCP connection for each PCEP
request (for instance when sending of path computation request is a
rare event).
5. Architectural Protocol Overview (Model)
The aim of this section is to describe the PCEP protocol 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.
5.1. Problem
The PCE-based architecture used for the computation of MPLS and GMPLS
TE LSP paths is described in [I-D.ietf-pce-architecture]. When the
PCC and the PCE are not collocated, a communication protocol between
the PCC and the PCE is required. PCEP is such a protocol designed
specifically for communications between a PCC and a PCE or between
two PCEs: a PCC may use PCEP to send a path computation request for
one or more TE LSP(s) to a PCE and such a PCE may reply with a set of
computed path(s) if one or more path(s) obeying the set of
constraints can be found.
5.2. Architectural Protocol Overview
PCEP operates over TCP, which allows the requirements of reliable
messaging and flow control to be met 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 path(s) if the request could be satisfied or a negative
reply otherwise.
- PCNtf: a PCEP notification message either sent by a PCC to a PCE or
a PCE to a PCC to notify of specific event.
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- 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 PCE(s) may be either statically configured on a
PCC or dynamically discovered (the mechanism for that discovery is
out of the scope of this document). Note that the PCE selection
algorithm is 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.
A PCEP session establishment is always triggered by the PCC.
5.2.1. 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 a PCEP session establishment
during which various session parameters are negotiated. These
parameters are carried within Open messages and include the keepalive
timer 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 exchanged 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 exponential back-off.
Keepalive messages are used to acknowledge Open messages and once the
PCEP session has been successfully established, Keepalive messages
are exchanged between PCEP peers to ensure the liveness of the PCEP
session.
Details about the Open message and the Keepalive messages can be
found in . (Section 6.2) and Section 6.3respectively.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---- Open message --->|
| |
|<--- Open message ----|
| |
| |
| |
|<--- Keepalive -------|
| |
|---- Keepalive ------>|
Figure 1: PCEP Initialization phase (triggered by a PCC)
5.2.2. Path computation request sent by a PCC to a PCE
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1)Path computation | |
event | |
2)PCE Selection | |
3)Path computation |---- PCReq message--->|
request sent to | |
the selected PCE | |
Figure 2: Path computation request
Once a PCC (or a PCE) has successfully established a PCEP session
with one or more PCEs, if an event is triggered that requires the
computation of a set of path(s), the PCC first selects one of more
PCE(s) to send the request to. 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 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=X
Mbit/s, Priority=Y, ...". 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 addresses pair. The process is shown in a schematic form in
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figure 2.
Details about the PCReq message can be found in Section 6.4
5.2.3. Path computation reply sent by the PCE to a PCC
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---- PCReq message--->|
| |1) Path computation
| |request received
| |
| |2)Path successfully
| |computed
| |
| |3) Computed path(s) 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:
- Positive (Figure 3-a): the PCE manages to compute a path satisfying
the set of required constraints. The PCE returns the set of computed
path(s) to the requesting PCC. Note that PCEP supports the
capability to send a single request which refers to the computation
of multiple paths: for example, compute two link-diverse paths.
- Negative (Figure 3-b): no path could be found that satisfies the
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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.
5.2.4. Notification
There are several circumstances whereby a PCE may want to notify a
PCC of a specific event. For example, suppose that the PCE suddenly
experiences some congestion that would lead 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. Such notification may
potentially result in path computation redirections on the PCC
towards another PCE, if an alternate PCE is available. Similarly, a
PCC may desire to notify a PCE of particular event such as the
cancellation of pending request(s).
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1)Path computation | |
event | |
2)PCE Selection | |
3)Path computation |---- PCReq message--->|
request X sent to | |4) Path computation
the selected PCE | |triggered
| |
| |
5) Path computation| |
request X cancelled| |
|---- PCNtf message -->|
| |6) Path computation
| |request X cancelled
Figure 4: Example of PCC notification (request cancellation) sent to a PCE
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1)Path computation | |
event | |
2)PCE Selection | |
3)Path computation |---- PCReq message--->|
request X sent to | |4) Path computation
the selected PCE | |triggered
| |
| |
| |5) PCE experiencing
| |congestion
| |
| |6) Path computation
| |request X cancelled
| |
|<--- PCNtf message----|
Figure 5: Example of PCE notification (request(s) cancellation) sent to a PCC
Details about the PCNtf message can be found in Section 6.6.
5.2.5. 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 close the TCP connection.
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If the PCEP session is terminated by the PCE, the PCC clears all the
states related to pending requests 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 SHOULD be
maintained for a period of time equal to the Deadtimer.
Details about the Close message can be found in Section 6.8.
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 in such
message for the message to be considered as valid. Thus a missing
mandatory object in a PCEP message MUST be considered as a malformed
message and such condition MUST trigger an Error message.
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 7.1) that can be set by a PCEP peer to
enforce a PCE to take into account the related information during the
path computation. For example, the COST object allows a PCC to
specify a bounded acceptable path cost. The COST object is optional
but a PCC may set a flag to ensure that such constraint is taken into
account. Similarly to the previous case, if such constraint cannot
be taken into account by the PCE, this should trigger an Error
message.
