Port 138: NetBIOS-DGM
Port 138 is the NetBIOS Datagram Service, used for connectionless communication such as browsing the network neighborhood on older Windows systems. It is part of the same legacy NetBIOS stack as ports 137 and 139.
UDPWindowsUnencrypted by defaultIANA assigned
| Port number | 138 |
|---|---|
| Service | NetBIOS Datagram Service |
| Protocol | UDP |
| Category | Windows |
| Default encryption | No |
Security note. Port 138 is not encrypted by default. Restrict it to trusted networks, or use an encrypted alternative where one exists, to avoid exposing credentials and data in transit.
Frequently asked questions
What is port 138 used for?
Port 138 is the NetBIOS Datagram Service, used for connectionless communication such as browsing the network neighborhood on older Windows systems. It is part of the same legacy NetBIOS stack as ports 137 and 139.
Is port 138 TCP or UDP?
Port 138 (NetBIOS-DGM) uses UDP.
Is port 138 secure?
Port 138 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 138 on my firewall?
Only if you specifically need NetBIOS-DGM. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.