Proxy firewalls, also known as proxy servers, are broken down into several different categories, depending on how they function. Features that govern proxy firewall categories include the firewall's level of anonymity, its protocol type or proxy agent type, and how the proxy identifies itself to those who request its information. Proxy firewalls can also be categorized by their features, which can change the purpose for which a firewall is used.
Types of proxy firewall agents are numerous, but common protocols include domain name service (DNS), hypertext transfer protocol (HTTP) and Telnet. These protocols are called application layer protocols, which are used in computer networking to help two computers in different locations connect to each other remotely. Different types of application protocols are used to accomplish different types of connection tasks on a network.
A proxy firewall is a server used as an intermediary between a user and a direct Internet connection. Proxy firewall setups are often used to hide the identity of the user accessing the Internet and to protect the user's computer from attacks sent from the Internet. A user accessing the Internet using a proxy server to protect his computer and hide his identity should know that a proxy is not infallible. Even with a proxy, privacy and protection can be compromised. Advanced hackers can use techniques to get past the protection afforded by proxy servers to acquire information and attack the user's computer.
Transparent proxies and non-transparent proxies are two types of proxy firewall categorized based on the anonymity they offer to the user. A transparent proxy offers protection against Internet attacks, but is less anonymous than a non-transparent proxy firewall. More anonymous than a transparent firewall, a non-transparent proxy firewall offers additional protections that alter proxy information or response patterns to prevent others from learning the computer information of the user behind the proxy.
In addition to privacy and protection against attacks, proxy servers can also be used to control web traffic traveling to and from a busy server. When a network has many users connecting to it, servers supplying that network can experience an overload if network traffic exceeds that which any individual server can handle. A proxy network can help keep servers from going down by controlling traffic to them.
Firewalls made for keeping servers afloat work by distributing server requests evenly. This can prevent heavy traffic from overloading and crashing a web server. Another use for this type of proxy is blocking unwanted web traffic, like when an employer blocks social networking sites within the network at the workplace. Since unwanted traffic on the server caused by casual browsing uses valuable web resources, this feature can also help improve network stability.