Network Working Group J.L. Le Roux, Ed.
Request for Comments: 4674 France Telecom
Category: Informational October 2006
Requirements for Path Computation Element (PCE) Discovery
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document presents a set of requirements for a Path Computation
Element (PCE) discovery mechanism that would allow a Path Computation
Client (PCC) to discover dynamically and automatically a set of PCEs
along with certain information relevant for PCE selection. It is
intended that solutions that specify procedures and protocols or
extensions to existing protocols for such PCE discovery satisfy these
requirements.
Table of Contents
1. Introduction ....................................................2
1.1. Conventions Used in This Document ..........................3
1.2. Terminology ................................................3
2. Problem Statement and Requirements Overview .....................4
2.1. Problem Statement ..........................................4
2.2. Requirements Overview ......................................5
3. Example of Application Scenario .................................6
4. Detailed Requirements ...........................................7
4.1. PCE Information to Be Disclosed ............................7
4.1.1. General PCE Information (Mandatory Support) .........8
4.1.1.1. Discovery of PCE Location ..................8
4.1.1.2. Discovery of PCE Domains and
Inter-domain Functions .....................8
4.1.2. Detailed PCE Information (Optional Support) .........9
4.1.2.1. Discovery of PCE Capabilities ..............9
4.1.2.2. Discovery of Alternate PCEs ...............10
4.2. Scope of PCE Discovery ....................................10
4.2.1. Inter-AS Specific Requirements .....................10
Le Roux Informational [Page 1]
RFC 4674 Requirements for PCE Discovery October 2006
4.3. PCE Information Synchronization ...........................11
4.4. Discovery of PCE Deactivation .............................11
4.5. Policy Support ............................................12
4.6. Security Requirements .....................................12
4.7. Extensibility .............................................13
4.8. Scalability ...............................................13
4.9. Operational Orders of Magnitudes ..........................13
4.10. Manageability Considerations .............................14
4.10.1. Configuration of PCE Discovery Parameters .........14
4.10.2. PCE Discovery MIB Modules .........................14
4.10.2.1. PCC MIB Module ...........................14
4.10.2.2. PCE MIB module ...........................15
4.10.3. Monitoring Protocol Operations ....................15
4.10.4. Impact on Network Operations ......................16
5. Security Considerations ........................................16
6. Acknowledgements ...............................................16
7. Contributors ...................................................17
8. References .....................................................17
8.1. Normative References ......................................17
8.2. Informative References ....................................17
1. Introduction
The PCE-based network architecture [RFC4655] defines a Path
Computation Element (PCE) as an entity capable of computing TE-LSP
paths based on a network graph, and applying computational
constraints. A PCE serves path computation requests sent by Path
Computation Clients (PCC).
A PCC is a client application requesting a path computation to be
performed by a PCE. This can be, for instance, an LSR requesting a
path for a TE-LSP for which it is the head-end, or a PCE requesting a
path computation of another PCE (inter-PCE communication). The
communication between a PCC and a PCE requires a client-server
protocol whose generic requirements are listed in [RFC4657].
The PCE based architecture requires that a PCC be aware of the
location of one or more PCEs in its domain, and also potentially of
some PCEs in other domains, e.g., in case of inter-domain path
computation.
Le Roux Informational [Page 2]
RFC 4674 Requirements for PCE Discovery October 2006
In that context, it would be highly desirable to define a mechanism
for automatic and dynamic PCE discovery, which would allow PCCs to
automatically discover a set of PCEs, to determine additional
information required for PCE selection, and to dynamically detect new
PCEs or any modification of the PCEs' information. This includes the
discovery by a PCC of a set of one or more PCEs in its domain, and
potentially in some other domains. The latter is a desirable
function in the case of inter-domain path computation, for example.
This document lists a set of functional requirements for such an
automatic and dynamic PCE discovery mechanism. Section 2 points out
the problem statement. Section 3 illustrates an application
scenario. Finally, Section 4 addresses detailed requirements.
It is intended that solutions that specify procedures and protocols
or protocol extensions for PCE discovery satisfy these requirements.
There is no intent either to specify solution-specific requirements
or to make any assumption on the protocols that could be used for the
discovery.
Note that requirements listed in this document apply equally to PCEs
that are capable of computing paths in MPLS-TE-enabled networks and
PCEs that are capable of computing paths in GMPLS-enabled networks
(and PCEs capable of both).
