dig
dig txt example.com @8.8.8.8 dig example.com | grep -v ";" | grep A dig -x 8.9.10.11 | grep IN
Flush DNS cache
sudo systemd-resolve --flush-caches
SystemV
# flush DNS systemctl restart nscd # resolvconf sudo systemctl enable resolvconf
SPF
http://wiki.hetzner.de/index.php/DNS_SPF
DNSSEC
https://www.scip.ch/?labs.20140911
# validator
https://dnsviz.net/
https://dnssec-analyzer.verisignlabs.com/