OSPF Network Types
OSPF message addresses are determined by the type of network to which the OSPF interface is connected. One of the following OSPF network types must be selected when configuring an interface on an OSPF router.
Broadcast A network that can connect more than two routers with a hardware broadcast facility where a single packet sent by a router is received by all routers attached to that network. Ethernet, Token Ring, and FDDI are broadcast networks. OSPF messages sent on broadcast networks use IP multicast addresses.
Point-to-Point A network that can connect only two routers. Leased-line WAN links such as Dataphone Digital Service (DDS) and T-Carrier are point-to-point networks. OSPF messages sent on point-to-point networks use IP multicast addresses.
Non-Broadcast Multiple Access A network that can connect more than two routers but has no hardware broadcast facility. X.25, Frame Relay, and ATM are Non-Broadcast Multiple Access (NBMA) networks. Because multicasted OSPF messages do not reach all the OSPF routers on the network, OSPF must be configured to unicast to the IP addresses of the routers on the NBMA network.
OSPF communication on these network types is discussed in "OSPF Communication on OSPF Networks" later in this chapter.
The use of OSPF over nonpermanent, non-persistent, dial-up WAN links such as analog phone lines or ISDN is not recommended.