Double NAT and External IP for OpenVPN Server

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Occasional Visitor
Requesting help. I'm using an RT-AC-56U with Merlin 384.5 and the WAN shows a private IP address. The ISP just placed us in a double NAT situation with the external IP changing every 5 minutes or so. If the WAN-->DDNS is placed to "Custom" and the following script is placed in ddns-start, will that allow an external client to reach the OpenVPN Server? I would create a cron job to run the script every 5 minutes.

#FreeDNS updater script


registered=$(nslookup $DOMAIN|tail -n2|grep A|sed s/[^0-9.]//g)

current=$(wget -q -O -|sed s/[^0-9.]//g)
[ "$current" != "$registered" ] && {
wget -q -O /dev/null $UPDATEURL
echo "DNS updated on:"; date

Thank you,
Last edited:


Regular Contributor
If you do not have a modem (box from your priovder but which you cotntrol) which holds public address in your home and attached to your router, you will not be able to use someone's else public address to connect back to your system.

You would need to be able to set port forwards on your provider computer to do so.

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