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Area 0.0.0.1<br />

Area 0.0.0.3 (Stub Area)<br />

RouterJ<br />

10.0.8.2/24<br />

RouterG<br />

10.0.8.1/24<br />

RouterF<br />

t1-0/0/3<br />

10.0.31.2/24<br />

RouterH<br />

RouterE<br />

t1-0/0/3<br />

10.0.13.1/24<br />

Figure 12-3. OSPF stub area topology<br />

Type 4 (ASBR Summary) and Type 5 (AS External) LSAs are not flooded into stub<br />

areas. When Area 0.0.0.3 is a regular area, not a stub area, the routers in that area<br />

receive Type 4 and Type 5 LSAs. Here are the entries in RouterE’s link-state database:<br />

aviva@RouterE> show ospf database summary<br />

Area 0.0.0.3:<br />

3 Router LSAs<br />

1 Network LSAs<br />

9 Summary LSAs<br />

1 ASBRSum LSAs<br />

Externals:<br />

2 Extern LSAs<br />

Interface lo0.0:<br />

Interface t1-0/0/3.0:<br />

Interface t1-0/0/3.0:<br />

The output shows one ASBR Summary and two External LSAs. After you configure<br />

the area as a stub, these routes are no longer sent from Area 0.0.0.0 so are not in the<br />

router’s link-state database:<br />

aviva@RouterE> show ospf database summary<br />

Area 0.0.0.3:<br />

3 Router LSAs<br />

1 Network LSAs<br />

9 Summary LSAs<br />

Externals:<br />

Interface lo0.0:<br />

Interface t1-0/0/3.0:<br />

Interface t1-0/0/3.0:<br />

You can further reduce the number of LSA packets flooded through the stub area by<br />

configuring the ABR so that it does not flood Type 3 (Network Summary) LSAs to<br />

the routers in the stub area:<br />

[edit protocols ospf]<br />

aviva@RouterJ# set area 0.0.0.3 stub no-summaries<br />

398 | Chapter 12: OSPF<br />

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

Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.

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