For each PCEP message type a set of rules is defined which specifies
the set of possible 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 order specified in this document.
6.1. Common header
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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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message-Lenght |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: PCEP message common header
Ver (Version - 4 bits): PCEP protocol version number. Current
version is version 1.
Flags (8 bits): no flags are currently defined.
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 (32 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 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. 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 that phase the PCEP peers exchange
several session characteristics. If both parties agree on such
characteristics the PCEP session is successfully established.
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Open message
<Open Message>::= <Common Header>
<OPEN>
The Open message MUST contain exactly one OPEN object (see
Section 7.2). Various session characteristics are specified within
the OPEN object.
Once an Open message has been sent to a PCEP peer, the sender MUST
start an initialization timer called InitOpen after the expiration of
which a similar Open message MUST be resent if no reply has been
received from the PCEP peer. The InitOpen timer has a fixed value of
1 minute. The maximum number of Open messages named MaxRetryOpen
that can be sent without any response from the PCEP peer is equal to
3.
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 characteristic(s) 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 7.14.
If the PCEP session characteristics are acceptable, the receiving
PCEP peer MUST consequently send a Keepalive message (defined in
Section 6.3) that would serve as 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 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.
Keepalive: 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 constraints
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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 KeepAliveTimer value is 1 second.
Keepalive messages are used either to acknowledge an Open message if
the receiving PCEP peer agrees on the session characteristics and to
ensure the liveness of the PCEP session. Keepalive messages are sent
at the frequency specified in the OPEN object carried within an Open
message. Because any PCEP message may serve as Keepalive an
implementation may either decide to send Keepalive messages at the
same frequency 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.
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 so as to request a
path computation. 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 7). If one
of these objects is missing, the receiving PCE MUST send an error
message to the requester. Other objects are optional.
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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>]
[<RRO>]
[<BANDWIDTH>]
[<IRO>]
The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, ERO, and IRO
objects are defined in Section 7. The special case of two BANDWIDTH
objects in details inSection 7.6.
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 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 7.3for the definition of the RP object).
A PCRep may comprise multiple computed path(s) corresponding to
multiple path computation requests originated by a common requesting
PCC and/or to multiple acceptable paths corresponding to the same
request. The bundling of multiple responses within a single PCRep
message is supported by the PCEP protocol. 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 reply each path in separate
PCRep messages.
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If the path computation request can be successfully satisfied (the
PCE manages to compute a set of path(s) that obey the requested
constraint(s)), the set of computed path(s) specified by means of ERO
object(s) is inserted in the PCRep message. The ERO object is
defined in Section 7.8. Such a situation where multiple computed
paths are provided in a PCRep message is discussed in detail in
Section 7.12.
If the path computation request cannot be satisfied, the PCRep
message MUST include a NO-PATH object. The NO-PATH object (further
described in Section 7.4) may also comprise other information (e.g
reasons for the path computation failure).
The format of a PCRep message is as follows:
<PCRep Message> ::= <Common Header>
[<svec-list>]
<response-list>
where:
<svec-list>::=<SVEC>[<svec-list>]
<response-list>::=<response>[<response-list>]
<response>::=<RP>
[<NO-PATH>]
[<path-list>]
<path-list>::=<path>[<path-list>]
<path>::= <ERO>
[<LSPA>]
[<BANDWIDTH>]
[<METRIC>]
[<IRO>]
6.6. Notification (PCNtf) message
The PCEP Notification message (also referred to as the PCNtf message)
can either be sent by a PCE to a PCC or by a PCC to a PCE so as 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 7.13. The PCNtf message may also contain an RP object (see
Section 7.3when the notification refers to a particular path
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computation request.
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
when a protocol error condition is met. The Message-Type field of
the PCEP common header is set to 6.
The PCErr message may be sent by a PCC or a PCE in response to a
request or in an unsolicited manner. In the former case, the PCErr
message MUST include the set of RP objects related to the pending
path computation request(s) which triggered the protocol error
condition. In the later case (unsolicited), no RP object is inserted
within the PCErr message. No RP object is inserted in a PCErr when
the error condition occurred during the initialization phase. A
PCErr message MUST comprise a PCEP-ERROR object specifying the PCEP
error condition. The PCEP-ERROR object is defined in section
Section 7.14.
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The format of a PCErr message is as follows:
<PCErr Message> ::= <Common Header>
<error-list>
[<Open>]
<error-list>:==<error>[<error-list>]
<error>::=[<request-id-list>]
<error-obj-list>
<request-id-list>:==<RP>[<request-id-list>]
<error-obj-list>:==<PCEP-ERROR>[<error-obj-list>]
The procedure upon the reception of a PCErr message is defined in
Section 7.14.
6.8. Close message
The Close message is a PCEP message sent by either a PCC to a PCE or
by a PCE to a PCC in order to close a PCEP session. The Message-Type
field of the PCEP common header for the Open 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).
Upon the receipt of a Close message, the receiving PCEP peer MUST
cancel all pending requests and MUST close the TCP connection.
7. Object Formats
7.1. Common object header
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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 are managed by IANA.
The Object-Class and Object-Type fields uniquely identify each PCEP
object.
Res (3 bits): Reserved.
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 if not supported.
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 MUST be cleared if the P
flag is set.
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".
Res flags (2 bits). Reserved field (MUST be set to 0).
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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.
7.2. OPEN object
The OPEN object MUST be present in each Open message and may be
present in 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
protocol version, Keepalive frequency, 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 such TLV is 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 | Keepalive | Deadtimer | SID | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: OPEN Object format
Ver (Ver - 3 bits): PCEP version. Current version is 1.
Keepalive (8 bits): minimum period of time (in seconds) between the
sending of PCEP messages that the sender of the Open message will
send Keepalive messages. The minimum value for the Keepalive is 1
second. When set to 0, once the session is established, no further
keepalives need to be 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 a PCEP peer declares the session with the sender of the Open
message down if no PCEP message has been received. The DeadTimer
MUST be set to 0 if the Keepalive is set to 0. A RECOMMENDED value
for the DeadTimer is 4 times the value of the Keepalive.
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SID (PCEP session-ID - 8 bits): specifies a 2 octet unsigned PCEP
session number that identifies the current session. The SID MUST be
incremented each time a new PCEP session is established and is mainly
used for logging and troubleshooting purposes.
Flags (5 bits): No Flags are currently defined.
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 a PCEP object
within the PCErr message so as to propose alternative session
characteristic values.
7.3. 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 P flag of the RP object MUST be set. The RP object is
used to specify various characteristics of the path computation
request.
7.3.1. 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)
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |N|O|B|R| Pri |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request-ID-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: RP object body format
The RP object body has a variable length and may contain additional
TLVs. No TLV is currently defined.
Flags: 18 bits - The following flags are currently defined:
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 requests 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 that case, the priority field
RECOMMENDED be set to 0 by the PCC 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 PCC(s). The ability of a PCE to support
requests prioritization may be dynamically discovered by the PCC(s)
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 the 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.
R (Reoptimization - 1 bit): when set, the requesting PCC specifies
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that the PCReq message relates to the reoptimization of an existing
TE LSP in which case the path of the existing TE LSP to be
reoptimized MUST be provided in the PCReq (except of 0-bandwidth TE
LSP) message by means of an RRO object defined in Section 7.9.
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, and resource requirements (e.g.
latency and jitter) in each direction. When cleared, the TE LSP is
unidirectional.
O (strict/lOose - 1 bit): when set, in a PCReq message, this
indicates that a strict/loose path is acceptable. Otherwise, when
cleared, this indicates to the PCE that an explicit path is required.
In a PCRep message, when the O bit is set this indicates that the
returned path is strict/loose, otherwise (the O bit is cleared), the
returned path is explicit.
F (new - 1 bit): when set, the requesting PCC requires the
computation of a new path for a TE LSP that has failed in which case
the path of the existing TE LSP MUST be provided in the PCReq (except
of 0-bandwidth TE LSP) message by means of an RRO object defined in
Section 7.9. This is to avoid double bandwidth booking should the
TED not be yet updated or the corresponding resources not be yet
released.
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. 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.
7.3.2. Handling of the RP object
If a PCReq message is received without containing 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 C bit of the RP message carried within a PCReq message is set
and local policy has been configured on the PCE to not provide the
computed path cost, a PCErr message MUST be sent by the PCE to the
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requesting PCC and the pending path computation request MUST be
discarded. The Error-type is "Policy Violation" and Error-value is
"C bit set".
If the O bit of the RP message carried within a PCReq message is set
and local policy has been configured on the PCE to not provide
explicit path(s) (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 set".
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
provide the explicit or strict/loose path by including an RRO object
in the PCReq message so as to avoid double bandwidth counting if and
only if the TE LSP is a non 0-bandwidth TE LSP. If the PCC has
previously requested a non-explicit path (O bit set), a
reoptimization can still be requested by the PCC but this implies for
the PCE to be either stateful (keep track of the previously computed
path with the associated list of strict hops) or to have the ability
to retrieve the complete required path segment. Alternatively the
PCC MUST be able to inform PCE of the working path with 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".
7.4. NO-PATH Object
The No-PATH object is used in PCRep messages in response to a path
computation request that was unsuccessful (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. In its simplest form, the NO-PATH
object is limited to a set of flags and just reports the
impossibility to find a path that satisfies the set of constraints.
Optionally, if the PCE supports such capability, 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 object 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.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: NO-PATH object format
The NO-PATH object body has a fixed length of 4 octets.
Flags (16 bits). The following flags are 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
reason is specified.
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 reasons for
the unsuccessful computation is the bandwidth constraint (in this
case, the 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).
When the NO-PATH object is absent from a PCRep message, the path
computation request has been fully satisfied and the corresponding
path(s) is/are provided in the PCRep message.
7.5. 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. 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)
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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 octets for IPv4
and 32 octets for IPv6.
7.6. BANDWIDTH Object
The BANDWIDTH object is optional and can be used to specify the
requested bandwidth for a TE LSP. In the case of a non existing TE
LSP, the BANDWIDTH object MUST be included in the PCReq message so as
to specify the required bandwidth for the new TE LSP. In the case of
the reoptimization of an existing 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 are defined that refer to the requested bandwidth and the
bandwidth of a existing TE LSP for which a reoptimization is being
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performed.
