In the earliest days of the web in 1990, web proxy servers were usually referred to as gateways. In fact the very first web gateway was created at CERN by the original WWW team , headed by Tim Berners-Lee.
Gateways are effectively devices which are used to forward packets between different networks. These devices can vary in complexity from simple pass through devices to complex system which are able to understand and convert different protocols. It was in 1993 that the name Web Proxy Server was chosen as a standard term to describe the different types of Web gateways.
These can be further classified into two distinct categories:
Proxy Server – internet/firewall gateways which act in response to client/PC requests.
Information Gateway – gateways which act in response to server requests.
However these are quite broad specification and below you will find some details of the key properties of the proxy servers and associated gateways. Remember that these classifications can be affected by any application software which is installed on the proxies. Particularly you may find that destinations and transparency may sometimes be modified.
Proxy Server Properties
These are the general properties which can be applied to any specific proxy server, there are variations which will affect these.
Transparency: these proxies do not modify the data passing through them. They will perform any filtering specified by rules but this will not affect the end result. The connection will be the same if it was direct or through the proxy server.
Control: the client will determine whether it is uses the proxy or not. This is typically controlled on the client by specifying the address of the proxy or through client based software.
Destination: the final destination of any request is not affected by any intermediate proxy. In fact a client or user will often be completely unaware of the existence of the proxy.
Proxies can provide all sorts of features some of which might affect these properties. They can be used to provide specific access controls, filtering, logging and even simply to speed up access to remote web resources through caching features.
It is in corporate environments that the transparency properties of proxies has usually been modified. Frequently these firewall proxy servers will sit in the DMZ (Demilitarized Zone) and control both inbound and outbound traffic. They will accept network requests from clients and forward them out to the internet if approved, then relay the replies back to the clients. Most of these will also operate caching services to ensure that duplicate requests don’t generate more network traffic and bandwidth charges.
The other advantage of the dual role proxies is that it can act as a single entry point for internet access. This means that all requests can be logged and monitored allowing an element of control to web access through the company infrastructure. It also allows replies to be monitored for harmful code such as malware and viruses, this is an important extra layer of security to protect the internal network.