Internet DRAFT - draft-pouyllau-pce-enhanced-errors
draft-pouyllau-pce-enhanced-errors
PCE Working Group H. Pouyllau
Internet-Draft Alcatel-Lucent
Intended status: Standards Track R. Theillaud
Expires: April 1, 2012 Marben Products
J. Meuric
France Telecom Orange
September 29, 2011
Extension to the Path Computation Element Communication Protocol for
Enhanced Errors and Notifications
draft-pouyllau-pce-enhanced-errors-03.txt
Abstract
This document defines new error and notification TLVs for the PCE
Communication Protocol (PCEP) [RFC5440]. It identifies the possible
PCEP behaviors in case of error or notification. Thus, this draft
extends error and notification types in order to associate predefined
PCEP behaviors.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on April 1, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . 4
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Error use-case . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Notification use-case . . . . . . . . . . . . . . . . . . 6
3.2. PCEP Description . . . . . . . . . . . . . . . . . . . . . 6
3.3. PCEP Behaviors . . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. PCEP Behaviors in Case of Error . . . . . . . . . . . . . 7
3.3.2. PCEP Behaviors in Case of Notification . . . . . . . . . . 7
3.3.3. PCE peer identification . . . . . . . . . . . . . . . . . 8
4. Error and Notification Handling in PCEP . . . . . . . . . 9
4.1. Propagation TLV . . . . . . . . . . . . . . . . . . . . . 9
4.2. Error-criticity TLV . . . . . . . . . . . . . . . . . . . 9
4.3. Notification type TLV . . . . . . . . . . . . . . . . . . 9
4.4. Behaviors and TLV combinations . . . . . . . . . . . . . . 10
5. Propagation Restrictions . . . . . . . . . . . . . . . . . 12
5.1. Time-To-Live object . . . . . . . . . . . . . . . . . . . 12
5.2. DIFFUSION-LIST Object (DLO) . . . . . . . . . . . . . . . 12
5.3. Extension rules applied to existing errors and
notifications . . . . . . . . . . . . . . . . . . . . . . 14
6. Error and Notification Scenarios . . . . . . . . . . . . . 18
6.1. Local Error with a low level of criticity . . . . . . . . 18
6.2. Propagated Error with a low level of criticity . . . . . . 18
6.3. Local Error with a medium level of criticity . . . . . . . 19
6.4. Propagated Error with a medium level of criticity . . . . 20
6.5. Local request-specific notification . . . . . . . . . . . 20
6.6. Local non request-specific notification . . . . . . . . . 21
6.7. Propagated request-specific notification . . . . . . . . . 21
6.8. Propagated non request-specific notification . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . 23
8. IANA Considerations . . . . . . . . . . . . . . . . . . . 24
8.1. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . . 24
8.2. New TTL object . . . . . . . . . . . . . . . . . . . . . . 24
8.3. New DLO object . . . . . . . . . . . . . . . . . . . . . . 25
9. References . . . . . . . . . . . . . . . . . . . . . . . . 26
9.1. Normative References . . . . . . . . . . . . . . . . . . . 26
9.2. Informational References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 28
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1. Terminology
PCE terminology is defined in [RFC4655].
PCEP Peer: An element involved in a PCEP session (i.e. a PCC or a
PCE).
Source PCC: the PCC which, for a given path computation query,
initiates the 1st PCEP request, which may trigger a chain of
successive requests.
Target PCE: the PCE that can compute a path to the destination
without having to query any other PCE.
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2. 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 [RFC2119].
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3. Introduction
The PCE Communication Protocol [RFC5440] is designed to be flexible
and extensible in order to allow future evolutions or specific
constraint support such as proposed in
[I-D.ietf-pce-vendor-constraints]. Crossing different PCE
implementations (e.g. from different providers or due to different
releases), a PCEP request may encounter unknown errors or
notification messages. In such a case, the PCEP RFC [RFC5440]
specifies to send a specific error code to the PCEP peer.
In the context of path computation crossing different routing domains
or autonomous systems, the number of different PCE system
specificities is potentially high, thus possibly leading to divergent
and unstable situations. Such phenomenon can also occur in
homogeneous cases since PCE systems have their own policies that can
introduce differences in requests treatment even for requests having
the same destination. Extending error and notification codes allow
generalizing PCEP behaviors over heterogeneous PCE systems. Dealing
with heterogeneity is a major challenge considering PCE
applicability, particularly in multi-domain contexts. Thus,
extending such error codes and PCEP behaviors accordingly would
improve interoperability among different PCEP implementations and
would solve some of these unstable issues. However, some of them
would still remain (e.g. the divergences in request treatment
introduced by different policies).