It is also important to note that the notion of a PCC encompasses a
PCE acting as PCC when requesting a path computation of another PCE
(inter-PCE communication). Hence, this document does not make the
distinction between PCE discovery by PCCs and PCE discovery by PCEs.
1.1. 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.
1.2. Terminology
Terminology used in this document:
LSR: Label Switch Router.
TE-LSP: Traffic Engineered Label Switched Path.
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.
Le Roux Informational [Page 3]
RFC 4674 Requirements for PCE Discovery October 2006
PCC: Path Computation Client. Any client application requesting a
path computation to be performed by a Path Computation Element.
Interior Gateway Protocol (IGP) Area: OSPF Area or ISIS level/area.
ABR: IGP Area Border Router (OSPF ABR or ISIS L1L2 router).
AS: Autonomous System.
ASBR: AS Border Router.
Intra-area TE LSP: A TE LSP whose path does not cross IGP area
boundaries.
Inter-area TE LSP: A TE LSP whose path transits through two or more
IGP areas.
Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or
more ASs or sub-ASs (BGP confederations).
Domain: Any collection of network elements within a common sphere of
address management or path computational responsibility. Examples of
domains include IGP areas and Autonomous Systems.
2. Problem Statement and Requirements Overview
2.1. Problem Statement
A routing domain may, in practice, contain multiple PCEs:
- The path computation load may be balanced among a set of PCEs to
improve scalability.
- For the purpose of redundancy, primary and backup PCEs may be used.
- PCEs may have distinct path computation capabilities (multi-
constrained path computation, backup path computation, etc.).
- In an inter-domain context, there can be several PCEs with distinct
inter-domain functions (inter-area, inter-AS, inter-layer), each
PCE being responsible for path computation in one or more domains.
In order to allow for effective PCE selection by PCCs, that is, to
select the appropriate PCE based on its capabilities and perform
efficient load balancing of requests, a PCC needs to know the
location of PCEs in its domain, along with some information relevant
to PCE selection, and also potentially needs to know the location of
some PCEs in other domains, for inter-domain path computation
purpose.
Le Roux Informational [Page 4]
RFC 4674 Requirements for PCE Discovery October 2006
Such PCE information could be learned through manual configuration,
on each PCC, of the set of PCEs along with their capabilities. Such
a manual configuration approach may be sufficient, and even desired
in some particular situations (e.g., inter-AS PCE discovery, where
manual configuration of neighbor PCEs may be preferred for security
reasons), but it obviously faces several limitations:
- This may imply a substantial configuration overhead.
- This would not allow a PCC to dynamically detect that a new PCE is
available, that an existing PCE is no longer available, or that
there is a change in the PCE's information.
Furthermore, as with any manual configuration approach, there is a
risk of configuration errors.
As an example, in a multi-area network made up of one backbone area
and N peripheral areas, and where inter-area MPLS-TE path computation
relies on multiple-PCE path computation with ABRs acting as PCEs, the
backbone area would comprise at least N PCEs, and the configuration
of PCC would be too cumbersome (e.g., in existing multi-area
networks, N can be beyond fifty).
Hence, an automated PCE discovery mechanism allowing a PCC to
dynamically discover a set of PCEs is highly desirable.
2.2. Requirements Overview
A PCE discovery mechanism that satisfies the requirements set forth
in this document MUST allow a PCC to automatically discover the
location of one or more of the PCEs in its domain.
Where inter-domain path computation is required and policy permits,
the PCE discovery method MUST allow a PCC to automatically discover
the location of PCEs in other domains that can assist with inter-
domain path computation.
A PCE discovery mechanism MUST allow a PCC to discover the set of one
or more domains where a PCE has TE topology visibility and can
compute paths. It MUST also allow the discovery of the potential
inter-domain path computation functions of a PCE (inter-area, inter-
AS, inter-layer, etc.).
A PCE discovery mechanism MUST allow the control of the discovery
scope, that is the set of one or more domains (areas, ASs) where
information related to a given PCE has to be disclosed.
Le Roux Informational [Page 5]
RFC 4674 Requirements for PCE Discovery October 2006
A PCE discovery mechanism MUST allow PCCs in a given discovery scope
to dynamically discover that a new PCE has appeared or that there is
a change in a PCE's information.
