Firewall Fundamentals

Application proxy firewalls are perhaps the most complex firewalls to implement. This complexity is due in large part to the fact that unlike other firewall technologies, application proxy firewalls can make filtering decisions based on the actual application data, which requires that firewall administrators better understand the applications that will traverse the firewall. Practically speaking, two elements comprise an application proxy firewall:

• Application layer filtering

• Proxy server functionality

This chapter looks at those two elements to an application proxy firewall and then specifically examines how the Microsoft ISA Server 2004 firewall functions.