draft-ietf-pce-discovery-reqs-00.txt   draft-ietf-pce-discovery-reqs-01.txt 
PCE Working Group J.L. Le Roux (Editor) Network Working Group J.L. Le Roux (Editor)
Internet Draft France Telecom Internet Draft France Telecom
Category: Informational Category: Informational
Expires: January 2006 Expires: January 2006
July 2005 July 2005
Requirements for Path Computation Element (PCE) Discovery Requirements for Path Computation Element (PCE) Discovery
draft-ietf-pce-discovery-reqs-00.txt draft-ietf-pce-discovery-reqs-01.txt
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Abstract Abstract
This document presents a set of requirements for a Path Computation This document presents a set of requirements for a Path Computation
Element (PCE) discovery mechanism that would allow a Path Computation Element (PCE) discovery mechanism that would allow a Path Computation
Client (PCC) to discover dynamically and automatically a set of PCEs Client (PCC) to discover dynamically and automatically a set of PCEs
along with their capabilities. It is intended that solutions that along with certain information relevant for PCE selection. It is
specify procedures and protocol extensions for such PCE discovery intended that solutions that specify procedures and protocol(s) or
satisfy these requirements. protocol(s) extensions for such PCE discovery satisfy these
requirements.
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119. document are to be interpreted as described in RFC-2119.
Table of Contents Table of Contents
1. Contributors................................................2 1. Contributors................................................2
2. Terminology.................................................3 2. Terminology.................................................3
3. Introduction................................................3 3. Introduction................................................3
4. Problem Statement and Requirements overview.................4 4. Problem Statement and Requirements overview.................4
4.1. Problem Statement...........................................4 4.1. Problem Statement...........................................4
4.2. Requirements overview.......................................5 4.2. Requirements overview.......................................5
5. Example of application scenario.............................6 5. Example of application scenario.............................6
6. Detailed Requirements.......................................7 6. Detailed Requirements.......................................7
6.1. PCE Information to be disclosed.............................7 6.1. PCE Information to be disclosed.............................7
6.1.1. Discovery of PCE Location...................................7 6.1.1. Discovery of PCE Location...................................7
6.1.2. Discovery of PCE computation scopes and domain(s) under 6.1.2. Discovery of PCE computation scope(s) and domain(s)
control...................................................7 under control...............................................7
6.1.3. Discovery of PCE Capabilities...............................8 6.1.3. Discovery of PCE Capabilities...............................8
6.1.4. Discovery of Alternate PCEs.................................9 6.1.4. Discovery of Alternate PCEs.................................8
6.2. Scope of PCE Discovery......................................9 6.2. Scope of PCE Discovery......................................9
6.3. PCE Information Synchronization.............................9 6.3. PCE Information Synchronization.............................9
6.4. Detecting PCE Liveliness...................................10 6.4. Detecting PCE Liveliness....................................9
6.5. Discovery of PCE capacity and congestion...................10 6.5. Discovery of PCE capacity and congestion...................10
6.6. Extensibility..............................................10 6.6. Security Requirements......................................10
6.7. Scalability................................................10 6.7. Extensibility..............................................10
6.8. PCE Selection..............................................10 6.8. Scalability................................................10
7. Security Considerations....................................11 7. Security Considerations....................................11
8. Acknowledgments............................................11 8. Acknowledgments............................................11
9. References.................................................11 9. References.................................................11
10. Authors' Addresses:........................................12 10. Authors' Addresses:........................................11
11. Intellectual Property Statement............................13 11. Intellectual Property Statement............................12
1. Contributors 1. Contributors
The following are the authors that contributed to the present The following are the authors that contributed to the present
document: document:
Jean-Louis Le Roux (France Telecom) Jean-Louis Le Roux (France Telecom)
Paul Mabey (Qwest Communications) Paul Mabey (Qwest Communications)
Eiji Oki (NTT) Eiji Oki (NTT)
Richard Rabbat (Fujitsu) Richard Rabbat (Fujitsu)
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route based on a network graph, and applying computational route based on a network graph, and applying computational
constraints. constraints.
