CGNAT Inspector

Thu, 02 Jul 2026 18:10:04 +0000

If you've ever tried to self-host a website, game server, VPN, or NAS from your home network, you've probably encountered one frustrating problem: Carrier-Grade NAT (CGNAT).

Many Internet Service Providers now place customers behind CGNAT to conserve IPv4 addresses. While this works fine for everyday internet browsing, it can prevent inbound connections, making self-hosting much more difficult.

The challenge is that many people don't even realize they're behind CGNAT.

That's why I built CGNAT Inspector.

What is CGNAT?

Carrier-Grade NAT allows an ISP to let multiple customers share a single public IPv4 address.

Instead of your router receiving a unique public IP address, it receives another private or shared address from your ISP. As a result, services like:

Home servers
WireGuard VPN
Minecraft servers
Plex
Nextcloud
SSH access
Port forwarding etc.

may not work as expected.

Introducing CGNAT Inspector

CGNAT Inspector is a lightweight Bash utility that performs several independent tests to determine whether your network is behind CGNAT.

Rather than relying on a single check, it combines multiple detection techniques to provide a more reliable result.

Features

Detect Carrier-Grade NAT
Compare router WAN IP with your public IP
Detect private WAN addresses
Analyze traceroute for ISP NAT
Identify Double NAT scenarios
JSON output for automation
Colorized terminal output
Machine-readable exit codes
Lightweight with minimal dependencies

Example Output

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
      CGNAT Inspector v1.0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Local Address
192.168.1.54

Router WAN
100.91.14.23

Public IP
102.89.32.17

Result

STATUS : CGNAT DETECTED

Confidence : 100%

Why I Built It

As someone who enjoys building homelabs and self-hosted services, I've spent countless hours troubleshooting networking issues that eventually turned out to be CGNAT.

Existing methods often involve manually comparing IP addresses, checking router settings, or running multiple networking tools. I wanted a simple command-line utility that could perform these checks automatically and present the results in a clear, actionable way.

CGNAT Inspector is the result.

Who Is It For?

This tool is useful for:

Homelab enthusiasts
Self-hosting beginners
Linux users
System administrators
DevOps engineers
Network engineers
Anyone wondering why port forwarding isn't working

Future Plans

The project is just getting started. Planned improvements include:

IPv6 diagnostics
STUN-based NAT detection
Docker image
Prometheus exporter
Home Assistant integration
Interactive terminal interface
Port reachability testing

Get Involved

CGNAT Inspector is open source, and contributions are always welcome. Whether you'd like to report a bug, suggest a feature, improve the documentation, or submit code, your help is appreciated.

If you find the project useful, consider starring the repository and sharing it with other homelab and self-hosting enthusiasts.

Happy networking!

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