In the beginning there was nothing, which exploded. ~ Terry Pratchett, Lords and Ladies
Warning: Do not execute these on a network or system that you do not own. Execute only on your own network or system for learning purposes. Do not execute these on any production network or system, unless Rules of engagement have been agreed on, and you have a Get out of jail free card.
Routers and switches route and direct packets on the network and enable communications at the lowest layer. Gaining control over these devices, one can likely gain control over the entire network.