Settings systemd-resolved on ubuntu 18.04 up
nano /etc/systemd/resolved.conf
[Resolve]
DNS=8.8.8.8 8.8.4.4
#FallbackDNS=
#Domains=
#LLMNR=no
....
systemctl restart systemd-resolved
systemd-resolve --status
Global
DNS Servers: 8.8.8.8
8.8.4.4
DNSSEC NTA: 10.in-addr.arpa
16.172.in-addr.arpa
168.192.in-addr.arpa
17.172.in-addr.arpa
.....