All Networks Include VAT
A firewall is a network security system, either hardware- or software-based, that uses rules to control incoming and outgoing network traffic.
A firewall acts as a barrier between a trusted network and and an untrusted network. A firewall controls access to the resources of a network through a positive control model. This means that the only traffic allowed onto the network is defined in the firewall policy; all other traffic is denied.
Computer security borrowed the term firewall from firefighting and fire prevention, where a firewall is a barrier established to prevent the spread of fire.
When organizations began moving from mainframe computers and dumb clients to the client-server model, the ability to control access to the server became a priority. Before firewalls emerged in the late 1980s, the only real form of network security was performed by access control lists (ACLs) residing on routers. ACLs determined which IP addresses were granted or denied access to the network.
The growth of the internet and the resulting increased connectivity of networks meant that this type of filtering was no longer enough to keep out malicious traffic as only basic information about network traffic is contained in the packet headers. Digital Equipment Corp. shipped the first commercial firewall (DEC SEAL in 1992) and firewall technology has since evolved to combat the increasing sophistication of cyberattacks.