OSPF determines routes dynamically by obtaining
information from other routers and advertising routes to other routers
by way of Link State Advertisements (LSAs). The router keeps information
about the links between it and the destination and can make highly
efficient routing decisions. A cost is assigned to each router interface,
and the best routes are determined to be those with the lowest costs,
when summed over all the encountered outbound router interfaces
and the interface receiving the LSA.
Hierarchical techniques
are used to limit the number of routes that must be advertised and
the associated LSAs. Because OSPF dynamically processes a considerable
amount of route information, it has greater processor and memory
requirements than does RIP.