Exchange Without a Designated Router

As discussed in Chapter 7, an OSPF interface’s network type tells a router whether to attempt to elect a DR on that interface. The most common case for which routers do not elect a DR occur on point-to-point topologies, such as true point-to-point serial links and point-to-point subinterfaces. This section examines the database exchange process on such interfaces, in preparation for the slightly more complex process when using a DR on an OSPF broadcast network type, like a LAN.

Each OSPF neighborship begins by exchanging Hellos until the neighbors (hopefully) reach the 2-Way state. During these early stages, the routers discover each other by sending multicast Hellos and then check each other’s parameters ...

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