Along with a firewall, a proxy server provides additional security. The proxy server acts on behalf of either a server or client. It takes packet requests and process them through a firewall, if one is present, and passes the results back to the original requestor. This handing off provides a shield to the client that uses the proxy server by masking and filtering requests. This looks like a firewall, but a firewall does not provide alias identities to its users—only filtering. A single computer might run multiple servers, with each server connection identified by a port number. A proxy server, like an HTTP server or an FTP server, occupies a port. Typically, a connection uses standardized port numbers for each protocol. For example, HTTP is 80, and FTP is 21. Unlike common server protocols, however, the proxy server has no default port. Many of today's proxy servers also provide caching capabilities. The caching capability gives the end user the impression of wider bandwidth. This is because it takes information that has been passed and saves it in cache. When the user requests the information again, it is provided via the cache instead of going onto the Internet. Proxy servers also can be used in exclusive intranet situations in which the use of the caching capability has more significance. There are currently no proxy servers for the NT system.
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