A transparent proxy is an HTTP proxy that is placed between client computers and a webserver to intercept client requests for authentication, acceptable use, or caching purposes.
As the name indicates, the proxy (also known as a forced proxy or intercepting proxy), is transparent, and clients are not aware that all their Web traffic is first processed through a proxy server before being sent to the server they want to connect to. Transparent proxies are often used by large organizations to configure a large number of clients consistently without having to configure each one of these on an individual basis.
What you’ll learn
How does transparent proxy work?
The principle of operation of a transparent proxy is pretty straightforward.
- Users make HTTP requests to a web server.
- All these Web requests are intercepted by a proxy server that determines if the requests are allowed to be executed based on its rules.
- If the request is permitted as per the proxy’s rules, it will send the request to the server. If the request is denied, a warning or error message will be sent to the user.
- If the request is allowed, the proxy will send the Web request to the destination server, and when a response is received, this will be sent back to the client.
What is the use of a transparent proxy?
Transparent proxies are implemented for various reasons. As mentioned above, large organizations often use them, but Internet Service Providers (ISPs) also often use transparent proxies to reduce bandwidth usage by employing caching functions. There are many other scenarios where organizations use transparent proxies as useful tools.
- They don’t want clients to know their Web requests go through a proxy.
- They need to set up proxies without having to configure each machine individually.
- They want their clients to use a proxy whether they want to or not.
Although using this type of proxy can be an advantage in that the clients don’t know that their HTTP requests go through a proxy, there are a number of ways that can be used to determine if a proxy is being used. Detecting if a transparent proxy is being used can be done in the following ways:
- Looking at the response when trying to connect to an IP where it is known that there is no server.
- Using HTTP vs. HTTPS to compare results of online IP checkers.
- Examining the traceroute for the proxy protocol (post 80) vs. a non-proxy protocol (post 25).
Transparent proxies could also be used in the following ways:
- Caching Proxy: In this implementation, the proxy receives a request from a client and then stores a copy of that information once it has fetched it. When the proxy receives a request for the same information, it will serve the saved information rather than fetching it from the destination server again. This method saves on resources that would otherwise be required from the origin server to deliver the response.
- Content Filtering Proxy: In large organizations such as the government or corporations, it is often a requirement to restrict users from using certain websites, i.e., social media sites, or sites that are deemed to be time-wasters. Transparent proxies record logs based on user activity and URLs accessed and are primarily implemented to reduce the number of user distractions, thereby increasing productivity.
Advantages of transparent proxies
Using a transparent proxy is an unobtrusive way in which features and functionality can be added to a user’s browsing experience.
The user’s interaction with web services is done quickly as their connections are passed through the proxy invisibly and seamlessly, leaving configuration the responsibility of the service provider.
Enterprises gain more control over how their customers interact with their websites by modifying and routing requests as they are made.back to menu ↑
Does a transparent proxy hide your IP address?
- REMOTE-ADDR = Proxy’s IP address
- HTTP-VIA = Proxy’s IP address
- HTTP-X-FORWARDED-FOR = The IP address of the proxy client (Your real IP address)
To determine if a proxy server is anonymous or not, there are many online tools that can be used to show your IP address. You could also set up your own HTTP server and look out for HTTP headers that may be leaking your IP address.back to menu ↑
How to set up a transparent proxy?
There are many ways to install a transparent proxy server and configure it as a caching proxy or as a content filtering proxy. Here are several tutorials that may help you get started:
- Minimal Squid as Transparent Proxy
- How to set up a Transparent Squid Proxy Server using pfSense
- How to set up a Transparent Content Filter on Gateway with Privoxy
How to use a transparent proxy?
After you set up your proxy or you get the proxy credentials (IP, username, password) from your company/school administrator you need to perform some settings to your computer.
For example, if you are using the Chrome web browser on a Mac device you may need the perform the following operations:
- Open the Google Chrome browser.
- Go to Settings > Advanced > System > Open proxy settings. It will open the Network settings of your macOS.
- Select and check Web Proxy (HTTP) or Secure Web Proxy (HTTPS).
- Fill in the (Secure) Web Proxy Server IP address and port (provided by the network admin). Also, if the transparent proxy requires authentication, enter the Username and Password.
- Click Ok, and you have completed the setup of the transparent proxy.
Transparent proxy security issues
By implementing a so-called SSL bump, a transparent proxy can intercept, log and view the traffic passed through by its users, even if the proxy uses HTTPS/SSL.
In such a situation, when a proxy client connects to the proxy HTTPS, the proxy terminates the SSL connection, assesses the data, and it establishes a connection to the remote server using HTTPS/SSL. In the meanwhile, the client is unaware of the transparent proxy interception. This is possible if the client and proxy have matching certificates that validate the interception.
Such proxy implementations are common in companies where the IT policies state that all Internet traffic has to be filtered and assessed for information leakage or other purposes.
However, the security implications are significant as private data of the employees (like medical data, banking information, etc.) may become available to the administrator of the proxy.back to menu ↑
Transparent proxies are very useful for caching and for bulk overriding of client settings. For both ISPs and large organizations, they are precious as configuring client machines individually takes a lot of time. For ISPs that need to save bandwidth, a transparent caching proxy is a viable solution that will also help decrease web page response times.