check_soa - Check a domain's nameservers
check_soa queries each of a domain's nameservers for the Start of Authority (SOA) record and prints the serial number. Errors are printed for nameservers that couldn't be reached or didn't answer authoritatively.
The original Bourne Shell and C versions were printed in DNS and BIND by Paul Albitz & Cricket Liu.
This Perl version was written by Michael Fuhr.