STUN (Session Traversal Utilities for NAT)

A protocol (RFC 8489) that helps clients behind NAT discover their public IP address and port by querying a STUN server on the public internet. The server reflects the client's observed transport address back in the response. WebRTC and SIP use STUN during ICE candidate gathering to find server-reflexive candidates, enabling peer-to-peer connections through many types of NAT.