Proxy services

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A proxy server as the name implies acts as a replacement for another computer. It takes over the requests from a client for a web page for example and starts the requests instead of the clients. So the client is hidden for the server. The proxy server additionally can filter for viruses or unwanted content. It can also make the requested sites faster.

 

In simplest cases the proxy only forwards information. The user does not recognize the existence of it when it runs in transparent mode. The proxy - in most cases a http proxy - only controls the communication between the web browser (client) and the web server. Main functionalities are:

 

Cache: The proxy saves the sites that are visited by a user in a cache. When the same site is requested by another user it is fetched from the cache and not from the web page directly again. This functionality fastens the requests and decreases the load at the net.
Filter: The proxy allows filtering the visited sites for viruses or unwanted content. This can only be done because the proxy can put the single packets together to a whole http packet. It understands the traffic passing. The proxy is situated at the application level of the ISO/OSI layers model. Filtering can only be done by a proxy.
Access control: A proxy can be used to control the access to separate sites or the whole Internet to single users or groups of users.

 

There are proxy servers for several Internet services. The following proxies are part of the Gibraltar firewall software:

 

HTTP proxy: Acts as sub-agent and checks for viruses and unwanted content (only with separate licenses).
SMTP proxy: Checks email traffic between mail servers. Allows checks for viruses and unsolicited bulk emails (spam) - also called Mail Relay.
POP3 proxy: Checks emails traffic that is fetched by the client from a POP3 server. Allows checks for viruses and spam.
FTP proxy: Checks ftp traffic for viruses (only with separate license).

 

 

Transparent Proxy

 

A proxy is called transparent if the client does not need to change anything at his client to use the proxy. Additionally it is not possible to bypass the proxy. Requests to the special port (e.g. HTTP proxy to port 80) are redirected to the port where the proxy listens. The user has no possibility to bypass the proxy. All proxies within the Gibraltar software can be run in transparent mode.