On multi-access networks, the Designated Router and Backup Designated Router form what are called FULL adjacencies. They form those with each other and they form those with all routers on the multi-access network. Databases are synchronized and LSAs propagate along the adjacencies, as the diagram shows. Otherwise, neighbor relationships between routers which are not DR or BDR are called 2WAY. They see each other in "Hello" packets, but do not exchange topology information. These neighbors are then not adjacent. And we can see in the diagram two routers which are operating in 2WAY state. Looking at some examples using the Cisco IOS configuration syntax, to find an adjacency state we use the: "show ip ospf neighbor" command. For OSPFv3 we can do: "show ipv6 ospf neighbor" For a Point-to-Point link, will see the state sitting as FULL. On our broadcast media we can see routers in a FULL state, but with either DR or BDR or in 2WAY state, as the slide shows.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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