4-14 OSPF ConfigurationWhen configuring OSPF, go to these sections for information you are interested in:z OSPF Overviewz OSPF Configuration Task Listz Displaying and Maintaining OSPF Configurationz OSPF Configuration Examplesz Troubleshooting OSPF ConfigurationThe term router in this chapter refers to a router in a generic sense or an Ethernet switch running arouting protocol.OSPF OverviewIntroduction to OSPFOpen Shortest Path First (OSPF) is a link state-based interior gateway protocol developed by IETF. Atpresent, OSPF version 2 (RFC 2328) is used, which has the following features:z High applicability: OSPF supports various networks in size, and even networks with up to severalhundred routers.z Fast convergence: OSPF can transmit update packets immediately after the network topologychanges so that the change can be synchronized in the autonomous system (AS).z Loop-free: Since OSPF calculates routes with the shortest path first algorithm according to thecollected link states, it guarantees that no loop routes will be generated.z Area partition: OSPF allows an autonomous system network to be divided into different areas forconvenient management so that routing information transmitted between the areas is summarizedfurther, thereby reducing network bandwidth consumption.z Equivalent route: OSPF supports multiple equivalent routes to the same destination.z Routing hierarchy: OSPF has a four-level routing hierarchy. It prioritizes the routes as intra-area,inter-area, external type-1, and external type-2 routes.z Authentication: OSPF supports interface-based packet authentication to guarantee the security ofroute calculation.z Multicast transmission: OSPF supports transmitting protocol packets in multicast mode.OSPF Route CalculationTaking no account of area partition, the routing calculation process of the OSPF protocol is as follows:z Each OSPF-supported router maintains a link state database (LSDB), which describes thetopology of the whole AS. According to the network topology around itself, each router generates a
