Alcatel Carrier Internetworking Solutions 060187-10 REV D manual

OSPF Overview	Configuring OSPF

Virtual Links

It is possible to define areas in such a way that the backbone is no longer contiguous. (This is not an ideal OSPF configuration, and maximum effort should be made to avoid this situation.) In this case the system administrator must restore backbone connectivity by configuring virtual links.

Virtual links can be configured between any two backbone routers that have a connection to a common non-backbone area. The protocol treats two routers joined by a virtual link as if they were connected by an unnumbered point-to-point network. The routing protocol traffic that flows along the virtual link uses intra-area routing only, and the physical connection between the two routers is not managed by the network administrator (i.e., there is no dedicated connection between the routers as there is with the OSPF backbone).

Router A

Router B

Area 1

Backbone

Virtual Link

Backbone

OSPF Routers Connected with a Virtual Link

In the above diagram, Router A and Router B are connected via a virtual link in Area 1, which is known as a transit area. See “Creating Virtual Links” on page 1-25for more information.

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OmniSwitch 6600 Family Advanced Routing Configuration Guide March 2005

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Alcatel Carrier Internetworking Solutions 060187-10 REV D manual Virtual Links, Ospf Routers Connected with a Virtual Link

Contents

OmniSwitch 6600 Family Advanced Routing Configuration Guide Page Contents Alcatel INTERNETWORKING, INC. AII Supported Platforms Unsupported Platforms When Should I Read this Manual? What is in this Manual?What is Not in this Manual? Who Should Read this Manual? Documentation Roadmap Stage 1 Using the Switch for the First TimeHow is the Information Organized? Anytime Stage 2 Gaining Familiarity with Basic Switch FunctionsStage 3 Integrating the Switch Into a Network OmniSwitch 6600 Family Getting Started Guide Related Documentation Technical Support Configuring Ospf This Chapter Ospf Specifications Ospf Defaults Table Parameter Description Command Default Value/Comments Ospf Quick Steps Router ID Admin Status = Enabled Operational Status = Up Admin Status = EnabledShow ip ospf area Area Identifier Area Type = normal Ospf Overview Ospf Hello Protocol Ospf Areas Ospf Intra-Area and Inter-Area Routing Classification of Routers Virtual Links Ospf Routers Connected with a Virtual Link Stub Areas Ospf Stub Area Not-So-Stubby-Areas Totally Stubby Area Example Graceful Restart on Stacks with Redundant Switches Equal Cost Multi-Path Ecmp RoutingNon Broadcast Ospf Routing Multiple Equal Cost Paths Ospf Graceful Restart Helping and Restarting Router Example Configuring Ospf Preparing the Network for Ospf Activating Ospf Loading the SoftwareEnabling Ospf Removing Ospf from Memory Creating an Ospf Area Creating an AreaEnabling an Area Specifying an Area Type Deleting an Area Enabling and Disabling SummarizationDisplaying Area Status Configuring Stub Area Default Metrics Setting Area RangesConfiguring a Totally Stubby Area No ip ospf area 1.1.1.1 default-metric Enter the following commands on Router B Creating Ospf Interfaces Creating an InterfaceAssigning an Interface to an Area Activating an Interface MD5 Encryption Interface AuthenticationSimple Authentication Modifying Interface Parameters Ip ospf interface 120.5.80.1 dead-interval 50 costIp ospf interface 120.5.80.1 hello-interval Ip ospf interface 120.5.80.1 dead-interval Modifying Virtual Link Parameters Creating Virtual LinksCreating a Virtual Link Enabling Redistribution Creating Redistribution Policies and FiltersSpecifying an Autonomous System Boundary Router Creating a Redistribution Policy Creating a Redistribution Filter Show ip ospf redist-filter Show ip ospf redist-filter ripShow ip ospf redist-filter rip 1.1.0.0 No ip ospf redist-filter rip 1.1.0.0 Configuring Router Capabilities Ip ospf neighbor 1.1.1.8 eligible Configuring Static NeighborsIp ospf interface 1.1.1.1 type non-broadcast Ip ospf restart-support planned-only No ip ospf restart-support Ospf Application Example Three Area Ospf Network Prepare the Routers Ospf Application ExampleConfiguring Ospf Enable Ospf Router Ospf Application Example Examine the Network Verifying Ospf Configuration Software License and Copyright Statements Alcatel License Agreement Alcatel License Agreement Software License and Copyright Statements OpenLDAP Public License Version 2.4, 8 December Booting and Debugging Non-Proprietary SoftwareThird Party Licenses and Notices Preamble LinuxGNU General Public License Version 2, June 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 Random.c University of CaliforniaCarnegie-Mellon University Apptitude, Inc AgranatRSA Security Inc Sun Microsystems, Inc Wind River Systems, Inc Network Time Protocol Version Index Index