Reload iptables if... (e.g. ip was changed)

reload-iptables-if.sh

#!/bin/bash
# Reload iptables if... (e.g. ip was changed)
# Dependencies: dig (apt-get install dnsutils in debian/ubuntu)
# Note: Run "touch ~/current_ip" and add a new cron job with cmd "crontab -e" to run this script periodically. 

HOSTNAME=<hostname-to-check.dyndns.org>
LOGFILE=~/current_ip

Current_IP=$(dig +short $HOSTNAME)

if [ $LOGFILE = "" ] ; then
   iptables-restore < /etc/iptables/rules.v4
   echo $Current_IP > $LOGFILE
else
   Old_IP=$(cat $LOGFILE)

   if [ "$Current_IP" != "$Old_IP" ] ; then
       iptables-restore < /etc/iptables/rules.v4
       echo $Current_IP > $LOGFILE
   fi
fi