The purpose of this draft is to specify some PCEP error codes in
order to generalize PCEP behaviors.
3.1. Examples
The two following scenarios underline the need for a normalization of
the PCEP behaviors according to the error or notification type.
3.1.1. Error use-case
PCE(i-1) has sent a request to PCE(i) which has also sent a request
to PCE(i+1). PCE(i-1) and PCE(i+1) have the same error semantic but
not PCE(i). If PCE(i+1) throws an error type and value unknown by
PCE(i). PCE(i) could then adopt any other behaviors and sends back
to PCE(i-1) an error of type 2 (Capability not supported), 3 (Unknown
Object) or 4 (Not supported Object) for instance. As a consequence,
the path request would be cancelled but the error has no meaning for
PCE(i-1) whereas if PCE(i) had simply forwareded the error sent by
PCE(i+1), it would have been understood by PCE(i-1).
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3.1.2. Notification use-case
PCE(i-1) has sent a request to PCE(i) which has also sent a request
to PCE(i+1) but PCE(i+1) is overloaded. Without extensions, PCE(i+1)
should send a notification of type 2 and a value flag giving its
estimated congestion duration. PCE(i) can choose to stop the path
computation and send a NO_PATH reply to PCE(i-1). Hence, PCE(i-1)
ignores the congestion duration on PCE(i+1) and could seek it for
further requests.
3.2. PCEP Description
One of the purposes of the PCE architecture is to compute paths
across networks, but an added value is to compute such paths in
inter-area/layer/domain environments. The PCE Communication Protocol
[RFC5440] is based on the Transport Communication Protocol (TCP).
Thus, to compute a path within the PCE architecture, several TCP/
PCECP sessions have to be set up, in a peer-to-peer manner, along a
set of identified PCEs.
When the PCEP session is up for 2 PCEP peers, the PCC of the first
PCE System (the source PCC) sends a PCReq message. If the PCC does
not receive any reply before the dead timer is out, then it goes back
to the idle state. A PCC can expect two kinds of replies: a PCRep
message containing one or more valid paths (EROs) or a negative PCRep
message containing a NO-PATH object.
Beside PCReq and PCRep messages, notification and error messages,
named respectively PCNtf and PCErr, can be sent. There are two types
of notification messages: type 1 is for cancelling pending requests
and type 2 for signaling a congestion of the PCE. Several error
values are described in [RFC5440]. The error types concerning the
session phase begin at 2, error type 1 values are dedicated to the
initialization phase.
As the PCE Communication Protocol is built to work in a peer-to-peer
manner (i.e. supported by a TCP Connection), it supposes that the
''deadtimer'' of the source PCC is long enough to support the end-to-
end distributed path computation process.
3.3. PCEP Behaviors
The exchange of messages in the PCE Communication Protocol is
described in details when PCEP is in states OpenWait and KeepWait in
[RFC5440]. When the session is up, message exchange is defined in
[RFC5440] but detailed behavior is mostly let free to any specific
implementation. [RFC5441] describes the Backward Recursive Path
Computation (BRPC) procedure, and, because it considers an inter-
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domain path computation, gives a bigger picture of the possible
behaviors when the session is up.
3.3.1. PCEP Behaviors in Case of Error
[RFC5440] specifies that "a PCEP Error message is sent in several
situations: when a protocol error condition is met or the request is
not compliant with the PCEP specification". On this basis, and
according to the other RFCs, the identified PCEP behaviors are the
followings:
"Propagation": the received message requires to be propagated
forwardly or backwardly (depending on which PCEP peer has sent the
message) to a set of PCE peers;
Criticity level: in the different RFCs, error-types affects the
state of the PCEP request or session in different manner; hence,
different level of criticity can be observed:
Low-level of criticity: the received message does not affect
the PCEP connection and futher answer can still be expected;
Medium-level of criticity: the received message does not affect
the PCEP connection but the request(s) is(are) cancelled;
High-level of criticity: the received message indicates that
the PCE peer will close the session with its peer (and so
pending requests associated by the error, if any, are
cancelled)
The high-level of criticity has been extracted from [RFC5440] which
associates such a behavior to error-type of 1 (errors raised during
the PCEP session establishment). Hence, such errors are quite
specific for the moment. For the sake of completeness, they have
been included in this document.
