A STUN server runs here on port 3478. The code for the server is available.
You can make simple https requests (e.g., curl) here to discover your IPv4 and IPv6 addresses:
Additionally, you can hit echo.nat-poker.com to retrieve v4 and/or v6 addresses in a JSON struct. Fields will be absent if no address is discovered.
All content, including images, © Stephen D. Strowes, 2000–2015. Hosted by Digital Ocean.