An organization should secure both its LAN and its Internet server. Computer security threats continue to increase. Part of the problem is that break-ins often go undetected. One study used common hacker tools to break into Department of Defense systems. With the Internet, security policy and technology must reflect distributed computing.
More entrances equal more risk.
Firewalls should deny all access except that explicitly allowed. Similarly, hosts should provide no services except those explicitly intended. Firewalls may use a packet inspection or proxy architecture. In packet inspection, the system picks information off at the datalink layer and filters it against a rules table. Depending on compliance, the system may respond by dropping the incoming packet, passing it through, logging it, sending an acknowledgment, and so forth.