A PCE discovery mechanism MUST allow PCCs to dynamically discover
that a PCE is no longer available.
A PCE discovery mechanism MUST support security procedures. In
particular, key consideration MUST be given in terms of how to
establish a trust model for PCE discovery.
OPTIONALLY, a PCE discovery mechanism MAY be used so as to disclose a
set of detailed PCE capabilities so that the PCC may make advanced
and informed choices about which PCE to use.
3. Example of Application Scenario
<----------------AS1--------------------> <----AS2---
Area 1 Area 0 Area 2
R1---------R3-----R5-------R6-----------R9----------R11----R13
| | | |
| | | |
R2---------R4-----R7-------R8-----------R10---------R12----R14
|
|
--
|S1|
--
Figure 1
Figure 1 illustrates a multi-area/AS network with several PCEs:
- The ABR R3 is a PCE that can take part in inter-area path
computation. It can compute paths in area 1 and area 0.
- The ABR R6 is a PCE that can take part in inter-area path
computation. It can compute paths in area 0 and area 2.
- The ASBR R9 is a PCE that can take part in inter-AS path
computation. It is responsible for path computation in AS1 towards
AS2.
- The ASBR R12 is a PCE that can take part in inter-AS path
computation. It is responsible for path computation in AS2 towards
AS1.
- The server S1 is a PCE that can be used to compute diverse paths
and backup paths in area 1.
Le Roux Informational [Page 6]
RFC 4674 Requirements for PCE Discovery October 2006
By meeting the requirements set out in this document, the PCE
discovery mechanism will allow:
- each PCC in areas 1 and 0 to dynamically discover R3, as a PCE for
inter-area path computation, and that R3 can compute paths in area
0 and area 1.
- each PCC in areas 0 and 2 to dynamically discover R6, as a PCE for
inter-area path computation, and that R6 can compute paths in area
2 and area 0.
- each PCC in AS1 and one or more PCCs in AS2 to dynamically discover
R9 as a PCE for inter-AS path computation in AS1 towards AS2.
- each PCC in AS2 and one or more PCCs in AS1 to dynamically discover
R12 as a PCE for inter-AS path computation in AS2 towards AS1.
- each PCC in area 1 to dynamically discover S1, as a PCE for intra-
area path computation in area1, and optionally to discover its path
computation capabilities (diverse path computation and backup path
computation).
4. Detailed Requirements
4.1. PCE Information to Be Disclosed
We distinguish two levels of PCE information to be disclosed by a PCE
discovery mechanism:
- General information. Disclosure MUST be supported by the PCE
discovery mechanism.
- Detailed information. Disclosure MAY be supported by the PCE
discovery mechanism.
The PCE discovery mechanism MUST allow disclosure of general PCE
information that will allow PCCs to select appropriate PCEs. This
comprises discovery of PCE location, PCE domains supported by the
PCEs, and PCE inter-domain functions.
The PCE discovery mechanism MAY also allow disclosure of detailed PCE
information. This comprises any or all information about PCE path
computation capabilities and alternate PCEs. This information is not
part of PCE discovery; this is additional information that can
facilitate the selection of a PCE by a PCC. Support of the exchange
of this information is optional in the context of the PCE discovery
mechanism itself. This does not mean that the availability of this
information is optional in the PCE-based architecture, but such
information could also be obtained by other mechanisms, such as the
PCC-PCE communication protocol.
Le Roux Informational [Page 7]
RFC 4674 Requirements for PCE Discovery October 2006
4.1.1. General PCE Information (Mandatory Support)
4.1.1.1. Discovery of PCE Location
The PCE discovery mechanism MUST allow the discovery, for a given
PCE, of the IPv4 and/or IPv6 address to be used to reach the PCE.
This address will typically be an address that is always reachable,
if there is any connectivity to the PCE.
This address will be used by PCCs to communicate with a PCE, through
a PCC-PCE communication protocol.
4.1.1.2. Discovery of PCE Domains and Inter-domain Functions
Inter-domain path computation is a key application of the PCE-based
architecture. This can rely on a multiple-PCE path computation,
where PCEs in each domain compute a part of the end-to-end path and
collaborate with each other to find the end-to-end-path. Inter-
domain path computation can also rely on a single-PCE path
computation where a PCE has visibility inside multiple domains and
can compute an entire end-to-end inter-domain path (that is, a path
from the inter-domain TE-LSP head-end to the inter-domain TE-LSP tail
end).
