A Firewall is a dedicated network box (usually
implemented in the organisation's "gateway" router) situated
between the Internet and an organisation's private network, thus:
There are three classes of Firewall:
Packet filtering firewalls
Application gateways
Circuit level gateways
Of these, the packet filtering type is the most common.
Because the firewall is not a general-purpose host, it does not
itself run any vulnerable server processes.
