Alcatel Carrier Internetworking Solutions 060187-10 REV D Stub Areas

Configuring OSPF OSPF Overview

OmniSwitch 6600 Family Advanced Routing Configuration Guide March 2005 page 1-11

Stub Areas

OSPF allows certain areas to be configured as stub areas. A stub area is an area with routers that have no

AS external Link State Advertisements (LSAs).

In order to take advantage of the OSPF stub area support, default routing must be used in the stub area.

This is accomplished by configuring only one of the stub area’s border routers to advertise a default route

into the stub area. The default routes will match any destination that is not explicitly reachable by an intra-

area or inter-area path (i.e., AS external destinations).

OSPF Stub Area

Area 1 and Area 3 could be configured as stub areas. Stub areas are configured using the OSPF ip ospf

area command, described in “Creating an Area” on page1-18. For more overview information on areas,

see “OSPF Areas” on page 1-8.

The OSPF protocol ensures that all routers belonging to an area agree on whether the area has been

configured as a stub. This guarantees that no confusion will arise in the flooding of AS external advertise-

ments.

Two restrictions on the use of stub areas are:

•Virtual links cannot be configured through stub areas.

•AS boundary routers cannot be placed internal to stub areas.

Area 3

(stub)

Area 2

Area 1

(stub)

Backbone

Backbone

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Contents

Main Page Contents Page About This Guide Supported Platforms Unsupported Platforms Who Should Read this Manual? When Should I Read this Manual? What is in this Manual? What is Not in this Manual? How is the Information Organized? Documentation Roadmap Stage 1: Using the Switch for the First Time Stage 2: Gaining Familiarity with Basic Switch Functions Stage 3: Integrating the Switch Into a Network Anytime Related Documentation User Manual CD Technical Support 1 Configuring OSPF In This Chapter OSPF Specifications OSPF Defaults Table Enables OSPF. Enables an area. Enables an interface. Sets the overflow interval value. OSPF Quick Steps 9Assign the OSPF interface to the area and the backbone using the ip ospf interface area command. For example: or 10Enable the OSPF interfaces using the ip ospf interface status command. For example: or 11You can now display the router OSPF settings by using the show ip ospf command. The output gener- 12You can display OSPF area settings using the show ip ospf area command. For example: 13You can display OSPF interface settings using the show ip ospf interface command. For example: OSPF Overview OSPF Areas Classification of Routers Virtual Links Stub Areas OSPF Stub Area Not-So-Stubby-Areas Totally Stubby Areas Equal Cost Multi-Path (ECMP) Routing Non Broadcast OSPF Routing Graceful Restart on Stacks with Redundant Switches Page Configuring OSPF Preparing the Network for OSPF Activating OSPF Loading the Software Enabling OSPF Removing OSPF from Memory Creating an OSPF Area Creating an Area Enabling an Area Specifying an Area Type Enabling and Disabling Summarization Displaying Area Status Deleting an Area Configuring Stub Area Default Metrics Setting Area Ranges Configuring a Totally Stubby Area 1Enter the following commands on Router B: 2Enter the following on Router A: Creating OSPF Interfaces Creating an Interface Assigning an Interface to an Area Activating an Interface Interface Authentication Modifying Interface Parameters belonging to this interface. Creating Virtual Links Creating a Virtual Link Modifying Virtual Link Parameters Creating Redistribution Policies and Filters Specifying an Autonomous System Boundary Router Enabling Redistribution Creating A Redistribution Policy Creating a Redistribution Filter Page Configuring Router Capabilities Configuring Static Neighbors Configuring Redundant Switches in a Stack for Graceful Restart OSPF Application Example Three Area OSPF Network Step 1: Prepare the Routers Page Step 2: Enable OSPF Step 3: Create and Enable the Areas and Backbone Step 4: Create, Enable, and Assign Interfaces Page Step 5: Examine the Network Verifying OSPF Configuration A Software License and Copyright Statements Alcatel License Agreement ALCATEL INTERNETWORKING, INC. (AII) SOFTWARE LICENSE AGREEMENT Page Page Third Party Licenses and Notices A.Booting and Debugging Non-Proprietary Software B. The OpenLDAP Public License: Version 2.4, 8 December 2000 C. Linux D. GNU GENERAL PUBLIC LICENSE: Version 2, June 1991 Preamble GNU GENERAL PUBLIC LICENSE TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION Page Page Page Appendix: How to Apply These Terms to Your New Programs E. University of California F. Carnegie-Mellon University G.Random.c H.Apptitude, Inc. I. Agranat J. RSA Security Inc. K. Sun Microsystems, Inc. L. Wind River Systems, Inc. M.Network Time Protocol Version 4 Index A B D E O R S T V