Glossary

The Session Traversal Utilities for NAT (STUN) protocol allows entities behind a Network Address Translators (NAT) to learn
the address bindings allocated by the NAT, to keep those bindings open, and communicate with other STUN-aware entities to validate connectivity and vitality.

The STUN protocol was developed as a solution to some drawbacks in NATs, while providing many benefits, have the drawback of breaking many existing IP applications, and making it difficult to deploy new ones. Guidelines were developed that describe how to build “NAT-friendly” protocols, but many protocols simply cannot be constructed according to these guidelines. Examples of such protocols include almost all peer-to-peer protocols, such as multimedia communications, file sharing, and games. The problem appears when the protocol requires one of the session peers to code its address-related data within the protocol payload, causing the other peer to try using the “behind-the-NAT” address which is not accessible in most cases.

Many existing proprietary protocols developed workarounds that allow them to operate through NATs. The STUN protocol takes some of these ideas and codifies them into an interoperable protocol that can meet the needs of many
applications.

STUN is defined by the IETF in RFC 3489 and RFC 5389.

RADVISION offers a STUN NAT Traversal Toolkit for developers.