Need help setting up simple DMZ from OpenWRT > Router 2

Hi OpenWRT community,

Firstly I just want to say I hope everybody is keeping safe during the current blight that is Covid.

First post here as I simply can't figure this one out yet it seems like such a simple task to accomplish.

I am new to OpenWRT I only recently discovered it when my new ISP required Vlan Tagging =2 which is outside the available parameters of the Linksys WRT 1900 ACS V1 so I flashed my device to be able to do this but it gets more complicated.. in a simple way.

The setup:

Linksys WRT 1900 ACS (Running OpenWRT) (Tried to set it up basically in bridged mode as I only need it to handle Vlan tagging and my PPPOE connection)

Router 2 Netgear XR500 which I want to act as my main router handling everything on my network setup to receive it's connection to the internet from Linksys.

The connections:

I have connected my Internet to my Wan port of my Linksys, then my Lan port of my Linksys to my XR500 Wan port

The reason?

Basically the XR500 has a bug in it's current firmware which disables QOS when connected via PPPOE + Vlan. So I have set up my Linksys to connect to PPPOE and set it to do the Vlan tagging. Now this setup currently works, and my QOS is working however as I am connecting two routers I believe this is causing what is considered a Double NAT? and when I say do a connection test with my Nintendo switch I am getting a B instead of my normal A so I think this is right?

The solution i am attempting to accomplish

I believe all I need to do now is create a DMZ from Linksys > XR500 so that they aren't interrupting each other so to speak. As my XR500 is handling all my routing this should mean that even though my DMZ is open it's still safe as my second router is handling it? This is all very confusing to me.

Attempted to implement

I have opened up a ton of forums but I can't quite seem to get it to work. Some say I have to change more VLan stuff, others say to simply create a port forwarding rule in the firewall. I really don't know how the best way is to implement this simple DMZ. Also once it's setup I have read some people suggest turning off firewall, and DHCP on the linksys is this what I should do?

Anybody that can help a simple confused man such as myself would really be appreciated. I have turned to the forums after 3 days of not being able to figure this out XD

Thanks in advance :slight_smile: