stun

Test NAT traversal and external addressing

TLDR

Test NAT type

$ stun [stun.example.com]

Use specific port

$ stun -p [3478] [stun.example.com]

Verbose output

$ stun -v [stun.example.com]

Local port binding

$ stun -L [54321] [stun.example.com]

SYNOPSIS

stun [-p port] [-L localport] [-v] server

stun is a STUN (Session Traversal Utilities for NAT) client that queries STUN servers to determine NAT type and discover external addressing information. It sends binding requests to a STUN server and analyzes the responses to classify the NAT behavior of the network the client is behind.The tool can identify various NAT types including full cone, restricted cone, port-restricted cone, and symmetric NAT. It also reports the external IP address and port mapping as seen by the STUN server, which is essential information for peer-to-peer connectivity.This is useful for troubleshooting VoIP and SIP connectivity issues, diagnosing WebRTC connection failures, and understanding network topology. The NAT type directly affects whether peer-to-peer connections can be established, with symmetric NAT being the most restrictive.