Hence, the PCE discovery mechanism MUST allow the discovery of the
set of one or more domains where a PCE has visibility and can compute
paths. These domains could be identified using a domain identifier:
For instance, an IGP area can be identified by the Area ID (OSPF or
ISIS), and an AS can be identified by the AS number.
Also the PCE discovery mechanism MUST allow discovery of the inter-
domain functions of a PCE, i.e., whether a PCE can be used to compute
or to take part in the computation of end-to-end paths across domain
borders. The inter-domain functions include nonexhaustively: inter-
area, inter-AS and inter-layer path computation. Note that these
functions are not mutually exclusive.
Note that the inter-domain functions are not necessarily inferred
from the set of domains where a PCE has visibility. For instance, a
PCE may have visibility limited to a single domain, but may be able
to take part in the computation of inter-domain paths by
collaborating with PCEs in other domains. Conversely, a PCE may have
visibility in multiple domains, but the operator may not want the PCE
to be used for inter-domain path computations.
The PCE discovery mechanisms MUST also allow discovery of the set of
one or more domains toward which a PCE can compute paths. For
instance, in an inter-AS path computation context, there may be
Le Roux Informational [Page 8]
RFC 4674 Requirements for PCE Discovery October 2006
several PCEs in an AS, each one responsible for taking part in the
computation of inter-AS paths toward a set of one or more destination
ASs, and a PCC may have to discover the destination ASs each PCE is
responsible for.
4.1.2. Detailed PCE Information (Optional Support)
4.1.2.1. Discovery of PCE Capabilities
In the case where there are several PCEs with distinct capabilities
available, a PCC has to select one or more appropriate PCEs.
For that purpose, the PCE discovery mechanism MAY support the
disclosure of some detailed PCE capabilities.
For the sake of illustration, this could include the following path-
computation-related PCE capabilities:
- The link constraints supported: e.g., bandwidth, affinities.
- The path constraints supported: maximum IGP/TE cost, maximum hop
count.
- The objective functions supported: e.g., shortest path, widest
path.
- The capability to compute multiple correlated paths: e.g., diverse
paths, load balanced paths.
- The capability to compute bidirectional paths.
- The GMPLS-technology-specific constraints supported: e.g., the
supported interface switching capabilities, encoding types.
And this could also include some specific PCE capabilities:
- The capability to handle request prioritization.
- The maximum size of a request message.
- The maximum number of path requests in a request message.
- The PCE computation power (static parameters to be used for
weighted load balancing of requests).
Such information regarding PCE capabilities could then be used by a
PCC to select an appropriate PCE from a list of candidate PCEs.
Note that the exact definition and description of PCE capabilities
are out of the scope of this document. It is expected that this will
be described in one or more separate documents which may be
application specific.
Le Roux Informational [Page 9]
RFC 4674 Requirements for PCE Discovery October 2006
4.1.2.2. Discovery of Alternate PCEs
In the case of a PCE failure, a PCC has to select another PCE, if one
is available. It could be useful in various situations for a PCE to
indicate a set of one or more alternate PCEs that can be selected in
case the given PCE fails.
Hence, the PCE discovery mechanism MAY allow the discovery, for a
given PCE, of the location of one or more assigned alternate PCEs.
The PCE discovery mechanism MAY also allow the discovery, for a given
PCE, of the set of one or more PCEs for which it acts as alternate
PCE.
4.2. Scope of PCE Discovery
The PCE discovery mechanism MUST allow control of the scope of the
PCE information disclosure on a per-PCE basis. In other words, it
MUST allow control of to which PCC or group of PCCs the information
related to a PCE may be disclosed.
The choice for the discovery scope of a given PCE MUST include at
least the followings settings:
- All PCCs in a single IGP area.
- All PCCs in a set of adjacent IGP areas.
- All PCCs in a single AS.
- All PCCs in a set of ASs.
- A set of one or more PCCs in a set of one or more ASs.
In particular, this also implies that the PCE discovery mechanism
MUST allow for the discovery of PCE information across IGP areas and
across AS boundaries.
The discovery scope MUST be configurable on a per PCE basis.