3.3.2. PCEP Behaviors in Case of Notification
Notification messages can be employed in two different manners:
during the treatment of a PCEP request, or independently from it to
advertise information (in [RFC5440] the request id list within a
PCNtf message is optional). Hence, three different behaviors can be
identified:
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o "Local": the notification is or is not request-specific but does
not imply any forward or backward propagation of the message;
o "Request-specific Propagation": the received message requires to
be propagated forwardly or backwardly (depending on which peer has
sent the message) to the PCEP peers;
o "Non request-specific Propagation": the received message must be
propagated to any known peers (e.g. if PCE discovery is activated)
or to a list of identified peers.
3.3.3. PCE peer identification
The propagation of errors and notifications affects the state of the
PCE peers along the chain. In some cases, for instance a
notification that a PCE is overloaded, the identification of the PCE
peer - or that the sender PCE is not the direct neighbor - might be
an important information for the PCE peers receiving the message.
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4. Error and Notification Handling in PCEP
This section describes extensions to support error and notification
messages with respect to the PCEP behavior description defined in
Section 3.3.1. This document does not intend to modify errorsand
notification types previously defined in existing documents (e.g.
[RFC5440], [RFC5441], etc.).
4.1. Propagation TLV
To support the propagation behavior mentioned in Section 3.3.1, we
extend the PCEP-ERROR and NOTIFICATION objects by creating a new
optional TLV to indicate whether the message has to be propagateed or
not. The allocation from the "PCEP TLV Type Indicators" sub-registry
will be assigned by IANA and the request is documented in Section 8.
The description is "Propagation", the length value is 2 bytes. The
value field is set to default value 0 meaning that the message MUST
NOT be propagated. If the value field is set to 1, the message MUST
be propagated. Section 5 specifies the destination and to limit the
number of messages.
4.2. Error-criticity TLV
To support the shutdown behavior mentioned in Section 3.3.1, we
extend the PCEP-ERROR object by creating a new optional TLV to
indicate whether the error is recoverable or not. The allocation
from the "PCEP TLV Type Indicators" sub-registry will be assigned by
IANA and the request is documented in Section 8.
The description is "Error-criticity", the length value is 2 bytes and
the value field is 1 byte. The value field is set to default value 0
meaning that the error has a low-level of criticity (so further
messages can be expected for this request). If the value field is
set to 1, the error has a medium-level of criticity and requests
whose the identifiers appear MUST be cancelled (so no further
messages can be expected for these requests). If the value field is
set to 2, the error has a high-level of criticity, the connection is
closed by the sender PCE peer.
4.3. Notification type TLV
To support the request-specific behavior mentioned in Section 3.3.1,
we extend the NOTIFICATION object by creating a new optional TLV to
indicate whether the notification is request-specific or not. The
allocation from the "PCEP TLV Type Indicators" sub-registry will be
assigned by IANA and the request is documented in Section 8.
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The description is "Notification Type", the length value is 2 bytes
and the value field is 1 byte. The value field is set to default
value 0 meaning that the notification is not request-specific. If
the value field is set to 1, the notification is request-specific.
4.4. Behaviors and TLV combinations
The propagation behavior MIGHT be combined with all criticity levels,
thus leading to 6 different behaviors. In the case of a criticity
level of 2, the session is closed by the PCE peer which sends the
message. Hence, the criticity level is purely informative for the
PCE peer which receives the message. If it is combined with a
propagation behavior, then the PCE propagating the message MUST
indicate the same level of criticity if it closes the session.
Otherwise, it MUST use a criticity level of 1 if it does not close
the sesssion.
