why do we put router above the bridge?

Answer 1

Wow, their is a term I haven't heard in a while. We don;t us "bridges" anymore, a Switch does the same thing. Either way, in he old days before switches, when we had hubs (which were just dumb devices) we used bridges to join local networks together that were on the same subnet. A router joins networks that are on different subnets.

Answer 2

Bridges work at layer 2 of the OSI model.
Routers work at layer 3 of the OSI model.

You use a bridge when you've exceeded the maximum number of repeater hops or you need to change topology.

You use a router to divide the layer 3(tcp/ip) network into logical segments.

Answer 3

Bridge is also use to breakup collision domains,

in a switched network this is not needed as every port on a switch is its own collision domain.

Answer 4

to connect two routers together i.e. to expand your network either direct or via a computer.