Foundation Summary 217
Two types of summarization exist:
■ Interarea summarization—Performed at the ABR, creates Type 3 and Type 4 LSAs.
■ External summarization—Performed at the ASBR, creates Type 5 LSAs.
Conﬁguration commands for a multi-area OSPF network are as follows:
■ area area-id range address mask
■ summary-address address mask [not-advertise][tag tag]
■ area area-id stub
■ area area-id stub no-summary
■ area area-id default-cost cost
■ area area-id virtual-link
■ area area-id virtual-link router-id
Commands to verify the conﬁguration and monitor the network are
■ show ip ospf border-routers
■ show ip route
■ show ip ospf virtual-links
■ show ip ospf database
Useful debug commands are as follows:
■ debug ip packet
■ debug ip ospf events
Use the following guidelines when troubleshooting adjacencies:
■ Make sure that both routers are conﬁgured with the same IP mask, MTU, interface Hello
timer, OSPF Hello interval, and OSPF dead interval.
■ Make sure that both neighbors are the same area type and part of the same area.
■ Use the debug and show commands to trace the problem.