draft-ietf-pce-inter-area-as-applicability-02.txt   draft-ietf-pce-inter-area-as-applicability-03.txt 
PCE Working Group D. King PCE Working Group D. King
Internet Draft Old Dog Consulting Internet Draft Old Dog Consulting
Intended status: Informational J. Meuric Intended status: Informational J. Meuric
Expires: June 16, 2012 O. Dugeon Expires: 25 August 2013 O. Dugeon
France Telecom France Telecom
Q. Zhao Q. Zhao
Huawei Technologies Huawei Technologies
Oscar Gonzalez de Dios Oscar Gonzalez de Dios
Francisco Javier Jimenex Chico
Telefonica I+D Telefonica I+D
January 16, 2012 25 February 2013
Applicability of the Path Computation Element to Inter-Area and Applicability of the Path Computation Element to Inter-Area and
Inter-AS MPLS and GMPLS Traffic Engineering Inter-AS MPLS and GMPLS Traffic Engineering
draft-ietf-pce-inter-area-as-applicability-02 draft-ietf-pce-inter-area-as-applicability-03
Abstract Abstract
The Path Computation Element (PCE) may be used for computing services The Path Computation Element (PCE) may be used for computing services
that traverse multi-area and multi-AS Multiprotocol Label Switching that traverse multi-area and multi-AS Multiprotocol Label Switching
(MPLS) and Generalized MPLS (GMPLS) Traffic Engineered (TE) networks. (MPLS) and Generalized MPLS (GMPLS) Traffic Engineered (TE) networks.
This document examines the applicability of the PCE architecture, This document examines the applicability of the PCE architecture,
protocols, and protocol extensions for computing multi-area and protocols, and protocol extensions for computing multi-area and
multi-AS paths in MPLS and GMPLS networks. multi-AS paths in MPLS and GMPLS networks.
skipping to change at page 1, line 50 skipping to change at page 1, line 49
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html http://www.ietf.org/shadow.html
This Internet-Draft will expire on October 18, 2012. This Internet-Draft will expire on July 22, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction.................................................3 1. Introduction.................................................3
1.1. Domains....................................................4 1.1. Domains.................................................4
1.2. Path Computation...........................................4 1.2. Path Computation........................................4
1.2.1 PCE-based Path Computation Procedure......................5 1.2.1 PCE-based Path Computation Procedure.................5
1.3. Traffic Engineering Aggregation and Abstraction............5 1.3. Traffic Engineering Aggregation and Abstraction.........5
1.4. Traffic Engineered Label Switched Paths....................6 1.4. Traffic Engineered Label Switched Paths.................6
1.5. Inter-area and Inter AS Connectivity Discovery.............6 1.5. Inter-area and Inter-AS Connectivity Discovery..........6
2. Terminology..................................................6 1.6. Objective Functions.....................................6
2. Terminology..................................................7
3. Issues and Considerations....................................7 3. Issues and Considerations....................................7
3.1 Multi-homing.............................................7 3.1 Multi-homing.............................................7
3.2 Domain Confidentiality ..................................7 3.2 Domain Confidentiality ..................................8
3.3 Destination Location.....................................7 3.3 Destination Location.....................................8
4. Domain Topologies............................................8 4. Domain Topologies............................................8
4.1 Selecting Domain Paths...................................8 4.1 Selecting Domain Paths...................................9
4.2 Multi-Homed Domains......................................8 4.2 Multi-Homed Domains......................................9
4.3 Domain Meshes............................................8 4.3 Domain Meshes............................................9
4.4 Domain Diversity.........................................8 4.4 Domain Diversity.........................................9
4.5 Synchronized Path Computations...........................9 4.5 Synchronized Path Computations...........................9
5. Applicability of the PCE to Inter-area Traffic Engineering...9 4.6 Domain Inclusion or Exclusion............................10
5.1. Inter-area Routing......................................10 5. Applicability of the PCE to Inter-area Traffic Engineering...10
5.1.1. Area Inclusion and Exclusion..........................10 5.1. Inter-area Routing......................................11
5.1.1. Area Inclusion and Exclusion..........................11
5.1.2. Strict Explicit Path and Loose Path...................11 5.1.2. Strict Explicit Path and Loose Path...................11
5.1.3. Inter-Area Diverse Path Computation...................11 5.1.3. Inter-Area Diverse Path Computation...................12
5.2. Control and Recording of Area Crossing..................11 5.2. Control and Recording of Area Crossing..................12
6. Applicability of the PCE to Inter-AS Traffic Engineering.....11 6. Applicability of the PCE to Inter-AS Traffic Engineering.....12
6.1. Inter-AS Routing........................................12 6.1. Inter-AS Routing........................................13
6.1.1. AS Inclusion and Exclusion............................12 6.1.1. AS Inclusion and Exclusion............................13
6.1.2. Strict Explicit Path and Loose Path...................12 6.1.2. Strict Explicit Path and Loose Path...................13
6.1.3. AS Inclusion and Exclusion............................12 6.1.3. AS Inclusion and Exclusion............................13
6.2. Inter-AS Bandwidth Guarantees...........................12 6.2. Inter-AS Bandwidth Guarantees...........................13
6.3. Inter-AS Recovery.......................................13 6.3. Inter-AS Recovery.......................................14
6.4. Inter-AS PCE Peering Policies...........................13 6.4. Inter-AS PCE Peering Policies...........................14
7. Multi-Domain PCE Deployment..................................14
7. Multi-Domain PCE Deployment..................................13
7.1 Traffic Engineering Database.............................14 7.1 Traffic Engineering Database.............................14
7.2 Provisioning Techniques..................................15 7.2 Provisioning Techniques..................................14
7.3 Pre-Planning and Management-Based Solutions..............15 7.3 Pre-Planning and Management-Based Solutions..............16
7.4 Per-Domain Computation...................................15 7.4 Per-Domain Computation...................................16
7.5 Cooperative PCEs.........................................15 7.5 Cooperative PCEs.........................................16
7.6 Hierarchical PCEs ......................................16 7.6 Hierarchical PCEs ......................................16
8. Domain Confidentiality.......................................16 8. Domain Confidentiality.......................................17
8.1 Loose Hops...............................................16 8.1 Loose Hops...............................................17
8.2 Confidential Path Segments and Path Keys.................16 8.2 Confidential Path Segments and Path Keys.................17
9. Point-to-Multipoint..........................................17 9. Point-to-Multipoint..........................................17
10. Optical Domains.............................................17 10. Optical Domains.............................................18
10.1. PCE applied to the ASON Architecture......................17 10.1. PCE applied to the ASON Architecture....................18
11. Manageability Considerations................................18 11. Policy......................................................19
12. Security Considerations.....................................18 12. TED Topology and Synchronization............................19
13. IANA Considerations.........................................18 12.1. Applicability of BGP-LS to PCE..........................20
14. References..................................................18 13. Manageability Considerations................................20
14.1. Normative References......................................18 13.1 Control of Function and Policy...........................20
14.2. Informative References....................................18 13.2 Information and Data Models..............................21
15. Acknowledgements............................................20 13.3 Liveness Detection and Monitoring........................21
16. Author's Address............................................20 13.4 Verifying Correct Operation..............................21
13.5 Impact on Network Operation..............................21
14. Security Considerations.....................................21
15. IANA Considerations.........................................22
16. Acknowledgements............................................22
17. References..................................................22
17.1. Normative References....................................22
17.2. Informative References..................................22
18. Author's Addresses..........................................25
1. Introduction 1. Introduction
Computing paths across large multi-domain environments may Computing paths across large multi-domain environments may
require special computational components and cooperation between require special computational components and cooperation between
entities in different domains capable of complex path computation. entities in different domains capable of complex path computation.
