2.1.3 How routing information is maintained
Link-state routing uses the following features:
Link-state advertisements (LSAs)
A topological database
The shortest path first (SPF) algorithm
The resulting SPF tree
A routing table of paths and ports to each network to determine the best paths for packets 
Link-state routing protocols were designed to overcome the limitations of distance vector routing protocols. For example, distance vector protocols only exchange routing updates with immediate neighbors while link-state routing protocols exchange routing information across a much larger area.
When a failure occurs in the network, such as a neighbor becomes unreachable, link-state protocols flood LSAs using a special multicast address throughout an area. Each link-state router takes a copy of the LSA and updates its link-state, or topological database. The link-state router will then forward the LSA to all neighboring devices. LSAs cause every router within the area to recalculate routes. Because LSAs need to be flooded throughout an area, and all routers within that area need to recalculate their routing tables, the number of link-state routers that can be in an area should be limited.
A link is the same as an interface on a router. The state of the link is a description of an interface and the relationship to its neighboring routers. For example, a description of the interface would include the IP address of the interface, the subnet mask, the type of network to which it is connected, the routers connected to that network, and so on. The collection of link-states forms a link-state database, sometimes called a topological database. The link-state database is used to calculate the best paths through the network. Link-state routers find the best paths to destinations. Link-state routers do this by applying the Dijkstra shortest path first (SPF) algorithm against the link-state database to build the shortest path first tree, with the local router as the root. The best paths are then selected from the SPF tree and placed in the routing table.
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