A DNS leak is a type of VPN defect that reveals one’s Domain Name System requests to their Internet service provider, i.e., the latter’s DNS servers. Seeing how any given ISP’s DNS servers are the default destination for such queries, we tend to think of DNS leaks as VPN failures. However, they can also be encountered by proxy users.
DNS solutions are primarily used for translating easy-to-memorize domain names to IP addresses associated with those domains’ servers. Masking DNS requests is hence a big part of a typical VPN feature set. Once you establish a VPN connection, all your Internet traffic is supposed to be routed through this new virtual network, DNS queries included.
But if that isn’t the case and your ISP can still access your original DNS queries, then you’re dealing with a DNS leak. Of course, a DNS leak usually isn’t as revealing as a direct Internet connection. And yet, it’s likely to be left unchecked for much longer because you probably won’t be aware of it being an issue in the first place.
How DNS leaks happen
You don’t need to know everything about DNS leaks to detect them reliably. With that said, understanding some basic concepts associated with such security flaws goes a long way toward informing responsible VPN use.
A DNS leak most commonly occurs due to a wrongly configured VPN network. Such erroneous configuration can happen on the user’s end, but it’s usually the VPN service provider that’s at fault. After all, most users don’t configure their Internet connections manually.
Even a properly configured VPN network won’t amount to much if you’re having connectivity issues that you haven’t accounted for in advance. That’s why ensuring all of your outgoing traffic is routed through a virtual private network is only half of the equation when it comes to preventing DNS leaks. The other half being fail-safes against local DNS queries following dropped connections.
Fortunately, implementing a proper defense mechanism against DNS leaks isn’t nearly as complicated as it once was, which brings us to our next point:
How to detect DNS leaks
The most straightforward manual method for detecting DNS leaks is to use a specialized service such as DNSleaktest.com. Granted, regular checkups of this sort are hardly convenient, but that’s why many of today’s most popular VPN platforms offer built-in protection against DNS leaks.
For example, apps like ExpressVPN and NordVPN will prevent all Internet connectivity if they detect any attempts at sending data packets that aren’t being routed through their own DNS servers and are instead reverting to the default ones from your ISP. This behavior is what’s commonly referred to as a VPN kill switch nowadays.
Due to the sheer volume of market competition, most of today’s major service providers offer VPN kill switch functionality at no extra cost. And we tend to frown upon any that lack this feature or want to charge extra for it. Because at the end of the day, having a reliable VPN kill switch will keep you safe against all but the most niche types of DNS leaks – without requiring any extra effort on your part.