Incomputer networks, aproxy server is aserver (computer) whichclients (people or computers) use to access other computers.[1][2] A proxy server that passes information to its clients without changing it is usually called agateway or sometimes calledtunneling proxy.[3][4]
Proxy servers get their name because they act like aproxy (a stand-in) and act on behalf of a client's computer.
A client that connects to the proxy server will ask for some service, such as a file, connection,web page, or other resource, that is available on adifferent server. The proxy server then goes to theother server and asks for what the client wants for them.
A proxy server can change the information that it gives to the client, and if the same information is accessed many times or by many different clients it can use what is called acache to make things faster. A cache is the term for information that has been accessed and saved for future use; if a proxy server has what the client is accessing in its cache, it will make it faster because it does not need to go and access the other server to provide what the client wants.
A proxy server can be placed anywhere in the connection between the client and the server, which could includesoftware on the client computer itself or on any computer between.
Some proxy servers useSecure Sockets Layer to secure the connection between the client and the remote server.[5] This security layer helps to make sure that no other computers can read or understand what the client is asking from the server.
There are many benefits of using a proxy server. First, the client machine can exchange data with the remote server without making a direct connection. This way, the client's realinternet address will not be known to the remote server. This is sometimes called anonymizing because it makes the clientanonymous. A second advantage is that when the proxy server itself is able to serve the request made by the client, it will not contact the remote server any more. So the load on the remote server will be reduced by using a proxy server.[6] This type of proxy servers is calledcaching servers.
Big organizations (or even countries) sometimes use proxy servers to control access to the Internet. A largebank may use a proxy server that only allows connections to other websites relevant to banking. The proxy server might block access to Websites offering free email or servingpornographic material. It might also block access tofile sharing applications. Limiting access to specific content on the internet is also calledinternet filtering.[7]
A proxy server may have one or more of the functions described below:
A caching proxy server can service requests from clients, without contacting the remote server; instead, it sends the data which it has stored from a previous request. This is calledcaching. Caching proxy servers reduce the work load of the remote server. However, they have their own problems, especially if they are not configured well. Some problems are described inRFC 3143.
A web proxy is a proxy server that focuses on the traffic over theWorld Wide Web. It may be used to block offensive web content, or to control access of clients to online content. They may be used bycorporations orcountries. Web proxies can also be used to track how different individuals have used internet access.
An anonymizing proxy server removes identifying information from the clients' requests, for the purpose ofanonymity. They may also be used to break through filtered contents on the internet.
A proxy server is called anopen proxy if everyone can connect to it and use it. Usually, open proxies are proxy servers which are badlyconfigured.[8] Open proxies may be abused easily; for example, a bad user may send a corrupting request to a remote server, but hide themself behind an open proxy, so the administrators of the remote server cannot stop them. Open proxies can also be used forspamming.[9] For this reason, some websites do not allow connections to their web servers or to edit content on them through known open proxies, including onWikipedia.
Aforced proxy server is a proxy server which handles all of the traffic from the client to the Internet.[10] The client will not know that the proxy exists, but all of the information passes through the proxy server. They are sometimes called "transparent" proxy servers, because the user does not know a proxy server is between the client and remote server.
ATransparent SMTP Proxy is aSMTP proxy server that is in between a sending mail server and a receiving mail server. The main purpose of the SMTP proxy is to filter outbound spam. The client and server believe that they are talking to each other even though there is a proxy in between.
There is a lot of software which can be used for running a proxy server. Some software can only work as a proxy server, while other software can also work as afirewall or caching server.[11]Squid,Varnish andMicrosoft Internet Security and Acceleration Server (ISA Server) are among the best known pieces of proxy server software.[12] Some proxy software uses theSOCKS protocol. An example is the Java SOCKS Proxy Server.[13]
