Network Working Group JP Vasseur (Editor)
Cisco System Inc.
IETF Internet Draft JL Le Roux
France Telecom
Arthi Ayyangar
Juniper Networks
Eiji Oki
Yuichi Ikejiri
NTT
Alia Atlas
Google, Inc
Andrew Dolganow
Alcatel
Proposed Status: Standard
Expires: May 2006 November 2005
Path Computation Element (PCE) communication Protocol (PCEP)
- Version 1 -
draft-ietf-pce-pcep-00.txt
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Abstract
This document specifies the Path Computation Element communication
Protocol (PCEP) for communications between a Path Computation Client
(PCC) and a Path Computation Element (PCE), or between two PCEs. Such
interactions include path computation requests and path computation
replies as well as notifications of specific states related to the
use of a PCE in the context of 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.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
Table of Contents
1. Terminology................................................3
2. Introduction...............................................4
3. Assumptions................................................4
4. Transport protocol.........................................5
5. Architectural Protocol Overview (Model)....................5
5.1. Problem..................................................5
5.2. Architectural Protocol Overview..........................6
5.2.1. Initialization phase...................................6
5.2.2. Path computation request sent by a PCC to a PCE........7
5.2.3. Path computation reply sent by the PCE to a PCC........8
5.2.4. Notifications..........................................9
5.2.5. Termination of the PCEP Session........................10
6. PCEP messages..............................................10
6.1. Common header............................................10
6.2. Open message.............................................11
6.3. Keepalive message........................................13
6.4. Path Computation Request (PCReq) message.................13
6.5. Path Computation Reply (PCRep) message...................14
6.6. Notification (PCNtf) message.............................15
6.7. Error (PCErr) message....................................15
7. Object Formats.............................................16
7.1. Common object header.....................................16
7.2. OPEN Object..............................................18
7.3. RP Object................................................19
7.4. NO-PATH Object...........................................20
7.5. END-POINTS Object........................................21
7.6. BANDWIDTH object.........................................22
7.7. DELAY Object.............................................23
7.8. ERO Object...............................................24
7.9. RRO Object...............................................24
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7.10. LSPA Object.............................................24
7.11. IRO Object..............................................26
7.12. SVEC Object.............................................27
7.13. NOTIFICATION object.....................................28
7.14. PCEP-ERROR object.......................................31
8. Independent versus synchronized path computation requests..34
9. Elements of procedure......................................35
9.1. Non recognized or non support object received in a
PCReq message
9.2. RP object................................................35
9.3. SVEC object..............................................36
10. Manageability Considerations..............................36
11. IANA Considerations.......................................36
11.1. TCP port................................................36
11.2. PCEP Objects............................................36
11.3. Notification............................................39
11.4. PCEP Error..............................................39
12. Security Considerations...................................40
12.1. PCEP Authentication and Integrity.......................40
12.2. PCEP Privacy............................................40
12.3. Protection against Denial of Service attacks............41
13. Intellectual Property Statement...........................41
14. Acknowledgment............................................42
15. References................................................42
15.1. Normative references....................................42
15.2. Informative References..................................43
16. Authors' Address..........................................44
Appendix A: Compliance of PCEP to the set of requirements
specified in draft-ietf-pce-comm-protocol-gen-reqs........... 45
1. Terminology
Terminology used in this document
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).
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PLR: Point of Local Repair. The head-end LSR of a backup tunnel or a
Detour LSP.
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.
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.
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
[PCE-ARCH] describes the motivations and architecture for a PCE-based
model to perform path computation for 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.
[PCE-COM-GEN-REQ] states the generic requirements for such a protocol
including a requirement that the same protocol must be used between
PCC and PCE, and between PCEs. Additional application-specific
requirements (for scenarios such as inter-area, inter-AS, etc.) are
not included in [PCE-COM-GEN-REQ], 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.
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.
The compliance of PCEP to the set of requirements stated in [PCE-COM-
GEN-REQ] is covered in Appendix A.
3. Assumptions
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[PCE-ARCH] describes various types of PCE: it is important to note
that no assumption is made on the nature of the PCE in this document.
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 select a PCE to send its path computation
request(s) to. For the sake of reference [PCE-DISC-REQ] defines a
list of requirements for dynamic PCE discovery.
4. Transport protocol
PCEP operates over TCP using the well-known TCP port (TBD 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
unlimited time (this may for instance be the case should an
implementation have to send new requests frequently in which case the
TCP session will already be in place). Another motivation for leaving
the TCP connection open would be to avoid TCP connection
establishment time. This mode is also referred to as the "Permanent
mode". Conversely, in some other circumstances, it may be desirable
to systematically open and close the TCP connection for each PCEP
request (this may for instance be the case if sending of PCEP path
computation request is a rare event). This mode is referred to as the
"Per-request mode".
Since there are circumstances where the TCP connection state is used
to detect the PCC/PCE liveness (e.g case of a stateful PCE detecting
a PCC failure thanks to the TCP state), the desired mode MUST be
known by both the PCC and the PCE and is determined during the
initialization phase.
5. Architectural Protocol Overview (Model)
The aim of this section is to describe the PCEP protocol model in the
spirit of [WP]. An architecture protocol overview (the big picture of
the protocol) is provided in this section where details of the
protocol 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 [PCE-ARCH]. 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
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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 message sent by a PCC to a PCE to request a path
computation.
