Because of the interrelationship of OSPF terms and concepts, this chapter frequently uses terms before they are fully defined. The reader is advised to read this section more than once to ensure a complete understanding of OSPF operation. It will also be useful to review the section “Link State Routing Protocols” in Chapter 4, “Dynamic Routing Protocols.”
At a very high level, the operation of OSPF is easily explained:
OSPF-speaking routers send Hello packets out all OSPF-enabled interfaces. If two routers sharing a common data link agree on certain parameters specified in their respective Hello packets, they will become neighbors.
Adjacencies, which may be thought of as virtual point-to-point links, are formed ...