Overview
Open Shortest Path First (OSPF) is a link-state routing protocol based on open standards. Described in several RFCs, most recently RFC 2328, the Open in Open Shortest Path First means that OSPF is open to the public and nonproprietary. Among nonproprietary routing protocols, such as RIPv1 and RIPv2, OSPF is preferred because of its remarkable scalability. Recall that both versions of RIP are very limited. RIP can not scale beyond 15 hops, it converges slowly, and it chooses suboptimal routes that ignore critical factors such as bandwidth. OSPF addresses all of these limitations and proves to be a robust, scalable routing protocol appropriate for today's networks.

OSPF's considerable capability to scale is achieved through hierarchical design. You can divide an OSPF network into multiple areas, which allows for extensive control of routing updates. By defining areas in a properly designed network, an administrator can reduce routing overhead and improve performance. Multiarea OSPF is discussed in Chapter 5, Multiarea OSPF.