OSPF - NBMA neighbors listen on 224.0.0.5
In an OSPF topology, an OSPF router configured using the NBMA network type will listen for hellos on the 224.0.0.5 multicast address to discover OSPF neighbors. If an OSPF hello is received, an NBMA OSPF router will respond with a unicast hello to that neighbor. This means that an OSPF neighbor configured with a broadcast network type can create an adjacency with an NBMA network type neighbor.
This is the case even if the NBMA neighbor has no manually configured neighbor command.