A static forwarding table works only while topology and policy remain unchanged. Dynamic routing protocols let routers exchange information and recompute routes when the network changes.

A routing protocol must answer three questions: what information is exchanged, how that information determines preferred routes, and how routers react when links or neighbors change.

After a change, routers need time to reach a mutually consistent set of routes. This process is called convergence. During convergence, packets may temporarily take suboptimal paths, encounter loops or become unreachable.

Routing protocols therefore balance several goals: route quality, fast convergence, communication and computation cost, scalability, and administrative policy.

Different protocol families solve these trade-offs differently; distance-vector, link-state and path-vector routing are major reusable approaches.