How does a firewall effectively control traffic?

Answer 1

A firewall intercepts and controls traffic between networks with differing levels of trust. It is part of the network perimeter defense of an organization and should enforce a network security policy.

Answer 2

A firewall can help you bring in or block out certain types of traffic. If you are being bogged down with loads of traffic from a certain network you can set the firewall to block those connections. Same goes as if you wanted to allow certain other connections. It's basically like a toll gate, you can pass along certain things and reverse others.

Answer 3

Thru firewall you can block ports which you normally dont use and also restrict certain programmers that you dont want to give internet access .