The BANDWIDTH object may be carried within PCReq and PCRep messages.
The absence of the BANDWIDTH object MUST be interpreted by the PCE as
a path computation request related to a 0 bandwidth TE LSP.
BANDWIDTH Object-Class is to be assigned by IANA (recommended
value=5)
Two Object-Type 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
performed. 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.
The BANDWIDTH object body has a fixed length of 4 octets.
7.7. METRIC Object
The METRIC object is optional and can be used for several purposes.
In a PCReq message, a PCC MAY insert a METRIC object:
o To indicate the metric that must be optimized by the path
computation algorithm. Currently, two metrics are defined: the
IGP cost and the TE metric (see [RFC3785]).
o To indicate a bound on the path cost than 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.
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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 metric is only meaningful if
used consistently: for instance, if the delay of a path computation
segment is exchanged between two PCE 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 the PCE may choose the metric to
be used.
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
T (Type - 3 bits): Specifies the metric type. Two values are
currently defined:
o T=1: The IGP metric
o T=2: The TE cost
B (Bound - 1 bit): When set in a PCReq message, the metric-value
indicates a bound (a maximum) for the path cost that must not be
exceeded for the PCC to consider the computed path as acceptable.
When the B flag is cleared, the metric-value field MUST be set to
0x0000. In a PCReq message, if the B-flag is cleared, then the
metric-value field MUST be set to 0. The B flag MUST always be
cleared in a PCRep message.
C (Cost - 1 bit): When set in a PECReq message, this indicates that
the PCE MUST provide the computed path cost (should a path satisfying
the constraints be found) in the PCRep message with regards to the
corresponding metric.
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Metric-value (32 bits): metric value encoded in 32 bits in IEEE
floating point format.
The METRIC object body has a fixed length of 8 octets.
Multiple METRIC Objects MAY be inserted in a PCRep or the PCReq
message.
In a PCReq message the presence of multiple METRIC object can be used
to specify a multi-parameters (e.g. a metric may be a constraint or a
parameter to minimize/maximize) objective function or multiple bounds
for different constraints.
In a PCRep message, unless not allowed by PCE policy, at least one
METRIC object MUST be present that reports the computed path cost if
the C bit of the RP object was set in the corresponding path
computation request (the B-flag MUST be cleared); 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 path metric cost (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 a constraint metric (B-Flag was set in the path
computation request) that cannot 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, 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 no policy preventing to provide the path cost in place, 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.
7.8. ERO Object
The ERO object is used to encode a TE LSP. The ERO Object is carried
within a PCRep message to provide the computed TE LSP should have the
path computation been successful.
The contents of this object are identical in encoding to the contents
of the Explicit Route Object defined in [RFC3209], [RFC3473] and
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[RFC3477]. That is, the object is constructed from a series of sub-
objects. Any RSVP ERO sub-object already defined or that could be
defined in the future for use in the ERO is acceptable in this
object.
PCEP ERO sub-object types correspond to RSVP 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)
7.9. RRO Object
The RRO object is used to record the route followed by a TE LSP. The
PCEP RRO object is exclusively carried within a PCReq message so as
to specify 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 RRO sub-object already defined or that could be
defined in the future for use in the 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 RRO.
PCEP RRO sub-object types correspond to RSVP 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)
7.10. 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 either be carried within a PCReq
message or a PCRep message in case of unsuccessful path computation
(in this case, the PCRep message also comprises a NO-PATH object and
the LSPA object is used to indicate the set of constraint(s) that
could not be satisfied). Most of the fields of the LSPA object are
identical to the fields of the SESSION-ATTRIBUTE object defined in
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[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)
Two Objects-Types are defined for the LSPA object: LSPA without
resource affinity (Object-Type to be assigned by IANA with
recommended value=1) and LSPA with resource affinity (Object-type=2).
The format of the LSPA object body with and without resource affinity
are as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Setup Prio | Holding Prio | Flags |L| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: LSPA object body format (without resource affinity)
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 TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: LSPA object body format (with resource affinity)
Setup Prio (Setup Priority - 8 bits). The priority of the session
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
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session 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
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].
7.11. IRO Object
The IRO (Include Route Object) object is optional and can be used to
specify that the computed path must traverse a set of specified
network elements. The IRO object 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 could not be
included.
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 18: IRO object body format
Subobjects The IRO object is made of sub-object(s) identical to the
ones defined in [RFC3209], [RFC3473] and [RFC3477] for use in EROs.
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 object.
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7.12. SVEC Object
7.12.1. Independent versus synchronized path computation requests
The PCEP protocol allows for the bundling of multiple independent
path computation requests within a single PCRep message. 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 independent. Note that the PCC may
chose to distribute the set of N requests across K PCEs for load
balancing reasons. 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 grouped
within a single PCReq message. This is of course a viable solution
if and only if such requests are independent. That said, 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 criteria 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.
Furthermore, if the PCC has to send a large number of path
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computation requests, it may also be desirable to pack multiple
requests within a single PCReq object so as to minimize the control
plane overhead. Note that the algorithm used by the PCC to "pack" a
set of requests introduces some unavoidable trade-off between control
plane load and delays and such algorithm is outside of the scope of
this document.