- PCRep: a 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 notification message either sent by a PCC to a PCE or a
PCE to a PCC to notify of specific event.
- PCErr: a message related to a protocol error condition.
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). 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 can either be triggered
by the PCC or the PCE.
5.2.1 Initialization phase
The initialization phase consists of two successive steps:
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 advertised. Those
parameters are carried within Open messages and include the keepalive
timer, the PCEP session mode (per-request or permanent), potential
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 peers does not
answer, the transport 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 is established Keepalive messages
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are exchanged between PCEP peers to ensure the liveness of the PCEP
session.
+-+-+ +-+-+
|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
Consider the diagram depicted in figure 2.
+-+-+ +-+-+
|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 path, the PCC first selects the PCE it desires to
send a path computation request to (note that the PCE selection may
be performed prior to the PCEP session establishment). Once a 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. It is worth pointing out
that 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 figure 2.
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5.2.3. Path computation reply sent by the PCE to a PCC
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---- PCReq message--->|
| |1) Path computation
| |request received
| |
| |2)Path successfully
| |computed
| |
| |3) Computed path(s) sent
| |to the PCC
|<--- PCRep message ---|
| (Positive reply) |
Figure 3a: Path computation request with successful 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 unsuccessfull computation
Upon receiving a path computation request from a PCC, the PCE
triggers a path computation, the result of which can either be:
- Positive: the PCE manages to compute a path satisfying the set of
required constraints and returns the set of computed path(s) (note
that the PCEP protocol supports the capability to send a single
request which refers to the computation of multiple paths: for
example, compute two link diverse paths). This is illustrated in
figure 3a.
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- Negative: no path could be computed that satisfies the request. In
this case, a PCE may provide the set of constraints that led to path
computation failure. Upon receiving a negative reply, a PCC may
decide to resend a modified request or take any other appropriate
action. This is illustrated in figure 3b.
5.2.4 Notifications
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,
potentially resulting 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).
+-+-+ +-+-+
|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
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| |
| |6) Path computation
| |request X cancelled
| |
|<--- PCNtf message----|
Figure 5: Example of PCEP notification (request(s) cancellation) send
to a PCC
5.2.5. Termination of the PCEP Session
When one of the PCEP peers desires to terminate a PCEP session it
MUST close the TCP connection. If the PCEP session is terminated by
the PCE, the PCC MUST clear all the states related to pending
requests sent to the PCE. Similarly, if the PCC terminates a PCEP
session the PCE MUST clear all pending path computation requests sent
by the PCC in question as well as the related states.
In case of TCP connection failure, the PCEP session SHOULD be
maintained for a period of time equal to the Deadtimer.
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 valid. Conversely, an object is said to
be optional the object may or may not be present. As specified in
section 7.1, a specific flag is also defined in each object 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
DELAY object allows a PCC to specify in a path computation request a
bounded acceptable delay for the computed path. The DELAY object is
optional (does not have to be present in each path computation
request message) but a PCC may set a flag to ensure that the delay
constraint is being taken into account when present in a 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.
If a mandatory object is missing in a received PCEP message the
recipient of the PCEP message MUST trigger a protocol error
condition.
6.1. Common header
0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Message-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message-Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 - PCEP message common header
Ver (Version): 3 bits
PCEP protocol version number. The current version is version 1
Flags: 8 bits
No Flags are currently defined
Message Length: 24 bits
Total length of the PCEP message expressed in bytes including
the common header.
Message-Type: 8 bits
The following message types are currently defined.
Value Meaning
1 Open
2 Keepalive
3 Path Computation Request
4 Path Computation Reply
5 Notification
6 Error
6.2. Open message
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. The aim of the Open message is 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.
The Message-Type field of the PCEP common header for the Open message
is set to 1.
<Open Message>::= <Common Header>
<OPEN>
The Open message MUST only contain a single OPEN object defined in
section 7. The various session characteristics specified within the
OPEN object are the keepalive frequency, session mode (permanent or
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per-request) and potentially some optional parameters such as the
detailed PCE capabilities and policy rules that specify the
conditions under which path computation requests may be sent to the
PCE. Details related to PCE capabilities discovery by means of PCEP
are out of the scope of this document.
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 the keepalive messages.
Asymmetric values may be chosen; thus there is no constraints
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). The minimum Keepalive
value is 1 second and the Deadtimer value is equal to 4 times the
Keepalive value.
Session mode: PCEP supports two session modes referred to as the
"permanent" and "per-request" modes. In the permanent mode, the PCEP
peers maintained a permanent PCEP session (and thus the TCP session
is also maintained) regardless of the rate at which PCEP messages are
exchanged. Such mode would typically be used to speed-up response
times. In the permanent mode, a loss of TCP session MUST be
interpreted as a communication failure. Conversely, in the
"per-request" mode, a PCEP session is established on-demand, when one or
more path computation requests are required and then closed by the
PCC once those path computation requests are satisfied. Both PCEP
peers MUST agree on the session mode; in case of disagreement, the
PCEP session establishment fails.
Elements of procedure:
- Once an Open message has been sent to a PCEP peer, the sender MUST
start an initialization timer called INIT-OPEN after the expiration
of which a similar Open message MUST be resent if no reply has been
received from the PCEP peer. The INIT-OPEN timer has a fixed value of
one minute. The maximum number of Open messages 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 one or more characteristic(s) is not acceptable by the
receiving peer, it MUST send a PCErr message with Error-type=8,
Error-value=1. The PCErr message MUST also comprise an Open object:
for each unacceptable session parameter, an acceptable parameter
value MUST 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.
