stunner: Check Your NAT Type with STUN
Summary
Stunner is a Go command-line tool that compares STUN responses from multiple servers to estimate your NAT behavior. Use it to assess how readily devices behind your network may connect through hole punching.
At a glance
- Language
- Go
- License
- MIT
- Stars
- 182
- Forks
- 10
- Added to OSRepos
- May 13, 2026
- Last analyzed
- October 3, 2026
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Overview
Stunner probes multiple STUN servers and compares the external IP and port mappings they observe. It turns those results into a best-effort NAT classification and an indication of how easy or hard hole punching may be.
It is useful when you need a quick network diagnostic, such as checking connectivity conditions for peer-to-peer connections. It is an experimental assessment, not a guarantee that a particular connection method will work.
Key Features
- Sends STUN Binding Requests to multiple servers for comparison.
- Fetches the Tailscale DERP map and selects servers automatically when none are specified.
- Accepts user-specified STUN servers and port settings.
- Supports binding to a chosen local IP address and port.
- Reports external mappings and an overall NAT classification in tables.
- Includes optional debug logging for STUN requests and responses.
Use Cases
- Network administrators can quickly inspect NAT behavior while troubleshooting connectivity.
- Developers building peer-to-peer applications can check whether a test network appears suitable for hole punching.
- Tailscale users can run a quick diagnostic using automatically selected DERP servers.
- Users comparing network environments can provide the same custom STUN servers to each test.
Project Facts
- Language: Go
- License: MIT
- Stars: 182
- Forks: 10
- Topics: network, tailscale
- Archived: No
Getting Started
Install with Go:
go install github.com/jaxxstorm/stunner@latest
Then run stunner to use automatically selected servers, or pass --stun-server values. See the README for installation alternatives and flags.
Considerations
- The README describes Stunner as an experimental proof of concept, and its NAT classification is a best-effort interpretation.
- Real NAT and firewall behavior can be more complex than the tests capture, so results may not predict whether a connection will succeed.
- Building from source requires Go 1.18 or later, as recommended by the project.
Source repository
Open the original repository on GitHub.
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