In the usual case, all the clients within a given subnet use the same proxy server. This makes it possible for the proxy to cache documents efficiently that are requested by a number of clients. People using a proxy server should feel as if they are getting responses directly from remote servers . The proxy IP address is the only information they need. Most proxy servers are implemented on a per-access method basis.
Proxy servers can allow or deny internet requests according to the protocol of the requests.
For instance a proxy server can allow calls to FTP servers while denying calls to HTTP servers. Some machines on your local network might not be able to directly access Internet resources. For instance, some browsers might not be able to directly access Internet resources because they run on systems behind a protective firewall. In these cases, a proxy server can retrieve the desired files for them. You could also run the proxy server on another internal host that has full internet access, or on a machine inside the firewall.