Consecutive retries SHOULD make use of exponential back-off so as to
avoid undesirable burden of session initialization. If a second Open
message is received with the same set of parameters or with
parameters differing from the proposed values, the receiving peer
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MUST send a PCErr message with Error-Type=8, Error-value=2 and it
MUST immediately close the TCP connection.
If the PCEP session characteristics are acceptable, the receiving
PCEP peer MUST immediately send a Keepalive message as an
acknowledgment.
The PCEP session is considered as operational once both PCEP peers
have received a Keepalive message from their peer.
6.3. Keepalive message
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.
The Message-Type field of the PCEP common header for the Open message
is set to 2.
<Keepalive Message>::= <Common Header>
6.4. Path Computation Request (PCReq) message
A Path Computation Request message (also referred to as a PCReq
message) is sent by a PCC to a PCE so as to request a path
computation. The Message-Type field of the PCEP common header is set
to 3.
There are two mandatory objects that MUST be included within a PCReq
message: the RP and the END-POINTS objects (see section 7). If one of
these objects is missing, the receiving PCE MUST send an error
message to the requester (PCErr message). Other objects are optional.
The format of a PCReq message is as follows:
<PCReq Message>::= <Common Header>
[<SVEC-list>]
<request-list>
where:
<svec-list>::=<SVEC>[<svec-list>]
<request-list>::=<request>[<request-list>]
<request>::= <RP>
<END-POINTS>
[<LSPA>]
[<BANDWIDTH>]
[<DELAY>]
[<RRO>]
[<XRO>]
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[<IRO>]
The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, DELAY, ERO, XRO and IRO
objects are defined in section 7.
6.5. Path Computation Reply (PCRep) message
The PCEP Path Computation reply message (also referred to as a PCRep
message) is 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.
The PCRep message MUST comprise a RP object with a Request-ID-number
identical to the one specified in the RP object carried in the
corresponding PCReq message (see section 7 for 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. 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.
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. Such a situation where
multiple computed paths are provided in a PCRep message is discussed
in detail in section 8.
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) 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>]
<path-list>
where:
<svec-list>::=<SVEC>[<svec-list>]
<path-list>::=<path>[<path-list>]
<path>::=<RP>
[<NO-PATH>]
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[<ero-list>]
[<LSPA>]
[<BANDWIDTH>]
[<DELAY>]
[<XRO>]
[<IRO>]
where:
<ero-list>:==<ERO>[<ero-list]>
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.
The PCNtf message MUST carry at least one NOTIFICATION object and may
comprise several NOTIFICATION objects should the PCE or the PCC
intend to notify of multiple events. The NOTIFICATION object is
defined in section 7. The PCNtf message may also comprise an RP
object when the notification refers to a particular path 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>
The procedure upon the reception of a PCNtf message is defined in
section 9.
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
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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 7.
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 9.
7. Object Formats
7.1. Common object header
A PCEP object carried within a PCEP message consists of one or more
32-bit words with a common header which has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Object-Class | OT |Res|I|P| Object Length (bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Object body) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 - PCEP common object header
Object-Class (to be managed by IANA)
8-bit field that identifies the PCEP object class
OT (Object-Type) (to be managed by IANA)
4-bit field that identifies the PCEP object type
P flag (Processing-Rule)
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1-bit flag which specifies whether the object must be taken into
account by the receiving PCEP peer or is just optional. When the P
flag is cleared, the object MUST be taken into account by the
receiving entity. If the PCC or the PCE does not understand the
object or understands the object but decides to ignore the object,
this MUST trigger a protocol error condition as defined in section
7. Conversely, when the P flag is set the object is optional and
can be silently ignored.
I flag
1-bit flag: the PCE set the I flag when the object is carried
within a PCRep message so as to indicate when the constraint was
optional and was ignored during path computation.
Res flags: 2-bit flag reserved (MUST be set to 0)
Object Length
16-bit field containing the total object length 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. The Object-Class
and Object-Type fields uniquely identify each PCEP object.
The P bit is used to determine what action a node should take if it
does not recognize the Object-Class or Object-Type of a PCEP object
or decides not to take into account the object: there are two
possible ways a PCEP implementation can react. This choice is
determined by the P bit, as follows.
If P flag=0
The entire PCEP message MUST be rejected and the receiving PCEP peer
MUST send a PCErr message with a PCEP-ERROR Object ("Unkown Object"
or "Not supported Object").
If P flag=1
The node MAY ignore the object and process the PCEP message if
possible. In that case (the message can be processed by ignoring the
object in question), the PCE SHOULD include the object in the
corresponding PCERep message. The I flag of the common header for
this object MUST be set. If the path computation cannot be performed,
a PCErr message MUST be sent to the requesting entity with a PCEP-
ERROR object (Error-type=2, "Unknown Object").
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7.2. OPEN Object
The OPEN object MUST be present in each Open message. There MUST be
only one OPEN object per Open 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
capability, policy rules and so on. No 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 | SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | |R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9 - OPEN Object format
Version (Ver): 3 bits - Current version is 1.