The TLVs defined in the sections above allow to cover all the
possible behaviors listed in Section 3.3.1. Hence, for an error
message, the behaviors are covered as ensued, with TLVs included in a
PCEP-ERROR object:
o "Local Error with a low level of criticity" : TLV "Propagation"
with value 0 and TLV "Error-criticity" with value 0
o "Local Error with a medium level of criticity": TLV "Propagation"
with value 0 and TLV "Error-criticity" with value 1
o "Local Error with a high level of criticity": TLV "Propagation"
with value 0 and TLV "Error-criticity" with value 2
o "Propagated Error with a low level of criticity": TLV
"Propagation" with value 1 and TLV "Error-criticity" with value 0
o "Propagated Error with a medium level of criticity": TLV
"Propagation" with value 1 and TLV "Error-criticity" with value 1
o "Propagated Error with a high level of criticity": TLV
"Propagation" with value 1 and TLV "Error-criticity" with value 2
For a notification message, the behaviors are covered as ensued, with
TLVs included in a NOTIFICATION object:
o "Local request-specific": TLV "Propagation" with value 0 and TLV
"Notification Type" with value 1
o "Local non request-specific": TLV "Propagation" with value 0 and
TLV "Notification Type" with value 0
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o "Request-specific Propagation": TLV "Propagation" with value 1 and
TLV "Notification Type" with value 1
o "Non request-specific Propagation": TLV "Propagation" with value 1
and TLV "Notification Type" with value 0
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5. Propagation Restrictions
In order to limit the propagation of errors and notifications, the
following mechanisms SHOULD be used:
A Time-To-Live object: to limit the number of PCEP peers that will
recursively receive the message;
A DIFFUSION-LIST object (DLO) which specifies the PCEP peer
addresses or domains of PCEP peers the message must be propagate
to;
History mechanisms: if a PCEP peer keeps track of the messages it
has relayed, it could avoid propagating an error or notification
it already received.
Such mechanisms SHOULD be used jointly or independently depending the
error or notification behaviors they are associated to. Note that, a
non request-specific propagated notification (TLV "Propagation" at
value 1 and TLV "Notification Type" at value 0) MUST include a DLO
and SHOULD include a TTL. The conditions of use for the TTL and
DIFFUSION-LIST object are described in sections below.
5.1. Time-To-Live object
The TTL value is set to any integer value to indicate the number of
PCEP peers that will recursively receive the message. This TTL
SHOULD be used with propagated errors or notifications (TLV
"Propagation" at value 1 in PCEP-ERROR or NOTIFICATION objects).
Each PCEP peer MUST decrement the TTL value before propagating the
message. When the TTL value is at 0, the message is no more
propagated.
If the message has to be propagated, is request-specific (TLV
"Propagation" at value 1 in PCEP-ERROR or NOTIFICATION objects, and
TLV "Notification Type" at value 1 in a NOTIFICATION object), and
there is no TTL or DIFFUSION-LIST object included, the message MUST
reach the source PCC (or alternatively the target PCE).
5.2. DIFFUSION-LIST Object (DLO)
The DIFFUSION-LIST Object can be carried within a PCErr and 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. The DLO MAY be used with propagated errors (TLV
"Propagation"at value 1 in PCEP-ERROR object) and request-specific
propagated notifications (TLV "Propagation" at value 1 and TLV
"Notification Type" at value 1), and it MUST be used with non
request-specific propagated notifications (TLV "Propagation" at value
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1 and TLV "Notification Type" at value 0).
DIFFUSION-LIST Object-Class is 25.
DIFFUSION-LIST Object-Type is 1.
The format of the DIFFUSION-LIST body object is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags | TT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Sub-objects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved (8 bits): This field MUST be set to zero on transmission and
MUST be ignored on receipt.
Flags (16 bits): No flags are currently defined. Unassigned flags
MUST be set to zero on transmission and MUST be ignored on receipt.
TT (8 bits): The Target-type restricts the diffusion to certain
peers. The following values are currently defined:
0: Any PCEP peer indicated in the list must be reached.
1: Only PCEs must be reached (and not PCC).
2: All PCEP peers with which a session is still opened must be
reached
The DLO is made of sub-objects similar to the IRO defined in
[RFC5440]. The following sub-object types are supported.
Type Sub-object
1 IPv4 address
2 IPv6 address
4 Unnumbered Interface ID
5 OSPF area ID
32 Autonomous System number
33 Explicit eXclusion Route Sub-object (EXRS)
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If the error or notification codes target specific PCEP peers, a
DIFFUSION-LIST object avoids partially flooding all PCEP peers. Any
PCEP peer receiving a PCErr or PCNTf message containing a PCEP-ERROR
object, respectively a NOTIFICATION object, including a TLV
"Propagation" at value 1, and where a DLO appears MUST remove from
the DLO the addresses of the PCEP peers to whom it will propagate the
message, before sending them the message. This is performed adding
the PCEP peer addresses to the Explicit eXclusion Route Sub-object of
the DLO. If a DIFFUSION-LIST object is empty, the PCEP peer MUST NOT
propagate the message to any peer.
