Internet Engineering Task Force H. Chen
Internet-Draft Huawei Technologies
Intended status: Standards Track March 5, 2012
Expires: September 6, 2012
The Applicability of the PCE to Computing Protection and Recovery Paths
for Single Domain and Multi-Domain Networks
draft-chen-pce-protection-applicability-00.txt
Abstract
The Path Computation Element (PCE) provides path computation
functions in support of traffic engineering in Multiprotocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) networks.
A link or node failure can significantly impact network services in
large-scale networks. Therefore it is important to ensure the
survivability of large scale networks which consist of various
connections provided over multiple interconnected networks with
varying technologies.
This document examines the applicability of the PCE architecture,
protocols, and procedures for computing protection paths and
restoration services, for single and multi-domain networks.
Status of this Memo
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Domains . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1. Inter-domain LSPs . . . . . . . . . . . . . . . . . . 4
1.2. Recovery . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Conventions used in this document . . . . . . . . . . . . 5
2. Path Computation Element Architecture Considerations . . . . . 5
2.1. Online Path Computation . . . . . . . . . . . . . . . . . 5
2.2. Offline Path Computation . . . . . . . . . . . . . . . . . 5
3. Protection Service Traffic Engineering . . . . . . . . . . . . 6
3.1. Path Computation . . . . . . . . . . . . . . . . . . . . . 6
3.2. Bandwidth Reservation . . . . . . . . . . . . . . . . . . 6
3.3. Disjoint Path . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Service Preemption . . . . . . . . . . . . . . . . . . . . 6
3.5. Share Risk Link Groups . . . . . . . . . . . . . . . . . . 6
3.6. Multi-Homing . . . . . . . . . . . . . . . . . . . . . . . 6
3.6.1. Ingress and Egress Protection . . . . . . . . . . . . 7
4. Packet Protection Applications . . . . . . . . . . . . . . . . 7
4.1. Single Domain Service Protection . . . . . . . . . . . . . 7
4.2. Multi-domain Service Protection . . . . . . . . . . . . . 8
4.3. Backup Path Computation . . . . . . . . . . . . . . . . . 8
4.4. Fast Reroute (FRR) Path Computation . . . . . . . . . . . 8
4.5. Point-to-Multipoint Path Protection . . . . . . . . . . . 8
5. Optical Protection Applications . . . . . . . . . . . . . . . 9
5.1. ASON Applicability . . . . . . . . . . . . . . . . . . . . 9
5.2. Multi-domain Restoration . . . . . . . . . . . . . . . . . 9
6. Path and Service Protection Gaps . . . . . . . . . . . . . . . 9
7. Manageability Considerations . . . . . . . . . . . . . . . . . 9
8. Security Requirements . . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
Network survivability remains a major concern for network operators
and service providers, particularly as expanding applications such as
private and Public Cloud drive increasingly more traffic across
longer ranges, to a wider number of users. A variety of well-known
pre-planned protection and post-fault recovery schemes have been
developed for IP, MPLS and GMPLS networks.
The Path Computation Element (PCE) [RFC4655] can be used to perform
complex path computation in large single domain, multi-domain and
multi-layered networks. The PCE can also be used to compute a
variety of restoration and protection paths and services.
This document examines the applicability of the PCE architecture,
protocols, and protocol extensions for computing protection paths and
restoration services.
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]), or specific switching environment.
In the context of GMPLS, a particularly important example of a domain
is the Automatically Switched Optical Network (ASON) subnetwork
[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
nodes may, in fact, be subnetworks. Furthermore, a domain might be
an ASON routing area [G-7715]. A PCE may perform the path
computation function of an ASON routing controller as described in
[G-7715-2].
It is assumed that the PCE architecture should be applied to small
inter-domain topologies and not to solve route computation issues
across large groups of domains, I.E. the entire Internet.
Most existing protocol mechanisms for network survivability have
focused on single-domain scenarios. Multi-domain scenarios are much
more complex and challenging as domain topology information is
typically not shared outside each specific domain.
Therefore multi-domain survivability is a key requirement for today's
complex networks. It is important to develop more adaptive multi-
domain recovery solutions for various failure scenarios.
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1.1.1. Inter-domain LSPs
Three signaling options are defined for setting up an inter-area or
inter-AS LSP [RFC4726]:
- Contiguous LSP
- Stitched LSP
- Nested LSP
Three signaling options are defined for setting up an inter-area or
inter-AS LSP [RFC4726]:
1.2. Recovery
Typically traffic-engineered networks such as MPLS-TE and GMPLS, use
protection and recovery mechanisms based on the pre-established use
of a packet or optical LSP and/or the availability of spare resources
and the network topology.
1.3. Terminology
ABR: IGP Area Border Router, a router that is attached to more than
one IGP area.