Keepalive frequency (Keepalive): 16 bits.
Specifies the frequency in seconds at which the sender of the
Open message will send Keepalive messages. The minimum value for
the Keepalive is 1 second. When set to 0, no keepalive is sent
to the remote peer. A RECOMMENDED value for the keepalive
frequency is 30 seconds.
PCEP session-ID (SID): 13 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.
Flags
One flag is currently defined.
R flag: when cleared, this indicates that the sending PCEP peer
requires the establishment of a PCEP session in permanent mode.
When set, a per-request mode is requested.
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Optional TLVs may be included within the Open message body to specify
PCC or PCE characteristics.
7.3. RP Object
The RP (Request Parameters) object MUST be carried within every PCReq
and PCRep messages and MAY be carried within PCNtf and PCErr
messages.
RP Object-Class is to be assigned by IANA (recommended value=2)
RP Object-Type is to be assigned by IANA (recommended value=1)
The format of the RP object body is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |O|C|B|R| Pri |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request-ID-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10 - RP object body format
The RP object 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) field (3 bits)
This field may be used by the requesting PCC to specify to the
PCE the request's priority. 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 SHOULD 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
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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
Pri field: in other words, the path computation request has been
honoured but without taking the request priority into account.
R (Reoptimization) bit: when set, the requesting PCC specifies
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 message by means of
an RRO object defined in section 7.
B (Bi-directional) bit: when set, the PCC specifies that the
path computation request relates to a bidirectional TE LSP (LSPs
that have 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.
C (Cost) bit: when set, the PCE MUST provide the cost of the
computed path in the PCRep message.
O (strict/lOose): In a PCReq message, when set, this means 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.
Request-ID-number: 32 bits
This value (combined with the source IP address of the PCC)
uniquely identifies the path computation request context and
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.
7.4. NO-PATH Object
When a PCE cannot find a path satisfying a set of constraints, it
MUST include a NO-PATH object in the corresponding 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,
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the PCRep message MAY also comprise a list of objects that specify
the set of constraints that could not be satisfied. When an object
specifies a variety of constraints, the set of unsatisfied
constraints can be unambiguously determined by the PCC after a simple
comparison with the original requested constraints.
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|S| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11 - NO-PATH object format
The NO-PATH object has a fixed length of 4 octets.
Flags: 16 bits - The following flags are currently defined:
C bit: when set, this indicates that the set of unsatisfied
constraints (reasons why a path could not be found) is specified in
the PCRep message by means of the relevant PCEP objects. When
cleared, no reason is specified.
For 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 includes in its path
computation reply a NO-PATH object with the C flag set. In addition,
the PCRep message carries the BANDWIDTH object and the bandwidth
field value is equal to X.
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-POINTS Object
The END-POINTS object is used in a PCReq message to specify the
source IP address and the destination IP address of the TE LSP for
which a path computation is requested. Two END-POINTS objects (for
IPv4 and IPv6) are defined.
END-POINTS Object-Class is to be assigned by IANA (recommended
value=4)
END-POINTS Object-Type is to be assigned by IANA (recommended
value=1 for IPv4 and 2 for IPv6)
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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
7.6. BANDWIDTH object
The BANDWIDTH object is optional and can be used to specify the
requested bandwidth and 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.
When carried within a PCReq message, the BANDWIDTH object specifies a
bandwidth constraint that must be satisfied by the computed path(s)
if P flag is cleared and MAY be ignored if the P flag is set. In a
PCRep message, the BANDWIDTH object indicates that the bandwidth
belong to the set of one or more constraint(s) that could be not
satisfied. When absent from the PCRep message that means that the
computed path satisfies the requested bandwidth constraint.
BANDWIDTH Object-Class is to be assigned by IANA (recommended
value=5)
BANDWIDTH Object-Type is to be assigned by IANA (recommended
value=1)
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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.
7.7. DELAY Object
The DELAY object can be used to specify a strict delay constraint for
the TE LSP. The delay constraint MUST be taken into account during
path computation if P flag is cleared and MAY be ignored if the P
flag is set. Note that the mechanism used by the PCE to retrieve the
delays of each link is outside of the scope of this document (for the
sake of illustration the link delay could be the IGP metric or a
Service Provider may choose to use the TE metric to represent link
delays). 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 delay metric may be carried within PCReq and PCRep
messages. The absence of the DELAY object MUST be interpreted by the
PCE as a path computation request without delay constraint. When
carried within a PCReq message, the DELAY object specifies a delay
constraint that must be satisfied by the computed path(s). In a PCRep
message and when the path computation was successful, the DELAY
object indicates the delay(s) of the computed path(s). When the path
computation was unsuccessful and the delay constraint was one of the
mandatory constraints that could be satisfied the DELAY object MUST
be present in the PCRep message.
DELAY Object-Class is to be assigned by IANA (recommended value=6)
DELAY Object-Type is to be assigned by IANA (recommended value=1)
The format of the DELAY 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15 - DELAY object body format
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Delay: 32 bits. The requested delay constraint is encoded in 32 bits
in IEEE floating point format, expressed in milliseconds.
7.8. ERO Object
The ERO object is used to encode a TE LSP path. If can either be
carried within a PCReq message to specify the existing path of a TE
LSP to be reoptimize or within a PCRep message to provide a computed
TE LSP.
