So:
sudo apt-get --purge remove avahi-autoipd avahi-daemon avahi-utils(this is causing A LOT of issues, and it is not needed for Linux networking).- Open file
/etc/systemd/resolved.conf - Edit like this:
[Resolve]
DNS=172.16.21.2
#FallbackDNS=
Domains=local
#LLMNR=no
#MulticastDNS=no
#DNSSEC=no
#Cache=yes
#DNSStubListener=yes
sudo systemctl restart systemd-resolved.service