If you have installed virtualmin and csf spi firewall and you see the warning
"Check for DNS recursion restrictions in Virtualmin"
after you hit "Check server security button"
here is what you have to do to avoid your dns server being used for random queries by random ips:
1) Go to Webmin -> Servers -> Bind DNS server
2) Hit "Edit config file"
3) place before "options {" the following
acl "trusted"{127.0.0.1;};
4) inside options block now place the following
recursion yes;
allow-recursion { trusted;};
allow-notify { trusted;};
allow-transfer { trusted;};
forwarders {127.0.0.1;};
5) save and restart dns server