There are other cases where the computation of M requests must be
synchronized an obvious example of which being 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.
The synchronization of a set of path computation requests is achieved
by using the SVEC object that specifies the list of synchronized
requests along with the nature of the synchronization.
7.12.2. SVEC Object
Section 7.12.1 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 such synchronization. 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
specify the correlation 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)
One Object-Type is defined for this object to be assigned by IANA
with a recommended value of 1.
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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 19: SVEC body object format
Flags: Defines the synchronization type between multiple path
computation requests.
L (Link diverse) bit: when set, this indicates that the computed
paths corresponding to the requests specified by the following RP
objects MUST not have any link in common.
N (Node diverse) bit: when set, this indicates that the computed
paths corresponding to the requests specified by the following RP
objects MUST not have any node in common.
S (SRLG diverse) bit: when set, this indicates that the computed
paths corresponding to the requests specified by the following RP
objects MUST not share any SRLG (Shared Risk Link Group).
The flags defined above are not exclusive.
7.12.3. 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 the nature of the
synchronization. The set of M path computation requests may be sent
within a single PCReq message or multiple PCReq message. In the
later case, it is RECOMMENDED for the PCE to implement a local timer
upon the receipt of the first PCReq message that comprises 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). In this case the PCE MUST cancel the
whole set of path computation requests and MUST send a PCErr message
with Error-Type="Synchronized path computation request missing".
Note that such PCReq message may also comprise 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.
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7.13. 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)
One Object-Type is defined for this object to be assigned by IANA
with a recommended value of 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 TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: NOTIFICATION body object format
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.
Flags: no flags are currently defined.
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 request(s).
A Notification-type=1, Notification-value=1 indicates that the
PCC wants to inform a PCE of the cancellation of a set of
pending request(s). Such event could be triggered because of
external conditions such as the receipt of a positive reply
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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 event(s) local to the PCC. A NOTIFICATION object
with Notification-type=1, Notification-value=1 is exclusively
carried within a PCNtf message sent by the PCC to the PCE. The
RP object 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 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 request(s).
A Notification-type=1, Notification-value=2 indicates that the
PCE wants to inform a PCC of the cancellation of a set of
pending request(s). Such event could be triggered because of
some PCE congested state or because of some path computation
requests that are part the set of synchronized path computation
requests are missing. A NOTIFICATION object with Notification-
type=1, Notification-value=2 is exclusively carried within a
PCNtf message sent by a PCE to a PCC. The RP object MUST also
be present in the PCNtf message. Multiple RP objects may be
comprised 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: PCE congestion
* Notification-value=1. A Notification-type=2, Notification-
value=1 indicates to the PCC(s) that the PCE is currently in a
congested state. If no RP objects are comprised in the PCNtf
message, this indicates that no other requests SHOULD be sent
to that PCE until the congested state is cleared: the pending
requests are not affected and will be served. If some pending
requests cannot be served due to the congested state, the PCE
MUST also include a set of RP object(s) that identifies the set
of pending requests that are now 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 object(s).
If such notification is received by a PCE from a PCC, the PCE
MUST silently ignore the notification and no errors should be
generated.
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Optionally, a TLV named CONGESTION-DURATION may be included in the
NOTIFICATION object that specifies the duration during which no further
request should be sent to the PCE. Once this period has expired the PCE
should no longer be considered in congested state.
The CONGESTION-DURATION TLV is composed of 1 octet for the type,
1 octet specifying the number of bytes in the value field, 2 octets
for an "Unused" field (the value of which MUST be set to 0), followed by
a fix length value field of 4 octets specifying the estimated PCE
congestion duration in seconds. The CONGESTION-DURATION TLV is padded
to eight-octet alignment.
TYPE: To be assigned by IANA
LENGTH: 4
VALUE: estimated congestion duration in seconds
* If a new PCEP session is established while the PCE is in
congested state, the PCE MUST immediately send a PCErr with
Notification-type=2, Notification-value=1 along with optionally
the CONGESTION-DURATION TLV.
* 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 MUST 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
a CONGESTION-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. An implementation may decide to cancel such
notification if the PCC is in down state for a specific period.
A RECOMMENDED value for such delay is 1 hour. 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 notifications and releases. For example, an
implementation could make use of an hysteresis approach using a
dual-thresholds mechanism triggering the sending of congestion
notifications and releases. 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.
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7.14. PCEP-ERROR Object
The PCEP-ERROR object is exclusively carried within a PCErr message
to notify of a PCEP protocol 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)
One Object-Type is defined for this object to be assigned by IANA
with a recommended value of 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 TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: PCEP-ERROR object body format
A PCEP-ERROR object is used to report a PCEP protocol 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).
Flags (8 bits): no flag is currently defined.
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. No TLV is
currently defined.
A single PCErr message may contain multiple PCEP-ERROR objects.
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For each PCEP protocol error, an Error-type and an Error-value are
defined.