The Path Computation Element (PCE) [RFC4655] provides an architecture The Path Computation Element (PCE) [RFC4655] provides an architecture
and a set of functional components to address this problem space. and a set of functional components to address this problem space.
Computing optimal routes for LSPs that cross domains in MPLS-TE and
GMPLS networks presents a problem because no single point of path
computation is aware of all of the links and resources in each
domain. A solution may be achieved using the PCE architecture
[RFC4655].
A domain can be defined as a separate administrative, geographic, or
switching environment within the network. A domain may be further
defined as a zone of routing or computational ability. Under these
definitions a domain might be categorized as an Antonymous System
(AS) or an Interior Gateway Protocol (IGP) area ( as per [RFC4726]
and [RFC4655]).
A PCE may be used to compute end-to-end paths across multi-domain A PCE may be used to compute end-to-end paths across multi-domain
environments using a per-domain path computation technique [RFC5152]. environments using a per-domain path computation technique [RFC5152].
The so called backward recursive path computation (BRPC) mechanism The so called backward recursive path computation (BRPC) mechanism
[RFC5441] defines a PCE-based path computation procedure to compute [RFC5441] defines a PCE-based path computation procedure to compute
inter-domain constrained (G)MPLS TE LSPs. However, both per-domain inter-domain constrained Multiprotocol Label Switching (MPLS) and
and BRPC techniques assume that the sequence of domains to be crossed Generalized MPLS (GMPLS) Traffic Engineered (TE) networks. However,
from source to destination is known, either fixed by the network both per-domain and BRPC techniques assume that the sequence of
operator or obtained by other means. In more advanced deployments domains to be crossed from source to destination is known, either
(including multi-area and multi-AS environments) the sequence of fixed by the network operator or obtained by other means.
domains may not be known in advance and the choice of domains in the
end-to-end domain sequence might be critical to the determination of
an optimal end-to-end path
In this case the use of the Hierarchical PCE [H-PCE] architecture and In more advanced deployments (including multi-area and multi-AS
environments) the sequence of domains may not be known in advance
and the choice of domains in the end-to-end domain sequence might
be critical to the determination of an optimal end-to-end path. In
this case the use of the Hierarchical PCE [RFC6805] architecture and
mechanisms may be used to discovery the intra-area path and select mechanisms may be used to discovery the intra-area path and select
the optimal end-to-end domain sequence. the optimal end-to-end domain sequence.
This document examines the applicability and describes the processes This document describes the processes and procedures available when
and procedures available when using the PCE architecture, protocols using the PCE architecture, protocols and protocol extensions for
and protocol extensions for computing inter-area and inter-AS MPLS computing inter-area and inter-AS MPLS and GMPLS Traffic TE paths.
Traffic Engineered paths.
1.1 Domains 1.1 Domains
A domain can be defined as a separate administrative, geographic, or
switching environment within the network. A domain may be further
defined as a zone of routing or computational ability. Under these
definitions a domain might be categorized as an Antonymous System
(AS) or an Interior Gateway Protocol (IGP) area ( as per [RFC4726]
and [RFC4655]).
For the purposes of this document, a domain is considered to be a For the purposes of this document, a domain is considered to be a
collection of network elements within an area or AS that has a common collection of network elements within an area or AS that has a common
sphere of address management or path computational responsibility. sphere of address management or path computational responsibility.
Wholly or partially overlapping domains are not within the scope of Wholly or partially overlapping domains are not within the scope of
this document. this document.
In the context of GMPLS, a particularly important example of a domain In the context of GMPLS, a particularly important example of a domain
is the Automatically Switched Optical Network (ASON) subnetwork is the Automatically Switched Optical Network (ASON) subnetwork
[G-8080]. In this case, computation of an end-to-end path requires [G-8080]. In this case, computation of an end-to-end path requires
the selection of nodes and links within a parent domain where some the selection of nodes and links within a parent domain where some
nodes may, in fact, be subnetworks. Furthermore, a domain might be an nodes may, in fact, be subnetworks. Furthermore, a domain might be an
ASON routing area [G-7715]. A PCE may perform the path computation ASON routing area [G-7715]. A PCE may perform the path computation
function of an ASON routing controller as described in [G-7715-2]. function of an ASON routing controller as described in [G-7715-2].
It is assumed that the PCE architecture should be applied to small It is assumed that the PCE architecture should only be applied to
inter-domain topologies and not to solve route computation issues small inter-domain topologies and not to solve route computation
across large groups of domains, I.E. the entire Internet. issues across large groups of domains, i.e. the entire Internet.
1.2 Path Computation 1.2 Path Computation
For the purpose of this document it is assumed that the For the purpose of this document it is assumed that the
path computation is the sole responsibility of the PCE as per the path computation is the sole responsibility of the PCE as per the
architecture defined in [RFC4655]. When a path is required the Path architecture defined in [RFC4655]. When a path is required the Path
Computation Client (PCC) will send a request to the PCE. The PCE will Computation Client (PCC) will send a request to the PCE. The PCE will
apply the required constraints and compute a path and return a apply the required constraints and compute a path and return a
response to the PCC. In the context of this document it maybe response to the PCC. In the context of this document it maybe
necessary for the PCE to co-operate with other PCEs in adjacent necessary for the PCE to co-operate with other PCEs in adjacent
domains (as per BRPC [RFC5441]) or cooperate with the Parent PCE domains (as per BRPC [RFC5441]) or cooperate with a Parent PCE
(as per [H-PCE]). (as per [RFC6805]).
It is entirely feasible that an operator could compute a path across It is entirely feasible that an operator could compute a path across
multiple domains without the use of a PCE if the relevant domain multiple domains without the use of a PCE if the relevant domain
information is available to the network planner or network management information is available to the network planner or network management
platform. The definition of what relevant information is required to platform. The definition of what relevant information is required to
perform this network planning operation and how that information is perform this network planning operation and how that information is
discovered and applied is outside the scope of this document. discovered and applied is outside the scope of this document.
1.2.1 PCE-based Path Computation Procedure 1.2.1 PCE-based Path Computation Procedure
As discussed, the PCE is an entity capable of computing an As highlighted, the PCE is an entity capable of computing an
inter-domain TE path upon receiving a request from a PCC. There could inter-domain TE path upon receiving a request from a PCC. There could
be a single PCE per domain, or single PCE responsible for all be a single PCE per domain, or single PCE responsible for all
domains. A PCE may or may not reside on the same node as the domains. A PCE may or may not reside on the same node as the
requesting PCC. A path may be computed by either a single PCE node requesting PCC. A path may be computed by either a single PCE node
or a set of distributed PCE nodes that collaborate during path or a set of distributed PCE nodes that collaborate during path
computation. computation.
[RFC4655] defines that a PCC should send a path computation request [RFC4655] defines that a PCC should send a path computation request
to a particular PCE, using [RFC5440] (PCC-to-PCE communication). to a particular PCE, using [RFC5440] (PCC-to-PCE communication).
This negates the need to broadcast a request to all the PCEs. Each This negates the need to broadcast a request to all the PCEs. Each
PCC can maintain information about the computation capabilities PCC can maintain information about the computation capabilities
of the PCEs it is aware of. The PCC-PCE capability awareness can of the PCEs it is aware of. The PCC-PCE capability awareness can
configured using static configuration or by listening to configured using static configuration or by listening to the
the periodic advertisements generated by PCEs. periodic advertisements generated by PCEs.
