STUN uses which port number?

STUN uses which port number?

• A. 8080
• B. 161
• C. 3478
• D. 512

Answer: (C)

STUN helps a device discover how it appears to the outside world by having it send small messages to a STUN server over UDP and then report back what address and port the server sees. The standard, well-known port for STUN is 3478. This port is defined in the protocol specification as the default UDP port used by STUN servers and clients. When a client sends a binding request to the server on this port, the server replies with the mapped external address, enabling the client to understand its public IP and NAT behavior. The other numbers correspond to different services (for example, 8080 is often used for web proxies, 161 for SNMP, and 512 for older remote login services), so they aren’t used for STUN.

STUN helps a device discover how it appears to the outside world by having it send small messages to a STUN server over UDP and then report back what address and port the server sees. The standard, well-known port for STUN is 3478. This port is defined in the protocol specification as the default UDP port used by STUN servers and clients. When a client sends a binding request to the server on this port, the server replies with the mapped external address, enabling the client to understand its public IP and NAT behavior. The other numbers correspond to different services (for example, 8080 is often used for web proxies, 161 for SNMP, and 512 for older remote login services), so they aren’t used for STUN.