PlayInfoBox

Home /Network /What Is CGNAT (Carrier-Grade NAT)? Why Port Forwarding Doesn't Work

What Is CGNAT (Carrier-Grade NAT)? Why Port Forwarding Doesn't Work

If port forwarding is set up correctly but still doesn't work from outside, CGNAT may be the reason.

What is CGNAT?

Carrier-Grade NAT is large-scale address translation that an ISP applies across its own network so multiple subscribers can share a single public IP address. It works like a second layer on top of what a home router already does: just as a router translates every device's private IP into the router's one public IP, the ISP translates that 'public' IP again into a real public address shared by many subscribers.

Why it exists: IPv4 exhaustion

The world has roughly 4.3 billion usable IPv4 addresses total, and most of that space has already been allocated. With not enough left to give every subscriber their own public IP, ISPs use CGNAT to serve far more subscribers with a much smaller pool of public addresses.

Typical symptoms of a CGNAT connection

Port forwarding set up on the router for remote access to a home camera or NAS simply doesn't work, and some online games report a 'Strict' NAT type that causes matchmaking problems with other players β€” both are classic signs.

How to check if you're behind CGNAT

Compare the public IP address shown by an 'IP lookup' search engine query with the WAN status IP shown on the router's admin page. If the two don't match, there's a good chance an extra layer of address translation is happening somewhere in the ISP's network.

How it differs from a home router's NAT

A home router's NAT lets multiple devices share one public IP, but that public IP is still uniquely yours. CGNAT goes a step further β€” even that 'public-looking' address is itself shared with other subscribers inside the ISP's network.

How to work around it

Options include requesting a static public IP from the ISP (sometimes a dedicated line or paid add-on), or configuring external access over IPv6 if it's supported. For a quicker fix aimed just at remote access, DDNS combined with a cloud relay service, or a VPN-based workaround, are both commonly used.

When port forwarding still fails after following the guide

If port forwarding was set up correctly following a standard port forwarding guide for remote access to a NAS or home camera and it still fails, checking for a carrier-grade NAT situation on the ISP side should come before re-checking the router again.

If NAT type is affecting online gaming

When NAT type shown in a console or PC game is affecting matchmaking, a dedicated guide to NAT types for gaming covers additional fixes worth trying alongside addressing CGNAT.

Frequently Asked Questions

Does CGNAT slow down my internet speed?

CGNAT by itself has little effect on ordinary browsing or streaming speed. The problems it causes show up specifically for services that need something to connect directly inbound to your device β€” port forwarding, and some P2P-based game matchmaking.

Will my ISP just turn off CGNAT if I ask?

It depends on the ISP and plan. Some ISPs offer a static public IP as a paid add-on or separate product, so contacting support to ask about availability and cost is the most reliable way to find out.