So I have my main router in a room far away and pretty much no devices connect to it but i sometimes use it so I cant turn it off then I grab a cable from it and connect it to wan port of the router inside the house which everybody uses. I used to have it set to Access point mode but some features like qos werent avaliable so I switched it over to router mode. Any downsides to doing this? Im already behind a cgnat so im not gonna be port forwarding and no ipv6 if I wanted to anyways.

Why not use the router with more features as the main router and the second one as the AP?

Why not put it in bridge mode? Just have it pass traffic through

Yes there is, a lot of stuff can break, just use it as an ap

There are some, but it really comes down to whether you are experiencing problems. When my main internet, xfinity, goes out, my starlink mini takes over automatically and I keep it in router mode plugged into wan2 on my gateway. No issues at all with our devices or network. I can still access my cameras and such remotely, and my wife who works from home can still use her vpn after reconnecting to it after the swap.

The isp router doesnt have a bridge mode for some reason unfortunately

Bgw320 from att?

No just a random isp in the middle east

Bridge wouldn't fix your case anyway more that i think about it. It would be rendered inert by doing so preventing anyone from connecting to it that does currently.

Ideally you'd put your current router in place instead and use an AP or a small switch for your remote location.

Otherwise you'll just have to use what you got and see if anything breaks because you're doublenat

Double NAT is not automatically bad. It mostly depends on whether you need inbound connections or clean device-to-device discovery.

In your case, because you are already behind CGNAT, the big downside people worry about, port forwarding from the internet, is already mostly off the table. Adding another NAT layer inside the house usually will not change normal browsing, streaming, gaming, or basic VPN client use very much.

The things I would watch for are:

- devices on the first router may not easily see devices behind the second router
- Chromecast/AirPlay/printers/cameras can get awkward if they are split across both networks
- online games or voice chat may show stricter NAT
- troubleshooting gets more confusing because you now have two DHCP/NAT/firewall layers
- QoS on the second router can only really manage traffic after it reaches that router, not the whole ISP connection perfectly

If everyone uses the inside router and the first router is mostly just upstream, this setup can be fine. I would avoid connecting normal client devices to both routers unless you intentionally want two separate networks. If you start seeing discovery or console NAT problems, AP mode or making the feature-rich router the main router would be the cleaner design.

If you are behind CGNAT, then you already have double NAT. Adding another router means you have triple NAT.

Is there any downside? Keep in mind that a router is basically a one-way firewall. That means that any devices connected to your ISP router will not be able to connect to devices connected to your personal router. If there are no devices connected to the ISP router, then there's probably going to be no real downside.

How fast is your Internet connection? If it's 500 Mbps or greater, then many routers can not perform QoS at those speeds. Unless you are regularly experiencing bufferbloat, you may not need QoS. Ultimately, it depends on how the people in your house use the Internet. If people are regularly downloading large files, then QoS may still be useful.

Thanks alot for the detailed breakdown. It's unfortunately lower than 500 so I may end up using qos in the end

Added latency. A common misconfiged setup in many home or apartment wifi setups.

Often users will keep old network equipment and add to this double nat situation. But this is just leaving the back door wide open. Older equipment are vulnerable to exploits because they are no longer being patched. And a router behind a router can see everything going on in the first network.