We fixed the problem with slow connection to Google domains in AdGuard DNS


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Apr 24, 2016
Over the last one or two weeks we've been receiving a large amount of complaints about the AdGuard DNS's speed. And we couldn't have figured out the culprit — we measure speed in multiple locations all over the world, and according to our measurements it was fine in all of them.

But we finally found the root of the problem. Turns out, it wasn't about AdGuard DNS per se. It was doing its job just like it was designed to. But when it comes to IP addresses that it was returning, it's not all that good. For some domains (mainly Google-owned ones) AdGuard DNS was returning IP addresses belonging to Google China. As expected, these addresses would work rather slowly for most users.

What happened? How did it happen? We will give answers to this questions in a minute, but first we apologize for taking much more time to solve this problem than it could have taken.
So what was the problem?

There are four authoritative nameservers that are responsible for all of Google domains. They are configured in such way so that any client gets the IP address of the closest Google server. AdGuard DNS has almost 50 servers over the worild (and soon will have more), so why Google was returning Chinese servers' addresses to some of them?

You see, AdGuard DNS servers have several IP addresses — IPv6 as well as IPv4. And it seems Google failed to detect the IP address location properly when IPv6 was in use. They were serving records for China instead of the records for AdGuard DNS servers location.

So in the end, this turned out to be not much of a mystery. Be careful if you're using your own recursive DNS server — with IPv6 you can't make predictions.

To avoid this in the future we configured all our DNS servers to prefer IPv4. So you will not encounter slow connection speed when visiting Google domains anymore.
Read the full story with a detailed explanation on AdGuard's blog: