Networking 2 min read

There are not enough IPv4 addresses for every home and phone. Many providers solve this with carrier-grade NAT (CGNAT): they give your router a private address and translate it, together with those of many other customers, into a small pool of shared public addresses.

How CGNAT works

At home, your router already uses NAT to let all your devices share one public IP. With CGNAT there is a second layer:

  1. Your device has a private address, like 192.168.1.20.
  2. Your router translates it to the address your provider gave it, which is not public, typically in the range 100.64.0.0/10 (reserved for this purpose by RFC 6598).
  3. The provider's CGNAT equipment translates that into a public IP shared with other customers.

Mobile networks almost always use CGNAT. Many fiber, cable and satellite providers do too.

How to tell if you are behind CGNAT

  1. Find your router's WAN or Internet IP address in its settings page.
  2. Compare it with the public IP on our home page.
Router WAN address Meaning
Same as the home page You have your own public IP. No CGNAT.
Starts with 100.64–100.127 You are behind CGNAT.
Starts with 10., 172.16–172.31 or 192.168. Another NAT layer, either CGNAT or a modem in router mode.

Problems CGNAT causes

  • No port forwarding. You cannot host a game server, a camera, a NAS or a website at home reachable from the internet.
  • Online gaming: strict NAT types and trouble joining or hosting sessions.
  • Shared reputation: if another customer on your public IP misbehaves, you can get captchas or blocks. Your shared address may also appear on a blacklist.
  • IP-based logins can see many users on the same address.

Workarounds

  • Use IPv6. Most providers that use CGNAT also offer IPv6, which gives each device a public address.
  • Ask your provider for a public IPv4. Some do it free on request, others charge a small fee.
  • Use a tunnel service or a VPN with port forwarding to reach home devices from outside.

Frequently asked questions

Does CGNAT make me anonymous?

Not really. Your provider logs which customer used which shared address and port at what time.

Is CGNAT bad for normal browsing?

No. Browsing, streaming and video calls work normally.

Will CGNAT go away?

As IPv6 spreads, providers need it less, but it will remain common for years.