| 6.3 |  | Routing Protocols Overview |
| 6.3.6 |  | Link-state |

| Link-state algorithms (also known as shortest path first algorithms) flood routing information to all routers in the internetwork that creates a map of the entire network. Each router sends packets to all its neighbors. These packets contain descriptions of the network or networks to which the router is linked. The routers assemble all the information into a complete view of the internetwork topology to calculate the shortest path to all known sites on the network. It then generates routing tables showing the best path for any destination on the network. Once converged, link state protocols use small update packets, which contain only changes rather than copies of the entire routing table. Update packets are passed across the network in event-triggered updates, so convergence is fast. Because they converge more quickly than distance vector protocols, link-state algorithms are less prone to routing loops. Link-state protocols are also less prone to routing errors, but they use more system resources. Link-state protocols, therefore, can be more expensive to implement and support. However, they are generally more scalable than distance vector protocols. When a network link changes state, a notification called a link-state advertisement (LSA) is flooded throughout the network. All the routers note the change and adjust their routes accordingly. This method is more reliable, easier to debug, and less bandwidth-intensive than distance vector. OSPF and IS-IS are examples of link-state routing protocols.