ually configure them. Area 0 in Figure 10-12 could be configured as an NBMA network. This is the default OSPF network type on serial interfaces with Frame Relay encapsulation. OSPF 100 Area 1 OSPF 100 OSPF 100 OSPF 100 Area 2 Area 3 Area 0 Figure 10-12. Simple OSPF network OSPF enables interfaces using the network router command. It is a classless protocol, SO you must use inverse subnet masks to limit the interfaces included. Unlike with EIGRP, you must include the inverse mask. If you do not, OSPF will not assume a classful network, but will instead report an error: R3 (config-router) #network 10.10.10.0 % Incomplete command. Specific Routing Protocols In addition to the inverse mask, you must also specify the area in which the network resides: R3 (config-router): #network 10.10.10.0 0.0.0.255 area 0 My preference is to specifically configure interfaces SO there are no surprises. You do this with an inverse mask of 0.0.0.0: R3 (config-router)#network 10.10.10.1 0.0.0.0 area 0 OSPF routes are marked by the letter 0 in the first column of the routing table: R3#sho ip route [Text Removed] Gateway of last resort is 192.168.1.2 to network 0.0.0.0 192.192.192.0/30 is subnetted, 1 subnets 192.192.192.4 is directly connected, Serialo/o 172.16.0.0/32 is subnetted, 1 subnets 172.16.1.1 [110/11] via 10.10.10.4, 00:00:09, Etherneto/o 10.0.0.0/24 is subnetted, 1 subnets 10.10.10.0 is directly connected, Etherneto/o 192.168.1.0/24 is directly connected, Ethernet1/0 0.0.0.0/0 [254/0] via 192.168.1.2 Various OSPF route types are described in the routing table. They are: 0 (OSPF), IA (OSPF interarea), 0 N1 (OSPF NSSA external type 1), and 0 N2 (OSPF NSSA external type 2). OSPF stores its routes in a database, much like EIGRP. The command to show the database is show ip ospf database: R3#sho ip ospf database OSPF Router with ID (192.192.192.5) (Process ID 100) Router Link States (Area 0) Link ID ADV Router Checksum Link count 192.192.192.5 192.192.192.5 0x8000002A 0x00C190 1 Summary Net Link States (Area 0) Link ID ADV Router Ch