What is a firewall? A firewall is a security device whose main purpose is to allow or deny data into or out of a network based on a set of configured rules.
Typically firewall rules use a combination of source IP, destination IP, source MAC, destination MAC, TCP port, UDP port, and protocol to determine if traffic is allowed. Within traditional firewalls (as opposed to Next Generation Firewalls) once a traffic stream has been allowed based on a rule, there is no further inspection of that traffic stream.
|Basic Firewall Example|
Firewalls do not look any deeper than source, destination, port, and protocol to determine if traffic is allowed or not.
Firewalls can be used to control traffic into or out of any network at any place in your LAN or WAN. Firewalls are most often put at the internet edge and are often seen controlling traffic into and out of the data-center or segmenting the desktop networks from the rest of the LAN.