Port 137: NetBIOS-NS
Port 137 is the NetBIOS Name Service, the legacy Windows name resolution that predates DNS on the LAN. It is commonly blocked at the perimeter for security.
UDPWindowsUnencrypted by defaultIANA assigned
| Port number | 137 |
|---|---|
| Service | NetBIOS Name Service |
| Protocol | UDP |
| Category | Windows |
| Default encryption | No |
Security note. Port 137 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 137 used for?
Port 137 is the NetBIOS Name Service, the legacy Windows name resolution that predates DNS on the LAN. It is commonly blocked at the perimeter for security.
Is port 137 TCP or UDP?
Port 137 (NetBIOS-NS) uses UDP.
Is port 137 secure?
Port 137 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 137 on my firewall?
Only if you specifically need NetBIOS-NS. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.