The contents of this object are identical in encoding to the contents
of the Explicit Route Object defined in [RSPV-TE], [GRSVP] and [RSVP-
UNNUM]. 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 [RSPV-TE], [G-RSVP] and [RSVP-
UNNUM]. 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 specifies various TE LSP attributes to be taken into
account by the PCE during path computation. The LSPA (LSP Attributes)
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object can either be carried within a PCReq message or a PCRep
message in case of unsuccessful path computation (in this case, the
PCReq 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 [RSVP-TE] and
[FRR].
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 |N|B|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 |N|B|L| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17 - LSPA object body format (with resource affinity)
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
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preempt another session.
Holding Priority
The priority of the 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 flags L, B and N correspond to the "Local protection desired"
bit ([RSVP-TE]), "Bandwidth protection desired" bit ([FRR]) and
the "Node protection desired" bit ([FRR]) of the SESSION-ATTRIBUTE Object
respectively.
L Flag (Local protection desired)
When set, this means that the computed path MUST included links
protected with Fast Reroute as defined in [FRR].
B Flag (Bandwidth protection desired)
When set, this means that the computed path MUST included links
protected with Fast Reroute as defined in [FRR] and that benefit
from bandwidth protection. The B flag MUST only be set if the L
flag is set.
N Flag (Node protection desired)
When set, this means that the computed path MUST included links
protected with Fast Reroute as defined in [FRR] and that such
links MUST be protected with NNOP (Next-next hop backup tunnel).
The N flag MUST only be set of the L flag is set.
Note that the B flag and N flag are not exclusive.
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.
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
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) |
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| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18 - IRO objet body format
Subobjects
The IRO object is made of sub-object(s) identical to the ones defined
in [RSVP-TE], [G-MPLS] and [RSVP-UNNUM] 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.
The ERO object carried within a PCReq message is exclusively used in
the context of a reoptimization path computation request, thus the
need to define a new object (IRO) to specify the inclusion of
specified network element(s) in a path.
7.12. SVEC Object
Section 8 details the circumstances under which it may be desirable
and/or required to correlate several path computation requests. This
leads to the specification of the SVEC object (Synchronization
VECtor). The SVEC object is optional in a PCEP 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 requests
the computation of which 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.
The SVEC object is carried within PCReq messages.
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.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Reserved | Flags |S|N|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Object #1 |
| |
// //
| RP Object #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.
7.13. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Flags | Notification- | Notification- |
| | | type | value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
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// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20 - NOTIFICATION body object format
Length
The Length contains the total length of the object in bytes and
includes the Type and Length fields. This length must be a
multiple of 4 and must be at least 12.
Flags
No flags are currently defined
A NOTIFICATION object is characterized by a Notification-type that
specifies the class of notification and the Notification-value that
provides additional information related to the nature of the
notification. Both the Notification-type and Notification-value
should be managed by IANA (see IANA section).
The following Notification-type and Notification-value values are
currently defined:
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 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
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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.
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 which will not be
honored and which will be cancelled by the PCE. 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.
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
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
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-
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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.
7.14. PCEP-ERROR object
The PCEP-ERROR object is exclusively carried within a PCErr message
and can either be used in a message sent by a PCC to a PCE or by a
PCE to a PCC 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | 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
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type. Both the Error-Type and the Error-Value should be managed by
IANA (see the IANA section).
Length (8 bits)
The Length contains the total length of the object in bytes
including the Type and Length fields. This length must be a
multiple of 4 and must be at least 8.
Flags (8 bits)
No flag is currently defined.
Error-type (8 bits)
The Error-type defines the class of error.
Error-value (8 bits)
Provides additional details about the error.
Optionally the PCErr message 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.
For each PCEP protocol error, an Error type and value is 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 set (request rejected)
Error-value=2: O bit set (request rejected)
5 Required 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
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In case of the 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 then be cancelled.
If a PCEP message is received that carries a mandatory PCEP object (P
flag cleared) not recognized by the PCEP peer or recognized but not
supported, then the PCEP peer 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.
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.
If a path computation request is received that does not contain a
required 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 per
missing object. The corresponding path computation MUST be cancelled.
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 during a
configurable period of time, the PCE MUST send a PCErr message with a
PCEP-ERROR object (Error-Type=6). The corresponding synchronized path
computation MUST be cancelled.
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=6). In addition, the PCC MUST include in the
PCErr message the unknown RP object.
If one or more characteristic(s) is not acceptable by the receiving
peer, it MUST send a PCErr message with Error-type=8, Error-value=1.
The PCErr message MUST also comprise an Open object: for each
unacceptable session parameter, an acceptable parameter value MUST be
proposed in the appropriate field of the Open object in place of the
originally proposed value. If a second Open message is received with
the same set of parameters or with parameters differing from the
proposed values, the receiving peer MUST send a PCErr message with
Error-Type=8, Error-value=2 and it MUST immediately close the TCP
connection.
If a PCEP peer does not receive any PCEP message (Keepalive, PCReq,
PCRep, PCNtf) during the Deadtimer period (equal to four times the
Keepalive value advertised in the OPEN object) the PCEP peer MUST
send a PCErr message with a PCEP-ERROR object (Error-type=9, Error-
value=1). Additionally, the PCEP session MUST be terminated and the
TCP connection MUST be closed.
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8. Independent versus synchronized path computation requests
The PCEP protocol permits 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 so as to obtain their respective
paths. 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
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
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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 are
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.
