In this case, backbone connectivity must be restored through virtual links . Virtual links are configured between any backbone routers that share a link to a nonbackbone area, and function as if they were direct links. The SPF routing algorithm is the basis for OSPF operations. When an SPF router is powered up, it initializes its routing protocol data structures and then waits for indications from lower-layer protocols that its interfaces are functional. Hello protocol to acquire neighbors .
Neighbors are routers with interfaces to a common network.
The router sends hello packets to its neighbors and receives their hello packets. In addition to helping acquire neighbors, hello packets also act as keepalives to let routers know that other routers are still functional. The designated router is responsible, among other things, for generating LSAs for the entire multiaccess network. Designated routers allow a reduction in network traffic and in the size of the topological database. When the link state databases of two neighboring routers are synchronized, the routers are said to be adjacent .