> Imagine a situation with no access to any means of direct communication > (phone etc). You've got a message to deliver to some person, and have no > idea where to find that person. Chances are there's a group of people > nearby you can ask. They may know how to find the one you're looking > for. If not they may know others they can ask on your behalf. Several > iterations later the person is located and you've established a path > through which you can pass the information you wanted. > > Translated into cisco terms this mean that the FIB is just a partial > routing database, enough to start the search and otherwise handle > communications in the neighborhood (no more than X router-hops, maybe > AS-hops away). When the destination is located you keep that information > for a while in case there are more packets going to the same place, > similar to what you do with traditional route-cache.
check out "The Landmark Hierarchy: A New Hierarchy for Routing in Very Large Networks"; Paul Tsuchiya; 1989. randy