9. Elements of procedure
9.1. Non recognized or non support object received in a PCReq message
If a PCEP message is received that carries a mandatory PCEP object (P
flag cleared) 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). In addition, the PCRep
message MUST comprise the set of non recognized or non supported
object(s). The corresponding path computation request MUST be
cancelled by the PCE without further notification.
9.2. RP object
The absence of a RP object in the PCReq message MUST trigger the
sending of a PCErr message with Error-type=5 and Error-value=1.
If the C bit of the RP message carried within a PCReq message is set
and some local policy has been configured on the PCE not to provide
such cost, 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 and Error-value of the PCEP-ERROR object MUST be set to 4
and 1 respectively.
If the O bit of the RP message carried within a PCReq message is set
and some local policy has been configured on the PCE to not provide
explicit path(s) (for instance, for confidentiality reasons), then 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
and Error-value of the PCEP-ERROR object MUST be set to 4 and 2
respectively.
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
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provide the explicit or strict/loose path by including an RRO object
in the PCReq message so as to avoid double bandwidth counting (unless
the TE LSP is a 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, or for PCC to inform PCE of the
working path with associated list of strict hops in PCReq. The
absence of an RRO in the PCReq message when the R bit of the RP
object is set MUST trigger the sending of a PCErr message with Error-
type=5 and Error-value=2.
If the PCC receives a PCRep message which contains a RP object
referring to an unknown Request-ID-Number, it MUST trigger the
sending of a PCErr message with Error-Type=7 and Error-value=1.
9.3. SVEC object
When a requesting PCC desires to send multiple synchronized path
computation requests, it MUST send all the path computation requests
within a single PCReq message that contains all the synchronized path
computation requests: in that case, the PCReq message MUST also
comprise a SVEC object listing all the synchronized path computation
requests. 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.
If some RPs objects carried with the SVEC object are missing in the
PCReq message, the PCE MUST send a PCErr message with Error-Type = 6
to the PCC.
10. 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.
11. IANA Considerations
11.1. TCP port
The PCEP protocol will use a well-known TCP port to be assigned by
IANA.
11.2. PCEP Objects
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Several new PCEP objects are defined in this document that have an
Object-Class and an Object-Type. The new Object-Class and Object-Type
should be assigned by IANA.
- Open Object
The Object-Class of the Open object is to be assigned by IANA
(recommended value=1).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- RP Object
The Object-Class of the RP object is to be assigned by IANA
(recommended value=2).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- NO-PATH Object
The Object-Class of the NO-PATH object is to be assigned by IANA
(recommended value=3).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- END-POINTS Object
The Object-Class of the END-POINTS object is to be assigned by IANA
(recommended value=4).
Two Object-Type are defined for this object and should be assigned by
IANA with a recommended value of 1 and 2 for IPv4 and IPv6
respectively.
- BANDWIDTH Object
The Object-Class of the BANDWIDTH object is to be assigned by IANA
(recommended value=5).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- DELAY Object
The Object-Class of the DELAY object is to be assigned by IANA
(recommended value=6).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
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- ERO Object
The Object-Class of the ERO object is to be assigned by IANA
(recommended value=7).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- RRO Object
The Object-Class of the RRO object is to be assigned by IANA
(recommended value=8).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- LSPA Object
The Object-Class of the LSPA object is to be assigned by IANA
(recommended value=9).
Two Object-Types are defined for this object and should be assigned
by IANA with a recommended value of 1 (without resource affinity) and
2 (with resource affinity).
- IRO Object
The Object-Class of the IRO object is to be assigned by IANA
(recommended value=10).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- SVEC Object
The Object-Class of the SVEC object is to be assigned by IANA
(recommended value=11).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- NOTIFICATION Object
The Object-Class of the NOTIFICATION object is to be assigned by IANA
(recommended value=12).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
- PCEP-ERROR Object
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The Object-Class of the PCEP-ERROR object is to be assigned by IANA
(recommended value=13).
One Object-Type is defined for this object and should be assigned by
IANA with a recommended value of 1.
11.3. 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
should be managed by IANA (see IANA section).
The following Notification-type and Notification-value values are
currently defined:
Notification-type=1: Pending Request cancelled
Notification-value=1: PCC cancels a set of pending request(s)
Notification-value=2: PCE cancels a set of pending request(s)
Notification-type=2: PCE congestion
Notification-value=1: PCE in congested state
Notification-value=2: PCE no longer in congested state
11.4. PCEP Error
A PCEP-ERROR object is used to report a PCEP protocol error and is
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 should be managed by
IANA.
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 set (request rejected)
Error-value=2: O bit set (request rejected)
5 Required Object missing
Error-value=1: RP object missing
Error-value=2: RRO object missing for a reoptimization
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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
12. Security Considerations
PCEP communication could be the target of the following attacks:
-Spoofing (PCC or PCE impersonation)
-Snooping (message interception)
-Falsification
-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.
12.1. 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 [BGP-SEC-REQ]. 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.
12.2. 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 [IPSEC] 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.
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12.3. Protection against Denial of Service attacks
PCEP can be the target of TCP DoS attacks, such as for instance SYN
attacks, as all protocols running on top of TCP. PCEP can use the
same mechanisms as defined in [LDP] to mitigate the threat of such
attacks:
- A PCE should avoid promiscuous TCP listens for PCEP TCP session
establishment. It should use only listens that are specific to
authorized PCCs.