It MUST be possible to deactivate PCE discovery on a per PCE basis.
4.2.1. Inter-AS Specific Requirements
When using a PCE-based approach for inter-AS path computation, a PCC
in one AS may need to learn information related to inter-AS capable
PCEs located in other ASs. For that purpose, and as pointed out in
the previous section, the PCE discovery mechanism MUST allow
Le Roux Informational [Page 10]
RFC 4674 Requirements for PCE Discovery October 2006
disclosure of information related to inter-AS-capable PCEs across AS
boundaries.
Such inter-AS PCE discovery must be carefully controlled. For
security and confidentiality reasons, particularly in an inter-
provider context, the discovery mechanism MUST allow the discovery
scope to be limited to a set of ASs and MUST also provide control of
the PCE information to be disclosed across ASs. This is achieved by
applying policies (see also Section 4.4). This implies the
capability to contain a PCE advertisement to a restricted set of one
or more ASs, and to filter and translate any PCE parameter (PCE
domains, PCE inter-domain functions, PCE capabilities, etc.) in
disclosures that cross AS borders. For the sake of illustration, it
may be useful to disclose detailed PCE information (such as detailed
capabilities) locally in the PCE's AS but only general information
(such as location and supported domains) in other ASs.
4.3. PCE Information Synchronization
The PCE discovery mechanism MUST allow a PCC to discover any change
in the information related to a PCE that it has previously
discovered. This includes changes to both general information (e.g.,
a change in the PCE domains supported) and detailed information if
supported (e.g., a modification of the PCE's capabilities).
In addition, the PCE discovery mechanism MUST allow dynamic discovery
of new PCEs in a given discovery scope.
Note that there is no requirement for real-time detection of these
changes; the PCE discovery mechanism SHOULD rather allow discovery of
these changes in a range of 60 seconds, and the operator should have
the ability to configure the discovery delay.
Note that PCE information is relatively static and is expected to be
fairly stable and not to change frequently.
4.4. Discovery of PCE Deactivation
The PCE discovery mechanism MUST allow a PCC to discover when a PCE
that it has previously discovered is no longer alive or is
deactivated. This may help in reducing or avoiding path computation
service disruption.
Note that there is no requirement for real-time detection of PCE
failure/deactivation; the PCE discovery mechanism SHOULD rather allow
such discovery in a range of 60 seconds, and the operator should have
the ability to configure the discovery delay.
Le Roux Informational [Page 11]
RFC 4674 Requirements for PCE Discovery October 2006
4.5. Policy Support
The PCE discovery mechanism MUST allow for policies to restrict the
discovery scope to a set of authorized domains, to control and
restrict the type and nature of the information to be disclosed, and
also to filter and translate some information at domains borders. It
MUST be possible to apply these policies on a per-PCE basis.
Note that the discovery mechanisms MUST allow disclosing policy
information so as to control the disclosure policies at domain
boundaries.
Also, it MUST be possible to apply different policies when disclosing
PCE information to different domains.
4.6. Security Requirements
The five major threats related to PCE discovery mechanisms are
- impersonation of PCE;
- interception of PCE discovery information (sniffing);
- falsification of PCE discovery information;
- information disclosure to non-authorized PCCs (PCC spoofing);
- Denial of Service (DoS) Attacks.
Note that security of the PCE discovery procedures is of particular
importance in an inter-AS context, where PCE discovery may increase
the vulnerability to attacks and the consequences of these attacks.
Hence, mechanisms MUST be defined to ensure authenticity, integrity,
confidentiality, and containment of PCE discovery information:
- There MUST be a mechanism to authenticate discovery information.
- There MUST be a mechanism to verify discovery information
integrity.
- There MUST be a mechanism to encrypt discovery information.
- There MUST be a mechanism to restrict the scope of discovery to a
set of authorized PCCs and to filter PCE information disclosed at
domain boundaries (as per defined in Section 4.5).
A PCE and PCC MUST be identified by a globally unique ID, which may
be, for instance, a combination of AS number and IP address.
Mechanisms MUST be defined in order to limit the impact of a DoS
attack on the PCE discovery procedure (e.g., filter out excessive PCE
information change and flapping PCEs). Note also that DoS attacks
may be either accidental (caused by a misbehaving PCE system) or
intentional. As discussed in [RFC4657], such mechanisms may include
Le Roux Informational [Page 12]
RFC 4674 Requirements for PCE Discovery October 2006
packet filtering, rate limiting, no promiscuous listening, and where
applicable use of private addresses spaces.
