A firewall is a network security system, whether based on software or hardware. This system is used to control outbound and inbound network traffic.
The firewall acts as a barrier between a trusted network and an untrusted network. Firewalls control access to a network’s resources through a positive control model. This means that if the allowed traffic into the network is determined by the firewall policy, all other traffic is rejected.
Firewall itself borrowed from the term firefighting and fire prevention. A firewall is a barrier created to prevent the spread of fire.
As organizations or companies begin to move from mainframe computers and dispose of client computer models to client-server, the ability to control access to the server becomes a priority. Before a firewall emerged in the late 1980s, the network security form was performed by access control lists (ACLs) that existed on the router. ACLs specify the IP addresses that are allowed or not allowed to access the network.
The growth of the internet and the result of increased network connectivity means that this type of filtering is no longer enough to prevent malicious traffic as basic information about network traffic contained in the packet header. Digital Equipment Corp. marketed its first commercial firewall (DEC SEAL in 1992) and since then the firewall technology has begun to evolve to counter the increasingly sophisticated cyber attacks.