dyndns-permissions-script.pl is a script that reads and updates /etc/hosts. It was written 2008 by Stephan Schwarz (@stearz) to implement IP based authentication for Apache based on DynDNS entries. Then it also supported updating iptables and a postfix relay list to allow access for my systems behind my home router.

I have not used this script for years and as I accidently found it in 2019 on an old hard drive I decided to put it on GitHub so others could use, learn from or laugh at it. It is damn old code and it really feels as if someone else had written it. Do not use it in production - there is always a better way to authenticate instead of giving permissions on IP addresses.

Add your DynDNS hostname to your /etc/hosts between the scripts delimiter lines:

[...]

# BEGIN: Automagic DynDNS - Updater

127.0.0.1     myhostname.at.dyndns.provider.example.com

# END: Automagic DynDNS - Updater

[...]

Then simply run the script without arguments (e.g. from a cronjob)

dyndns-permissions-script.pl

The variables have to be changed inside the Perl script as I did not implement reading args from the command line:

# enables debug mode without writing to hosts file
my $TESTING    = 0;

# Nameserver to ask
my $NAMESERVER = '8.8.8.8';

The script reads all lines between $DELIMITER1 and $DELIMITER2 from $HOSTS_HOSTFILE and tries to get the actual IP addresses of the hostnames it read.

# File to read from and write to
my $HOSTS_HOSTSFILE  = '/etc/hosts';

# Start delimiter
my $DELIMITER1 = '# BEGIN: Automagic DynDNS - Updater';

# End delimiter
my $DELIMITER2 = '# END: Automagic DynDNS - Updater';

[optional] Can be disabled by removing the reference to the sub in @modules.

The file the script should write the resolved IP addresses to so that postfix can use it as mynetworks

# File where postfix reads its mynetworks parameter from
my $POSTF_MYNETWORKSFILE = '/etc/postfix/dyndnshosts.cf';

[optional] Can be disabled by removing the reference to the sub in @modules.

Exact path to the iptables binary and iptables table that the script should write the resolved IP addresses to.

# iptables binary
my $IPTAB_COMMAND = '/sbin/iptables';

# name of the table to update
my $IPTAB_TABLE   = 'dynaddrs';