Testing your VPN’s Encryption and Privacy – Complete Guide

One little secret of the VPN industry is that most VPNs leak .In one in-depth study of Android free VPN apps, researchers found that 84% of the VPNs tested leaked the user’s IP address. Here we will dive into the deeper facts about VPN and making sure we are protected.

In other words, many of the VPN services that market themselves as privacy and security solutions are in fact leaking your IP address and/or DNS requests. These leaks leave you exposed, which in turn could put you in a dangerous situation depending on your circumstances, location, and online activities – such as political dissidents and journalists in oppressive countries.

Also concerning is the fact that many VPNs have broken features. This is often the case with “kill switches” that do not effectively block traffic or “IPv6 leak protection” that does not secure your IPv6 address. It only takes one leaked packet to expose your identity and activities to third parties.

In this guide we’ll cover two different levels of VPN tests:

  1. Basic tests – These are the tests that anyone can run. Simply connect to your VPN and then hit the testing sites. Unfortunately, these basic tests may not identify all leaks (such as brief reconnection leaks).
  2. Advanced tests – These tests require more technical proficiency to get everything setup correctly, but they will identify any leaks you may have with your VPN. ExpressVPN put together the best testing suite available for in-depth leak testing. These testing tools are open source and available here on GitHub.

We’ll start with basic VPN test procedures to identify obvious problems.

Basic VPN tests

Below are basic steps for identifying:

  • DNS leaks
  • IP address leaks (IPv4 and IPv6)
  • WebRTC leaks

With these basic tests, you are relying on the testing website to identify problems.

For basic tests, I like to use ipleak.net as a general all-in-one testing site (created by AirVPN) along with the different Perfect Privacy test tools.

Test for VPN leaks

To test for active leaks, simply connect to a VPN server and visit the test site. You are checking to see how the VPN performs when the tunnel is active and stable.

You can also simulate different interruptions to see how well the VPN does if network connectivity drops. For example:

  1. Connect to a VPN server and load ipleak.net in your internet browser.
  2. Manually interrupt your internet connection (disconnect) while the VPN client is running.
  3. Reconnect to the internet and also load a few different test websites to see if your VPN is leaking upon reconnection.

This will help you to identify obvious problems with your VPN, but it won’t definitively identify all leaks (see advanced tests below).

VPN test websites

Here are a few testing sites you can use to check for different leaks:

Now let’s see what a VPN leak looks like.

Identifying VPN leaks

When you use the testing site ipleak.net, it is fairly easy to identify leaks and problems, especially when you are connected to a VPN server outside your country. Note, the WebRTC leak test will show local IP addresses (usually beginning with 10.xxx or 192.xxx or sometimes an alpha-numeric IPv6 address that is also local). These are not leaks, but rather your local IP addresses (further explained here). If you see your real (Public) IPv4 or IPv6 under the WebRTC section, then these are indeed WebRTC leaks.

Below you can see that I redacted the IP addresses in red where I experienced leaks with a VPN Unlimited server in the UK.

vpn check
IPv6, WebRTC and DNS leaks.

With the test results above you find:

  • IPv4 address from UK server, but my real IPv6 address below (leak).
  • Local IP address on the left (redacted, not a leak), but my public IPv6 address on right (WebRTC leak).
  • IP address (DNS) from VPN server on left, but my internet service provider’s IP address on the right (DNS leak).

Example with no leaks

Now here are the test results when connected to a Perfect Privacy server in Sweden. Note, in the screenshot below, I am using a multi-hop VPN cascade, using servers in Frankfurt, Copenhagen, Calais, and Malmo. The last server in the chain (Sweden) corresponds to the VPN tests results below.

ipv6 and ipv4 vpn test
This is a multi-hop VPN chain with no leaks.

In the screenshot above you see:

  • IPv4 and IPv6 addresses from the Perfect Privacy server
  • Local IP addresses under WebRTC detection (no public IP addresses, no leaks)
  • DNS addresses from Perfect Privacy servers (Perfect Privacy uses multiple, secure DNS resolves)


Advanced VPN tests

The best method for identifying VPN leaks is to create a testing suite for your operating system and then run a barrage of tests to analyze traffic for leaked packets.

Creating a testing suite to capture and analyze traffic can be somewhat complex depending on the operating system you are using. Thankfully, ExpressVPN released and advanced VPN testing suite, which they use internally to leak-proof all of their VPN apps.

ExpressVPN’s leak-testing tools are free, open source, and available on GitHub here.

vpn leak test
These advanced leak test tools are available on GitHub.

This level of testing should effectively identify any leaks with Windows, Mac OS, and Linux.

If you are serious about security and online anonymity, you will want to run your VPN through these advanced tests to identify any problems, rather than just relying on the basic tests to identify problems.

Quick start – Check out the quick start guide to set up your test machines to identify leaks with your VPN service.

DNS leaks

The Domain Name System (DNS) is a system for converting URLs, into a numerical IP address, such as

Without a VPN, this translation process is handled by your internet service provider (ISP). But this can be problematic because your DNS requests are clear text logs of every website you visit. Internet service providers can easily log these requests to record all browsing history of their customers. In the United States, the data can be sold to advertisers and other third parties. In the UK and Australia, the data is recorded and stored for up to two years and is available to authorities for whatever they want to do with it.

