Introduced in 1991, OSPFv2 is a link-state routing protocol for IPv4. OSPF was designed as an alternative to another IPv4 routing protocol, RIP.

The figure shows the topology used for configuring OSPFv2 in this section. The types of serial interfaces and their associated bandwidths may not necessarily reflect the more common types of connections found in networks today. The bandwidths of the serial links used in this topology were chosen to help explain the calculation of the routing protocol metrics and the process of best path selection.

The routers in the topology have a starting configuration, including interface addresses. There is currently no static routing or dynamic routing configured on any of the routers. All interfaces on routers R1, R2, and R3 (except the loopback on R2) are within the OSPF backbone area. The ISP router is used as the routing domain’s gateway to the Internet.

Note: In this topology the loopback interface is used to simulate the WAN link to the Internet.