Port 138
NetBIOS-DGMNetBIOS datagram broadcasts on Windows networks
Full name:
NetBIOS Datagram Service
What is port 138?
UDP port 138 is the NetBIOS Datagram Service, used by Windows for LAN broadcasts such as the browser service, logon notifications, and similar announcements. It is no longer necessary on modern networks that rely on DNS and Active Directory. This port should always be blocked at the internet perimeter, as it exposes internal Windows network structure.