Whenever you use anonymity or privacy solutions to protect your Internet traffic from being snooped on or to bypass censorship and location-based restrictions, you need to make sure data about your actual location in the world or underlying system does not leak.
A basic recent example is WebRTC, a new technology that most modern browsers support. Websites and services may use WebRTC to find out about IP addresses of your computer when enabled even if you use a VPN service.
Computers use the DNS system to translate domain names to IP addresses. When you enter a domain name in the browser, DNS is used to look up the corresponding IP address to establish the connection.
The DNS server of the Internet Service Provider is used most of the time but it can be changed to third-party DNS providers like OpenDNS or Google DNS which promise faster look ups and may offer advanced features such as filtering of malicious sites.
DNS Leaks occur when look ups are made using the DNS server of the ISP when you are connected to a virtual private network or other anonymity and privacy solutions.
This may not always be an issue but if you work or live in a country that is censoring the Internet and blocking resources, then you better make sure that you are not affected by these leaks as you may end up with connection errors or repercussions even.
To check whether you are affected, visit the DNS Leak Test website and run the standard and then the extended test while you are connected to a VPN or other solution.
The start page displays your IP address and location. The tests check whether information about visited sites and servers are leaked while you are using a VPN service.
If you only see the DNS server of the VPN service then you are not affected by leaks but if you see your ISP's server used there as well or exclusively, then you are affected and information about all sites and servers you visit manually or automatically are leaked to the ISP.
Transparent DNS proxies are one reason why DNS information may leak while you are using a VPN and have configured your system to either use the VPN's DNS server or a third-party server.
When this technology is used by the ISP, DNS lookup requests are intercepted by it which enforces the use of the ISP's DNS server even if you have changed DNS servers on the computer.
If you are using a third-party DNS provider, you may want to run the leak test on your system to make sure that it is indeed being used.
The test site lists two solutions to fix DNS leaks if that is the case. The automatic solution requires the use of OpenVPN, the manual that you run a series of commands on the command line. Both instructions are only provided for Windows systems.
Now You: Are you affected by DNS Leaks?
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Ghacks is a technology news blog that was founded in 2005 by Martin Brinkmann. It has since then become one of the most popular tech news sites on the Internet with five authors and regular contributions from freelance writers.