Network name resolution configuration file
/etc/systemd/resolved.conf
When starting, systemd-resolved will read the configuration file resolved.conf. This configuration file determines the fallback DNS servers.
DNS=
A space separated list of IPv4 and IPv6 addresses to be used as the fallback DNS servers. Note that the servers obtained from systemd-networkd.service(8) take precedence. If this option is not given, a compiled-in list of DNS servers is used instead.