what constitutes a firewall
A firewall is a system designed to prevent unauthorized access to or from a private network. You can implement a firewall in either hardware or software form, or a combination of both. Firewalls prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. The firewall capabilities lie in the fact that a proxy can be configured to allow only certain types of traffic to pass (e.g., HTTP files, or web pages). 2  A proxy server has the potential drawback of slowing network performance, since it has to actively analyze and manipulate traffic passing through it.