One a path computation request is received, the PCC will send a Once a path computation request is received, the PCC will send a
request to the PCE. A PCE may compute the end-to-end path request to the PCE. A PCE may compute the end-to-end path
if it is aware of the topology and TE information required to if it is aware of the topology and TE information required to
compute the entire path. If the PCE is unable to compute the compute the entire path. If the PCE is unable to compute the
entire path, the PCE architecture provides co-operative PCE entire path, the PCE architecture provides co-operative PCE
mechanisms for the resolution of path computation requests when an mechanisms for the resolution of path computation requests when an
individual PCE does not have sufficient TE visibility. individual PCE does not have sufficient TE visibility.
A PCE may cooperate with other PCEs to determine intermediate loose A PCE may cooperate with other PCEs to determine intermediate loose
hops. End-to-end path segments may be kept confidential through the hops. End-to-end path segments may be kept confidential through the
application of path keys, to protect partial or full path application of path keys, to protect partial or full path
information. A path key that is a token that replaces a path segment information. A path key that is a token that replaces a path segment
in an explicit route. The path key mechanism is described in in an explicit route. The path key mechanism is described in
[RFC5520] [RFC5520]
1.3 Traffic Engineering Aggregation and Abstraction 1.3 Traffic Engineering Aggregation and Abstraction
Networks are often constructed from multiple areas or ASs that are Networks are often constructed from multiple areas or ASes that are
interconnected via multiple interconnect points. To maintain interconnected via multiple interconnect points. To maintain
network confidentiality and scalability TE properties of each area network confidentiality and scalability TE properties of each area
and AS are not generally advertized outside each specific area or AS. and AS are not generally advertized outside each specific area or AS.
TE aggregation or abstraction provide mechanism to hide information TE aggregation or abstraction provide mechanism to hide information
but may cause failed path setups or the selection of suboptimal but may cause failed path setups or the selection of suboptimal
end-to-end paths [RFC4726]. The aggregation process may also have end-to-end paths [RFC4726]. The aggregation process may also have
significant scaling issues for networks with many possible routes significant scaling issues for networks with many possible routes
and multiple TE metrics. Flooding TE information breaks and multiple TE metrics. Flooding TE information breaks
confidentiality and does not scale in the routing protocol. confidentiality and does not scale in the routing protocol.
The PCE architecture and associated mechanisms provide a solution The PCE architecture and associated mechanisms provide a solution
to avoid the use of TE aggregation and abstraction. to avoid the use of TE aggregation and abstraction.
1.4 Traffic Engineered Label Switched Paths 1.4 Traffic Engineered Label Switched Paths
This document highlights the PCE techniques and mechanisms that exist This document highlights the PCE techniques and mechanisms that exist
for establishing TE packet and optical LSPs across multiple areas for establishing TE packet and optical LSPs across multiple areas
(inter-area TE LSP) and ASs (inter-AS TE LSP). In this context and (inter-area TE LSP) and ASes (inter-AS TE LSP). In this context and
within the remainder of this document, we consider all LSPs to be within the remainder of this document, we consider all LSPs to be
constraint-based and traffic engineered. constraint-based and traffic engineered.
Three signaling options are defined for setting up an inter-area or Three signaling options are defined for setting up an inter-area or
inter-AS LSP [RFC4726]: inter-AS LSP [RFC4726]:
- Contiguous LSP - Contiguous LSP
- Stitched LSP - Stitched LSP
- Nested LSP - Nested LSP
All three signaling methods are applicable to the architectures and All three signaling methods are applicable to the architectures and
procedures discussed in this document. procedures discussed in this document.
1.5 Inter-area and Inter-AS Connectivity Discovery 1.5 Inter-area and Inter-AS Connectivity Discovery
When using a PCE-based approach for inter-area and inter-AS path When using a PCE-based approach for inter-area and inter-AS path
computation, a PCE in one area or AS may need to learn information computation, a PCE in one area or AS may need to learn information
related to inter-AS capable PCEs located in other ASs. The PCE related to inter-AS capable PCEs located in other ASes. The PCE
discovery mechanism defined in [RFC5088] and [RFC5089] allow discovery mechanism defined in [RFC5088] and [RFC5089] allow
the discovery of PCEs and disclosure of information related to the discovery of PCEs and disclosure of information related to
inter-area and inter-AS capable PCEs across area and AS boundaries. inter-area and inter-AS capable PCEs across area and AS boundaries.
1.6 Objective Functions
An Objective Function (OF) [RFC5541], or set of OFs, specify the
intentions of the path computation and so define the "optimality"
in the context of that computation request.
An OF specifies the desired outcome of a computation. An OF does not
describe or specify the algorithm to use, and an implementation may
apply any algorithm or set of algorithms to achieve the result
indicated by the OF. [RFC5541] provides the following OFs when
computing inter-domain paths:
o Minimum Cost Path (MCP);
o Minimum Load Path (MLP);
o Maximum residual Bandwidth Path (MBP);
o Minimize aggregate Bandwidth Consumption (MBC);
o Minimize the Load of the most loaded Link (MLL);
o Minimize the Cumulative Cost of a set of paths (MCC).
OFs can be included in the PCE computation requests to satisfy the
policies encoded or configured at the PCC, and a PCE may be
subject to policy in determining whether it meets the OFs included
in the computation request, or applies its own OFs.
During inter-domain path computation, the selection of a domain
sequence, the computation of each (per-domain) path fragment, and
the determination of the end-to-end path may each be subject to
different OFs and policy.
2. Terminology 2. Terminology
Terminology used in this document. This document also uses the terminology defined in [RFC4655] and
[RFC5440]. Additional terminology is defined below:
ABR: IGP Area Border Router, a router that is attached to more than ABR: IGP Area Border Router, a router that is attached to more than
one IGP area. one IGP area.
ASBR: Autonomous System Border Router, a router used to connect ASBR: Autonomous System Border Router, a router used to connect
together ASs of a different or the same Service Provider via one or together ASes of a different or the same Service Provider via one or
more inter-AS links. more inter-AS links.
CSPF: Constrained Shortest Path First. CSPF: Constrained Shortest Path First.
Inter-area TE LSP: A TE LSP whose path transits through two or more Inter-area TE LSP: A TE LSP whose path transits through two or more
IGP areas. IGP areas.
Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or
more ASs or sub-ASs (BGP confederations more ASes or sub-ASes (BGP confederations
SRLG: Shared Risk Link Group. SRLG: Shared Risk Link Group.
TED: Traffic Engineering Database, which contains the topology and TED: Traffic Engineering Database, which contains the topology and
resource information of the domain. The TED may be fed by Interior resource information of the domain. The TED may be fed by Interior
Gateway Protocol (IGP) extensions or potentially by other means. Gateway Protocol (IGP) extensions or potentially by other means.
This document also uses the terminology defined in [RFC4655] and
[RFC5440].
3. Issues and Considerations 3. Issues and Considerations
3.1 Multi-homing 3.1 Multi-homing
Networks constructed from multi-areas or multi-AS environments Networks constructed from multi-areas or multi-AS environments
may have multiple interconnect points (multi-homing). End-to-end path may have multiple interconnect points (multi-homing). End-to-end path
computations may need to use different interconnect points to avoid computations may need to use different interconnect points to avoid
single point failures disrupting primary and backup services. single point failures disrupting primary and backup services.
Domain and path diversity may also be required when computing Domain and path diversity may also be required when computing
skipping to change at page 8, line 11 skipping to change at page 8, line 40
information as part of the path computation request. However, information as part of the path computation request. However,
if the PCC does not know the egress domain this information must if the PCC does not know the egress domain this information must
be determined by another method. be determined by another method.