Note that, a Diffusion List Object could contain strict or loose
addresses to refer to a network domain (e.g. an Autonomous System
number, an OSPF area, an IP address). Hence, the PCEP peers targeted
by the message would be the PCEP peers covering the corresponding
domain. If an address is loose, each time a PCEP peer forwards a
message to another PCEP peer of this address, it MUST add it to the
Explicit eXclusion Route Sub-object (EXRS) of the DLO for any
forwarded message. Hence, a PCE SHOULD avoid forwarding several
times the same message to the same set of peers. Finally, when an
address is loose, the forwarding SHOULD be restrained indicating what
type of PCEP peers are targeted (i.e. PCE and/or PCC). Hence, a
Target-Type is specified.
5.3. Extension rules applied to existing errors and notifications
Many existing normative references states on error definitions (see
for instance [RFC5440], [RFC5441],[RFC5455], [RFC5521], [RFC5557],
[RFC5886], [RFC6006]). According to the definitions provided in this
document, the follwoing rules are applicable:
Error-type 1, described in [RFC5440], relates to PCEP session
establishement failures. All errors of this type are local (not
to be propagated). Hence, if a TLV "Propagation" is added to the
error message it MUST be set to value 0. Error-values 1,2,6,7
have a high level of criticity. Hence, if the TLV "Error-
criticity" is included within a PCErr message of type 1 and value
1,2,6 or 7, it MUST have a value of 2.
Error-type 2,3,4, "Capability not supported", "Unknown object" and
"Not supported object" respectively, described in [RFC5440]:
errors of this type MIGHT be propagated using the TLV
"Propagation". Their level of criticity is defined as leading to
cancel the path computation request (cf. [RFC5440]). Hence, if
the TLV "Error-criticity" is included, it MUST have a value of 1.
The error-value 4 of error-type 4 ("Unsupported parameter")
associated to the BRPC procedure [RFC5441] SHOULD contain the TLV
"Propagation" with a DIFFUSION-LIST object requesting a
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propagation to the PCC at the origin of the request.
Error-type 5 refers to "Policy violation", error values for this
type have been defined in [RFC5440], [RFC5541], [RFC5557],
[RFC5886] and [RFC6006]. In [RFC5440], it is specified that the
path computation request MUST be cancelled when an error of type 5
occurs. Hence, if the TLV "Error-criticity" is included, it MUST
have a value of 1. As such errors might be conveyed to several
PCEs, the TLV "Propagation" MIGHT be used.
Error-type 6 described as "Mandatory object missing" in [RFC5440],
leads to the cancellation of the path computation request. Hence,
if the TLV "Error-criticity" is included, it MUST have a value of
1. The TLV "Propagation" MIGHT be used with such errors. The
error-value defined in Monitoring object missing [RFC5886] is no
exception to the rule.
Error-type 7 is described as "synchronized path computation
request missing". In [RFC5440], it is specified that the reffered
synchronized path computation request MUST be cancelled when an
error of type 5 occurs. Hence, if the TLV "Error-criticity" is
included, it MUST have a value of 1. The TLV "Propagation" MIGHT
be used with such errors.
Error-type 8 is raised when a PCE receives a PCRep with an unknown
request reference. If the TLV "Propagation" is used with error-
type 8, it SHOULD be set at a value of 0. The TLV "Error-
criticity" is not particularly relevant for error-type 8. Hence,
if it used, it MUST have the value of 0.
Error-type 9 is raised when a PCE attempts to establish a second
PCEP session. The existing session must be preserved. Hence, if
the TLV "Error-criticity" is included, it MUST have a value of 0.
By definition, such an error message SHOULD NOT be propagated.
Thus, if the TLV "Propagation" is used with error-type 9, it
SHOULD be set at a value of 0.
Error-type 10 which refers to the reception of an invalid object
is described in [RFC5440] no indication is provide on the
cancellation of the path computation request. Hence, if the TLV
"Error-criticity" is included, it MUST have a value of 0. The TLV
"Propagation" MIGHT be used with such errors with any value
depending on the expected behavior.
Error-type 11 relates to "Unrecognized EXRS subobject" and is
described in [RFC5521]. No path computation request cancellation
is required by [RFC5521]. Hence, if the TLV "Error-criticity" is
included, it MUST have a value of 0. The TLV "Propagation" MIGHT
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be used with such errors with any value depending on the expected
behavior.
Error-type 12 refers to "Diffserv-aware TE error" and is described
in [RFC5455]. Such errors are raised when the CLASSTYPE object of
a PCReq is recognized but not supported by a PCE. [RFC5455] does
not state about the path computation request when such errors are
met. Hence, both "Propagation" and "Error-criticity" TLVs could
be used within such error-types' messages and set to any specified
values.
