stunner: Check Your NAT Type with STUN

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.