ASBR: Autonomous System Border Router, a router used to connect
together ASs of a different or the same Service Provider via one or
more inter-AS links.
CSPF: Constrained Shortest Path First.
Inter-area TE LSP: A TE LSP whose path transits through two or more
IGP areas.
Inter-AS MPLS TE LSP: A TE LSP whose path transits through two or
more ASs or sub-ASs (BGP confederations.
SRLG: Shared Risk Link Group.
TED: Traffic Engineering Database, which contains the topology and
resource information of the domain. The TED may be fed by Interior
Gateway Protocol (IGP) extensions or potentially by other means.
This document also uses the terminology defined in [RFC4655] and
[RFC5440].
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1.4. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
2. Path Computation Element Architecture Considerations
For the purpose of this document it is assumed that the path
computation is the sole responsibility of the PCE as per the
architecture defined in [RFC4655]. When a path is required the Path
Computation Client (PCC) will send a request to the PCE. The PCE
will apply the required constraints and compute a path and return a
response to the PCC. In the context of this document it may be
necessary for the PCE to co-operate with other PCEs in adjacent
domains (as per BRPC [RFC5441]) or cooperate with the Parent PCE (as
per [H-PCE]).
A PCE may be used to compute end-to-end paths across single or
multiple domains. Multiple PCEs may be dedicated to each area to
provide sufficient path computation capacity and redundancy for each
domain.
During path computation [RFC5440], a PCC request may contain backup
LSP requirements in order to setup in the same time the primary and
backup LSPs. This request is known as dependent path computations.
A typical dependent request for a primary and backup service would
request that the computation assign a set of diverse paths, so both
services are disjointed from each other.
2.1. Online Path Computation
Online path computation is performed on-demand as nodes in the
network determine that they need to know the paths to use for
services.
2.2. Offline Path Computation
Offline path computation is performed ahead of time, before the LSP
setup is requested. That means that it is requested by, or performed
as part of, a management application.
This method of computation allows the optimal placement of services
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and explicit control of services. A CSP can plan where new
protection services will be placed ahead of time. Furthermore by
computing paths offline specific scenarios can be considered and a
global view of network resources is available.
Finally, offline path computation provides a method to compute
protection paths in the event of a single, or multiple, link
failures. This allows the placement of backup services in the event
of catastrophic network failures.
3. Protection Service Traffic Engineering
3.1. Path Computation
This document describes how the PCE architecture defined in [RFC4655]
may be utilized to compute protection and recovery paths for critical
network services. In the context of this document (inter-domain) it
may be necessary for the PCE to co-operate with other PCEs in
adjacent domains (as per BRPC [RFC5441]) or cooperate with the Parent
PCE (as per [H-PCE]).
3.2. Bandwidth Reservation
3.3. Disjoint Path
Disjoint paths are required for end-to-end protection services. A
backup service may be required to be fully disjoint from the primary
service, link disjoint (allowing common nodes on the paths), or best-
effort disjoint (allowing shared links or nodes when no other path
can be found).
3.4. Service Preemption
3.5. Share Risk Link Groups
3.6. Multi-Homing
Networks constructed from multi-areas or multi-AS environments may
have multiple interconnect points (multi-homing). End-to-end path
computations may need to use different interconnect points to avoid
single point failures disrupting primary and backup services.
Domain and path diversity may also be required when computing end-to-
end paths. Domain diversity should facilitate the selection of paths
that share ingress and egress domains, but do not share transit
domains. Therefore, there must be a method allowing the inclusion or
exclusion of specific domains when computing end-to-end paths.
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3.6.1. Ingress and Egress Protection
An end-to-end primary service carried by a primary TE LSP from a
primary ingress node to a primary egress node may need to be
protected against the failures in the ingress and the egress. In
this case, a backup ingress and a backup egress are required, which
are different from the primary ingress and the primary egress
respectively. The backup ingress should be in the same domain as the
primary ingress, and the backup egress should be in the same domain
as the primary egress.
A source of the service traffic may be sent to both the primary
ingress and the backup ingress (dual-homing). The source may not be
in the same domain as the primary ingress and the backup ingress.
When the primary ingress fails, the service traffic is delivered
through the backup ingress.
A receiver of the service traffic may be connected to both the
primary egress and the backup egress (dual-homing). The receiver may
not be in the same domain as the primary egress and the backup
egress. When the primary egress fails, the receiver gets the service
traffic from the backup egress.
4. Packet Protection Applications
Network survivability is a key objective for CSPs, particularly as
expanding revenue services (cloud and data center applications) are
increasing exponentially.
Pre-fault paths are pre-computed and protection resources are
reserved a priory for rapid recovery. In the event of a network
failure on the primary path, the traffic is fast switched to the
backup path. These pre-provisioned mechanisms are capable of
ensuring protection against single link failures.
