Alcatel Carrier Internetworking Solutions 060187-10 REV D manual Not-So-Stubby-Areas

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OSPF Overview

Configuring OSPF

 

 

 

 

Not-So-Stubby-Areas

NSSA, or not-so-stubby area, is an extension to the base OSPF specification and is defined in RFC 1587. An NSSA is similar to a stub area in many ways: AS-external LSAs are not flooded into an NSSA and virtual links are not allowed in an NSSA. The primary difference is that selected external routing informa- tion can be imported into an NSSA and then redistributed into the rest of the OSPF routing domain. These routes are imported into the NSSA using a new LSA type: Type-7 LSA. Type-7 LSAs are flooded within the NSSA and are translated at the NSSA boundary into AS-external LSAs so as to convey the external routing information to other areas.

NSSAs enable routers with limited resources to participate in OSPF routing while also allowing the import of a selected number of external routes into the area. For example, an area which connects to a small exter- nal routing domain running RIP may be configured as an NSSA. This will allow the import of RIP routes into this area and the rest of the OSPF routing domain and at the same time, prevent the flooding of other external routing information (learned, for example, through IP) into this area.

All routers in an NSSA must have their OSPF area defined as an NSSA. To configure otherwise will ensure that the router will be unsuccessful in establishing an adjacent in the OSPF domain.

Totally Stubby Areas

In Totally Stubby Areas the ABR advertises a default route to the routers in the totally stubby area but does not advertise any inter-area or external LSAs. As a result, routers in a totally stubby area know only the routes for destination networks in the stub area and have a default route for any other destination outside the stub.

Note. Virtual links cannot be configured through totally stubby areas.

The router memory is saved when using stub area networks by filtering Type 4 and 5 LSAs. This concept has been extended with Totally Stubby Areas by filtering Type 3 LSAs (Network Summary LSA) in addi- tion to Type 4 and 5 with the exception of one single Type 3 LSA used to advertise a default route within the area.

The following is an example of a simple totally stubby configuration with Router B being an ABR between the backbone area 0 and the stub area 1. Router A is in area 1.1.1.1, totally stubby area:

 

 

OSPF Area 0

 

 

192.168.50.0/24

192.168.12.1

OSPF Area 1

192.168.12.2

Totally Stubby

Router A

 

Router B

Totally Stubby Area Example

Note. See “Configuring a Totally Stubby Area” on page 1-20for information on configuring Totally Stubby Areas.

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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?How is the Information Organized? Stage 1 Using the Switch for the First TimeDocumentation Roadmap Stage 3 Integrating the Switch Into a Network Stage 2 Gaining Familiarity with Basic Switch FunctionsAnytime 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 TypeDisplaying Area Status Enabling and Disabling SummarizationDeleting 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 InterfaceSimple Authentication Interface 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 a Virtual Link Creating Virtual LinksModifying Virtual Link Parameters Specifying an Autonomous System Boundary Router Creating Redistribution Policies and FiltersEnabling 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 Ip ospf interface 1.1.1.1 type non-broadcast Configuring Static NeighborsIp 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 Third Party Licenses and Notices Booting and Debugging Non-Proprietary SoftwareOpenLDAP Public License Version 2.4, 8 December GNU General Public License Version 2, June LinuxPreamble 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 Carnegie-Mellon University University of CaliforniaRandom.c RSA Security Inc Apptitude, IncAgranat Sun Microsystems, IncWind River Systems, Inc Network Time Protocol VersionIndex Index