Quelle: [[https://unix.stackexchange.com/a/91711]]

<code bash ufw_ip_open.sh>
#!/bin/bash
#allow a dyndns name

HOSTNAME=HOST_NAME_HERE
LOGFILE=LOGFILE_NAME_HERE
PORT=22

Current_IP=$(dig +short $HOSTNAME)

if [ ! -f $LOGFILE ] ; then
  ufw allow from $Current_IP proto tcp to any port $PORT
  echo $Current_IP > $LOGFILE
else

  Old_IP=$(cat $LOGFILE)

  if [ "$Current_IP" = "$Old_IP" ] ; then
    echo IP address has not changed
  else
    ufw delete allow from $Old_IP proto tcp to any port $PORT
    ufw allow from $Current_IP proto tcp to any port $PORT
    echo $Current_IP > $LOGFILE
    echo ufw have been updated
  fi
fi
</code>

source: Using UFW with Dynamic IP hostnames like dyndns.org

With this script saved you could create a crontab entry like so in the file /etc/crontab:

<code>
*/5 * * * * root /etc/ufw_update.bash > /dev/null 2>&1
</code>

This entry would then run the script every 5 minutes, checking to see if the IP address assigned to the hostname has changed. If so then it will create a new rule allowing it, while deleting the old rule for the old IP address.