Error-Type Meaning
1 Capability not supported
2 Unknown Object
Error-value=1: Unrecognized object class
Error-value=2: Unrecognized object Type
3 Not supported object
Error-value=1: Not supported object class
Error-value=2: Not supported object Type
4 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)
5 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)
Error-value=3: END-POINTS object missing
6 Synchronized path computation request missing
7 Unknown request reference
8 Unacceptable PCEP session characteristics
Error-value=1: parameter negotiation
Error-value=2: parameters negotiation failed
9 Deadtimer expired
Error-Type=1: the PCE indicates that the path computation request
cannot be completed because it does not support one or more required
capability. The corresponding path computation request MUST be
cancelled.
Error-Type=2 or Error-Type=3: 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=2 and 3 respectively).
The corresponding path computation request MUST be cancelled by the
PCE without further notification.
Error-Type=4: if a path computation request is received which 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=4).
The corresponding path computation MUST be cancelled. Policy-
specific TLV(s) carried within the PCEP-ERROR object may be defined
in other documents to specify the nature of the policy violation.
Error-Type=5: 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=5). If there are multiple mandatory
objects missing, the PCErr message MUST contain one PCEP-ERROR object
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per missing object. The corresponding path computation MUST be
cancelled.
Error-Type=6: 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 7.12.3, the PCE MUST send a PCErr message with a PCEP-ERROR
object (Error-Type=6). The corresponding synchronized path
computation MUST be cancelled. It is RECOMMENDED for the PCE to
include the REQ-MISSING TLV(s) (defined below) that identifies the
missing request(s).
The REQ-MISSING TLV is composed of 1 octet for the type,
1 octet specifying the number of bytes in the value field, 2 octets
for an "Unused" field (the value of which MUST be set to 0), followed by
a fix length value field of 4 octets specifying the request-id-number
that correspond to the missing request. The REQ-MISSING TLV is padded
to eight-octet alignment.
TYPE: To be assigned by IANA
LENGTH: 4
VALUE: request-id-number that corresponds to the missing request
Error-Type=7: 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=7). In addition, the PCC MUST include
in the PCErr message the unknown RP object.
Error-Type=8: if one or more PCEP session characteristic(s) are not
acceptable by the receiving peer and are not negotiable, it MUST send
a PCErr message with Error-type=8, Error-value=1. Conditions under
which such error message is sent are detailed in Section 6.2
Error-Type=9: If a PCEP peer does not receive any PCEP message
(Keepalive, PCReq, PCRep, PCNtf) during the Deadtimer period, the
PCEP peer MUST send a PCErr message with a PCEP-ERROR object (Error-
type=9, Error-value=1). The PCEP session MUST be terminated
according to the procedure defined in Section 6.8.
7.15. CLOSE Object
The CLOSE object MUST be present in each Close message. There MUST
be only one CLOSE object per Close message.
CLOSE Object-Class is to be assigned by IANA (recommended value=14)
CLOSE Object-Type is to be assigned by IANA (recommended value=1)
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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 TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: CLOSE Object format
Reason (4 bits): specifies the reason for closing the PCEP session.
The setting of this field is optional. Two values are currently
defined.
Reasons
Value Meaning
1 No explanation provided
2 DeadTimer expired
3 PCEP session characteristics negotiation failure
Flags (4 bits): No Flags are currently defined.
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
It is expected and required to specify a MIB for the PCEP
communication protocol (in a separate document). Furthermore,
additional tools related to performance, fault and diagnostic
detection are required which will also be specified in separate
documents.
9. IANA Considerations
9.1. TCP Port
The PCEP protocol will use a well-known TCP port to be assigned by
IANA.
9.2. PCEP Messages
Each PCEP message has a Message-Type.
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Value Meaning
1 Open
2 Keepalive
3 Path Computation Request
4 Path Computation Reply
5 Notification
6 Error
7 Close
9.3. PCEP Object
IANA assigns value to PCEP parameters. Each PCEP object has an
Object-Class and an Object-Type.
Object-Class Name
1 OPEN
Object-Type
1
2 RP
Object-Type
1
3 NO-PATH
Object-Type
1
4 END-POINTS
Object-Type
1 : IPv4 addresses
2: IPv6 addresses
5 BANDWIDTH
Object-Type
1: Requested bandwidth
2: Bandwidth of an existing TE LSP
for which a reoptimization is performed.
6 METRIC
Object-Type
1
7 ERO
Object-Type
1
8 RRO
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Object-Type
1
9 LSPA
Object-Type
1: without resource affinity
2: with resource affinity
10 IRO
Object-Type
1
11 SVEC
Object-Type
1
12 NOTIFICATION
Object-Type
1
13 PCEP-ERROR
Object-Type
1
14 CLOSE
Object-Type
1
9.4. Notification
A NOTIFICATION object is characterized by a Notification-type that
specifies the class of notification and a Notification-value that
provides additional information related to the nature of the
notification. Both the Notification-type and Notification-value are
managed by IANA (see IANA section).
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Notification-type Name
1 Pending Request cancelled
Notification-value
1: PCC cancels a set of pending request(s)
2: PCE cancels a set of pending request(s)
2 PCE Congestion
Notification-value
1: PCE in congested state
2: PCE no longer in congested state
9.5. PCEP Error
PCEP-ERROR objects are used to report a PCEP protocol error and are
characterized by an Error-Type which specifies the type of error and
an Error-value that provides additional information about the error
type. Both the Error-Type and the Error-Value are managed by IANA.
