Using IPTables with Dynamic IP hostnames like

Whenever IPTables has a hostname in a rule it looks up the hostname’s IP address and uses that instead of the actual hostname – so it’s stuck with the IP until the next time IPTables is flushed/restarted. Here’s a quick little python script to stick in a crontab which checks the IP of your dynamic IP hostname (free ones provided by and will restart iptables if it catches a change in your hostname. The script was made for CentOS so should work on Red Hat based distributions – if you don’t have an /etc/init.d/iptables file you’ll have to modify the reload iptables command in the source. Viewable Source After Jump

I just set this up as root and in root’s crontab.

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Bash Script: Confirm domains in your DNS Bind server are still pointed at your address (haven’t moved to other DNS)

Here’s a quick script I wrote last year which I forgot about until today. I thought I should share it since it works fairly well with some modifications – it could be refined/improved quite a bit; I’m not the best bash/shell scripter. Be prepared to get your hands dirty with mods if you want to use this. Here’s a quick run down & description of what’s going on.

The script’s input is the bind9 file containing all zone entries you want to confirm are pointed to your server, I suggest making a copy – not working with any live configs. The script will run an lookup using `host -t ns` on google’s DNS server to find out what the outside world thinks the domains’ name servers are; I tried `whois` in the past but it was too unreliable due to timeouts & limits on the number of calls per minute. Then it checks the results of that host lookup against the hostnames, all capitalized hostnames, and IP addresses of your DNS servers (3 in my case). If any one of the DNS servers matches than we know the domain is still using our DNS. The other options are 1) it doesn’t find any DNS servers that are ours 2) it finds the phrase ‘not found’ which host returns if the domain is expired or there are no ‘NS’ type records in DNS. The script echos to shell what DNS servers match as it runs, but it only logs the DNS servers that don’t have any matches (so they can be removed by automation or manually later).

With the zone-audit.log output I then can remove the domains that aren’t using our DNS since they’re no longer in use. Please leave feedback in the comments if you think of a good improvement.

Code after the jump or Here
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