Error-type 13 on "BRPC procedure completion failure" is described
in [RFC5441]. [RFC5441] states that in such cases, the PCErr
message MUST be relayed to the PCC. Hence, such messages SHOULD
contain a TLV "Propagation" and a DIFFUSION-LIST object with a
Target-Type of 0 and corresponding adresses or with a Target-Type
of 2. It is not specified in [RFC5441] whether the path
computation request should be canceled or not. If the procedure
is not supported, it does not necessarily imply to cancel the path
computation request if another procedure is able to read and write
VSPT objects. Thus, the TLV "Error-criticity" MIGHT be used with
any value depending on the expected behavior.
Error-type 15 refers to "Global Concurrent Optimization Error"
defined in [RFC5557]. [RFC5557] states that the corresponding
global concurrent path optimization MUST be cancelled at the PCC.
Hence, if the TLV "Error-criticity" is included, it MUST have a
value of 1. The TLV "Propagation" MIGHT be used with such errors.
Error-type 16 relates to "P2MP Capability Error" defined in
[RFC6006]. Such errors lead to the cancellation of the path
computation request. Hence, if the TLV "Error-criticity" is
included, it MUST have a value of 1. The TLV "Propagation" MIGHT
be used with such errors.
Error-type 17, titled "P2MP END-POINTS Error" is defined
[RFC6006]. Such errors are thrown when a PCE tries to add or
prune nodes to or from a P2MP Tree. [RFC6006] does not specify if
such errors lead to cancel the path computation request. Hence,
TLVs "Error-criticity" and "Propagation" MIGHT be used with this
type of errors with any value depending on the expected behavior.
Error-type 18 on "P2MP Fragmentation Error" is described [RFC6006]
which does not specify whether the path computation request should
be cancelled. But, as messages are fragmented, it is natural to
think that the PCE should wait at least a bit for further
messages. The TLV "Error-criticity" MIGHT be included in such
error messages and is particularly adapted to differ the semantic
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of the same error-type message: if it is included with a value of
0 then the PCE will still wait for further fragmented messages,
when this waiting time ends, the TLV can be included with a value
of 1 in order to finally cancel the request. The TLV
"Propagation" MIGHT also be used with such errors.
Among the existing normative references, only the [RFC5440] defines
some notification-types and values. The recommendations with respect
to the TLVs definitions provided in this document are the followings:
Notitification-type=1, Notification-value=1 or 2: a PCC,
respectively a PCE, cancels a set of pending requests, such a
notification SHOULD be propagated to the list of PCEs which were
implied in the path computation requests. Hence, the NOTIFICATION
object SHOULD contains the TLV "Propagation" with value 1 and the
TLV "Notification Type" with value 1, together with a DIFFUSION-
LIST object containing the list of PCEs.
Notitification-type=2, Notification-value=1 or 2 : indicates to
the PCC that the PCE is, respectively is no longer, in an
overloaded state, such a notification can be propagated or stay
local. It is therefore RECOMMENDED to specify this behavior using
the TLV "Propagation" and associated restriction mechanims.
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6. Error and Notification Scenarios
This section provides some examples depicting how the error and
notification types described above can be used in a PCEP session.
The origin of the errors or notifications is only illustrative and
has no normative purpose. Sometimes the PCE features behind may be
implementation-specific (e.g. detection of flooding). This section
does not provide scenarios for errors with a high-level of critcity
since such errors are very specific and until now have been
normalized only during the session establishment (error-type of 1).
6.1. Local Error with a low level of criticity
In this example, a PCC attempts to establish a second PCEP session
with the same PCE for another request. Consequently the PCE sent an
error of error-type 9. This error stay local and does not affect the
former session. The second session is ignored.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1) Path computation | |
event | |
2) PCE Selection | |
3) Path computation |---- PCReq message--->|
request X sent to | |4) Path computation
the selected PCE | | request queued
| |
5) Path computation | |
event | |
6) PCE Selection | |
7) Path computation |---- PCReq message--->|
request X' sent to | | 8) Session already
the selected PCE | | opened
| |
|<--- PCErr message----| Error-type=9
| |
6.2. Propagated Error with a low level of criticity
In this example, a PCC sends a path computation requests with no P
flag set whereas (e.g. END-POINT object with P-flag cleared). This
is detected by another PCE in the sequence. The path computation
request can thus be treated but the P-Flag will be ignored. Hence,
this error is not critical but the source PCC should be informed of
this fact. So, a PCErr message with error-type 10 ("Reception of an
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invalid object"). The PCEP-ERROR object of the message contains a
TLV "Propagation" at value 1 and a TLV "Error-criticity" at value 0.
