In computing, a firewall is a piece of hardware or software which functions in a networked environment to prevent some communications forbidden by the network policy, analagous to the function of firewalls in building construction.
The firewall has the basic task of controlling traffic between different zones of trust.
Typical zones of trust include the Internet ( a zone with no trust ) and an internal network ( a zone with high trust ).
The ultimate goal of the firewall is to prevent intrusion from a connected network device into other networked devices.
There are two kind of firewall:
The latter definition corresponds to the conventional meaning of "firewall" in networking, but the "port security check" addresses these two types of firewall.
These two types of firewall may overlap; indeed, single systems have implemented both together.