4. Domain Topologies 4. Domain Topologies
Constraint-based inter-domain path computation is a fundamental Constraint-based inter-domain path computation is a fundamental
requirement for operating traffic engineered MPLS [RFC3209] and requirement for operating traffic engineered MPLS [RFC3209] and
GMPLS [RFC3473] networks, in inter-area and inter-AS (multi-domain) GMPLS [RFC3473] networks, in inter-area and inter-AS (multi-domain)
environments. Path computation across multi-domain networks is environments. Path computation across multi-domain networks is
complex and requires computational cooperational entities like the complex and requires computational co-operational entities like the
PCE. PCE.
4.1 Selecting Domain Paths 4.1 Selecting Domain Paths
Where the sequence of domains is known a priori, various techniques Where the sequence of domains is known a priori, various techniques
can be employed to derive an optimal multi-domain path. If the can be employed to derive an optimal multi-domain path. If the
domains are simply-connected, or if the preferred points of domains are simply-connected, or if the preferred points of
interconnection are also known, the Per-Domain Path Computation interconnection are also known, the Per-Domain Path Computation
[RFC5152] technique can be used. Where there are multiple connections [RFC5152] technique can be used. Where there are multiple connections
between domains and there is no preference for the choice of points between domains and there is no preference for the choice of points
of interconnection, BRPC [RFC5441] can be used to derive an optimal of interconnection, BRPC [RFC5441] can be used to derive an optimal
path. path.
When the sequence of domains is not known in advance, the optimum When the sequence of domains is not known in advance, the optimum
end-to-end path can be derived through the use of a hierarchical end-to-end path can be derived through the use of a hierarchical
relationship between domains [H-PCE]. relationship between domains [RFC6805].
4.2 Multi-Homed Domains 4.2 Multi-Homed Domains
Networks constructed from multi-areas or multi-AS environments Networks constructed from multi-areas or multi-AS environments
may have multiple interconnect points (multi-homing). End-to-end path may have multiple interconnect points (multi-homing). End-to-end path
computations may need to use different interconnect points to avoid computations may need to use different interconnect points to avoid
single point failures disrupting primary and backup services. single point failures disrupting primary and backup services.
4.3 Domain Meshes 4.3 Domain Meshes
skipping to change at page 9, line 17 skipping to change at page 9, line 47
diversity, or by ensuring diverse connection within a domain. In diversity, or by ensuring diverse connection within a domain. In
order to compute the route diversity, it could be helpful to have order to compute the route diversity, it could be helpful to have
SRLG information in the domains. SRLG information in the domains.
4.5 Synchronized Path Computations 4.5 Synchronized Path Computations
In some scenarios, it would be beneficial for the operator to rely on In some scenarios, it would be beneficial for the operator to rely on
the capability of the PCE to perform synchronized path computation. the capability of the PCE to perform synchronized path computation.
Synchronized path computations, known as Synchronization VECtors Synchronized path computations, known as Synchronization VECtors
(SVECs) are used for dependent path computations. [RFC6007] provides (SVECs) are used for dependent path computations. SVECs are
an overview for the use of the PCE SVEC list for synchronized path defined in [RFC5440] and [RFC6007] provides an overview for the
computations when computing dependent requests. use of the PCE SVEC list for synchronized path computations when
computing dependent requests.
A non-comprehensive list of synchronized path computations include A non-comprehensive list of synchronized path computations include
the following examples: the following examples:
o Route diversity: computation of two disjoint paths from a source to o Route diversity: computation of two disjoint paths from a source to
a destination (as drafted in the previous section). a destination (as drafted in the previous section).
o Synchronous restoration: joint computation of a set of alternative o Synchronous restoration: joint computation of a set of alternative
paths for a set of affected LSPs as a consequence of a failure paths for a set of affected LSPs as a consequence of a failure
event. Note that in this case, the requests will potentially event. Note that in this case, the requests will potentially
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a synchronized path computation is needed. a synchronized path computation is needed.
o Network optimization: After some time of operation, the o Network optimization: After some time of operation, the
distribution of the established LSP paths results in a non optimal distribution of the established LSP paths results in a non optimal
use of resources. Also, inter-domain policies/agreements may have use of resources. Also, inter-domain policies/agreements may have
been changed. In such cases, a full (or partial) network planning been changed. In such cases, a full (or partial) network planning
action regarding the inter-domain connections will be triggered. action regarding the inter-domain connections will be triggered.
This will involve the request of potentially a big amount of This will involve the request of potentially a big amount of
connections. connections.
4.6 Domain Inclusion or Exclusion
A domain sequence is an ordered sequence of domains traversed to
reach the destination domain, a domain sequence may be supplied
during path computation to guide the PCEs or derived via use of
Hierarchical PCE (H-PCE).
During multi-domain path computation, a PCC may request
specific domains to be included or excluded in the domain sequence
using the Include Route Object (IRO) [RFC5440] and Exclude Route
Object (XRO) [RFC5521]. The use of Autonomous Number (AS) as an
abstract node representing a domain is defined in [RFC3209],
[DOMAIN-SEQ] specifies new sub-objects to include or exclude domains
such as an IGP area or an Autonomous Systems.
5. Applicability of the PCE to Inter-area Traffic Engineering 5. Applicability of the PCE to Inter-area Traffic Engineering
As networks increase in size and complexity it may be required to As networks increase in size and complexity it may be required to
introduce scaling methods to reduce the amount information flooded introduce scaling methods to reduce the amount information flooded
within the network and make the network more manageable. An IGP within the network and make the network more manageable. An IGP
hierarchy is designed to improve IGP scalability by dividing the hierarchy is designed to improve IGP scalability by dividing the
IGP domain into areas and limiting the flooding scope of topology IGP domain into areas and limiting the flooding scope of topology
information to within area boundaries. This restricts visibility of information to within area boundaries. This restricts visibility of
the area to routers in a single area. If a router needs to compute a the area to routers in a single area. If a router needs to compute a
route to destination located in another area a method is required to route to destination located in another area a method is required to
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path computation request, if a strict explicit path is required or path computation request, if a strict explicit path is required or
not. An inter-area path may be strictly explicit or loose (e.g., a not. An inter-area path may be strictly explicit or loose (e.g., a
list of ABRs as loose hops). list of ABRs as loose hops).
A PCC request to a PCE does allow the indication of if a strict A PCC request to a PCE does allow the indication of if a strict
explicit path across specific areas is required or desired, or if explicit path across specific areas is required or desired, or if
the path request is loose. the path request is loose.
5.1.3. Inter-Area Diverse Path Computation 5.1.3. Inter-Area Diverse Path Computation
It may be neccessary (for protection or load-balancing) to compute It may be necessary (for protection or load-balancing) to compute
a path that is diverse, from a previously computed path. There are a path that is diverse, from a previously computed path. There are
various levels of diversity in the context of an inter-area network: various levels of diversity in the context of an inter-area network:
- Per-area diversity (intra-area path segments are link, node or - Per-area diversity (intra-area path segments are link, node or
SRLG disjoint. SRLG disjoint.
- Inter-area diversity (end-to-end inter-area paths are link, - Inter-area diversity (end-to-end inter-area paths are link,
node or SRLG disjoint). node or SRLG disjoint).
Note that two paths may be disjoint in the backbone area but non- Note that two paths may be disjoint in the backbone area but non-
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5.2. Control and Recording of Area Crossing 5.2. Control and Recording of Area Crossing
In some environments it be useful for the PCE to provide a PCC the In some environments it be useful for the PCE to provide a PCC the
set of areas crossed by the end-to-end path. Additionally the PCE set of areas crossed by the end-to-end path. Additionally the PCE
can provide the path information and mark each segment so the PCC can provide the path information and mark each segment so the PCC
has visibility of which piece of the path lies within which area. has visibility of which piece of the path lies within which area.
