As organizations consider connecting to the Internet, the issue of internetwork security becomes more important. There are many tools and components that can be used to secure a network, one of which is a firewall. Modern firewalls offer highly flexible private network security by controlling and monitoring all communications passing into or out of the private network. Specifically designed for security, firewalls become the private network's single point of attack from Internet intruders. Application gateways (or proxies) that have been written to be secure against even the most persistent attacks ensure that only authorized users and services access the private network. One-time passwords prevent intruders from `sniffing' and replaying the usernames and passwords of authorized users to gain access to the private network. Comprehensive logging permits constant and uniform system monitoring. `Address spoofing' attacks are prevented. The private network may use registered or unregistered IP addresses behind the firewall. Firewall-to-firewall encryption establishes a `virtual private network' across the Internet, preventing intruders from eavesdropping on private communications, eliminating the need for costly dedicated lines.