DNS leak test
The Internet browser can connect to website only by IP address. But we know websites by domain names, not by IPs. It is possible to enter IP in the address bar, but it's inconvenient. IP of the website might be changed at any time and the website can have multiple IPs at once. The DNS (Domain Name System) is used to get rid of this and to answer the question: what IP address has the website. So we should know only one IP - the DNS server IP. And DNS server is able to answer the question what IP has the domain name.
The operating system (Windows, Linux, MacOs, iOS, ...) usually has several DNS servers. These servers are preinstalled by ISP in general and here might be a problem.
What is a DNS leak?
When your PC (or other device) is connected to VPN, the DNS servers are changed to VPN DNS. But, some VPNs can leave your DNS servers without changes at all, so you will use ISP DNS servers. Or VPN could change DNS servers but not the whole DNS servers (some servers can stay unchanged). Why ISP DNS servers are dangerous? Because ISP can watch you even if you are connected to VPN. ISP will know what websites you visit.
How does DNS leak test work?
When you click on start test button the bash.ws generates faked subdomain names like lala.blabla.bash.ws (to avoid DNS caching mechanism). Your browser will try to load nonexistent images from these subdomains (lala.blabla.bash.ws/some-image.png). And as a result the browser will try to detect IPs of faked subdomains. The DNS servers from your system will be used to do this work. bash.ws can catch all these DNS requests and is able to detect what IP has sent the DNS request. The bash.ws will show you all the IPs which has been sending the DNS requests. If the IP is not trusted (it owns by ISP or another untrusted company) you may be in trouble and the test will warn you.
Does DNS leak test support OpenVPN?
Yes. This test supports any kind of VPN connection (IKEv1, IKEv2, L2TP, IPsec, PPTP). This is a system test. It doesn't depend on VPN at all.
Does DNS leak test support Windows?
Yes. You can use it on all versions of Windows, MacOS, iOS, Android or Linux. This test doesn't depend on operating system. All you need is the Internet browser.
How can I check DNS leak in terminal (Linux)?
You should use the script available here https://github.com/macvk/dnsleaktest
How can I integrate the DNS leak test into my WordPress website?
Please use the plugin available here https://github.com/macvk/vpn-leaks-test
How can I test VPN for IPv6 DNS leak?
The IPv6 is supported by this test, just run it.