Re: Internet problems - avahi / .local domain
Do you have anything in your /etc/hosts file that contains a .local domain, or does your router somehow use that for a LAN domain? I used to use .local as a LAN domain in /etc/hosts or local DNS, but many years ago SuSE strongly suggested not to use "local" as a domain due to conflict with something else (which I thought was multicasting, but maybe it was Apple zeroconfig).
Avahi can be handy for some things and is installed by default in Ubuntu. For example if I want to connect to another computer on my LAN with unknown dynamic IP (especially a Raspberry Pi with avahi-daemon installed) I can connect to it by its hostname.local, for example: ssh raspberry-pi.local or http://raspberry-pi.local/ if running apache.
Zeroconfig is a little flaky in Windows though, because if you install Apple Bonjour in Windows, I think PuTTY can find other computers by hostname.local, but Internet Explorer or Firefox need to have it settings modified to NOT to use a default DNS search domain, nor search the internet if it thinks a domain is missing, and only use the hostname without .local to find a LAN web server by zeroconfig/avahi.
i5 650 3.2 GHz, 8 GB, nvidia GTX 1060, 32" 1080p & assorted older computers