Open Shortest Path First (OSPF) is a link-state routing protocol that was developed as a replacement for the distance vector routing protocol, RIP. RIP was an acceptable routing protocol in the early days of networking and the Internet. However, RIP's reliance on hop count as the only metric for determining best route quickly became problematic. Using hop count does not scale well in larger networks with multiple paths of varying speeds. OSPF has significant advantages over RIP in that it offers faster convergence and scales to much larger network implementations.

OSPF is a classless routing protocol that uses the concept of areas for scalability. This chapter covers basic, single-area OSPF implementations and configurations.