PCC: Path Computation Client: any client application requesting a PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element. path computation to be performed by a Path Computation Element.
IGP Area: OSPF Area or ISIS level/area IGP Area: OSPF Area or ISIS level/area
ABR: IGP Area Border Router (OSPF ABR or ISIS L1L2 router) 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 Intra-area TE LSP: A TE LSP whose path does not cross IGP area
boundaries. boundaries.
Inter-area TE LSP: A TE LSP whose path transits through Inter-area TE LSP: A TE LSP whose path transits through
two or more IGP areas. two or more IGP areas.
Inter-AS MPLS TE LSP: A TE LSP whose path transits Inter-AS MPLS TE LSP: A TE LSP whose path transits
through two or more ASes or sub-ASes (BGP confederations). through two or more ASes or sub-ASes (BGP confederations).
Domain: any collection of network elements within a common sphere Domain: any collection of network elements within a common sphere
of address management or path computational responsibility. of address management or path computational responsibility.
Examples of domains include IGP areas and Autonomous Systems. Examples of domains include IGP areas and Autonomous Systems.
3. Introduction 3. Introduction
The PCE Architecture [PCE-ARCH] defines a Path Computation Element The PCE Architecture [PCE-ARCH] defines a Path Computation Element
(PCE) as an entity capable of computing TE-LSPs paths satisfying a (PCE) as an entity capable of computing TE-LSPs paths satisfying a
set of constraints. The PCE function can be located on a router/LSR set of constraints. A PCE serves path computation requests sent by
(composite PCE) or on a network server (external PCE). Path Computation Clients (PCC).
A PCE serves TE-LSP path computation requests sent by Path A PCC is a client application requesting a path computation to be
Computation Clients (PCC). performed by a PCE. This can be, for instance, an LSR requesting a
A Path Computation Client (PCC) is a client application requesting a path for a TE-LSP for which it is the head-end, or a PCE requesting a
path computation to be performed by a PCE. This can be, for instance, path computation of another PCE (inter-PCE communication). The
an LSR requesting a path for a TE-LSP for which it is the head-end, communication between a PCC and a PCE requires a client-server
or a PCE requesting a path computation of another PCE (inter-PCE protocol whose generic requirements are listed in [PCE-COM-REQ].
communication). The communication between a PCC and a PCE requires a
client-server protocol whose requirements are listed in [PCE-COM-
REQ].
There are several motivations for the adoption of a PCE-based There are several motivations for the adoption of a PCE-based
architecture to perform a TE-LSP path computation. They are listed in architecture to perform a path computation. They are listed in [PCE-
[PCE-ARCH]. This includes applications such as CPU intensive path ARCH]. This includes applications such as CPU intensive path
computation, inter-domain path computation and backup path computation, inter-domain path computation and backup path
computation. computation.
The PCE architecture requires, of course, that a PCC be aware of the The PCE architecture requires, of course, that a PCC be aware of the
location and capabilities of one or more PCEs in its domain, and also location of one or more PCEs in its domain, and also potentially of
potentially of some relevant PCEs in other domains (in the context of some PCEs in other domains, for inter-domain path computation.
inter-domain path computation).
In that context it would be highly desirable to define a mechanism In that context it would be highly desirable to define a mechanism
for automatic and dynamic PCE discovery, which would allow PCCs to for automatic and dynamic PCE discovery, which would allow PCCs to
automatically discover a set of PCEs along with their capabilities, automatically discover a set of PCEs, including information required
and to dynamically detect new PCEs or any modification of the PCE for PCE selection, and to dynamically detect new PCEs or any
capabilities. This includes the discovery by a PCC of a set of one or modification of PCE's information. This includes the discovery by a
more PCEs in its domain, and potentially in some other domains. The PCC of a set of one or more PCEs in its domain, and potentially in
latter is a desirable function in the case of inter-domain path some other domains. The latter is a desirable function in the case of
computation for example. inter-domain path computation for example.
