Q.17,paper2,june 12. In which Routing Method do all the routers have a common database ?

Options            (A) Distance vector        (B) Link state     (C) Link vector   (D) Dijkestra method

Answer (B) Link state.

Explanation. 

Distance Vector" and "Link State" are terms used to describe the routing protocols which are used by routers to forward packets between networks. The purpose of any routing protocol is to dynamically communicate information about all network paths used to reach a destination and to select the from those paths, the best path to reach a destination network. The terms distance vector and link state are used to group routing protocols into two broad categories based on whether the routing protocol selects the best routing path based on a distance metric (the distance) and an interface (the vector), or selects the best routing path by calculating the state of each link in a path and finding the path that has the lowest total metric to reach the destination. Link state protocols know whether a link is up or down and how fast it is and calculates a cost to 'get there'. Since routers run routing protocols to figure out how to get to a destination, you can think of the 'link states' as being the status of the interfaces on the router. Link State protocols will take a path which has more hops, but that uses a faster medium over a path using a slower medium with fewer hops.

Because of their awareness of media types and other factors, link state protocols require more processing power (more circuit logic in the case of ASICs) and memory. Distance vector algorithms being simpler require simpler hardware.