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Error-type Meaning
1 Capability not supported
Error-value
1
2 Unknown Object
Error-value
1: Unrecognized object class
2: Unrecognized object Type
3 Not supported object
Error-value
1: Not supported object class
2: Not supported object Type
4 Policy violation
Error-value
1: C bit of the METRIC object set (request rejected)
2: O bit of the RP object set (request rejected)
5 Mandatory object missing
Error-value
1: RP object missing
2: RRO object missing for a reoptimization request
(R bit of the RP object set)
3: END-POINTS object missing
6 Synchronized path computation request missing
Error-value
1
7 Unknown request reference
Error-value
1
8 Unacceptable PCEP session characteristics
Error-value
1
9 Deadtimer expiration
Error-value
1
10. PCEP Finite State Machine (FSM)
The section describes the PCEP Finite State Machine (FSM).
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PCEP Finite State Machine
+-+-+-+-+-+-+<------+
+------| SessionUP |<---+ |
| +-+-+-+-+-+-+ | |
| | |
| +->+-+-+-+-+-+-+ | |
| | | KeepWait |----+ |
| +--| |<---+ |
|+-----+-+-+-+-+-+-+ | |
|| | | |
|| | | |
|| V | |
|| +->+-+-+-+-+-+-+----+ |
|| | | OpenWait |-------+
|| +--| |<------+
||+----+-+-+-+-+-+-+<---+ |
||| | | |
||| | | |
||| V | |
||| +->+-+-+-+-+-+-+ | |
||| | |TCPPending |----+ |
||| +--| | |
|||+---+-+-+-+-+-+-+<---+ |
|||| | | |
|||| | | |
|||| V | |
|||+--->+-+-+-+-+ | |
||+---->| Idle |-------+ |
|+----->| |----------+
+------>+-+-+-+-+
Figure 15: PCEP Finite State Machine for the PCC
PCEP defines the following set of variables:
TCPConnect: 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. TCPRetry: specifies the number of
times the system has tried to establish a TCP connection with a PCEP
peer without success. TCPMaxRetry: 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
TCPMaxRetry is 5. OpenWait: timer (in seconds) 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. KeepWait: timer (in
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seconds) 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. OpenRetry: specifies the number of times the
system has received an Open message with unacceptable PCEP session
characteristics. OpenMaxRetry: Maximum number of times the system
can receive an Open message with unacceptable PCEP sessions
characteristics before releasing the PCEP session with that peer and
go back to Idle state. The value of the OpenMaxRetry is 3. 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,
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, ...), the system:
o Starts the TCPConnect timer,
o Initiates of a TCP connection with the PCEP peer,
o Increments the TCPRetry variable,
o Moves to the TCPPending state.
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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
It is expected that an implementation will use an exponentially
increase timer between automatically generated Initialization events
and between retrials of TCP connection establishments.
TCPPending State
If the TCP connection establishment succeeds, the system:
o Sends an Open message,
o Starts the OpenWait timer,
o Starts the KeepWait timer,
o Moves to the OpenWait state.
If the TCP connection establishement fails (an error is detected
during the TCP connection establishment) or the TCPConnectTimer
expires:
If TCPRetry =TCPMaxRetry the system moves to the Idle State
If TCPRetry variable < TCPMaxRetry the system:
o Starts the TCPConnect timer,
o Initiates of a TCP connection with the PCEP peer,
o Increments the TCPRetry variable.
If the system detects that the PCEP peer tries to simultaneously
establish a TCP connection, it stops the TCP connection establishment
if and only if the PCEP peer has a higher IP address and moves to the
Idle state. This guarantees that in case of "collision" a single TCP
connection is established.
OpenWait State:
In the OpenWait state, the system waits for an Open message from its
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PCEP peer.
If the system receives an Open message from the PCEP peer before the
expiration of the OpenWait timer, PCEP checks the PCEP session
attributes (Keepalive frequency, DeadTimer, ...).
If an error is detected (malformed Open message, unsupported PCEP
session characteristics), PCEP generates an error notification,
release the PCEP resources for the PCEP peer, closes the TCP
connection and moves to the Idle state.
If no Open message is received before the expiration of the OpenWait
timer, 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 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 moves to the UP state
If LocalOK=0 the system moves to the KeepWait state.
If no errors are detected but there is a disagreement on the session
characteristics (such as the Keepalive frequency or the DeadTimer), a
PCErr message is sent to the peer (reporting the values for which a
disagreement exists).
If OpenRetry=OpenMaxRetry the system releases the PCEP resources for
that peer amd moves back to the Idle state.
If OpenRetry < OpenMaxRetry the system:
o sends a PCErr message containing proposed acceptable session
characteristics,
o Increments the OpenRetry variable.
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
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characteristics proposed in the Open message.
If a Keepalive message is received before the expiration of the
KeepWait timer, LocalOK=1
If RemoteOK=1, the system moves to the UP state.
If RemoteOK=0, the system 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 sytem 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 sytem 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 stays in the KeepWait
state. If RemoteOK=0, the system moves to the OpenWait state.
If neither a Keepalive nor a PCErr is received after the expiration
of the KeepWait timer, the system releases the PCEP resources for
that PCEP peer, closes the TCP connection and moves 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 systens sends a Keepalive
message.
