Advanced Infrastructure Penetration Testing

Open Shortest Path First

Open Shortest Path First (OSPF) is an open standard link state protocol based on RFC 1247. In an OSPF operation, routers send information to all the routers in the same area using link-state advertisements (LSA). Routers calculate the path using the Shortest Path First (SPF) algorithm. This algorithm is sometimes named the Dijkstra algorithm. It requires great processing power. OSPF also supports VLSM.

For better administration, OSPF uses a hierarchical topology. OSPF is composed by a backbone named Area 0 that connects with the other smaller areas. When a change occurs, routers get notified, get a copy of the LSA, and update the link state database (LSDB):

Before diving into how OSPF works, let's look at some important ...