I'm looking to set up a local server, but came across the term Carrier Group NAT, which may make it impossible to do.
I have a home fibre broadband connection.
Does anyone know how I can find out if I am behind a Carrier Group NAT?
Carrier *grade* NAT just means a honking big NAT box at your ISP. It's unusual for wired ISPs in the UK, but you may see it if you are on a small or new provider. It's very common for mobile.
The way to find out is to go to your router's management interface and see what IP address it has been assigned on its WAN interface. Then go to a site like whatsmyip.org which tells you what IP address it sees your incoming connection coming from. If they are the same, then you are not behind a CGN. If they are different, then you are.
If you are behind CGN, then your WAN address will have picked up some sort of private address, which the CGN NATs to a public address. In this context, "private" does include the well-known RFC1918 ranges (192.168.x.x, 172.16-31.x.x, 10.x.x.x) but there is also a block specially reserved for CGN (100.64-127.x.x). And occasionally I've seen networks just take random bits of public IP address space and treat it as if it were private.