Proxy Server : What is a proxy server ?

A proxy server, in simple terms can be defined thus - Proxy is a server application which forwards requests to other servers on behalf of a client. For example, as a client computer, you can connect to a proxy server and can request for a service available in a different server in the internet (request can be for a connection, a web page, or a file). Your proxy server in turn will connect to the server, and send request on behalf of you (remember, you are the client computer!), and return the service provided by the server to you. Main Purpose! - Your identity can be hidden using a Proxy server. Let's understand different types of proxy servers and their usage.

Web Proxy

Web proxies are designed to handle WWW traffic. Web proxies are generally used to block offensive and undesirable content to get into the network. Generally, organizations (corporations, countries, universities, colleges, and schools) use proxy servers to enforce acceptable policies for their network (internet and intranet) usage. However, the main overhead for these network administrators is the browser configuration administration in client computers.

Standard Proxy Cache

A proxy server may also act as a 'cache server', where it is designed to serve a client's request without contacting the specified server. What happens is that - the proxy would 'cache' the first request to the remote server, and save the information for later. The proxy cache server is designed to basically keep local copies of frequently requested resources. Whenever a client requests for the page, proxy cache server would serve the request from 'cache', thus improving performance in large organizations and ISPs. Such proxies will not help much in serving dynamic pages which require real time data exchange between the client and the remote server. If cache servers are not properly implemented, there can be security problems.

Transparent Proxy Cache

Transparent Proxy Cache is designed to function in the same way as Standard Proxy Cache and achieves the same goal. The difference is that it operates transparently to the browser (client). The browser need not be explicitly configured to browse the cache. The transparent cache takes care of intercepting the network traffic (request from the client), filters HTTP traffic, and handles the request if the item is in cache. If the item is not in the cache, it forwards the packets to the origin web server.

Forward Proxy

A forward proxy is built to act as a gateway to the client's browser, sending HTTP requests on the client's behalf to the internet. The main purpose of the forward proxy is to protect your inside network by hiding the client's actual IP address and using its own instead. When the outside HTTP Server receives the request, it sees the requestor's address as originating from the proxy server, not from the actual client.

Reverse Proxy

A reverse proxy proxies on behalf of the backend HTTP Server, not on behalf of the outside client's request, hence the term 'reverse'. It is an application proxy for servers using the HTTP protocol. It acts as a gateway to an HTTP server/server-farm by acting as the final IP address for requests from the outside. In most configurations, firewall is designed to work tightly with the reverse proxy to ensure that only the reverse proxy can access the HTTP Servers hidden behind it. From the outside client's point of view, the Reverse Proxy is the actual HTTP Server. Advantage - Clients have single point of access to your HTTP Servers and backend databases, and adds a layer of defense against attack. In addition, this provides a single facade for all applications even if they are on different operating systems. Disadvantage - If no failover is installed for the proxy, one point failure can jeopardize your HTTP presence to the outside world. If an attacker gains control of Reverse proxy, the HTTP servers behind the proxy are at high risk. Reverse proxies may be a little slow as lots of translations have to happen between proxy and the firewall, before a request is allowed into the HTTP Server.

Proxy Anonymizer : Anonymous Proxy

Anonymizers are used to protect one's identity on the internet. There are free and commercial anonymizers to choose from. With some anonymizers, connection can be encrypted, so any communication between the client and the website can be secure, and invisible to prying third party eyes. The encryption is achieved using either SSH or SSL technologies.

Commercial anonymizers are usually installed as plug-ins, so that as soon as the browser is loaded, the connection between the browser and website is automatically anonymous.

Many of the free anonymizers usually don't support other web applications such as email, IRC (Internet Relay Chat), and ICQ (I Seek You). Many of them use proxy servers from free, open proxy lists. Although some proxies are anonymous, some are not. Even though some free anonymizers provide secure connection, be wary about sending sensitive data across as your transactions may be logged. You need to be careful that your potentially sensitive data can be intercepted by the administrators of the web anonymizers.

Many free proxy anonymizers do not shield from cookies, hostile applets, and malware. Sometimes, malicious hackers and spammers setup proxies in the free proxy lists. Their intention is to hijack user details, and you may be open to identity theft, spamming or hacking attacks.

Commercial and some of the better free anonymizers tend to use anonymous proxies rather than being web-based. Since they use secure HTTP sites for operating, depending on the type of proxy servers that is being used, most of the other web applications like email and chat can also be anonymized.

PHP and CGI Proxy

Web proxies using CGI and PHP scripts are designed to allow users to browse the web anonymously. Such proxies provide services which are designed to allow users to unblock websites, and bypass filters enforced in organizations (ex: work filters and school filters). When you visit these proxy websites, you need to enter the URL that you would want to access which is otherwise blocked in your network.