It is hence propagated backwardly to the source PCC.
+-+-+ +-+-+-+-+ +-+-+
|PCC| |PCE|PCC| |PCE|
+-+-+ +-+-+-+-+ +-+-+
|---- PCReq message-->| |
| | |
| |---- PCReq message--->|
| | |
| | |1) Parameter is
| | | not supported
| | |
| |<--- PCErr message----| Error-type=10
|<--- PCErr message---| |
| | |
6.3. Local Error with a medium level of criticity
In this example, the PCC sends a DiffServ-aware path computation
request. The PCE receiving the request does not support the
indicated class-type and thus sends back a PCErr message with error-
type=12, error-value=1, a TLV "Propagation" at value 0 and a TLV
"Error-criticity" at value 1. Consequently, the request(s) is (are)
cancelled.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1) Path computation | |
event | |
2) PCE Selection | |
3) Path computation |---- PCReq message--->|
request X sent to | |4) Path computation
the selected PCE | | request queued
| |
| |5) DiffServ class-type
| | not supported
| |6) Path computation
| | request X
| | cancelled
|<--- PCErr message----| Error-type=12
| |
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6.4. Propagated Error with a medium level of criticity
In this example, PCEs are using the BRPC procedure to treat a path
computation request [RFC5441]. However, one of the PCE does not
support a parameter of the request. Hence, a PCErr message with
error-type 4 and error-value 4 is sent by this PCE and has to be
forwarded to the source PCC. The PCEP-ERROR object includes a TLV
"Propagation" at value 1 and TLV "Error-criticity" at value 1 and the
message is propagated backwardly to the source PCC. Consequently,
the request(s) is (are) cancelled.
+-+-+ +-+-+-+-+ +-+-+
|PCC| |PCE|PCC| |PCE|
+-+-+ +-+-+-+-+ +-+-+
|---- PCReq message-->| |
| | |
| |---- PCReq message--->|
| | |
| | |1) Unsupported
| | | Parameter BRPC
| | |2) Path
| | | computation
| | | request X
| | | cancelled
| |<--- PCErr message----| Error-type=4
|<--- PCErr message---| |
| | |
6.5. Local request-specific notification
In this example, a PCE sends a request-specific notification
indicating that, a set of pending requests are cancelled (e.g.
notification-type=1, notification-value=1 as described in [RFC5440]).
Hence, a PCNtf message is sent to the PCC with a NOTIFICATION object
including a TLV "Propagation" at value 0 and a TLV "Notification
Type" at value 1.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
1) Path computation | |
event | |
2) PCE Selection | |
3) Path computation |---- PCReq message--->|
request X sent to | |4) Path
the selected PCE | | computation
| | request queued
| |
| |5) Pending requests
| | cancelled
| |
|<--- PCNtf message----|Notification-Type=1
| |
6.6. Local non request-specific notification
In this example, a PCE sends a non request-specific notification
indicating that, due to multiple sendings (or for other reason),
further requests from this PCC will be ignored. Hence, a PCNtf
message is sent to the PCC with a NOTIFICATION object including a TLV
"Propagation" at value 0 and a TLV "Notification Type" at value 0.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
| |1) Further requests
| | will be ignored
| |
|<--- PCNtf message----|
| |
6.7. Propagated request-specific notification
In this example, a PCE receives a request but it is temporarily
congested. However, it can treat the request after few minutes which
might cause some time-out in the predecessor PCEs. Hence, a PCNtf
message with a NOTIFICATION object containing a TLV "Propagation" at
value 1 and a TLV "Notification Type" at value 1 is send to the PCC
and propagated backwardly in the PCE sequence. Such a notification
could include an OVERLOAD object as described in [RFC5886].
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+-+-+ +-+-+-+-+ +-+-+
|PCC| |PCE|PCC| |PCE|
+-+-+ +-+-+-+-+ +-+-+
|---- PCReq message-->| |
| | |
| |---- PCReq message--->|
| | |
| | |1)PCE is busy but
| | | will answer to X
| | | in M minutes
| | | (time-out update)
| |<--- PCNtf message----| Notification-type=2
|<--- PCNtf message---| |
6.8. Propagated non request-specific notification
In this example, a PCE is temporarily congested. A PCNtf message
with a NOTIFICATION object containing a TLV "Propagation" at value 1
and a TLV "Notification Type" at value 0 is send to a PCE and
propagated to a sequence of PCEs. Here, PCEk is congested and send a
PCNtf message to PCEi with the approapriate TLVs, an OVERLOAD object
as described in [RFC5886], and a DIFFUSION-LIST object indicating
PCEj as a target of the notification.
