the remote routers are assumed to be connected with virtual circuits, though only one IP network is used. No neighbors are configured, and no DR is chosen. Area 0 in Figure 10-12 could be configured as a point-to-multipoint OSPF network. Broadcast A broadcast network is an Ethernet, Token Ring, or FDDI network. Any num- ber of hosts may reside on a broadcast network, and any host may communicate directly with any other host. A DR must be chosen, and neighbors must be discovered or configured on a broadcast network. A broadcast network uses multicasts to send hello packets to discover OSPF routers. This is the default OSPF network type for Ethernet and Token Ring networks. Nonbroadcast multiaccess (NBMA) In a nonbroadcast multiaccess network, all nodes may be able to communicate with one another, but they do not share a single medium. Examples include frame-relay, X.25, and Switched Multimegabit Data Service (SMDS) networks. Because NBMA networks do not use multicasts to discover neighbors, you must manually 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 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. 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. This is done 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 