TURN
also: Traversal Using Relays around NAT
TURN (Traversal Using Relays around NAT) is a protocol that allows applications behind firewalls or NATs to communicate by relaying traffic through an external server.
TURN is a network protocol (RFC 5766) designed to overcome connectivity issues when direct peer-to-peer communication is impossible due to network address translation (NAT) or firewalls. It works by having both peers connect to a TURN server, which then relays all traffic between them.
Unlike STUN (which only helps discover your public IP), TURN actively mediates the connection by allocating resources on the relay server. Each peer sends data to the TURN server instead of directly to the other peer, and the server forwards it accordingly.
Common use cases include WebRTC applications, VoIP, and online gaming where participants may be behind restrictive corporate firewalls or consumer NATs. For example, a video conference participant behind a corporate firewall can establish a call by having their video stream sent to a TURN server, which then forwards it to the other participant's TURN server connection.