FritzBox router as a WLAN access point behind cable router - can't access NAS attached to cable router

Question

I have a FritzBox 7270 v3 as a WLAN access point for my mobile devices. This box is attached via LAN to my cable router (Hitron CVE-30360) as well as my NAS (QNAP TS-421).

My NAS and my cable router are configured to be accessible via internet and I can access them without issues.

What I can't do is accessing my NAS via mobile device when connected via my WLAN. I can't use the QNAP apps, I can't access the web frontend but I can access the front end from my cable router and my fritzbox.

So I can access everything from my WLAN except the devices attached via LAN to the cable router.

I am lost. How can I configure my FritzBox to work as a simple switch? It should just pass every request without checking ports.

Any ideas? Does my FritzBox even support what I am looking for?

Answer 1

As always as soon as you ask you find the issue.

My cable router had port forwarding active for the 443 to the NAS. That seems to have interfered with the routing internally so after disabling it it worked :)