Am I behind a CG-NAT?

A somewhat common cause for not being able to port forward and get users to join your server is caused by being behind a CG-NAT (Carrier-grade NAT). This will only happen on home networks and is very unlikely to happen with a VPS or host provider.

What is a CGNAT?

CGNAT is a technique used by some ISPs (internet service providers) where customers will all share a single IP address instead of getting their own.

How to check?

Windows:

1. Open command prompt.
2. Go to https://whatismyipaddress.com and copy the IPv4.
3. Type tracert <external IP> and replace <external IP> with your external/public IPv4, and wait for it to complete.
4. A good result will looks like this:
   

   Tracing route to 85.xx.xxx.xx over a maximum of 30 hops
   
     1     1 ms     1 ms     2 ms  85.xx.xxx.xx

    As shown above there is only one hop which is good and means you are not behind a CGNAT. If you have multiple hops especially ones between 100.64.0.0 to 100.127.255.255 (these are reserved for CGNAT), or the traceroute does not complete, then you are behind a CGNAT. You will have to contact your ISP about getting your own dedicated IP address.

Linux:

Follow the same steps above but use the traceroute command instead. You'll likely have to install this package with your distro package manager.