I was surprised today to find out that Firefox was using my ISP’s DNS server — even though I had a local Pi-hole set up to use Cloudflare’s 1.1.1.1.
It was my mistake. When I set up Pi-hole in my router’s DHCP settings, I forgot about DHCPv6.
Once I added the local IPv6 address of my Pi-hole as the DNS server for DHCPv6, my ISP’s DNS server stopped showing up in the test.
It took me a while to figure this out though. Most DNS leak test sites only showed the DNS server’s IPv4 address.
You can check which DNS server your connection is using here: