What is one fundamental difference between distance vector routing protocols and link state routing protocols?

Distance vector protocols exchange their routing tables, and add a metric to each route. Link-state routing protols exchange topology information, then calculate the routes. As a result, there are the following fundamental differences:

  • The information that is exchanged - routing table vs. topology information.
  • Link-state protocols know the topology of the network (or an area); distance vector routing protocols don't.
  • When the best route is calculated: in distance-vector routing protocols, a metric is added while the route is propagated from router to router. In link-state protocols, the best route is calculated separately by each router, only after having complete topology information.