History
Before the advent of stateful firewalls, a stateless firewall, a firewall that treats each network frame (or packet) in isolation, was normal. Such packet filters operate at the Network Layer (layer 3) and function more efficiently because they only look at the header part of a packet. A drawback of pure packet filters is that they are stateless; they have no memory of previous packets which makes them vulnerable to spoofing attacks. Such a firewall has no way of knowing if any given packet is part of an existing connection, is trying to establish a new connection, or is just a rogue packet. Modern firewalls are connection-aware (or state-aware), offering network administrators finer-grained control of network traffic.
The classic example of a network operation that may fail with a stateless firewall is the File Transfer Protocol (FTP). By design, such protocols need to be able to open connections to arbitrary high ports to function properly. Since a stateless firewall has no way of knowing that the packet destined to the protected network (to some host's destination port 4970, for example) is part of a legitimate FTP session, it will drop the packet. Stateful firewalls solve this problem by maintaining a table of open connections and intelligently associating new connection requests with existing legitimate connections.
Early attempts at producing firewalls operated at the Application Layer, which is the very top of the seven-layer OSI model. This method required exorbitant amounts of computing power and is rarely used in modern implementations.
Read more about this topic: Stateful Firewall
Famous quotes containing the word history:
“The only history is a mere question of one’s struggle inside oneself. But that is the joy of it. One need neither discover Americas nor conquer nations, and yet one has as great a work as Columbus or Alexander, to do.”
—D.H. (David Herbert)
“... in America ... children are instructed in the virtues of the system they live under, as though history had achieved a happy ending in American civics.”
—Mary McCarthy (1912–1989)
“To a surprising extent the war-lords in shining armour, the apostles of the martial virtues, tend not to die fighting when the time comes. History is full of ignominious getaways by the great and famous.”
—George Orwell (1903–1950)