Also, key consideration MUST be given in terms of how to establish a
trust model for PCE discovery. The PCE discovery mechanism MUST
explicitly support a specific set of one or more trust models.
4.7. Extensibility
The PCE discovery mechanism MUST be flexible and extensible so as to
easily allow for the inclusion of additional PCE information that
could be defined in the future.
4.8. Scalability
The PCE discovery mechanism MUST be designed to scale well with an
increase of any of the following parameters:
- Number of PCCs discovering a given PCE.
- Number of PCEs to be discovered by a given PCC.
- Number of domains in the discovery scope.
The PCE discovery mechanism MUST NOT have an adverse effect in the
performance of other protocols (especially routing and signaling)
already operating in the network.
Note that there is no scalability requirement with regards to the
amount of information to be exchanged.
Information disclosed in the PCE discovery mechanism is relatively
static. Changes in PCE information may occur as a result of PCE
configuration updates, PCE deployment/activation, or PCE
deactivation/suppression, and should not occur as a result of the PCE
activity itself. Hence, this information is quite stable and will
not change frequently.
4.9. Operational Orders of Magnitudes
This section gives minimum order of magnitude estimates of what the
PCE discovery mechanism should support.
- Number of PCCs discovering a given PCE: 1000
- Number of PCEs to be discovered by a given PCC: 100
Le Roux Informational [Page 13]
RFC 4674 Requirements for PCE Discovery October 2006
4.10. Manageability Considerations
Mechanisms are REQUIRED to manage PCE discovery operations. This
includes the configuration of PCE discovery functions and policies,
as well as the monitoring of the discovery protocol activity.
4.10.1. Configuration of PCE Discovery Parameters
It MUST be possible to enable and disable the PCE discovery function
at a PCC and at a PCE.
On the PCC, it MUST be possible for an operator to
activate/deactivate automatic PCE discovery. The activation of
automatic discovery MUST not prevent static configuration of PCE
information that may supplement discovered information.
On the PCE, it MUST be possible for an operator to control the
application of discovery policies by which the specific PCE is
discovered. As described in Section 4.5, this control MUST include
the ability to
- restrict the discovery scope to a set of authorized domains;
- define the type and nature of the information disclosed;
- specify the filtering and translation to be applied to the PCE
information disclosed at domain borders.
These configuration options MAY be supported through an
implementation-specific local configuration interface, or MAY be
supported via a standardised interface (such as a MIB module, as
below).
4.10.2. PCE Discovery MIB Modules
PCE discovery MIB modules MUST be specified for the control of the
function on PCCs and PCEs.
4.10.2.1. PCC MIB Module
The MIB module that will run on PCCs MUST include at least the
following:
- A control to disable automatic discovery by the PCC,
- The set of known PCEs,
- The number of known PCEs, and the number of discovered PCEs.
For each PCE reported in the MIB module, the following information
MUST be available:
Le Roux Informational [Page 14]
RFC 4674 Requirements for PCE Discovery October 2006
- Information advertised by the PCE (i.e., discovered information),
- Information locally configured about the PCE,
- The time since the PCE was discovered,
- The time since any change to the discovered information for the
PCE.
Note that when a PCE is no longer alive (see Section 4.4), it SHOULD
no longer be reported in the PCC MIB module.
The MIB module SHOULD also provide the average and maximum rates of
arrival, departure, and modification of PCE discovery to enable
effective analysis of the operation of the protocols. Furthermore,
the MIB module SHOULD report on the operation of the discovery
protocol by counting the number of unacceptable and incomprehensible
information exchanges.
The PCC MIB module SHOULD also be used to provide notifications when
thresholds (e.g., on the maximum rate of change, on the number of
unacceptable messages) are crossed, or when important events occur
(e.g., the number of discovered PCEs decreases to zero).
4.10.2.2. PCE MIB module
The MIB module that will run on PCEs MUST include at least
- a control to disable automatic discovery announcements by the PCE;
- information to be advertised by the PCE, although this information
MAY be present as read-only;
- the discovery policies active on the PCE, although this information
MAY be present as read-only.
