Remote file access via double NAT

[rwaterval]

Can anyone help me to access my files on my QNAP NAS remotely? I looked on youtube, but I'm not able to get it to work. My knowledge in home networking is fairly limited, so I hope you can explain it in easy terms to me.

I have the following situation: a Zyxel EX56 modem from my ISP, and behind this modem, an ASUS Zenwifi AX router (meshed with two other ASUS Zenwifi AX routers).

The Zyxel modem is connected to the internet (iii.sss.ppp.adr). It has the subset 192.168.1.xxx. The Asus Zenwifi AX is connected to this router on 192.168.1.yyy. To log into my Asus router at home, I have to use the subset 192.168.50.xxx. My QNAP NAS is located on 192.168.50.qqq. I think this is described as a double NAT configuration.

This is what I did sofar:
1. Set-up port forwarding on my Zyxel modem to (192.168.1.yyy, UDP, port 1194) to my Asus Zenwifi router
2. Set-up port forwarding on my Asus Zenwifi router to (192.168.50.xxx, UDP, port 1194)
3. Created an opvn file via my Asus Zenwifi router and changed the first line "remote 192.168.1.yyy 1194" to "remote iii.sss.ppp.adr 1194"
4. Added the opvn file to the OpenVPN client on my laptop. I included the username and password from my Asus Zenwifi router.

I then use the mobile hotspot wifi of my iPhone to connect my laptop to the internet. The OpenVPN client appears to connect without issues. However, I still can't open my files and/or folders on my QNAP NAS.

What am I doing wrong? Can anyone give me advice?

Thanks in advance!!!

[jzchen]

I don't know how to do that with double NAT, but if you can set the Zyxel to Bridge Mode you'll effectively remove the double NAT and shouldn't have much difficulty...

[rwaterval]

Thanks @jzchen! Apparently my provider has disabled the option the set the Zyxel to Bridge Mode. Instead, I enabled DMZ on the Zyxel modem to my Asus router. Now I can connect to my Asus router via my iPhone via OpenVPN. However, I still can't connect to the QNAP NAS.... Any ideas?

[jzchen]

I suspect it has to do with subnet 255.255.255.0, but not sure the best practice how to adjust, either change subnet or the IP 192.168.50.xxx to 192.168.1.xxx .  (Not sure that is the problem either)...

[rwaterval]

Hi @jzchen, I just enabled DMZ on my Asus router to my QNAP NAS. Now I managed to reach my files on my NAS on my iPhone. However, this now works even without VPN enabled on my iPhone. That doesn't look to be a safe option. I don't understand why the port forwarding rules aren't working.