A Firewall is usually implemented in the
organisation's "gateway" router, situated at the interface 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 simply an enhanced router (and
not a general-purpose computer system/host), it
does not itself run any vulnerable server processes.
