hmbsbige/nattypetester

NatTypeTester is a Windows tool written in C# that checks what kind of NAT your network connection uses. NAT stands for Network Address Translation, and it is the system your router uses to let multiple devices share a single public internet address. Different routers implement NAT in different ways, and the specific behavior matters for things like online games, video calls, and peer-to-peer applications. If two devices are both behind certain types of NAT, they may have trouble connecting directly to each other. The tool uses a protocol called STUN, which was designed specifically to help software figure out NAT behavior by contacting a server on the public internet and examining how responses come back. NatTypeTester supports three generations of the STUN specification: RFC 3489, RFC 5780, and RFC 8489. Running tests from multiple specs gives you a more complete picture of how your router behaves. Beyond just detecting your external IP address, the tool can determine your NAT mapping behavior (whether the same internal address always maps to the same external address) and your NAT filtering behavior (which incoming packets your router will allow through). It supports both IPv4 and IPv6, and it can run tests over UDP, TCP, and encrypted variants of both. The underlying STUN library is also published separately as a NuGet package called Stun.Net, so developers can use it in their own C# applications. The README for this project is sparse and mainly consists of protocol references and screenshots. No installation instructions are included in what was provided.