Part 1 of Essay
The term firewall has seen limited use since the late 1980s to describe a device to block unwanted network traffic while allowing other traffic to pass. The first published description of a "modern" firewall including use of that name was in 'Practical Unix Security' written in 1990 and published in 1991. The first descrip ....

Part 2 of Essay
.... means by which this is accomplished varies widely, but in principle, the firewall can be thought of as a pair of mechanisms: one that exists to block traffic, and the other that exists to permit traffic. Some place a greater emphasis on blocking traffic, while others emphasize permitting traffic. Probably the most important thing to recognize about a firewall is that it implements an access control policy. The Internet, like any other society, is plagued with the kind of jerks who enjoy the electronic equivalen ....