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192.168.19.1/32 *[Direct/0] 3d 01:51:49<br />

> via lo0.0<br />

192.168.42.1/32 *[OSPF/10] 00:05:31, metric 1<br />

> to 10.0.16.1 via fe-1/0/0.0<br />

224.0.0.5/32 *[OSPF/10] 2d 21:03:25, metric 1<br />

MultiRecv<br />

12.6 Setting Up Stub Areas<br />

Problem<br />

You want to optimize OSPF performance in an area that connects only to the OSPF<br />

backbone.<br />

Solution<br />

Configure the area as a stub area:<br />

[edit protocols ospf]<br />

aviva@RouterE# set area 0.0.0.3 interface t1-0/0/3.0<br />

aviva@RouterE# set area 0.0.0.3 stub<br />

<strong>Discussion</strong><br />

When some areas of your network have no external connections, you can make them<br />

into stub areas. This reduces the amount of OSPF protocol traffic that is flooded<br />

through the area, which improves performance on the router by decreasing the size<br />

of the OSPF routing database and thus decreasing the amount of CPU needed to perform<br />

the SPF calculations. Another common reason to set up a stub area is to allow<br />

legacy routers that don’t have enough memory or CPU horsepower to participate in<br />

the OSPF network. A stub area receives OSPF routing-database information from all<br />

the other areas in the network. However, instead of receiving all AS external advertisements,<br />

the stub area gets only a default summary (0.0.0.0/0) from ABRs to reach<br />

external destinations and gets summaries for destinations in other OSPF areas.<br />

You configure each router in the stub area as a stub router by including the stub<br />

statement when configuring the area. In our recipe, Area 0.0.0.3 is a stub area (see<br />

Figure 12-3). Configure the stub area on each router that is part of this area.<br />

Check that the stub area is up and running:<br />

aviva@RouterE> show ospf interface detail<br />

Interface State Area DR ID BDR ID Nbrs<br />

t1-0/0/3.0 PtToPt 0.0.0.3 0.0.0.0 0.0.0.0 1<br />

Type: P2P, Address: 0.0.0.0, Mask: 0.0.0.0, MTU: 1500, Cost: 65<br />

Adj count: 1<br />

Hello: 10, Dead: 40, ReXmit: 5, Stub<br />

Auth type: None<br />

This is the Title of the Book, eMatter Edition<br />

Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.<br />

Setting Up Stub Areas | 397

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