Single-area OSPFv2: neighbors and adjacencies, point-to-point vs broadcast networks, DR/BDR election

OSPF (Open Shortest Path First) is an open-standard link-state routing protocol, and OSPFv2 carries IPv4 routes. Instead of passing whole routing tables between neighbours, each OSPF router describes its own links in link-state advertisements (LSAs), floods them so every router in the area holds an identical link-state database (LSDB), and runs the SPF (shortest path first) algorithm to compute the best routes. In a single-area design, all routers are in area 0, the backbone. OSPF's metric is cost, based by default on interface bandwidth.