This document lists a set of functional requirements for such an This document lists a set of functional requirements for such an
automatic and dynamic PCE discovery mechanism. Section 3 points out automatic and dynamic PCE discovery mechanism. Section 3 points out
the problem statement. Section 4 illustrates an application scenario. the problem statement. Section 4 illustrates an application scenario.
Finally section 5 addresses detailed requirements. Finally section 5 addresses detailed requirements.
It is intended that solutions that specify procedures and protocol It is intended that solutions that specify procedures and protocol(s)
extensions for such PCE discovery satisfy these requirements. There or protocol(s) extensions for such PCE discovery satisfy these
is no intent either to specify solution specific requirements or to requirements. There is no intent either to specify solution specific
make any assumption on the protocol(s) that could be used for the requirements or to make any assumption on the protocol(s) that could
discovery. be used for the discovery.
Note that requirements listed in this document apply equally to MPLS- Note that requirements listed in this document apply equally to MPLS-
TE and GMPLS-capable PCEs. TE and GMPLS-capable PCEs.
It is also important to note that the notion of a PCC encompasses a It is also important to note that the notion of a PCC encompasses a
PCE acting as PCC when requesting a TE-LSP path computation of PCE acting as PCC when requesting a path computation of another PCE
another PCE (inter-PCE communication). Thus this document does not (inter-PCE communication). Hence, this document does not make the
make the distinction between PCE discovery by PCCs and PCE discovery distinction between PCE discovery by PCCs and PCE discovery by PCEs.
by PCEs.
4. Problem Statement and Requirements overview 4. Problem Statement and Requirements overview
4.1. Problem Statement 4.1. Problem Statement
A routing domain may in practice be comprised of multiple PCEs: A routing domain may in practice be comprised of multiple PCEs:
-The path computation load may be balanced among a set of PCEs -The path computation load may be balanced among a set of PCEs
to improve scalability; to improve scalability;
-For the purpose of redundancy, primary and backup PCEs may be -For the purpose of redundancy, primary and backup PCEs may be
used; used;
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computation in one or more domains within its scope. computation in one or more domains within its scope.
As an example, in a multi-area network made of one backbone area and As an example, in a multi-area network made of one backbone area and
N peripheral areas, and where inter-area MPLS-TE path computation N peripheral areas, and where inter-area MPLS-TE path computation
relies on multiple-PCE path computation with ABRs acting as PCEs, the relies on multiple-PCE path computation with ABRs acting as PCEs, the
backbone area would comprise at least N PCEs. In existing multi-area backbone area would comprise at least N PCEs. In existing multi-area
networks, N can be quite large (e.g. beyond fifty). networks, N can be quite large (e.g. beyond fifty).
In order to allow for efficient PCE selection by PCCs and efficient In order to allow for efficient PCE selection by PCCs and efficient
load balancing of requests, a PCC has to know the location of PCEs in load balancing of requests, a PCC has to know the location of PCEs in
its domain, along with their capabilities, and also potentially of its domain, along with some information relevant for PCE selection,
some relevant PCEs in other domains (for inter-domain path and also potentially of some PCEs in other domains, for inter-domain
computation purpose). path computation purpose.
Such PCE information could be learnt through manual configuration, on Such PCE information could be learnt through manual configuration, on
each PCC, of the set of PCEs along with their capabilities and each PCC, of the set of PCEs along with their capabilities. Such
scope(s). Such manual configuration approach may be sufficient, and manual configuration approach may be sufficient, and even desired in
even desired in some particular situations, but it obviously faces some particular situations, but it obviously faces several
several limitations: limitations:
-This may imply a substantial configuration overhead (see the -This may imply a substantial configuration overhead (see the
above example with N PCEs); above example with N PCEs);
-This would not allow a PCC to dynamically detect that a new -This would not allow a PCC to dynamically detect that a new
PCE is available, that an existing PCE is no longer available, PCE is available, that an existing PCE is no longer available,
or that there is a change in the PCE's capabilities. or that there is a change in the PCE's information.
