To configure OSPF adjustments, start with a basic implementation of the OSPF routing protocol.
OSPF defines five network types, as shown in Figures 1 to 5:
- Point-to-point - Two routers interconnected over a common link. No other routers are on the link. This is often the configuration in WAN links. (Figure 1)
- Broadcast multiaccess - Multiple routers interconnected over an Ethernet network. (Figure 2)
- Nonbroadcast multiaccess (NBMA) - Multiple routers interconnected in a network that does not allow broadcasts, such as Frame Relay. (Figure 3)
- Point-to-multipoint - Multiple routers interconnected in a hub-and-spoke topology over an NBMA network. Often used to connect branch sites (spokes) to a central site (hub). (Figure 4)
- Virtual links - Special OSPF network used to interconnect distant OSPF areas to the backbone area. (Figure 5)
A multiaccess network is a network with multiple devices on the same shared media, which are sharing communications. Ethernet LANs are the most common example of broadcast multiaccess networks. In broadcast networks, all devices on the network see all broadcast and multicast frames. They are multiaccess networks because there may be numerous hosts, printers, routers, and other devices that are all members of the same network.