Session Traversal Utilities for NAT (STUN)

The STUN protocol is currently being rewritten with rfc3489bis.

Changes to STUN Protocol

Originally, STUN (RFC 3489) was developed as a standalone solution for NAT traversal for several types of applications, including VoIP. However, practical experience found that the limitations of its usage in isolation made it impractical as a complete solution. There were too many NATs which didn't support hairpinning or which had address and port dependent mapping properties.

Consequently, STUN was revised:

• STUN now is not the standalone solution for NAT traversal, but rather it defines basic tools and mechanism for performing the traversal. The broader and most comprehensive solution for NAT traversal currently is ICE, which makes use of the new STUN protocol.
• now it is considered cutting-edge to NOT try to find out the type of NAT, and rather to discover the media path interactively using ICE. For SIP signaling, NAT traversal is being solved by the outbound draft.
• several older STUN attributes have been deprecated since STUN no longer serves the purpose to detect NAT type, and new attributes and request/indication types are introduced. Examples of deprecated STUN attributes: RESPONSE-ADDRESS, CHANGE-REQUEST, SOURCE-ADDRESS, CHANGED-ADDRESS, REFLECTED-FROM, and MAGIC-COOKIE.
• the new STUN also defines STUN usages, a mechanism to extend the STUN protocol. The STUN (draft) standard defines Binding Discovery and Binding usages. Other types of STUN usages include TURN.
• the new STUN now provides means to authenticate STUN requests and responses by using short-term or long-term credential.

Draft Standard

The latest STUN-bis standard as of November 2007 is draft-ietf-behave-rfc3489bis-13.txt.

Implementations

• PJNATH library from pjsip.org project is an Open Source NAT traversal library supporting ICE, STUN, and TURN.
• Numb is a free STUN/TURN server.

SIP Clients

• pjsua

See also:

• STUN (the older STUN protocol)
• TURN
• ICE