An access control list on a router consists of a table that stipulates which kinds of traffic are allowed to access the system. The router is placed between the incoming traffic and the rest of the network or a specific segment of the network, such as the demilitarized zone (DMZ). The ACL examines the information held within data packers lowing into or out of the network to determine where it came from and where it is going. The ACL on the router then decides whether the data packet should be allowed to pass to the other side.