- 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.
- The use of access-list on the PCE so as to restrict access to
authorized PCCs.
13. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress.
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14. Acknowledgment
We would like to thank Dave Oran, Dean Cheng, Jerry Ash, Igor Bryskin
for their very valuable input. Special thank to Adrian Farrel for his
very valuable suggestions.
15. References
15.1. Normative references
[RFC] Bradner, S., "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78,
RFC 3667, February 2004.
[RFC3979] Bradner, S., Ed., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3979, March 2005.
[RSVP] R. Braden et al., "Resource ReSerVation Protocol (RSVP) -
Version 1 Functional Specification", RFC 2205, November 1997.
[RSVP-TE] Awduche, D., et. al., "RSVP-TE: Extensions to RSVP for LSP
tunnels", RFC 3209, December 2001.
[G-RSVP] Berger, L, et. al., "GMPLS Signaling RSVP-TE extensions",
RFC 3473, January 2003.
[RSVP-UNNUM] Kompella, K., Rekhter Y., "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)",
RFC 3477, January 2003.
[COPS] Durham, D., "The COPS (Common Open Policy Service) Protocol",
RFC 2748, January 2000.
[SCTP] Stewart et al., "Stream Control Transmission Protocol",
RFC2960, October 2000.
[TCP] J. Postel, "Transmission Control Protocol", RFC 793, November
1981.
[DS-TE-PROTO] Le Faucheur et al,"Protocol extensions for support of
Differentiated-Service-aware MPLS Traffic Engineering", RFC 4124,
June 2005.
[G-RECV-E2E-SIG] J. P. Lang et al, "RSVP-TE Extensions in support of
End-to-End Generalized Multi-Protocol Label Switching (GMPLS)-based
Recovery", draft-ietf-ccamp-gmpls-recovery-e2e-signaling-03.txt
(working in progress).
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[FRR] P. Pan, G. Swallow, A. Atlas, JP. Vasseur, M. Jork, D.H Gan and
D. Cooper, "Fast Reroute Extensions to RSVP-TE for LSP Tunnels",
RFC4090, May 2005.
15.2 Informative References
[WP] E. Rescorla, "Writting Protocol Models", RFC 4101, June 2005.
[PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, "Path Computation
Element (PCE) Architecture", draft-ietf-pce-arch, work in
progress.
[PCE-GEN-COM-REQ] J. Ash, J.L Le Roux et al., "PCE Communication
Protocol Generic Requirements", draft-ietf-pce-comm-protocol-gen-
reqs, work Progress.
[GMPLS-RTG] Kompella, K., Rekhter, Y., "Routing Extensions in Support
of Generalized Multi-Protocol Label Switching", draft-ietf-ccamp-
gmpls-routing, work in progress.
[INT-AREA-REQ] Le Roux, J.L., Vasseur, J.P., Boyle, J. et al,
"Requirements for inter-area MPLS Traffic Engineering", RFC4105, June
2005.
[INT-AS-REQ] Zhang, R., Vasseur, J.P. et al, "MPLS Inter-AS Traffic
Engineering Requirements", draft-ietf-tewg-interas-mpls-te-req, work
in progress.
[INT-DOMAIN-FRWK] Farrel, A., Vasseur, J.P., Ayyangar, A., "A
Framework for Inter-Domain MPLS Traffic Engineering", draft-ietf-
ccamp-inter-domain-framework, work in progress.
[MGT] A. Farrel et al., "Requirements for Manageability Sections in
Routing Area Drafts", draft-farrel-rtg-manageability-requirements,
work in progress.
[XRO] Lee et al, "Exclude Routes - Extension to RSVP-TE", drfat-ietf-
ccamp-rsvp-te-exclude-route, work in progress.
[PCE-DISC-REQ] JL Le Roux et al., "Requirements for Path Computation
Element (PCE) Discovery", draft-ietf-pce-discovery-reqs, work in
progress.
[BGP-SEC-REQ] B. Christian Ed., "BGP Security Requirements",
draft-ietf-rpsec-bgpsecrec, work in progress
[LDP] L. Andersson, et al., "LDP Specification", RFC3036, January
2001
[DOBB] H. Dobbertin, "The Status of MD5 After a Recent Attack",
RSALabs' CryptoBytes, Vol. 2 No. 2, Summer 1996.
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Internet Draft draft-ietf-pce-pcep-02 November 2005
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm",RFC 1321,
April 1992.
[IPSEC] S. Kent, A. Atkinson, " IP Encapsulating Security Payload
(ESP)", RFC2406, November 1998
16. Authors' Address
Jean-Philippe Vasseur (Editor)
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
Email: jeanlouis.leroux@francetelecom.com
Arthi Ayyangar
Juniper Networks, Inc.
