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Collaboration, Voice & AV · Advanced

Session Traversal Utilities for NAT (STUN)

A protocol (RFC 8489) that lets an endpoint discover its public IP and port as seen by a server outside the NAT.

Definition

A STUN client sends a binding request to a STUN server, which replies with the reflexive transport address it observed. The endpoint advertises this address so remote peers can send media back through the NAT. STUN also provides keepalives and connectivity checks used by ICE. STUN alone does not work through symmetric NATs, which require TURN.

Example

A WebRTC client learns its public address 203.0.113.5:54012 from a STUN server and includes it as an srflx candidate.

Exam tip

STUN discovers public addresses; TURN relays media; ICE chooses between them.

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