check dyndns hostname and reload iptables to reavaluate dynamic hostnames from iptables config. put this in a cronjob and you can use dyndns entries in iptables configs.

check_dyn_hostname

#!/bin/bash
# check dyndns name of a host and reset iptables if change was detected

HOSTNAME=<hostname-to-check.dyndns.org>
LOGFILE=/var/run/check_home_ip

Current_IP=$(/usr/bin/dig +short $HOSTNAME)

if [ $LOGFILE = "" ] ; then
   iptables-restore </etc/iptables_rules
   echo $Current_IP > $LOGFILE
else
   Old_IP=$(cat $LOGFILE)

   if [ "$Current_IP" = "$Old_IP" ] ; then
       touch $LOGFILE
       echo IP address has not changed
   else
       iptables-restore </etc/iptables.rules
       echo $Current_IP > $LOGFILE
       echo iptables has been updated
   fi
fi