====== CG-NAT Detection =====

Determine if your ISP uses Carrier-Grade NAT which blocks port forwarding.

> //CG-NAT means you share a public IP with other customers, preventing port forwarding.//

===== Overview =====

Carrier-Grade NAT (CGNAT) means your ISP shares a single public IP among multiple customers. This prevents port forwarding from working because you don't have a unique public IP address.

===== What is CG-NAT =====

CGNAT, also called Large-Scale NAT (LSN), is NAT performed by your ISP before traffic reaches your home router. Multiple customers share the same public IP address.

===== How to Check for CG-NAT =====

**Check router WAN IP:**
  1. Log into router admin panel
  2. Find your router's WAN IP address
  3. Check if it starts with 100.64.x.x (CGNAT range)

**Compare with public IP:**
  1. Visit whatismyip.com or similar service
  2. Note your public IP address
  3. Compare with router WAN IP
  4. If they differ, you're behind CGNAT or double NAT

===== CG-NAT Symptoms =====

  * Port forwarding rules appear to work but don't
  * External port checkers show ports as closed
  * Router WAN IP is in 100.64.0.0/10 range
  * ISP is mobile provider or certain cable companies

===== If You Have CG-NAT =====

**Port forwarding will not work** because you don't have a unique public IP.

**Alternatives:**
  * Use Cloudflare Tunnel for external access
  * Request static IP from ISP (may cost extra)
  * Consider changing ISPs if hosting is important
  * Use VPN services that support CG-NAT

===== CG-NAT Range =====

The CG-NAT address range is 100.64.0.0/10. If your router's WAN IP falls in this range, you are behind CG-NAT.

===== References =====

  * [[https://oneuptime.com/blog/post/2026-03-20-detect-cgnat/view|How to Detect If You Are Behind Carrier-Grade NAT (CGNAT)]]
  * [[https://natchecker.com/blog/how-to-check-cgnat|CGNAT Checker: How to Test if You Are Behind Carrier-Grade NAT]]
  * [[https://blog.cloudflare.com/detecting-cgn-to-reduce-collateral-damage/|One IP address, many users: detecting CGNAT to reduce collateral damage]]

===== See Also =====

  * [[hosting:networking:start|Networking Overview]]
  * [[hosting:networking:alternatives|Alternatives to Port Forwarding]]

Last updated: 2026-06-19
  * [[hosting:start|Return to hosting]]