Although by implementing Path-Key, the hop-by-hop (area topology) Although by implementing Path-Key, the hop-by-hop (area topology)
information is kept confidential. information is kept confidential.
6. Applicability of the PCE to Inter-AS Traffic Engineering 6. Applicability of the PCE to Inter-AS Traffic Engineering
As discussed in section 4 (Applicability of the PCE to Inter-area As discussed in section 4 (Applicability of the PCE to Inter-area
Traffic Engineering) it is necessary to divide the network into Traffic Engineering) it is necessary to divide the network into
smaller administrative domains, or ASs. If an LSR within an AS needs smaller administrative domains, or ASes. If an LSR within an AS needs
to compute a path across an AS boundary it must also use an inter-AS to compute a path across an AS boundary it must also use an inter-AS
computation technique. [RFC5152] defines mechanisms for the computation technique. [RFC5152] defines mechanisms for the
computation of inter-domain TE LSPs using network elements along the computation of inter-domain TE LSPs using network elements along the
signaling paths to compute per-domain constrained path segments. signaling paths to compute per-domain constrained path segments.
The PCE was designed to be capable of computing MPLS and GMPLS paths The PCE was designed to be capable of computing MPLS and GMPLS paths
across AS boundaries. This section outlines the features of a across AS boundaries. This section outlines the features of a
PCE-enabled solution for computing inter-AS paths. PCE-enabled solution for computing inter-AS paths.
6.1 Inter-AS Routing 6.1 Inter-AS Routing
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or exclude from the inter-AS path computation. or exclude from the inter-AS path computation.
6.1.2. Strict Explicit Path and Loose Path 6.1.2. Strict Explicit Path and Loose Path
During path computation, the PCE architecture and BRPC algorithm During path computation, the PCE architecture and BRPC algorithm
allow operators to specify if the resultant LSP must follow a strict allow operators to specify if the resultant LSP must follow a strict
or a loose path. By explicitly specify the path, the operator or a loose path. By explicitly specify the path, the operator
request a strict explicit path which must pass through one or many request a strict explicit path which must pass through one or many
LSR. If this behaviour is well define and appropriate for inter-area, LSR. If this behaviour is well define and appropriate for inter-area,
it implies some topology discovery for inter-AS. So, this feature it implies some topology discovery for inter-AS. So, this feature
when the operator owns several ASs (and so, knows the topology of when the operator owns several ASes (and so, knows the topology of
its ASs) or restricts to the well-known ASBR to avoid topology its ASes) or restricts to the well-known ASBR to avoid topology
discovery between operators. The loose path, even if it does not discovery between operators. The loose path, even if it does not
allow granular specification of the path, protects topology allow granular specification of the path, protects topology
disclosure as it not obligatory for the operator to disclose disclosure as it not obligatory for the operator to disclose
information about its networks. information about its networks.
6.1.3. AS Inclusion and Exclusion 6.1.3. AS Inclusion and Exclusion
Like explicit and loose path, [RFC5441] allows to specify inclusion Like explicit and loose path, [RFC5441] allows to specify inclusion
or exclusion of respectively an AS or an ASBR. Using this method, or exclusion of respectively an AS or an ASBR. Using this method,
an operator might decide if an AS must be include or exclude from an operator might decide if an AS must be include or exclude from
the inter-AS path computation. Exclusion and/or inclusion could also the inter-AS path computation. Exclusion and/or inclusion could also
be specified at any step in the LSP path computation process by a PCE be specified at any step in the LSP path computation process by a PCE
(within the BRPC algorithm) but the best practice would be to specify (within the BRPC algorithm) but the best practice would be to specify
them at the edge. In opposition to the strict and loose path, AS them at the edge. In opposition to the strict and loose path, AS
inclusion or exclusion doesn't impose topology disclosure as ASs are inclusion or exclusion doesn't impose topology disclosure as ASes are
public entity as well as their interconnection. public entity as well as their interconnection.
6.2 Inter-AS Bandwidth Guarantees 6.2 Inter-AS Bandwidth Guarantees
Many operators with multi-AS domains will have deployed MPLS-TE Many operators with multi-AS domains will have deployed MPLS-TE
DiffServ either across their entire network or at the domain DiffServ either across their entire network or at the domain edges
edges on CE-PE links. In situations where strict QOS bounds are on CE-PE links. In situations where strict QOS bounds are required,
required, admission control inside the network may also be required. admission control inside the network may also be required.
When the propagation delay can be bounded, the performance targets, When the propagation delay can be bounded, the performance targets,
such as maximum one-way transit delay may be guaranteed by providing such as maximum one-way transit delay may be guaranteed by providing
bandwidth guarantees along the DiffServ-enabled path. bandwidth guarantees along the DiffServ-enabled path.
One typical example of this requirement is to provide bandwidth One typical example of this requirement is to provide bandwidth
guarantees over an end-to-end path for VoIP traffic classified as EF guarantees over an end-to-end path for VoIP traffic classified as EF
(Expedited Forwarding) class in a Diffserv-enabled (Expedited Forwarding) class in a DiffServ-enabled
network. In the case where the EF path is extended across multiple network. In the case where the EF path is extended across multiple
ASs, inter-AS bandwidth guarantee would be required. ASes, inter-AS bandwidth guarantee would be required.
Another case for inter-AS bandwidth guarantee is the requirement for Another case for inter-AS bandwidth guarantee is the requirement for
guaranteeing a certain amount of transit bandwidth across one or guaranteeing a certain amount of transit bandwidth across one or
multiple ASs. multiple ASes.
6.3 Inter-AS Recovery 6.3 Inter-AS Recovery
During path computation, a PCC request may contain backup LSP During path computation, a PCC request may contain backup LSP
requirements in order to setup in the same time the primary and requirements in order to setup in the same time the primary and
backup LSPs. It is also possible to request a backup LSP for a group backup LSPs. It is also possible to request a backup LSP for a group
of primary LSPs. [RFC4090] adds fast re-route protection to LSP. So, of primary LSPs. [RFC4090] adds fast re-route protection to LSP. So,
the PCE could be used to trigger computation of backup tunnels in the PCE could be used to trigger computation of backup tunnels in
order to protect Inter-AS connectivity. Inter-AS recovery order to protect Inter-AS connectivity. Inter-AS recovery
requirements needs not only PCE protection and redundancy but also requirements needs not only PCE protection and redundancy but also
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constraints. The PCE will generate the full set of strict hops from constraints. The PCE will generate the full set of strict hops from
source to destination. This information, encoded as an ERO, is then source to destination. This information, encoded as an ERO, is then
sent back to the PCC that requested the path. In the event that a sent back to the PCC that requested the path. In the event that a
path request from a PCC contains source and destination nodes that path request from a PCC contains source and destination nodes that
are located in different domains the PCE is required to co-operate are located in different domains the PCE is required to co-operate
between multiple PCEs, each responsible for its own domain. between multiple PCEs, each responsible for its own domain.
Techniques for inter-domain path computation are described in Techniques for inter-domain path computation are described in
[RFC5152] and [RFC5441], both techniques assume that the sequence of [RFC5152] and [RFC5441], both techniques assume that the sequence of
domains to be crossed from source to destination is well known. In domains to be crossed from source to destination is well known. In
the event that the sequence of domains is not well known, [H-PCE] the event that the sequence of domains is not well known, [RFC6805]
might be used. The sequence could also be retrieve locally from might be used. The sequence could also be retrieve locally from
information previously stored in the PCE database (preferably in information previously stored in the PCE database (preferably in
the TED) by OSS management or other protocols. the TED) by OSS management or other protocols.