Post-fault restoration schemes are reactive and require a reactive
routing procedure to set up new working paths in the event of a
failure. Post fault restoration can significantly impact network
services as they are typically impacted by longer restoration delays
and cannot guarantee recovery of a service. However, they are much
more network resource efficient and are capable of handling multi-
failure situations.
4.1. Single Domain Service Protection
A variety of pre-planned protection and post-fault restoration
recovery schemes are available for single domain MPLS and GMPLS
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networks, these include:
o Path Recovery
o Path Segment Recovery
o Local Recovery (Fast Reroute)
4.2. Multi-domain Service Protection
Typically network survivability has focused on single-domain
scenarios. By contrast, broader multi-domain scenarios are much more
challenging as no single entity has a global view of topology
information. As a result, multi-domain survivability is very
important.
A PCE may be used to compute end-to-end paths across multi-domain
environments using a per-domain path computation technique [RFC5152].
The so called backward recursive path computation (BRPC) mechanism
[RFC5441] defines a PCE-based path computation procedure to compute
inter-domain constrained LSPs.
4.3. Backup Path Computation
A PCE can be used to compute backup paths in the context of fast
reroute protection of TE LSPs. In this model, all backup TE LSPs
protecting a given facility are computed in a coordinated manner by a
PCE. This allows complete bandwidth sharing between backup tunnels
protecting independent elements, while avoiding any extensions to TE
LSP signaling. Both centralized and distributed computation models
are applicable. In the distributed case each LSR can be a PCE to
compute the paths of backup tunnels to protect against the failure of
adjacent network links or nodes.
4.4. Fast Reroute (FRR) Path Computation
[RFC409] extends RSVP-TE to establish backup LSPs for the local
repair of LSP tunnels. This extension allows CSPs to redirect
traffic onto the backup LSP tunnels in 10s of milliseconds.
This local repair of the LSP is applicable to explicitly-routed LSPs.
An FRR repair method is applicable to explicitly-routed LSPs across a
single domain environment.
4.5. Point-to-Multipoint Path Protection
A PCE utilizing the extensions outlined in [RFC6006] (Extensions to
PCEP for Point-to-Multipoint Traffic Engineering Label Switched
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Paths), can be used to compute point-to-multipoint (P2MP) paths.
A PCC requesting path computation for a primary and backup path can
request that these dependent computations use diverse paths.
Furthermore, the specification also defines two new options for P2MP
path dependent computation requests. The first option allows the PCC
to request that the PCE should compute a secondary P2MP path tree
with partial path diversity for specific leaves or a specific source-
to-leaf (sub-path to the primary P2MP path tree. The second option,
allows the PCC to request that partial paths should be link direction
diverse
5. Optical Protection Applications
5.1. ASON Applicability
5.2. Multi-domain Restoration
6. Path and Service Protection Gaps
7. Manageability Considerations
This document does not describe any specific protocol, protocol
extensions, or protocol usage, therefore no manageability
considerations need to be discussed here.
8. Security Requirements
This document is informational and does not describe any new specific
protocol, protocol extensions, or protocol usage. As such, it
introduces no new security concerns.
9. IANA Considerations
This document makes no requests for IANA action.
10. Acknowledgement
The authors would like to thank Daniel King for his valuable
contributions to this draft.
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11. References
11.1. Normative References
11.2. Informative References
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 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 for
Inter-Domain Multiprotocol Label Switching Traffic
Engineering", RFC 4726, November 2006.
[RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
Path Computation Method for Establishing Inter-Domain
Traffic Engineering (TE) Label Switched Paths (LSPs)",
RFC 5152, February 2008.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
Backward-Recursive PCE-Based Computation (BRPC) Procedure
to Compute Shortest Constrained Inter-Domain Traffic
Engineering Label Switched Paths", RFC 5441, April 2009.
[RFC6006] Zhao, Q., King, D., Verhaeghe, F., Takeda, T., Ali, Z.,
and J. Meuric, "Extensions to the Path Computation Element
Communication Protocol (PCEP) for Point-to-Multipoint
Traffic Engineering Label Switched Paths", RFC 6006,
September 2010.
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[G-8080] ITU-T Recommendation G.8080/Y.1304, Architecture for
the automatically switched optical network (ASON).
[G-7715] ITU-T Recommendation G.7715 (2002), Architecture
and Requirements for the Automatically Switched
Optical Network (ASON).
[G-7715-2] ITU-T Recommendation G.7715.2 (2007), ASON routing
architecture and requirements for remote route query.
[H-PCE] King, D. and A. Farrel, "The Application of the Path
Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS & GMPLS", July
Author's Address
Huaimo Chen
Huawei Technologies
Boston, MA
USA
Email: Huaimochen@huawei.com
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