A DNS leak occurs when these translation requests leak out of the VPN tunnel, exposing the IP address (and location) of your internet service provider, as well as your browsing history. Many VPNs do not provide adequate DNS leak protection, which means your DNS requests are still going through your ISP and thereby exposing your online activities.

DNS leak test sites

  • Perfect Privacy DNS Leak Test (This site seems to detect DNS leaks when other websites do not find problems. Below the tests results you can also find a detailed explanation of DNS leaks.)
  • IP/DNS Test at ipleak.net (This is another DNS leak test tool that also includes IP address leak results.)
dns leak test
Check to see if the IP address of your ISP is listed. If so, you have a DNS leak and your VPN is leaking DNS requests.

Connecting to a VPN server outside your country makes detecting DNS leaks easier. You can see above there are two DNS requests leaking out while connected to a VPN server in the United States.

A DNS leak does not expose your IP address, but instead the IP address and location of your internet service provider (which can be linked back to you). Additionally, this exposes your browsing history via DNS requests.

Solution to DNS leaks: Find a VPN that uses its own secured and encrypted DNS resolvers. Below are three VPNs that use only their own secure DNS resolvers and did not have any leaks when I tested them for the respective reviews:

  • ExpressVPN (based in the British Virgin Islands)
  • NordVPN (based in Panama)
  • Perfect Privacy (based in Switzerland)
  • VPN.ac (based in Romania)

You can also manually configure your DNS requests to use other third-party options. Here’s a list of alternative DNS options from WikiLeaks.

IP address leaks (IPv4 and IPv6)

IP address leaks are a problem with many free VPN services – as well as paid VPN services. This is often the case with IPv6 addresses because most VPN providers do not offer IPv6 support.

While many VPNs effectively block IPv6 addresses (see ExpressVPN), other providers offer full IPv6 support by giving you both an IPv4 and IPv6 address (see Perfect Privacy).

Test sites:

Solution for IP leaks: The best solution is to simply get a VPN that does not leak IPv4 or IPv6 addresses. Another option is to manually create firewall rules that block all non-VPN traffic, but this can be a hassle. IPv6 can also be manually disabled on most operating systems, but the gradual transition to IPv6 is still underway.

WebRTC leaks

A WebRTC leak test is important for anyone using Firefox, Chrome, Opera, or Chromium-based browsers. As explained in the WebRTC leak guide, the WebRTC issue is essentially a vulnerability with the browser – although there are some VPNs that protect against this. A WebRTC leak occurs when your IP address leaks out via WebRTC APIs.

Here are three different WebRTC leak tests:

Solution for WebRTC leaks: Follow the steps in the WebRTC leak guide to disable or block WebRTC in your browser.

Two VPNs that offer full WebRTC leak protection are:

  • Perfect Privacy
  • ExpressVPN

VPN speed test

If you’re looking to test VPN speed, here are three options:

What affects VPN speed?

There are many factors affecting speed that you should consider when testing. Here are a few:

  • Distance between you and the VPN server – This is usually the biggest factor affecting speed. The further the distance, the slower the speed.
  • Number of users on the VPN server – With so many VPNs over-selling their services, some VPNs have overloaded servers which results in slow speeds and dropped connections for their users.
  • Regional bandwidth restrictions – Many countries have poor bandwidth infrastructure, which will limit your speed, regardless of how fast your ISP or VPN server is. A few examples of this are Germany and Australia. Another regional consideration is how many people are online at a given time of the day. High usage times can slow down speeds for everyone.
  • Internet Service Provider – No matter how fast your VPN is, it won’t be faster than the speed provided by your ISP. The only (rare) exception to this rule is if your ISP is throttling (limiting) your bandwidth. They sometimes do this if you’re doing something they don’t like (such as torrenting). A VPN can potentially help with this issue by encrypting your connection and hiding your online activity from your ISP.
  • Processing Power – Whenever you’re using a VPN, your computer is working in the background to encrypt and decrypt packets of information. This takes processing power. The faster your internet speed when using a VPN, the more processing power is needed. So even if your ISP and VPN are fast, your CPU may be limiting your full speed potential (but this mainly applies to very high speeds).

VPN malware tests

Malware embedded in mobile VPN applications is a major problem to be aware of with free VPN services.

There has been an explosion of various free VPN apps available in the Google Play and Apple Stores. Just like with other free products, such as Gmail and Facebook, the platform is monetizing the user by collecting data and selling it to third parties.

One study found that 38% of Android VPN apps contain malware! I have also confirmed the presence of malware in Android apps.

Test for malware – To test for malware, simply upload the software file to VirusTotal. The database will scan the file using over 60 different Antivirus tests. While there is a chance for false positives, some researchers define a malicious app as one having four or more positive test results.

VPNs with the best leak protection

There are two VPNs that I have found to do the best job of protecting users against leaks in all types of scenarios including, reconnections, network interruptions, and VPN crashes. These two VPNs offer the best built-in leak protection features:

  • ExpressVPN – Offers advanced leak protection settings and a great selection of apps for different devices.
  • NordVPN – Offers very advanced leak protection settings along with full IPv6 support.

Whatever VPN you are using, it’s a good idea to periodically check for leaks and other issues, especially after any updates.

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