7.1 Traffic Engineering Database 7.1 Traffic Engineering Database
TEDs are automatically populated by the IGP-TE like IS-IS-TE or TEDs are automatically populated by the IGP-TE like IS-IS-TE or
OSPF-TE. However, no information related to AS path are provided OSPF-TE. However, no information related to AS path are provided
by such IGP-TE. It could be helpful for BRPC algorithm as AS path by such IGP-TE. It could be helpful for BRPC algorithm as AS path
helper, to populate a TED with suitable information regarding helper, to populate a TED with suitable information regarding
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is possible to populate TED information by means of provisioning. In is possible to populate TED information by means of provisioning. In
this case, the operator must regularly update and store all suitable this case, the operator must regularly update and store all suitable
information in the TED in order for the PCE to correctly compute LSP. information in the TED in order for the PCE to correctly compute LSP.
Such information range from policies (e.g. avoid this LSR, or use Such information range from policies (e.g. avoid this LSR, or use
this ASBR for a specific IP prefix) up to topology information (e.g. this ASBR for a specific IP prefix) up to topology information (e.g.
AS X is reachable trough a 100 Mbit/s link on this ASBR and 30 Mbit/s AS X is reachable trough a 100 Mbit/s link on this ASBR and 30 Mbit/s
are reserved for EF traffic). Operators may choose the type and are reserved for EF traffic). Operators may choose the type and
amount of information they can use to manage their traffic engineered amount of information they can use to manage their traffic engineered
network. network.
However, some LSPs might be provisioned to link ASs or areas. In this However, some LSPs might be provisioned to link ASes or areas. In
case, these LSP must be announced by the IGP-TE in order to this case, these LSP must be announced by the IGP-TE in order to
automatically populate the TED. automatically populate the TED.
7.3 Pre-Planning and Management-Based Solutions 7.3 Pre-Planning and Management-Based Solutions
Offline path computation is performed ahead of time, before the LSP Offline path computation is performed ahead of time, before the LSP
setup is requested. That means that it is requested by, or performed setup is requested. That means that it is requested by, or performed
as part of, a management application. This model can be seen in as part of, a management application. This model can be seen in
Section 5.5 of [RFC4655]. Section 5.5 of [RFC4655].
The offline model is particularly appropriate to long-lived LSPs The offline model is particularly appropriate to long-lived LSPs
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with the BRPC algorithm. Operator just computes the AS-Path as with the BRPC algorithm. Operator just computes the AS-Path as
parameter for the inter-AS path computation request and let each parameter for the inter-AS path computation request and let each
PCE along the AS path compute the LSP part on its own domain. PCE along the AS path compute the LSP part on its own domain.
7.4 Per-Domain Computation 7.4 Per-Domain Computation
[RFC5152] defines the mechanism to compute per-domain path and must [RFC5152] defines the mechanism to compute per-domain path and must
be used in that condition. Otherwise, BRPC [RFC5441] will be used. be used in that condition. Otherwise, BRPC [RFC5441] will be used.
7.5 Cooperative PCEs 7.5 Cooperative PCEs
When PCE cooperate to compute an inter-area or inter-AS LSP, both When PCE cooperate to compute an inter-area or inter-AS LSP, both
[RFC5152] and [RFC5441] could be used. [RFC5152] and [RFC5441] could be used.
7.6 Hierarchical PCEs 7.6 Hierarchical PCEs
The [H-PCE] draft defines how a hierarchy of PCEs may be used. An The [RFC6805] draft defines how a hierarchy of PCEs may be used. An
operator must define a parent PCE and each child PCE. A parent PCE operator must define a parent PCE and each child PCE. A parent PCE
can be announced in the other areas or ASs in order for the parent can be announced in the other areas or ASes in order for the parent
PCE to contact remote child PCEs. Reciprocally, child PCEs are PCE to contact remote child PCEs. Reciprocally, child PCEs are
announced in remote areas or ASs in order to be contacted by a announced in remote areas or ASes in order to be contacted by a
remote parent PCE. Parent and each child PCE could also be remote parent PCE. Parent and each child PCE could also be
provisioned in the TED if they are not announced. provisioned in the TED if they are not announced.
8. Domain Confidentiality 8. Domain Confidentiality
Confidentiality typically applies to inter-provider (inter-AS) PCE Confidentiality typically applies to inter-provider (inter-AS) PCE
communication. Where the TE LSP crosses multiple domains (ASes or communication. Where the TE LSP crosses multiple domains (ASes or
areas), the path may be computed by multiple PCEs that cooperate areas), the path may be computed by multiple PCEs that cooperate
together. With each local PCE responsible for computing a segment together. With each local PCE responsible for computing a segment
of the path. However, in some cases (e.g., when ASes are of the path. However, in some cases (e.g., when ASes are
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[RFC5440] supports the use of paths with loose hops, and it is a [RFC5440] supports the use of paths with loose hops, and it is a
local policy decision at a PCE whether it returns a full explicit local policy decision at a PCE whether it returns a full explicit
path with strict hops or uses loose hops. A path computation path with strict hops or uses loose hops. A path computation
request may request an explicit path with strict hops, or request may request an explicit path with strict hops, or
may allow loose hops as detailed in [RFC5440]. may allow loose hops as detailed in [RFC5440].
8.2 Confidential Path Segments and Path Keys 8.2 Confidential Path Segments and Path Keys
[RFC5520] defines the concept and mechanism of Path-Key. A Path-Key [RFC5520] defines the concept and mechanism of Path-Key. A Path-Key
is a token that replaces the path segment information in an explicit is a token that replaces the path segment information in an explicit
route. The Path-Key allows the explicit route enformation to be route. The Path-Key allows the explicit route information to be
encoded and in the PCEP ([RFC5440]) messages exchanged between the encoded and in the PCEP ([RFC5440]) messages exchanged between the
PCE and PCC. PCE and PCC.
This Path-Key technique allows explicit route information to used This Path-Key technique allows explicit route information to used
for end-to-end path computation, without disclosing internal topology for end-to-end path computation, without disclosing internal topology
information between domains. information between domains.
9. Point-to-Multipoint 9. Point-to-Multipoint
For the Point-to-Multipoint application scenarios for MPLS-TE LSP, For the Point-to-Multipoint application scenarios for MPLS-TE LSP,
the complexity of domain sequences, domain policies, choice and the complexity of domain sequences, domain policies, choice and
number of domain interconnects is magnified comparing to number of domain interconnects is magnified comparing to P2P path
P2P path computations. Also as the size of the network grows, computations. Also as the size of the network grows, the number of
the number of leaves and branches increase and it in turn puts the leaves and branches increase and it in turn puts the scalability of
scalability of the path computation and optimization into a bigger the path computation and optimization into a bigger issue. A
issue. A solution for the point-to-multipoint path computations may solution for the point-to-multipoint path computations may be
be achieved using the PCEP protocol extension for P2MP achieved using the PCEP protocol extension for P2MP [RFC6006] and
[RFC6006] and using the PCEP P2MP procedures defined in using the PCEP P2MP procedures defined in [PCEP-P2MP-INTER-DOMAIN].
[PCEP-P2MP-INTER-DOMAIN].
