Neighbors 395Static Neighbors On broadcast networks such as Ethernet, the OSPF Hello protocol usesthe broadcast capability to dynamically discover neighbors. Onnonbroadcast networks, such as X.25 Public Data Network, however, youmay need to assist in neighbor discovery by statically defining neighborson each interface. OSPF then uses the Hello protocol to maintain theneighbors that you statically define.When you statically define a neighbor on the system, you specify boththe router interface to which you want to add the neighbor and the IPaddress of the neighboring router that you want to associate with thespecified interface. The Hello protocol then dynamically retrieves theadditional neighbor information, as described in “Neighbor Information”in the previous section.ImportantConsiderationsConsider the following guidelines when you configure neighbors:n Routers use OSPF hello packets to learn neighbor addressesdynamically on broadcast networks.n Define static neighbors only on nonbroadcast interfaces, becauseneighbors are not learned dynamically on nonbroadcast networks.n Hello packets are the only OSPF packet type that is processed by allrouters within an area. All other packet types are sent and receivedonly on adjacencies.n Neighbor adjacencies cannot be formed if two routers have differentHello intervals, Dead intervals, or passwords.