Furthermore, as with any manual configuration approach, this may lead Furthermore, as with any manual configuration approach, this may lead
to undesirable configuration errors. to undesirable configuration errors.
Hence, an automated PCE discovery mechanism allowing a PCC to Hence, an automated PCE discovery mechanism allowing a PCC to
dynamically discover a set of PCEs and their capabilities is highly dynamically discover a set of PCEs is highly desirable.
desirable.
4.2. Requirements overview 4.2. Requirements overview
A PCE discovery mechanism that satisfies the requirements set forth A PCE discovery mechanism that satisfies the requirements set forth
in this document MUST allow a PCC to automatically discover the in this document MUST allow a PCC to automatically discover the
location of one or more PCEs in its domain and also, potentially, of location of one or more PCEs in its domain and also, potentially, of
PCEs in other domains, of interest for inter-domain path computation PCEs in other domains, of interest for inter-domain path computation
purpose. purpose.
A PCE discovery mechanism MUST allow discovering the path computation A PCE discovery mechanism MUST allow discovering the path computation
scope(s) of a PCE. It MUST also allow a PCC to discover the set of scope(s) of a PCE (intra-area, inter-area, inter-ASą). It MUST also
one or more domains under the path computation responsibility of a allow a PCC to discover the set of one or more domains under the path
PCE. computation responsibility of a PCE.
A PCE discovery mechanism MUST allow PCCs to dynamically discover A PCE discovery mechanism MUST allow PCCs to dynamically discover
that a new PCE has appeared or that there is a change in PCE that a new PCE has appeared or that there is a change in PCE's
information. information. It MUST also allow PCCs to dynamically discover that a
PCE is no longer available.
It MUST also allow PCCs to dynamically discover that a PCE is no The PCE discovery MUST be secure. In particular, key consideration
longer available. MUST be given in terms of how to establish a trust model for PCE
discovery.
A PCE discovery mechanism SHOULD also allow PCCs to learn about a set OPTIONALLY a PCE discovery mechanism MAY be used so as to disclose a
of PCE path computation capabilities. set of PCE capabilities.
5. Example of application scenario 5. Example of application scenario
<----------------AS1--------------------> <----AS2--- <----------------AS1--------------------> <----AS2---
Area 1 Area 0 Area 2 Area 1 Area 0 Area 2
R1---------R3-----R5-------R6-----------R9----------R11----R13 R1---------R3-----R5-------R6-----------R9----------R11----R13
| | | | | | | | | |
| | | | | | | | | |
R2---------R4-----R7-------R8-----------R10---------R12----R14 R2---------R4-----R7-------R8-----------R10---------R12----R14
S1 S1
Figure 1. Figure 1
Figure 1 above illustrates a network with several PCEs: Figure 1 above illustrates a network with several PCEs:
-The ABR R3 is a composite PCE that can take part in inter area path -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. computation. It can compute paths in area 1 and area 0;
-The ABR R6 is a composite PCE that can take part in inter-area path -The ABR R6 is a PCE that can take part in inter-area path
computation. It can compute paths in area 0 and area2 computation. It can compute paths in area 0 and area2;
-The ASBR R9 is a composite PCE that can take part in inter-AS path -The ASBR R9 is a PCE that can take part in inter-AS path
computation, responsible for path computation in AS1 towards AS2. computation, responsible for path computation in AS1 towards AS2;
-The ASBR R12 is a composite PCE that can take part in inter-AS path -The ASBR R12 is a PCE that can take part in inter-AS path
computation, responsible for path computation in AS2 towards AS1. computation, responsible for path computation in AS2 towards AS1;
-The server S1 is an external PCE that can be used to compute diverse -The server S1 is a PCE that can be used to compute diverse paths and
paths and backup paths in area 1. backup paths in area 1.
