I’ll preface this by saying that these issues are on a Surface Tablet that I’ve been using to play around with, so I haven’t been too diligent in documenting what changes were made when.
I’ve got a Surface Go 2 tablet with the LTE modem that I installed Linux Mint onto several months ago. When I first made the switch, cellular connectivity seemed very “touch and go” but Wi-Fi had been solid.
At some point in time (roughly 6 months ago), I switched my home network to using Control D for DNS resolution for about 2 months until I decided it wasn’t what I wanted and went back to my default setup which is a Unifi UCG Max gateway using the AdGuard public DNS servers coupled with the built-in ad blocking of the Unifi gateway. This feeds to a separate Wi-Fi mesh network in my home.
About a month ago I noticed that I could no longer reach internet locations on my tablet when connected to my home Wi-Fi network, but I could still access other computers on my LAN just fine, so Wi-Fi was working. Cellular connectivity seemed to have stopped working entirely even though I ran the “lte_modem_fix” that is on github and was seeing several bars of connectivity in the status bar.
Even though websites were inaccessible (Firefox gave me an error saying there was no network connection), in my attempt to try anything I found that I could visit the Control D website even though I stopped subscribing months ago.
On a lark I pulled up my Mullvad VPN app which I have an active subscription to and it let me connect to a server. As soon as I did this, ALL internet sites became available.
Next I took the tablet with me away from home, disabled Wi-Fi and activated the cellular network. Again the bars appeared but I couldn’t access any sites. I loaded up Mullvad and was able to connect, after which I could reliably connect to all internet sites. Again, cellular connectivity was never 100% but Wi-Fi was.
How do I even begin troubleshooting and fixing this? Needing a VPN isn’t the end of the world, but when at home it gets in the way of accessing local computers so I’d like to get to where the tablet works on Wi-Fi or cellular, with and without a VPN active.
Yes I believe that Mullvad routes you to their DNS server so that explains why it works when connected to VPN. If I attempt an nslookup when NOT connected to VPN it fails and the server it attempts to contact is 127.0.0.53. When I connect to VPN the nslookup succeeds, and it uses the same server address.
I then disconnect from VPN and ping the ip address that I just looked up (I chose etsy) and the ping goes through so this seems to be a DNS lookup issue. Is 127.0.0.53 the right server address? I would expect it to use my DHCP server address of 192.168.x.x format.
Ok, so something setup 127.0.0.53 as your DNS server, and isn’t removing it correctly. I think it’s safe to say it’s Mullvad, since it works using that DNS server IP when connected. Is that IP in your resolv.conf, or is resolv.conf maybe a stub, and you’re using systemd-resolved?