I've been running my own caching DNS server internally for a very long time, and have just hit an issue with bt.com.
I noticed this due to the shift from the YouView app to the BT TV app - initially when opening the new app, everything worked as well as could be expected. Then a few weeks ago, I started getting error 'GG104' and the app failed to launch properly.
I eventually got a response from the BT app supoprt team who informed me that GG104 indicates an Internet reachability issue, and asked me to check I could load www.player.bt.com without issue on the device. At this point I noticed that my home DNS server couldn't resolve that address, or any other bt.com address for that matter.
Checking on the server, it appears I just get a timeout from all of the registered nameservers for bt.com (EDDNS1.bt.com, DYDNS0.bt.com, EDDNS0.bt.com, DYDNS1.bt.com) using 'dig'. From other networks (work and google cloud) I get proper responses from all of these, so it looks like either PlusNet or BT are blocking DNS queries?
[root@fw-test ~]# domain=bt.com ; for server in $(dig +short $domain NS) ; do ip=$(dig +short $server A) ; echo $server $ip ; dig +short @$server www.$domain A ; done DYDNS1.bt.com. 22.214.171.124 ;; connection timed out; no servers could be reached EDDNS1.bt.com. 126.96.36.199 ;; connection timed out; no servers could be reached EDDNS0.bt.com. 188.8.131.52 ;; connection timed out; no servers could be reached DYDNS0.bt.com. 184.108.40.206 ;; connection timed out; no servers could be reached
I'm working around for now by forwarding queries for bt.com addresses to Google's DNS servers, but this doesn't seem right.