10. Optical Domains 10. Optical Domains
The International Telecommunications Union (ITU) defines the ASON The International Telecommunications Union (ITU) defines the ASON
architecture in [G-8080]. [G-7715] defines the routing architecture architecture in [G-8080]. [G-7715] defines the routing architecture
for ASON and introduces a hierarchical architecture. In this for ASON and introduces a hierarchical architecture. In this
architecture, the Routing Areas (RAs) have a hierarchical architecture, the Routing Areas (RAs) have a hierarchical
relationship between different routing levels, which means a parent relationship between different routing levels, which means a parent
(or higher level) RA can contain multiple child RAs. The (or higher level) RA can contain multiple child RAs. The
interconnectivity of the lower RAs is visible to the higher level RA. interconnectivity of the lower RAs is visible to the higher level RA.
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o Route query responder. An RC that performs path computation upon o Route query responder. An RC that performs path computation upon
reception of a route query message from a routing controller or reception of a route query message from a routing controller or
connection controller, sending a response back at the end of connection controller, sending a response back at the end of
computation. computation.
When computing an end-to-end connection, the route may be computed by When computing an end-to-end connection, the route may be computed by
a single RC or multiple RCs in a collaborative manner and the two a single RC or multiple RCs in a collaborative manner and the two
scenarios can be considered a centralized remote route query model scenarios can be considered a centralized remote route query model
and distributed remote route query model. RCs in an ASON environment and distributed remote route query model. RCs in an ASON environment
can also use the hierarchical PCE [H-PCE] model to fully match the can also use the hierarchical PCE [RFC6805] model to fully match the
ASON hierarchical routing model. ASON hierarchical routing model.
11. Manageability Considerations 11. Policy
This document does not describe any specific protocol, Policy is important in the deployment of new services and the
protocol extensions, or protocol usage, therefore no manageability operation of the network. [RFC5394] provides a framework for PCE-
considerations need to be discussed here. based policy-enabled path computation. This framework is based on
the Policy Core Information Model (PCIM) as defined in [RFC3060] and
further extended by [RFC3460].
12. Security Considerations When using a PCE to compute inter-domain paths, policy may be
invoked by specifying:
This document is informational and does not describe any new - Each PCC must select which computations will be delegated to a PCE;
specific protocol, protocol extensions, or protocol usage. As such,
it introduces no new security concerns.
13. IANA Considerations - Each PCC must select which PCEs it will use;
- Each PCE must determine which PCCs are allowed to use its services
and for what computations;
- The PCE must determine how to collect the information in its TED,
who to trust for that information, and how to refresh/update the
information;
- Each PCE must determine which objective functions and which
algorithms to apply.
Finally, due to the nature of inter-domain (and particularly using
H-PCE based) path computations, deployment of policy should also
consider the need to be sensitive to commercial and reliability
information about domains and the interactions of services crossing
domains.
12. TED Topology and Synchronization
The PCE operates on a view of the network topology as presented by a
Traffic Engineering Database. As discussed in [RFC4655] the TED
used by a PCE may be learnt by the relevant IGP extensions.
Thus, the PCE may operate its TED is by participating
in the IGP running in the network. In an MPLS-TE network, this
would require OSPF-TE [RFC3630] or ISIS-TE [RFC5305]. In a GMPLS
network it would utilize the GMPLS extensions to OSPF and IS-IS
defined in [RFC4203] and [RFC5307].
An alternative method to provide network topology and resource
information is offered by [BGP-LS], which is described in the
following section.
12.1 Applicability of BGP-LS to PCE
The concept of exchange of TE information between Autonomous Systems
(ASes) is discussed in [BGP-LS]. The information exchanged in this
way could be the full TE information from the AS, an aggregation of
that information, or a representation of the potential connectivity
across the AS. Furthermore, that information could be updated
frequently (for example, for every new LSP that is set up across the
AS) or only at threshold-crossing events.
There are a number of discussion points associated with the use of
[BGP-LS] concerning the volume of information, the rate of churn of
information, the confidentiality of information, the accuracy of
aggregated or potential-connectivity information, and the processing
required to generate aggregated information. The PCE architecture and
the architecture enabled by [BGP-LS] make different assumptions about
the operational objectives of the networks, and this document does
not attempt to make one of the approaches "right" and the other
"wrong". Instead, this work assumes that a decision has been made to
utilize the PCE architecture.
Indeed, [BGP-LS] may have some uses within the PCE model. For
example, [BGP-LS] could be used as a "northbound" TE advertisement
such that a PCE does not need to listen to an IGP in its domain, but
has its TED populated by messages received (for example) from a
Route Reflector. Furthermore, the inter-domain connectivity and
connectivity capabilities that is required optional information for
a parent PCE could be obtained as a filtered subset of the
information available in [BGP-LS].
13. Manageability Considerations
General PCE management considerations are discussed in [RFC4655].
In the case of multi-domains within a single service provider
network, the management responsibility for each PCE would most
likely be handled by the same service provider. In the case of
multiple ASes within different service provider networks, it will
likely be necessary for each PCE to be configured and managed
separately by each participating service provider, with policy
being implemented based on an a previously agreed set of principles.
13.1 Control of Function and Policy
As per PCEP [RFC5440] implementation allow the user to configure
a number of PCEP session parameters. These are detailed in section
8.1 of [RFC5440] and will not be repeated here.
13.2 Information and Data Models
A PCEP MIB module is defined in [PCEP-MIB] that describes managed
objects for modeling of PCEP communication including:
o PCEP client configuration and status,
o PCEP peer configuration and information,
o PCEP session configuration and information,
o Notifications to indicate PCEP session changes.
13.3 Liveness Detection and Monitoring
PCEP includes a keepalive mechanism to check the liveliness of a PCEP
peer and a notification procedure allowing a PCE to advertise its
overloaded state to a PCC. In a multi-domain environment [RFC5886]
provides the procedures necessary to monitor the liveliness and
performances of a given PCE chain.
13.4 Verifying Correct Operation
In order to verify the correct operation of PCEP, [RFC5440] specifies
the monitoring of key parameters. These parameters are detailed in
section 8.4 of [RFC5440] and will not be repeated here.
13.5 Impact on Network Operation
[RFC5440] states that in order to avoid any unacceptable impact on
network operations, a PCEP implementation should allow a limit to be
placed on the number of sessions that can be set up on a PCEP
speaker, it may also be practical to place a limit on the rate
of messages sent by a PCC and received my the PCE.
14. Security Considerations
PCEP security is defined [RFC5440]. Any multi-domain operation
necessarily involves the exchange of information across domain
boundaries. This does represent a significant security and
confidentiality risk. PCEP allows individual PCEs to maintain
confidentiality of their domain path information using path-keys
[RFC5520].
For further considerations of the security issues related to inter-
domain path computation, see [RFC5376].
15. IANA Considerations
This document makes no requests for IANA action. This document makes no requests for IANA action.
13. References 16. Acknowledgements
14.1. Normative References The author would like to thank Adrian Farrel for his review, and
Meral Shirazipour and Francisco Javier Jimenex Chico for their
comments.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 17. References
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5440] Ayyangar, A., Farrel, A., Oki, E., Atlas, A., Dolganow, 17.1. Normative References
A., Ikejiri, Y., Kumaki, K., Vasseur, J., and J. Roux,
"Path Computation Element (PCE) Communication Protocol
(PCEP)", RFC 5440, March 2009.
14.2. Informative References 17.2. Informative References
[RFC3060] Moore, B., Ellesson, E., Strassner, J., and A.
Westerinen, "Policy Core Information Model -- Version 1
Specification", RFC 3060, February 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001. Tunnels", RFC 3209, December 2001.
[RFC3460] Moore, B., Ed., "Policy Core Information Model (PCIM)
Extensions", RFC 3460, January 2003.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003. 3473, January 2003.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic
Engineering (TE) Extensions to OSPF Version 2", RFC
3630, September 2003.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute [RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May
2005. 2005.
[RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF
Extensions in Support of Generalized Multi-
Protocol Label Switching (GMPLS)", RFC
4203, October 2005.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework [RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework
for Inter-Domain Multiprotocol Label Switching Traffic for Inter-Domain Multiprotocol Label Switching Traffic
Engineering", RFC 4726, November 2006. Engineering", RFC 4726, November 2006.
[RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang, [RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"OSPF Protocol Extensions for Path Computation Element "OSPF Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5088, January 2008. (PCE) Discovery", RFC 5088, January 2008.
[RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R. [RFC5089] Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
Zhang, "IS-IS Protocol Extensions for Path Computation Zhang, "IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, January 2008. Element (PCE) Discovery", RFC 5089, January 2008.
[RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain [RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
Path Computation Method for Establishing Inter-Domain Path Computation Method for Establishing Inter-Domain
Traffic Engineering (TE) Label Switched Paths (LSPs)", Traffic Engineering (TE) Label Switched Paths (LSPs)",
RFC 5152, February 2008. RFC 5152, February 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS
Extensions in Support of Generalized Multi-Protocol
Label Switching (GMPLS)", RFC 5307,
October 2008.
[RFC5376] Bitar, N., et al., "Inter-AS Requirements for the Path
Computation Element Communication Protocol (PCECP)", RFC
5376, November 2008.
[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
"Policy-Enabled Path Computation Framework", RFC 5394,
December 2008.
[RFC5440] Ayyangar, A., Farrel, A., Oki, E., Atlas, A., Dolganow,
A., Ikejiri, Y., Kumaki, K., Vasseur, J., and J. Roux,
"Path Computation Element (PCE) Communication Protocol
(PCEP)", RFC 5440, March 2009.
[RFC5441] Vasseur, J.P., Ed., "A Backward Recursive PCE-based [RFC5441] Vasseur, J.P., Ed., "A Backward Recursive PCE-based
Computation (BRPC) procedure to compute shortest inter- Computation (BRPC) procedure to compute shortest inter-
domain Traffic Engineering Label Switched Paths", domain Traffic Engineering Label Switched Paths",
RFC5441, April 2009. RFC5441, April 2009.
[RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel, [RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel,
"Preserving Topology Confidentiality in Inter-Domain Path "Preserving Topology Confidentiality in Inter-Domain Path
Computation Using a Path-Key-Based Mechanism", RFC 5520, Computation Using a Path-Key-Based Mechanism", RFC 5520,
April 2009. April 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, J., Vasseur, J., Lee, Y., "Encoding
of Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC5541, December 2008.
[RFC5886] Vasseur, JP., Le Roux, JL., and Y. Ikejiri, "A Set of
Monitoring Tools for Path ComputationElement (PCE)-Based
Architecture", RFC 5886, June 2010.
[RFC6006] Takeda, T., Chaitou M., Le Roux, J.L., Ali Z., [RFC6006] Takeda, T., Chaitou M., Le Roux, J.L., Ali Z.,
Zhao, Q., King, D., "Extensions to the Path Computation Zhao, Q., King, D., "Extensions to the Path Computation
Element Communication Protocol (PCEP) for Element Communication Protocol (PCEP) for
Point-to-Multipoint Traffic Engineering Label Switched Point-to-Multipoint Traffic Engineering Label Switched
Paths", RFC6006, September 2010. Paths", RFC6006, September 2010.
[RFC6007] Nishioka, I., King, D., "Use of the Synchronization [RFC6007] Nishioka, I., King, D., "Use of the Synchronization
VECtor (SVEC) List for Synchronized Dependent Path VECtor (SVEC) List for Synchronized Dependent Path
Computations", RFC6007, September 2010. Computations", RFC6007, September 2010.
[G-8080] ITU-T Recommendation G.8080/Y.1304, Architecture for [G-8080] ITU-T Recommendation G.8080/Y.1304, Architecture for
the automatically switched optical network (ASON). the automatically switched optical network (ASON).
[G-7715] ITU-T Recommendation G.7715 (2002), Architecture [G-7715] ITU-T Recommendation G.7715 (2002), Architecture
and Requirements for the Automatically Switched and Requirements for the Automatically Switched
Optical Network (ASON). Optical Network (ASON).
[G-7715-2] ITU-T Recommendation G.7715.2 (2007), ASON routing [G-7715-2] ITU-T Recommendation G.7715.2 (2007), ASON routing
architecture and requirements for remote route query. architecture and requirements for remote route query.
[PCEP-P2MP-INTER-DOMAIN] Ali Z., Zhao, Q., King, D., "PCE-based [RFC6805] King, D. and A. Farrel, "The Application of the Path
Computation Procedure To Compute Shortest Constrained Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS & GMPLS", RFC6805, July
2010.
[PCEP-P2MP-INTER-DOMAIN] Zhao, Q., Dhody, D., Ali Z., King, D.,
Casellas, R., "PCE-based Computation
Procedure To Compute Shortest Constrained
P2MP Inter-domain Traffic Engineering Label Switched P2MP Inter-domain Traffic Engineering Label Switched
Paths", Paths", work in progress.
draft-zhao-pce-pcep-inter-domain-p2mp-procedures-07.txt,
work in progress, Januaury, 2011.
[H-PCE] King, D. and A. Farrel, "The Application of the Path [BGP-LS] Gredler, H., Medved, J., Previdi, S., Farrel, A., and
Computation Element Architecture to the Determination S. Ray, "North-Bound Distribution of Link-State and TE
of a Sequence of Domains in MPLS & GMPLS", July Information using BGP", work in progress.
2010.
15. Acknowledgements [PCEP-MIB] Stephan, E., Koushik, K., Zhao, Q., King, D., "PCE
Communication Protocol (PCEP) Management Information
Base", work in progress.
The author would like to thank Adrian Farrel for his review and [DOMAIN-SEQ] Dhody, D., Palle, U., and R. Casellas, "Standard
Meral Shirazipour for his comments. Representation Of Domain Sequence", work in progress.
16. Author's Address 18. Author's Addresses
Daniel King Daniel King
Old Dog Consulting Old Dog Consulting
UK UK
Email: daniel@olddog.co.uk
EMail: daniel@olddog.co.uk
Julien Meuric Julien Meuric
France Telecom France Telecom
2, avenue Pierre-Marzin 2, avenue Pierre-Marzin
22307 Lannion Cedex 22307 Lannion Cedex
Email: julien.meuric@orange-ftgroup.com
EMail: julien.meuric@orange-ftgroup.com
Olivier Dugeon Olivier Dugeon
France Telecom France Telecom
2, avenue Pierre-Marzin 2, avenue Pierre-Marzin
22307 Lannion Cedex 22307 Lannion Cedex
Email: olivier.dugeon@orange-ftgroup.com
EMail: olivier.dugeon@orange-ftgroup.com
Quintin Zhao Quintin Zhao
Huawei Technology Huawei Technology
125 Nagog Technology Park 125 Nagog Technology Park
Acton, MA 01719 Acton, MA 01719
US US
Email: qzhao@huawei.com
EMail: qzhao@huawei.com
Oscar Gonzalez de Dios Oscar Gonzalez de Dios
Telefonica I+D Telefonica I+D
Emilio Vargas 6, Madrid Emilio Vargas 6, Madrid
Spain Spain
Email: ogondio@tid.es
Francisco Javier Jimenex Chico EMail: ogondio@tid.es
Telefonica I+D
Emilio Vargas 6, Madrid
Spain
Email: fjjc@tid.es
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