What is a Proxy Server?

A proxy server is an application that acts as an intermediary between clients that send requests (such as browsers) and the servers that process those requests. The proxy server works on behalf of the client by sending a request to the target server and masking the true origin of the request (however, the proxy can disclose the client's real IP address to the target server using the X-Forwarded-For HTTP header).

Proxy servers act as a firewall and web filter between the client and the Internet, serving all outgoing network connections, caching data, and speeding up websites. Proxies protect users and intranets from external threats and provide a high level of privacy and security. Proxies were designed to add structure and encapsulation to distributed computing systems.

Proxies used for:

  • Caching web resources
  • Compressing network traffic
  • Load balancing
  • Hiding users' real IP addresses
  • Encrypting web requests
  • Gaining access to locked resources
  • Controlling Internet Usage

How does a proxy server work?

A proxy server is a separate computer or virtual machine on your local network or the Internet with its own IP address known to your browser. When your browser sends a request for a web page or image, that request is sent to the proxy server and not to the target server. The proxy server then sends your web request on your behalf to the server, receives a response from the server, and forwards the received data to your browser.

Before the proxy server sends you the server response, it can make changes to this data, for example, compress it. A proxy server can hide your IP address and prevent the web server from knowing where you are. It can encrypt your data and protect it from being read by sniffers while data is being transmitted over a local network. Finally, a proxy server can block access to certain web pages based on IP address or domain name.

What types of proxy servers are there?

Not all proxies work the same. There are several types of proxy servers:

  • Forward proxies

    A forward proxy, gateway, or simply "proxy" provides proxy services to the client. It sits between the client and the external network, evaluates outbound requests, and takes appropriate action before relaying this request to the external resource. Most of the proxies you are likely to come across are forward proxies. VPNs and web content filters are examples of direct access proxies. There are hundreds of thousands of open proxy servers on the Internet. Forward proxies can also be anonymous proxies and allow users to hide their IP addresses when browsing the web. Businesses commonly use forward proxies to:

    • Track employees' online activity and block them from visiting blacklisted websites
    • Block outgoing malicious traffic
    • Improving page speed by caching external site content

  • Reverse Proxies

    A reverse proxy does the opposite of what a forward proxy does. While forward proxies act on behalf of clients and hide client IDs, reverse proxies sit between the server and hide server IDs. The reverse proxy receives the initial HTTP connection requests from the client and forwards the request to the actual server. Reverse proxies typically process all policy management and traffic routing rules before forwarding traffic to the server. Reverse proxies have several use cases, such as:

    • Load balancing - distribute the load to several web servers
    • Cache static content - offload the web servers by caching static content like pictures
    • Compression - compress and optimize content to speed up load time.
    • Completing a TCP three-way handshake, terminating the initial connection
    • Encrypting content before sending it to clients

  • Transparent Proxy

    A transparent proxy tells the destination server that it is a proxy and passes the client's IP address to it. Companies, public libraries, and schools use transparent proxy servers to filter content. A transparent proxy does not provide anonymity for the client and is used as a cache for websites. The redirection can be easily detected by the HTTP headers present in requests from the transparent proxy server.

  • Anonymous Proxy

    The anonymous proxy identifies itself as a proxy using HTTP headers but does not pass the client's IP address to the host. This provides rational anonymity for the user, helps prevent identity theft, and maintains user privacy on the Internet. They can also prevent a website from displaying marketing content to you based on your location.

  • High Anonymity Proxy

    This type of proxy server does not pass the user's IP address to the host, nor does it pass any special HTTP headers that would identify it as a proxy server. Some proxies with high anonymity also change their IP address periodically, which prevents requests from these proxies from being tracked. Companies fight these proxies by creating lists of IP addresses belonging to anonymous proxies. Highly anonymous proxies like the TOR network are the safest way to surf the Internet.

  • DNS Proxy

    A DNS proxy improves surfing performance by caching previous DNS requests in its local cache and resolving subsequent queries for the same domain from the cache.

Why use a proxy server?

A proxy server can be used to:
  • Protect your real IP address and gain privacy and anonymity on the Internet
  • Control the use of the Internet by employees and children
  • Save bandwidth and improve the speed
  • Access blocked resources
  • Protect the webserver from threats from the external network

What are the dangers of using proxy servers?

Using proxy servers carries some risks:
  • Hacking

    Malicious proxy servers can intercept sensitive data such as usernames and passwords of your Internet accounts.

  • Spam and virus attacks

    When using free proxy servers, you will often come across banners and advertisements with which these proxy servers will fill your Internet session to generate income. In addition, malicious free proxies can inject viruses and spam into your browser.

  • Identity theft

    When you use a free proxy, you are essentially giving your IP address to an often unknown third party in exchange for using someone else's IP address to browse the Internet. Thus, you become vulnerable to potential abuse; some proxy servers can seriously compromise and abuse your network identity.

  • Slow Internet

    When hundreds of web users simultaneously send requests to the same proxy server to route data back and forth, this may not always provide the desired network speed. Sometimes, browsing the web through a proxy server can be excruciatingly slow and almost always insecure.


Proper use of proxy servers can benefit a working project: protect the network from outside attacks, hide your IP address, restrict unwanted content, and help clean up web pages. However, you should always remember and avoid the risks associated with using proxy servers.

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