The prevailing alternative and the one that is used in most operational networks today is link state routing. In link state routing, each node distributes a network map to every other node in the network. And then, each node performs a shortest path computation between itself and all other nodes in the network. So initially, each node adds the cost of its immediate neighbors, D(v), and every other distance to a node that is infinite. Then each node floods the cost between nodes u and v to all of its neighbors. And the distance to any node v becomes the minimum of the cost between u and w plus the cost to w. Or the current shortest path to v. The shortest path computation is often called the dijkstra, shortest path ROUTING ALGORITHM. Two common link state routing protocol are open shortest paths first or OSPF and intermediate system – intermediate system or IS-IS. In recent years, IS-IS has gained increasing use in large internet service providers and is the more commonly used. Link state routing protocol in large transit networks today. One problem with link state routing is scale. The complexity of a link state routing protocol grows as n cubed where n is the number of nodes in the network.