Curated port reference

Port 137: NetBIOS Name Service

NetBIOS Name Service commonly uses port 137 over TCP + UDP. Review its purpose, traffic direction and operational security considerations.

137TCP + UDP

NetBIOS Name Service

Legacy NetBIOS name registration and resolution.

Typical use

Older Windows networks and applications that have not moved entirely to DNS and direct-hosted SMB.

Traffic direction

Bidirectional

Security considerations

Avoid routing or exposing NetBIOS beyond trusted legacy segments; disable it where no dependency remains.

Server Message BlockActive Directory