Alcatel Carrier Internetworking Solutions 060187-10 REV D manual Ospf Areas

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OSPF Overview

Configuring OSPF

 

 

 

 

OSPF Areas

OSPF allows collections of contiguous networks and hosts to be grouped together as an area. Each area runs a separate copy of the basic link-state routing algorithm (usually called SPF). This means that each area has its own topological database, as explained in the previous section.

Intra-Area

Routing

Router 1

Link State Messages

Inter-Area Routing

Intra-Area

Routing

Backbone

Router 3

Link State

Messages

Router 2

Router 4

Area 1

Area 2

OSPF Intra-Area and Inter-Area Routing

An area’s topology is visible only to the members of the area. Conversely, routers internal to a given area know nothing of the detailed topology external to the area. This isolation of knowledge enables the proto- col to reduce routing traffic by concentrating on small areas of an AS, as compared to treating the entire AS as a single link-state domain.

Areas cause routers to maintain a separate topological database for each area to which they are connected. (Routers connected to multiple areas are called area border routers). Two routers belonging to the same area have identical area topological databases.

Different areas communicate with each other through a backbone. The backbone consists of routers with contacts between multiple areas. A backbone must be contiguous (i.e., it must be linked to all areas).

The backbone is responsible for distributing routing information between areas. The backbone itself has all of the properties of an area. The topology of the backbone is invisible to each of the areas, while the back- bone itself knows nothing of the topology of the areas.

All routers in an area must agree on that area’s parameters. Since a separate copy of the link-state algo- rithm is run in each area, most configuration parameters are defined on a per-router basis. All routers belonging to an area must agree on that area’s configuration. Misconfiguration will keep neighbors from forming adjacencies between themselves, and OSPF will not function.

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OmniSwitch 6600 Family Advanced Routing Configuration Guide March 2005

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Contents OmniSwitch 6600 Family Advanced Routing Configuration Guide Page Contents Alcatel INTERNETWORKING, INC. AII Supported Platforms Unsupported PlatformsWhat is Not in this Manual? When Should I Read this Manual?What is in this Manual? Who Should Read this Manual?Stage 1 Using the Switch for the First Time How is the Information Organized?Documentation Roadmap Stage 2 Gaining Familiarity with Basic Switch Functions Stage 3 Integrating the Switch Into a NetworkAnytime OmniSwitch 6600 Family Getting Started Guide Related DocumentationTechnical Support Configuring Ospf This ChapterOspf Specifications Ospf Defaults Table Parameter Description Command Default Value/CommentsOspf Quick Steps Router ID Show ip ospf area Area Identifier Admin Status = Enabled Operational Status = UpAdmin Status = Enabled Area Type = normalOspf Overview Ospf Hello ProtocolOspf Areas Ospf Intra-Area and Inter-Area RoutingClassification of Routers Virtual Links Ospf Routers Connected with a Virtual LinkStub Areas Ospf Stub AreaNot-So-Stubby-Areas Totally Stubby Area ExampleNon Broadcast Ospf Routing Graceful Restart on Stacks with Redundant SwitchesEqual Cost Multi-Path Ecmp Routing Multiple Equal Cost PathsOspf Graceful Restart Helping and Restarting Router Example Configuring Ospf Preparing the Network for Ospf Enabling Ospf Activating OspfLoading the Software Removing Ospf from MemoryEnabling an Area Creating an Ospf AreaCreating an Area Specifying an Area TypeEnabling and Disabling Summarization Displaying Area StatusDeleting an Area Configuring a Totally Stubby Area Configuring Stub Area Default MetricsSetting Area Ranges No ip ospf area 1.1.1.1 default-metricEnter the following commands on Router B Assigning an Interface to an Area Creating Ospf InterfacesCreating an Interface Activating an InterfaceInterface Authentication Simple AuthenticationMD5 Encryption Ip ospf interface 120.5.80.1 hello-interval Modifying Interface ParametersIp ospf interface 120.5.80.1 dead-interval 50 cost Ip ospf interface 120.5.80.1 dead-intervalCreating Virtual Links Creating a Virtual LinkModifying Virtual Link Parameters Creating Redistribution Policies and Filters Specifying an Autonomous System Boundary RouterEnabling Redistribution Creating a Redistribution Policy Creating a Redistribution FilterShow ip ospf redist-filter rip 1.1.0.0 Show ip ospf redist-filterShow ip ospf redist-filter rip No ip ospf redist-filter rip 1.1.0.0Configuring Router Capabilities Configuring Static Neighbors Ip ospf interface 1.1.1.1 type non-broadcastIp ospf neighbor 1.1.1.8 eligible Ip ospf restart-support planned-only No ip ospf restart-supportOspf Application Example Three Area Ospf NetworkPrepare the Routers Ospf Application ExampleConfiguring Ospf Enable Ospf RouterOspf Application Example Examine the Network Verifying Ospf Configuration Software License and Copyright Statements Alcatel License AgreementAlcatel License Agreement Software License and Copyright Statements Booting and Debugging Non-Proprietary Software Third Party Licenses and NoticesOpenLDAP Public License Version 2.4, 8 December Linux GNU General Public License Version 2, JunePreamble Third Party Licenses and Notices Software License and Copyright Statements Third Party Licenses and Notices Appendix How to Apply These Terms to Your New Programs University of California Carnegie-Mellon UniversityRandom.c RSA Security Inc Apptitude, IncAgranat Sun Microsystems, IncWind River Systems, Inc Network Time Protocol VersionIndex Index