1194 N.Mathilda Ave
Sunnyvale, CA 94089
USA
E-mail: arthi@juniper.net
Eiji Oki
NTT
Midori 3-9-11
Musashino, Tokyo 180-8585
JAPAN
Email: oki.eiji@lab.ntt.co.jp
Alia K. Atlas
Google Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
EMail: akatlas@alum.mit.edu
Andrew Dolganow
Alcatel
600 March Rd., K2K 2E6 Ottawa, ON, Canada
Phone: +1 (613)784 6285
Email: andrew.dolganow@alcatel.com
Yuichi Ikejiri
NTT Communications Corporation
1-1-6, Uchisaiwai-cho, Chiyoda-ku
Tokyo 100-8019
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JAPAN
Email: y.ikejiri@ntt.com
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Appendix A - Compliance of PCEP to the set of requirements specified
in draft-ietf-pce-comm-protocol-gen-reqs
[PCE-GEN-COM-REQ] lists a set of requirement for the PCE
communication protocol. The aim of the appendix A is to list the
compliance of PCEP to such requirements. Note that requirements that
are not satisfied in the context of the present version may be
satisfied in further revisions.
The following legend is used in the table below:
YES: PCEP fully fulfills the requirement
ME (Minor Extension): PCEP could satisfy the requirement with minor
extension(s).
SE (Substantial Extension): PCEP could satisfy the requirement with
substantial extension(s).
NO: PCEP cannot meet the requirement without substantial redesign of
the protocol.
Requirement Necessity Compliance
------------------------------------------------------------------
Commonality of PCC-PCE and PCE-PCE Communication MUST YES
Client-Server Communication MUST YES
Support PCC/PCE request message to request path
computation MUST YES
Support PCE response message with computed path MUST YES
Support unsolicited communication PCE-PCC MUST YES
Maintain PCC-PCE session NON-RQMT
Use of Existing Transport Protocol MAY YES
Transport protocol satisfy reliability & security
requirements MAY YES
Transport Protocol Limits Size of Message MUST NOT YES
Support Path Computation Requests MUST YES
Include source & destination
Support path constraints (e.g., bandwidth, hops,
affinities) to include/exclude MUST YES
Support path reoptimization & inclusion of a
previously computed path MUST YES
Allow to select/prefer from advertised list of
standard objective functions/options MUST ME
Allow to customize objective function/options MUST ME
Request a less-constrained path MAY ME
Support request for less-constrained path,
including constraint-relaxation policy's SHOULD ME
Support Path Computation Responses MUST YES
Negative response support reasons for failure,
constraints to relax to achieve positive result,
less-constrained path reflecting
constraint-relaxation policy's SHOULD ME
Cancellation of Pending Requests MUST YES
Multiple Requests and Responses MUST YES
Limit by configuration number of requests within
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a message MUST YES
Support multiple computed paths in response MUST YES
Support "continuation correlation" where related
requests or computed paths cannot fit within one
message MUST YES
Maximum message size & maximum number of requests
per message exchanged through PCE messages to PCC,
or indicated in request message MAY ME
Reliable Message Exchange (achieved by PCEP
itself or transport protocol MUST YES
Allow detection & recovery of lost messages to
occur quickly & not impede operation of PCEP MUST ME
Handle overload situations without significant
decrease in performance, e.g., through throttling
of requests MUST YES
Provide acknowledged message delivery with
retransmission, in order message delivery or
facility to restore order, message corruption
detection, flow control & back-pressure to
throttle requests, rapid partner failure
detection, informed rapidly of failure of PCE-PCC
connection MUST YES
Functionality added to PCEP if transport protocol
provides it SHOULD NOT N/A
Secure Message Exchange (provided by PCEP or
transport protocol MUST YES
Support mechanisms to prevent spoofing (e.g.,
authentication), snooping (e.g., encryption),
DOS attacks MUST YES
Request Prioritization MUST YES
Unsolicited Notifications SHOULD YES
Allow Asynchronous Communication MUST YES
PCC Has to Wait for Response Before Making
Another Request MUST NOT YES
Allow order of responses differ from order of
Requests MUST YES
Communication Overhead Minimization SHOULD YES
Give particular attention to message size SHOULD
Extensibility without requiring modifications to
the protocol MUST YES
Easily extensible to support intra-area,
inter-area, inter-AS intra provider, inter-AS
inter-provider, multi-layer path & virtual network
topology path computation MUST YES
Easily extensible to support future applications
not in scope (e.g., P2MP path computations) SHOULD YES
Scalability at least linearly with increase in
number of PCCs, PCEs, PCCs communicating with a
single PCE, PCEs communicated to by a single PCC,
PCEs communicated to by another PCE, domains, path
requests, handling bursts of requests MUST YES
Support Path Computation Constraints MUST ME
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Support Different Service Provider Environments
(e.g., MPLS-TE and GMPLS networks, centralized &
distributed PCE path computation, single &
multiple PCE path computation) MUST YES
Policy Support for policies to accept/reject
requests, PCC to determine reason for rejection,
notification of policy violation MUST ME
Aliveness Detection of PCCs/PCEs, partner failure
Detection MUST YES
PCC/PCE Failure Response procedures defined for
PCE/PCC failures, PCC able to clear pending
Request MUST YES
PCC select another PCE upon detection of PCE
failure MUST YES
PCE able to clear pending requests from a PCC
(e.g. when it detects PCC failure or request
buffer full) MUST YES
Protocol Recovery support resynchronization of
information & requests between sender & receiver MUST ME
Minimize repeat data transfer, allow PCE to
respond to computation requests issued before
failure without requests being re-issued SHOULD ME
Stateful PCE able to resynchronize/recover
states (e.g., LSP status, paths) after restart SHOULD SE
Full Copyright Statement
Copyright (C) The Internet Society (2005).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights."
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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