If no Keepalive message is received from the PCEP peer after the
expiration of the DeadTimer, the systems sends a PCEP CLOSE message,
releases the PCEP resources for that PCEP peer, closes the TCP
connection and moves to the Idle State.
In a malformed PCEP message is received or the TCP connection fails,
the systems sends a PCEP CLOSE message, the system releases the PCEP
resources for that PCEP peer, closes the TCP connection and moves to
the Idle State.
11. Security Considerations
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The PCEP protocol 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.
11.1. 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 per explained in [RFC2385].
Note that when one digest technique stronger than MD5 is specified
and implemented, PCEP could be easily upgraded to use it.
11.2. 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 [RFC2406] 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.
11.3. Protection against Denial of Service attacks
PCEP can be the target of TCP DoS attacks, such as for instance SYN
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attacks, as all protocols running on top of TCP. PCEP can use the
same mechanisms as defined in [RFC3036] to mitigate the threat of
such attacks:
o A PCE should avoid promiscuous TCP listens for PCEP TCP session
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.
11.4. 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 Providers
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.
12. Acknowledgements
The authors would like to thank Dave Oran, Dean Cheng, Jerry Ash,
Igor Bryskin, Carol Iturrade, Siva Sivabalan, Rich Bradford, Richard
Douville for their very valuable input. Special thank to Adrian
Farrel for his very valuable 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.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[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.
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[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-ccamp-inter-domain-rsvp-te]
Ayyangar, A. and J. Vasseur, "Inter domain GMPLS Traffic
Engineering - RSVP-TE extensions",
draft-ietf-ccamp-inter-domain-rsvp-te-03 (work in
progress), March 2006.
[I-D.ietf-pce-architecture]
Farrel, A., "A Path Computation Element (PCE) Based
Architecture", draft-ietf-pce-architecture-05 (work in
progress), April 2006.
[I-D.ietf-pce-comm-protocol-gen-reqs]
Roux, J. and J. Ash, "PCE Communication Protocol Generic
Requirements", draft-ietf-pce-comm-protocol-gen-reqs-06
(work in progress), May 2006.
[I-D.ietf-pce-disco-proto-igp]
Roux, J., "IGP protocol extensions for Path Computation
Element (PCE) Discovery",
draft-ietf-pce-disco-proto-igp-01 (work in progress),
March 2006.
[I-D.ietf-pce-discovery-reqs]
Roux, J., "Requirements for Path Computation Element (PCE)
Discovery", draft-ietf-pce-discovery-reqs-05 (work in
progress), June 2006.
[I-D.ietf-pce-inter-layer-req]
Oki, E., "PCC-PCE Communication Requirements for Inter-
Layer Traffic Engineering",
draft-ietf-pce-inter-layer-req-01 (work in progress),
March 2006.
[I-D.ietf-pce-pcecp-interarea-reqs]
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Roux, J., "PCE Communication Protocol (PCECP) Specific
Requirements for Inter-Area (G)MPLS Traffic Engineering",
draft-ietf-pce-pcecp-interarea-reqs-01 (work in progress),
February 2006.
[I-D.ietf-rpsec-bgpsecrec]
Christian, B. and T. Tauber, "BGP Security Requirements",
draft-ietf-rpsec-bgpsecrec-06 (work in progress),
June 2006.
[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.
[RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security
Payload (ESP)", RFC 2406, November 1998.
[RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A., and
B. Thomas, "LDP Specification", RFC 3036, January 2001.
[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.
[RFC4101] Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101,
June 2005.
Appendix A. Proposed Status and Discussion [To Be Removed Upon
Publication]
This Internet-Draft is being submitted for eventual publication as an
RFC with a proposed status of Standard. Discussion of this proposal
should take place on the following mailing list: pce@ietf.org.
Appendix B. Compliance with the PCECP Requirement Document
The aim of this section is to list the set of requirements set forth
in [I-D.ietf-pce-comm-protocol-gen-reqs] that are not satisfied by
the current revision of this document. This only concerns the
requirements listed as MUST according to [RFC2119].
Here is the list of currently unsatisfied requirements:
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o Allow to select/prefer from advertised list of standard objective
functions/options
o Allow to customize objective function/options
o Allow indicating if load-balancing is allowed
o Support "unsynchronized" & "synchronized" objective functions
o Protocol recovery support resynchronization of information &
requests between sender & receiver.
Appendix C. PCEP Variables
PCEP defines variable that can be configured. The following PCEP
variables are defined.
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 7.12.3.
Consider the case where a PCReq message is received by a PCE that
comprises 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.
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Authors' Addresses
JP Vasseur (editor)
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Email: jpv@cisco.com
JL Le Roux
France Telecom
2, Avenue Pierre-Marzin
Lannion, 22307
FRANCE
Email: jeanlouis.leroux@francetelecom.com
Arthi Ayyangar
Juniper Networks
1194 N.Mathilda Avenue
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
Google
1600 Amphitheatre Parkway
Montain View, CA 94043
USA
Email: akatlas@alum.mit.edu
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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
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Vasseur, et al. Expires December 24, 2006 [Page 62]
