OSPF network type

OSPF Network Broadcast
Default on broadcast medias (Ethernet / Token Ring)
Sends hellos as multicast
Performs DR/BDR Election

OSPF Network Non-Broadcast
Default on multipoint NBMA medias (Frame Relay / ATM)
Sends hellos as unicast ("neighbor" command)
Performs DR/BDR Election

OSPF Network Point-to-Point
Default on point-to-point medias (HDLC / PPP)
Sends hellos as multicast
No DR/BDR Election
Only two neighbors on the segment

OSPF Network Point-to-Multipoint
Not a default option
Sends hellos as multicast
No DR/BDR Election
Modifies next-hop processing (Best option for NBMA)

Point-to-Multipoint Non-Broadcast
Not a default option
Sends hellos as unicast ("neighbor" command)
No DR/BDR Election
Modifies next-hop processing

OSPF Network Loopback
Loopback and Looped back interfaces
Advertises network as a stub host (/32 host route)