Though this protocol was developed long ago enough, it is rather new (compared to the HTTP proxy). SOCKS allows to work with any (version SOCKS 4 - with TCP, SOCKS 5 - with TCP and UDP) protocols. A socks proxy simply transfers data from a client to a server, not penetrating into this data contents (therefore it can work with HTTP, FTP, SMTP, POP3, NNTP, etc.).
As SOCKS (as it was already marked above) transfers all data from a client to a server, nothing adding from itself, from the point of view of a web-server, a socks proxy is a client. Therefore anonymity of this type of proxy servers is really always absolute.
At present time there exist 2 versions of the SOCKS protocol: 4 and 5. The 4th version, as it appeared earlier, is more widespread. However, now the 5th version is also supported by many popular programs such as ICQ (old ICQ versions, in general, could use only SOCKS proxies), Napster, AudioGalaxy, EeDoonkey2000 (MP3 files downloaders) etc. Generally speaking, as a SOCKS proxy can "proxy" any TCP / UDP protocol, it could be used also by mail programs, but they do not do it. Therefore, for such programs (which cannot work with socks) there was developed a special software automatically enabling TCP and UDP networking client applications to traverse a SOCKS server.
The most popular program is the SocksCap (http://www.sockscap.com). It allows to capture all traffic of a program and to route it onto a SOCKS proxy 4 or 5.
As SOCKS proxies transfer data between computers without changes, it easily allows to create chains of SOCKS proxy servers of arbitrary length. However, for creation of these chains it is necessary to use special programs, as usual software is capable to use only one SOCKS proxy.
An example of a program, allowing to create SOCKS chains and to control chains of SOCKS proxies, is the SocksChain program (http://www.ufasoft.com). With its help you can work with chains of SOCKS proxies of any length.
SOCKS proxies can be united into a chain with other types of proxy servers (HTTP and CGI). But they should be in the appointed place of this chain, namely, in the beginning.
You can create the following types of chains:
SOCKS proxy >>>> HTTP proxy >>>> CGI proxy
SOCKS proxy >>>> HTTP proxy
HTTP proxy >>>> SOCKS proxy
SOCKS proxy >>>> CGI proxy
Also you can not create:
CGI proxy >>>> SOCKS proxy
You can use a SOCKS proxy only if your corporate proxy is a SOCKS proxy. Otherwise you can hardly manage to use external SOCKS proxies.
Mail programs in their majority do not allow using proxy servers. This feature is not built-in in them. However, as it was already mentioned above, a SOCKS proxy allows passing through itself any TCP protocols (including POP3 and SMTP). To use a socks proxy for getting a mail, one must use a special program (for example SocksCap, http://www.sockscap.com). How to use these programs, it was already told above.
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