Link State Routing Explained

A Fundamentally Different Approach to Routing

Instead of only trusting what neighbors report (as distance vector does), link state routing has every router build a complete map of the entire network's topology, then independently calculate the best path to every destination.

How Link State Routing Actually Works

1. Each router discovers its directly connected neighbors and the "cost" (a metric like bandwidth or delay) of each link.
2. Each router floods this information - its own local link states - to every other router in the network, not just its immediate neighbors.
3. Every router ends up with an identical, complete map of the whole network's topology.
4. Each router independently runs a shortest-path calculation (Dijkstra's algorithm) on that map to determine its own best routes.

Why Having the Full Map Helps

Distance Vector: "My neighbor says Network X is 2 hops away" (trust, no visibility)
Link State:      "I can see the entire network and calculate the actual shortest path myself"

Because every router has the same complete picture, link state protocols converge much faster after a change and are far less prone to the routing loops that can affect distance vector protocols.

The Trade-off: More Resources Required

Building and storing a full network map, and recalculating shortest paths, demands more memory and processing power than the simpler distance vector approach - a reasonable trade-off for the faster convergence and greater accuracy it provides.

Where This Approach Is Used

OSPF (covered in its own note in this section) is the most widely used link state protocol, and is the standard choice for medium-to-large enterprise networks where fast convergence genuinely matters.