+-+--+ +-+--+ +-+--+
|PCEj| |PCEi| |PCEk|
+-+--+ +-+--+ +-+--+
| | |
| | |1)PCE is busy
| | | for M minutes
| | | (time-out update)
| |<--- PCNtf message----| Notification-type=2
|<--- PCNtf message---| |
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7. Security Considerations
Within the introduced set of TLVs , the TLV "Propagation" affects
PCEP security considerations since it forces propagation behaviors.
Thus, a PCEP implementation SHOULD activate stateful mechanism when
receiving PCEP-ERROR or NOTIFICATION object including this TLV in
order to avoid DoS attacks.
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8. IANA Considerations
IANA maintains a registry of PCEP parameters. This includes a sub-
registry for PCEP Objects.
IANA is requested to make an allocation from the sub-registry as
follows. The values here are suggested for use by IANA.
8.1. PCEP TLV Type Indicators
As described in Section 5 the newly defined TLVs allows a PCE to
enforce specific error and notification behaviors within PCEP-ERROR
and NOTIFICATION objects. IANA is requested to make the following
allocations from the "PCEP TLV Type Indicators" sub-registry.
Value Description Reference
7 Propagation this document
8 Error-criticity this document
9 Notification type this document
8.2. New TTL object
TBC
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8.3. New DLO object
Object-class Value Object-Type and Name Reference
25 1: Diffusion list object this document
Target-Type Value Meaning Reference
0 Any PCEP peers this document
1 PCEs but excludes
PCC-only peers this document
2 PCEs and PCCs this document
with which a session
is still opened
Subobjects Reference
1: IPv4 prefix this document
2: IPv6 prefix this document
4: Unnumbered Interface ID this document
5: OSPF Area ID this document
32: Autonomous system number this document
33: Explicit Exclusion Route subobject (EXRS) this document
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
Backward-Recursive PCE-Based Computation (BRPC) Procedure
to Compute Shortest Constrained Inter-Domain Traffic
Engineering Label Switched Paths", RFC 5441, April 2009.
[RFC5455] Sivabalan, S., Parker, J., Boutros, S., and K. Kumaki,
"Diffserv-Aware Class-Type Object for the Path Computation
Element Communication Protocol", RFC 5455, March 2009.
[RFC5521] Oki, E., Takeda, T., and A. Farrel, "Extensions to the
Path Computation Element Communication Protocol (PCEP) for
Route Exclusions", RFC 5521, April 2009.
[RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC 5541, June 2009.
[RFC5557] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
Computation Element Communication Protocol (PCEP)
Requirements and Protocol Extensions in Support of Global
Concurrent Optimization", RFC 5557, July 2009.
[RFC5886] Vasseur, JP., Le Roux, JL., and Y. Ikejiri, "A Set of
Monitoring Tools for Path Computation Element (PCE)-Based
Architecture", RFC 5886, June 2010.
[RFC6006] Zhao, Q., King, D., Verhaeghe, F., Takeda, T., Ali, Z.,
and J. Meuric, "Extensions to the Path Computation Element
Communication Protocol (PCEP) for Point-to-Multipoint
Traffic Engineering Label Switched Paths", RFC 6006,
September 2010.
9.2. Informational References
[I-D.ietf-pce-vendor-constraints]
Farrel, A. and G. Bernstein, "Conveying Vendor-Specific
Constraints in the Path Computation Element Protocol",
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draft-ietf-pce-vendor-constraints-01 (work in progress),
March 2010.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
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Authors' Addresses
Helia Pouyllau
Alcatel-Lucent
Route de Villejust
NOZAY 91620
FRANCE
Phone: + 33 (0)1 30 77 63 11
Email: helia.pouyllau@alcatel-lucent.com
Remi Theillaud
Marben Products
176 rue Jean Jaures
Puteaux 92800
FRANCE
Phone: + 33 (0)1 79 62 10 22
Email: remi.theillaud@marben-products.com
Julien Meuric
France Telecom Orange
2, avenue Pierre Marzin
Lannion 22307
FRANCE
Email: julien.meuric@orange.com
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