What Is A Proxy?

A proxy is a program that sits between a client and a server, forwarding requests and responses between them. The client connects to the proxy instead of the server, and sends the requests. The proxy in turn connects to the server and forwards the client request, receives the response and forwards it to the client.
Unlike bridges and routers, which work at a level ISO / OSI lower proxies in most cases they work at application level and therefore a proxy program runs a limited number of application protocols.
Other uses of the term proxy

The SOCKS protocol achieves instead a form of transport-level proxy that simply forwards TCP and UDP connections between clients and servers, without analyzing the application protocols. There are two types of protocols Socks: Socks 4 and Socks 5. The Socks 4 proxy allows you to work only with TCP protocols such as HTTP (web browsing), NNTP newsgroup access, IRC, and the Socks 5 proxy is more advanced, allowing you to make anonymous even UDP protocols (e.g., ICQ).
Proxy ARP is a feature that can be taken on some routers to create special configurations.
The SIP proxy is a component of a VoIP or multimedia communications architecture, which is used as a contact point for terminals that must communicate with each other, and in some cases as an actual proxy between the terminals.
The proxy variable is used to give an approximate quantitative representation of a phenomenon related to the variable but not directly measurable in a most objective manner. For example, business education training hours provided to employees in a certain period may be a proxy that measures the increase of knowledge in employees, a phenomenon not measured objectively.

HTTP Proxy

A case in which a proxy is often used for web browsing (HTTP proxy called by the name of the protocol used).
To use a proxy you can configure your client that connects to the proxy server instead of, or establish a transparent proxy, in which case, depending on the configuration, some connections (for example, HTTP) are automatically sent to the proxy without need to configure a client (so the setting remains active even changing client).
A proxy can be used for one or more of the following reasons:
* Connectivity to enable a private network to access Internet you can configure a computer to make a proxy between the other computers and the Internet in order to keep a single computer connected to the outside, but allow all to access . In this situation, the proxy is usually used as a firewall.
* Caching: A proxy can be stored for a time the results of user requests, and if someone else makes the same requests can be answered without having to consult the original server. By placing a proxy in a position “close” to users, this allows improved performance and reduced consumption of bandwidth.

* Monitoring: A proxy can allow you to keep track of all transactions carried out (for example, all web pages visited), enabling network usage statistics and observations that may also violate privacy.
* Control: a proxy can apply rules defined by the system administrator to determine which applications to forward and which to reject or restrict the bandwidth used by the client, or filter web pages in transit, such as blocking those whose content is considered offensive according to certain rules.
* Privacy: A proxy can ensure a greater level of privacy by masking the true IP address of the client to the server is not aware of the person making the request.
When configuring the network can connect to the Internet only through a proxy, are obviously not used many types of applications based on protocols are not supported by proxy, for example:
* On-line Games
* Webcam: receiving and sending images via webcam with instant messaging programs
* Browsers that do not support the configuration of a proxy. This case is frequently on special devices like game consoles or mobile phones.
* VoIP services
* File sharing applications
Some of these applications have been modified to be able to pass its traffic encapsulated in HTTP, and then to be able to convey in a proxy.
HTTP proxy and anonymity
The external server to which you connect through a proxy will usually connections from the IP address of the proxy, not of the client. This provides a degree of privacy of the client (the server, or who inspect the traffic directed to it, can not know the client IP address), but can also cause problems if those sites use the IP address of the client for purposes of authentication or identification of the sessions.

The HTTP protocol, however, provides that a proxy can put in requests to the server that forwards standardized headers, which allows understanding that the request was forwarded by a proxy, and may also contain the client’s IP address, which in this way can be known to a server properly configured.
When using this feature, the web server “trusts” of the address sent by the client proxy, and can not in any way to verify this information. The administrator of a proxy can decide whether or not to send these headers.
The HTTP proxy, depending on the anonymity that can provide, can be divided into:
* Not anonymous: changing some header sent by the browser and adds others, also show the real IP address of the applicant. They are very easy to be recognized by the web server.
* Anonymous: do not send the IP of the applicant, but modify or add some headers. These are therefore easily recognizable.
* Distorting: transmitting a random IP, other than the applicant, and modify or add some headers. They are usually mistaken for anonymous proxy, but offer greater protection, because the web server sees the user requests from different IP addresses.
* Highly anonymous: do not send the IP of the applicant and do not alter the headers of the request. These are difficult to recognize through the normal controls.
There are programs that build on peer to peer technology to provide functionality proxy “anonymizing” (a proxy server that forwards to the IP address of client).
The HTTP protocol is stateless, ie a request not to leave any state in the server. However, to achieve complex web applications were developed in the higher level mechanisms such as cookies to build “sessions.” These mechanisms can enable the web server to obtain information on the client despite the efforts made by proxy to protect the anonymity, in particular, can afford to recognize a user to a web server even if they are connected by networks are completely different.
To see if the proxy server allows anonymous browsing, i.e., if the client IP does not disclose to any other server on the network, it is required to check the “Who-is”. The site server for the Who-is is supposed to return the IP of the proxy server. If instead, it reveals a different IP, then presumably this is a failed test for the client.