The MIB module SHOULD also include
- the time since the last change to the advertised PCE information;
- the time since the last change to the advertisement policies;
- control of on which interfaces the PCE issues advertisements where
this is applicable to the protocol solution selected.
Note that a PCE MAY also be configured to discover other PCEs. In
this case, it SHOULD operate the MIB module described in Section
4.10.2.1 as well as the module described here.
4.10.3. Monitoring Protocol Operations
It MUST be possible to monitor the operation of any PCE discovery
protocol. Where an existing protocol is used to support the PCE
discovery function, this monitoring SHOULD be achieved using the
techniques already defined for that protocol, enhanced by the MIB
Le Roux Informational [Page 15]
RFC 4674 Requirements for PCE Discovery October 2006
modules described above. Where those techniques are inadequate, new
techniques MUST be developed.
Monitoring of the protocol operation demands support for at least the
following functions:
- Correlation of information advertised against information received.
- Counts of dropped, corrupt, and rejected information elements.
- Detection of 'segmented' networks, that is, the ability to detect
and diagnose the failure of a PCE advertisement to reach a PCC.
4.10.4. Impact on Network Operations
Frequent changes in PCE information may have a significant impact on
PCCs that receive the advertisements, might destabilize the operation
of the network by causing the PCCs to swap between PCEs, and might
harm the network through excessive advertisement traffic. Hence, it
MUST be possible to apply at least the following controls:
- Configurable limit on the rate of announcement of changed
parameters at a PCE.
- Control of the impact on PCCs such as through discovery messages
rate-limiting.
- Configurable control of triggers that cause a PCC to swap to
another PCE.
5. Security Considerations
This document is a requirement document and hence does not raise by
itself any particular security issue.
A set of security requirements that MUST be addressed when
considering the design and deployment of a PCE discovery mechanism
has been identified in Section 4.6.
6. Acknowledgements
We would like to thank, in chronological order, Benoit Fondeviole,
Thomas Morin, Emile Stephan, Jean-Philippe Vasseur, Dean Cheng,
Adrian Farrel, Renhai Zhang, Mohamed Boucadair, Eric Gray, Igor
Bryskin, Dimitri Papadimitriou, Arthi Ayyangar, Andrew Dolganow, Lou
Berger, Nabil Bitar, and Kenji Kumaki.
Thanks also to Ross Callon, Ted Hardie, Dan Romascanu, Russ Housley
and Sam Hartman for their review and constructive discussions during
the final stages of publication.
Le Roux Informational [Page 16]
RFC 4674 Requirements for PCE Discovery October 2006
7. Contributors
The following are the authors who contributed to the present
document:
Jean-Louis Le Roux (France Telecom)
Paul Mabey (Qwest Communications)
Eiji Oki (NTT)
Richard Rabbat (Fujitsu)
Ting Wo Chung (Bell Canada)
Raymond Zhang (BT Infonet)
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
8.2. Informative References
[RFC4657] Ash, J., Ed. and J.L. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, September 2006.
Contributors' Addresses
Paul Mabey
Qwest Communications
950 17th Street
Denver, CO 80202
USA
EMail: pmabey@qwest.com
Eiji Oki
NTT
Midori-cho 3-9-11
Musashino-shi, Tokyo 180-8585
JAPAN
EMail: oki.eiji@lab.ntt.co.jp
Le Roux Informational [Page 17]
RFC 4674 Requirements for PCE Discovery October 2006
Richard Rabbat
Fujitsu Laboratories of America
1240 East Arques Ave, MS 345
Sunnyvale, CA 94085
USA
EMail: richard@us.fujitsu.com
Ting Wo Chung
Bell Canada
181 Bay Street, Suite 350
Toronto, Ontario, M5J 2T3
CANADA
EMail: ting_wo.chung@bell.ca
Raymond Zhang
BT Infonet
2160 E. Grand Ave.
El Segundo, CA 90025
USA
EMail: raymond_zhang@infonet.com
Editor's Address
Jean-Louis Le Roux (Editor)
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex
FRANCE
EMail: jeanlouis.leroux@orange-ft.com
Le Roux Informational [Page 18]
RFC 4674 Requirements for PCE Discovery October 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
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.
Intellectual Property
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.
Acknowledgement
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Le Roux Informational [Page 19]
RFC, FYI, BCP