| 2.1.2 Link state routing protocol
Link-state routing protocols collect routing information from all other routers in the network or within a defined area of the network. Once all of the information is collected, each router, independently of the other routers, calculates its best paths to all destinations in the network. Because each router maintains its own view of the network, it is less likely to propagate incorrect information provided by any of its neighboring routers.
Link-state routing protocols perform the following functions:
Each router keeps track of the state or condition of its directly connected neighbors by multicasting hello packets. Each router also keeps track of all the routers in its network or area of the network by using link-state advertisements (LSAs). The hello packets contain information about the networks that are attached to the router. In Figure  , P4 knows about its neighbors, P1 and P3, on Perth3 network. The LSAs provide updates on the state of links that are interfaces on other routers in the network.
A router running a link-state protocol has the following features:
Uses the hello information and LSAs it receives from other routers to build a database about the network
Uses the shortest path first (SPF) algorithm to calculate the shortest route to each network
Stores this route information in its routing table
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