frdns.pl - Forward and Reverse DNS Lint
The frdns.pl forward and reverse DNS checking script is one of those little mistake catchers that allow you to work with a safety net. In this case it checks that your deployed forward and reverse DNS records are present and correct; it checks the results from real DNS queries, not by zone file parsing.
frdns.pl accepts a CIDR range and polls each IP for a reverse DNS record. If it gets one it’ll try to forward resolve the name and compare the two results. If the forward record is missing, or the two parts don’t match, it’ll print the problem. You can supply a flag to make it only display valid or broken records and with a little bit of shell wrapping it (and iterating through your networks) you’ve got a nice cronjob that’ll give you a bit more confidence that your DNS is clean.