What is CGNAT?

CGNAT (carrier-grade NAT) means your internet provider puts you and many of your neighbors behind one shared public IPv4 address. Browsing works fine. Letting the internet reach a server in your house usually doesn't.

The short version

Your home router already does NAT: every device in your house shares one address on the internet. With CGNAT, your ISP adds a second layer of NAT on its side, so your router doesn't get a public address either. It gets a private one, and the public address is shared with other customers.

Without CGNAT:   laptop ─▶ your router (public IP 203.0.113.7) ─▶ internet
With CGNAT:      laptop ─▶ your router (100.72.14.9) ─▶ ISP's NAT (public IP shared by many homes) ─▶ internet

Why it matters for self-hosting

• Port forwarding stops working. You can forward port 443 on your router, but connections from the internet never reach it. They stop at the ISP's NAT, which has no idea which customer they're for.
• "Open NAT" for games and peer-to-peer apps may fail.
• IP-based allowlists get messy, because your public IP is shared and can change.
• IPv6 is separate. CGNAT only affects IPv4. If your ISP gives you real IPv6, devices can still be reachable over IPv6, from networks that also have IPv6.

How to tell if you're behind it

Compare the WAN (internet) IP your router shows with the public IP websites see. If they're different, or the router's WAN IP falls in 100.64.0.0–100.127.255.255 (the 100.64.0.0/10 range reserved for CGNAT by RFC 6598), you're behind CGNAT or another layer of NAT. Use the checker to walk through it, or follow the step-by-step guide.

What you can do (ISP-side options)

1. Ask for a public IPv4. Some ISPs move you off CGNAT for free if you ask. Others only do it with a paid static IP. Each ISP page lists what we've verified.
2. Buy a static IP if your ISP sells one to residential customers. Some only offer it on business plans.
3. Use IPv6 if your ISP supports it, and your router's IPv6 firewall lets you open specific ports.
4. Check the terms. Even with a public IP, some residential agreements forbid running servers. We quote the clause on each ISP page.
5. Compare providers available at your address using the ISP table.

This site sticks to ISP facts. It doesn't review or recommend third-party products or services.