We recently had 2degrees fibre set up in a small remote office down south.

We planned to run the connection for at least 2 weeks via the ISP supplied FRITZ!Box to ensure there were no issues before swapping it out for managed equipment & split tunnel VPN etc.

The connection is performing well but we have encountered a strange issue - DNS queries for youtube.com result in 'server error' or timeouts.

This behaviour is observed on multiple devices, including Windows laptops, Android phones, tablets and TVs. It's also interesting that changing DNS servers on devices to 8.8.8.8/1.1.1.1/9.9.9.9 makes no difference.

If we connect those same devices to Voda/Spark 4G, everything is fine. If we connect the laptops to our split tunnel corporate VPN on Fritzbox wifi, there are no issues with that either as queries for youtube.com are returned via our corporate VPN DNS servers.

Youtube works on the one Apple device that we have tested but I believe that's due to iOS14 using DNS over TLS by default.

During the course of troubleshooting with the support team, the public IP was changed, IPv6 was disabled temporarily, and the router was factory reset among other things.

nslookup/dig and equivalents were used to test. Does anyone know if it's possible to run a DNS host record query directly on the Fritzbox?

At this point, it seems like it could be an issue with the router, or something further upstream. We have arranged to supply our replacement equipment ahead of schedule to see if that will make a difference.

There is also an ISP web filter set on the connection. I asked about this and the support guys didn't think it could be the cause - is this correct? I might see if they will temporarily disable it to test as well.