The PCE discovery mechanism will allow: The PCE discovery mechanism will allow:
-each LSR in area 1 and 0 to dynamically discover R3, as a PCE for -each LSR in area 1 and 0 to dynamically discover R3, as a PCE for
inter-area path computation as well as its path computation domains: inter-area path computation as well as its path computation domains:
area1 and area0. area1 and area0;
-each LSR in area 0 and 2 to dynamically discover R6, as a PCE for -each LSR in area 0 and 2 to dynamically discover R6, as a PCE for
inter-area path computation, as well as its path computation domains: inter-area path computation, as well as its path computation domains:
area2 and area0. area2 and area0;
-each LSR in AS1 and some PCEs in AS2 to dynamically discover R9 as a -each LSR in AS1 and some PCEs in AS2 to dynamically discover R9 as a
PCE for inter-AS path computation as well as its path computation PCE for inter-AS path computation in AS1 towards AS2;
domain: AS1
-each LSR in area 1 to dynamically discover S1, as a PCE for diverse -each LSR in area 1 to dynamically discover S1, as a PCE for diverse
path computation and backup path computation in area1. path computation and backup path computation in area1.
6. Detailed Requirements 6. Detailed Requirements
6.1. PCE Information to be disclosed 6.1. PCE Information to be disclosed
The PCE discovery mechanism MUST disclose some PCE information that The PCE discovery mechanism MUST allow disclosing some PCE
will allow PCCs to select appropriate PCEs. information that will allow PCCs to select appropriate PCEs.
This section details the kind of information that has to be
disclosed. We distinguish two levels of information to be disclosed by the PCE
discovery mechanism:
-Mandatory information: This comprises discovery of PCE location,
PCE computation scopes and domains under control
-Optional information: This comprises discovery of PCE
capabilities and alternate PCEs.
Note that the latter information is optional in the context of the
PCE discovery mechanism. It could also be obtained by other
mechanisms, such as for instance the PCC-PCE communication protocol.
6.1.1. Discovery of PCE Location 6.1.1. Discovery of PCE Location
The PCE discovery mechanism MUST allow discovering, for a given PCE, The PCE discovery mechanism MUST allow discovering, for a given PCE,
the IPv4 and/or IPv6 address to be used to reach the PCE. This the IPv4 and/or IPv6 address to be used to reach the PCE. This
address will typically be a loop-back address that is always address will typically be a loop-back address that is always
reachable, if there is any connectivity to the PCE. reachable, if there is any connectivity to the PCE.
This address will be used by PCCs to communicate with a PCE, thanks This address will be used by PCCs to communicate with a PCE, thanks
to a PCC-PCE communication protocol. to a PCC-PCE communication protocol.
6.1.2. Discovery of PCE computation scopes and domain(s) under control 6.1.2. Discovery of PCE computation scope(s) and domain(s) under
control
Inter-domain path computation is a key application of the PCE Inter-domain path computation is a key application of the PCE
architecture. This can rely on a multiple-PCE path computation, 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 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. This can collaborate with each other to find the end-to-end-path. This can
also rely on a single-PCE path computation where a PCE has visibility also rely on a single-PCE path computation where a PCE has visibility
inside multiple domains and can compute an inter-domain path. inside multiple domains and can compute an inter-domain path.
Hence the PCE discovery mechanism MUST allow discovering the path Hence the PCE discovery mechanism MUST allow discovering the path
computation scope of a PCE, i.e. if a PCE can be used to compute or computation scope of a PCE, i.e. if a PCE can be used to compute or
to take part in the computation of intra-area, inter-area or inter-AS to take part in the computation of intra-area, inter-area or inter-AS
TE-LSP. Note that these path computation scopes are not mutually TE-LSP. Note that these path computation scopes are not mutually
exclusive. exclusive.
Also the PCE discovery mechanism MUST allow discovering the set of Also the PCE discovery mechanism MUST allow discovering the set of
one or more domains under the path computation responsibility of a one or more domains under the path computation responsibility of a
PCE, i.e. where a PCE has visibility and can compute TE-LSP paths. PCE, i.e. where a PCE has visibility and can compute paths. These
These domains can be identified using a domain identifier: For domains can be identified using a domain identifier: For instance, an
instance, an IGP area can be identified by the Area ID (OSPF or IGP area can be identified by the Area ID (OSPF or ISIS), and an AS
ISIS), and an AS can be identified by the AS number. can be identified by the AS number.
It MUST also allow discovering the set of one or more domain(s)
towards which a PCE can compute paths.
6.1.3. Discovery of PCE Capabilities 6.1.3. Discovery of PCE Capabilities
In the case where there are several PCEs with distinct capabilities, In the case where there are several PCEs with distinct capabilities
available, a PCC has to select one or more appropriate PCEs. available, a PCC has to select one or more appropriate PCEs.
For that purpose the PCE discovery mechanism SHOULD allow the For that purpose the PCE discovery mechanism MAY be used so as to
discovery of some PCE capabilities. disclose some PCE capabilities.
For the sake of illustration this could include for instance some For the sake of illustration this could include for instance some
path computation related capabilities: path computation related capabilities:
-The capability to compute MPLS-TE and/or GMPLS paths; -The capability to compute MPLS-TE and/or GMPLS paths;
-The type of link and path constraints supported: e.g. -The type of link and path constraints supported: e.g.
bandwidth, affinities, delay; bandwidth, affinities, delay;
-The objective functions supported: e.g. shortest constrained -The objective functions supported: e.g. shortest constrained
path, shortest bounded delay path; path, shortest bounded delay path;
-The capability to compute multiple paths in a synchronized -The capability to compute multiple paths in a synchronized
manner: e.g. diverse path computation, load balancing manner: e.g. diverse path computation, load balancing
computation; computation;
-Some GMPLS specific capabilities: e.g. the supported interface -Some GMPLS specific capabilities: e.g. the supported interface
switching capabilities, the capability to compute multi-layer switching capabilities, the support for multi-layer
paths. path computation;
And this could also include some general capabilities: And this could also include some general capabilities:
-The capability to handle request prioritization; -The capability to handle request prioritization;
-The capability to authenticate PCCs and to be authenticated. -The capability to authenticate PCCs and to be authenticated.
Such information regarding PCE capabilities could then be used by a Such information regarding PCE capabilities could then be used by a
PCC to select an appropriate PCE from a list of candidate PCEs. PCC to select an appropriate PCE from a list of candidate PCEs.
Note that the description of general and path computation specific Note that the description of general and path computation specific
PCE capabilities is out of the scope of this document. It is expected PCE capabilities is out of the scope of this document. It is expected
that this will be described in a separate document. that this will be described in a separate document.
It is paramount that dynamic capability discovery MUST NOT generate It is paramount that dynamic discovery of PCE capabilities MUST NOT
an excessive amount of information and SHOULD be limited to a small generate an excessive amount of information and SHOULD be limited to
set of generic capabilities. a small set of generic capabilities.
If required, the exhaustive discovery of detailed capabilities could If required, the exhaustive discovery of detailed capabilities could
be ensured by means of the PCC-PCE communication protocol. be ensured by means of the PCC-PCE communication protocol.
Actually a tradeoff should be found between capability discovery by Actually a tradeoff should be found between capability discovery by
the PCE discovery mechanism and by the PCC-PCE communication the PCE discovery mechanism and by the PCC-PCE communication
protocol. One of the objectives of the PCE discovery mechanism is to protocol. One of the objectives of the PCE discovery mechanism is to
help PCCs to select appropriate PCEs and limit the likelihood of PCC- help PCCs to select appropriate PCEs and limit the likelihood of PCC-
PCE communication rejections that may occur in case a PCE cannot PCE communication rejections that may occur in case a PCE cannot
support a given capability. support a given capability.
6.1.4. Discovery of Alternate PCEs 6.1.4. Discovery of Alternate PCEs
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6.3. PCE Information Synchronization 6.3. PCE Information Synchronization
The PCE discovery mechanism MUST allow a PCC to detect any change in The PCE discovery mechanism MUST allow a PCC to detect any change in
the information related to a PCE (e.g. capability modifications). the information related to a PCE (e.g. capability modifications).
In addition it MUST be possible to dynamically detect new PCEs. In addition it MUST be possible to dynamically detect new PCEs.
The PCE Discovery Mechanism SHOULD allow such detection under 60 The PCE Discovery Mechanism SHOULD allow such detection under 60
seconds. seconds.
Note that PCE capabilities are expected to be fairly stable and not Note that PCE information is expected to be fairly stable and not to
to change frequently. change frequently.
6.4. Detecting PCE Liveliness 6.4. Detecting PCE Liveliness
The PCE discovery mechanism MUST allow a PCC to detect when a PCE is The PCE discovery mechanism MUST allow a PCC to detect when a PCE is
no longer alive. This allows a PCC to rapidly switch to another PCE no longer alive. This allows a PCC to rapidly switch to another PCE
(for instance a predefined alternate PCE), and thus minimizes path (for instance a predefined alternate PCE), and thus minimizes path
computation service disruption. computation service disruption.
The PCE discovery mechanism SHOULD allow such PCE liveliness The PCE discovery mechanism SHOULD allow such detection under 60
detection under 60 seconds. seconds.
6.5. Discovery of PCE capacity and congestion 6.5. Discovery of PCE capacity and congestion
PCE WG feedback is requested on the following items: PCE WG feedback is requested on the following items:
-Is there a need for the discovery of PCE capacity in terms of -Is there a need for the discovery of PCE capacity in terms of
computation power? This static parameter could be used to computation power? This static parameter could be used to
ensure weighted load balancing of requests in case PCEs do not ensure weighted load balancing of requests in case PCEs do not
have the same capacity. have the same capacity.
-Would it be useful that a PCE report its status as "congested" -May the PCE discovery mechanism be used so that a PCE report
in case it is too busy? PCCs may then use this dynamic its status as "congested" in case it is too busy? PCCs may then
information to prefer a different PCE. use this dynamic information to prefer a different PCE.
6.6. Extensibility 6.6. Security Requirements
The PCE Discovery mechanism MUST address security issues across
multiple ASes.
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 ore more trust model(s).
The PCE discovery mechanism MUST deliver the operational security
objectives where required. The overall security objectives of
privacy, authentication, and integrity may take on varying level of
importance. These objectives MAY be met by other established means
and protocols.
Particularly, mechanisms MUST be defined to ensure authentication,
integrity and privacy of PCE discovery information.
It MUST be possible to restrict the scope of discovery to a set of
authorized PCCs. In particular, the identity of any PCE MUST only be
learnt by authorized PCCs.
It MUST be possible for PCEs to authenticate PCCs and for PCCs to
authenticate PCEs. It MUST also be possible to encrypt discovery
information.
6.7. Extensibility
The PCE discovery mechanism MUST be flexible and extensible so as to The PCE discovery mechanism MUST be flexible and extensible so as to
easily allow for the addition of some additional PCE information that easily allow for the inclusion of some additional PCE information
could be defined in the future. that could be defined in the future.
6.7. Scalability 6.8. Scalability
The PCE discovery mechanism MUST be designed to scale well with an The PCE discovery mechanism MUST be designed to scale well with an
increase of any of the following parameters: increase of any of the following parameters:
-Number of PCCs; -Number of PCCs;
-Number of PCEs; -Number of PCEs;
-Number of IGP Areas in the discovery scope; -Number of IGP Areas in the discovery scope;
-Number of ASs in the discovery scope. -Number of ASs in the discovery scope.
