STUN

Session Traversal Utilities for NAT (STUN) is a standardized set of methods, including a network protocol, used for traversal of network address translator (NAT) gateways in applications of real-time voice, video, messaging, and other interactive communications^[1].
It is primarily used to discover the public IP address of a device running behind a NAT^[2].

• Tell me my public ip address/port through NAT
• Works for Full-cone, Port/Address restricted NAT
• Doesn't work for symmetric NAT
• STUN server port 3478, 5349 for TLS
• Cheap to maintain

Problems STUN Solves

• NAT Traversal: STUN is used to overcome the problem of NAT traversal. It allows network devices to discover post-NAT IP addresses and port numbers of communicating parties and to use this information to establish peer-to-peer (P2P) data channels^[3].
• IP Discovery: STUN answers the question "what is my IP address?" by using a STUN server. This server runs on the public network and replies to incoming requests with the public IP address the request was sent from^[4].

Pros of STUN

• Compatibility: STUN works with existing NAT devices and does not require any changes to network devices^[3:1].
• Simplicity: STUN uses the client/server model, which is simple and easy to implement. Only one STUN server needs to be deployed on the network^[3:2].
• Use in Various Applications: STUN is used in several different network implementations and scenarios, one of which is in VoIP implementations^[2:1].

Cons of STUN

• Limited NAT Traversal: STUN is not a self-contained NAT traversal solution applicable in all NAT deployment scenarios. It works with three types of NAT: full cone NAT, restricted cone NAT, and port restricted cone NAT^[1:1].
• Security Concerns: STUN servers can be vulnerable to various security risks, such as man-in-the-middle attacks or unauthorized access^[5].

In the context of WebRTC, STUN is usually deployed with TURN servers. Configuring TURN/UDP implicitly also implements the STUN protocol^[4:1].

Also Read

• WebRTC
• TURN
• gRPC