Particularly, in case routing protocols (IGP, BGP) are extended to Particularly, in case routing protocols (IGP, BGP) are extended to
support PCE discovery, the extensions MUST NOT cause a degradation in support PCE discovery, the extensions MUST NOT cause a degradation in
routing protocol performance. The same applies to a signaling routing protocol performance. The same applies to a signaling
solution that could serve for this communication. solution that could serve for this discovery.
6.8. PCE Selection
A PCC may have to select among a set of candidate PCEs that have the
same capabilities. A specific PCE selection procedure SHOULD be
defined in order to ensure consistent behaviour when doing load
balancing and avoid that all PCCs send the requests to only one PCE.
The precise requirements and mechanisms for this function are out of
the scope of this document. It is expected that this requirement will
be covered in another document.
7. Security Considerations 7. Security Considerations
PCE discovery and particularly inter-AS PCE discovery may raise new This document is a requirement document and hence does not raise by
security issues. PCE discovery procedures or protocol extensions MUST itself any particular security issue.
deliver the operational security objectives where required. The
overall security objectives of confidentiality, integrity and
availability may take on varying level of importance. These
objectives MAY be met by other established means and protocols.
The PCE discovery mechanism MUST be able to restrict the scope of
discovery to a set of authorized PCCs. The identity of any PCE MUST
only be learnt by authorized PCCs. It MUST be possible to encrypt
discovery information.
Note that a threat analysis of the proposed procedures and/or A set of security requirements that MUST be addressed when
protocol extensions SHOULD address masquerade, eavesdropping, considering the design and deployment of a PCE Discovery mechanism
unauthorized access, loss or corruption of information (includes have been identified in section 6.6.
replay attacks), repudiation, forgery and denial of service attacks.
8. Acknowledgments 8. Acknowledgments
We would like to thank Benoit Fondeviole, Thomas Morin, Emile We would like to thank Benoit Fondeviole, Thomas Morin, Emile
Stephan, Jean-Philippe Vasseur, Dean Cheng and Mohamed Boucadair for Stephan, Jean-Philippe Vasseur, Dean Cheng, Adrian Farrel, Renhai
their useful comments and suggestions. Zhang, Mohamed Boucadair, Eric Gray, Igor Bryskin and Dimitri
Papadimitriou, for their useful comments and suggestions.
9. References 9. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC [RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3667, February 2004. 3667, February 2004.
[RFC3668] Bradner, S., "Intellectual Property Rights in IETF [RFC3668] Bradner, S., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004. Technology", BCP 79, RFC 3668, February 2004.
[PCE-ARCH] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation [PCE-ARCH] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE) Architecture", draft-ietf-pce-architecture-00.txt, work Element (PCE) Architecture", draft-ietf-pce-architecture, work in
in progress. progress.
[PCE-COM-REQ] Ash, J., Le Roux, J.L., " PCE Communication Protocol [PCE-COM-REQ] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs-00.txt, Generic Requirements", draft-ietf-pce-comm-protocol-gen-reqs, work in
work in progress. progress.
10. Authors' Addresses: 10. Authors' Addresses:
Jean-Louis Le Roux Jean-Louis Le Roux
France Telecom France Telecom
2, avenue Pierre-Marzin 2, avenue Pierre-Marzin
22307 Lannion Cedex 22307 Lannion Cedex
FRANCE FRANCE
Email: jeanlouis.leroux@francetelecom.com Email: jeanlouis.leroux@francetelecom.com
Paul Mabey Paul Mabey
Qwest Communications Qwest Communications
950 17th Street, 950 17th Street,
Denver, CO 80202, Denver, CO 80202,
USA USA
Email: pmabey@qwest.com Email: pmabey@qwest.com
Eiji Oki Eiji Oki
NTT NTT
Midori-cho 3-9-11 Midori-cho 3-9-11
 End of changes. 

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