Port 137

Q: What is port 137?

NetBIOS name resolution on Windows networks UDP port 137 is used by Windows for NetBIOS name resolution — mapping computer names (e.g., MYPC) to IP addresses. In modern networks it has been replaced by DNS. When exposed to the internet it can leak hostnames and domain information, and is exploited in NBNS poisoning attacks using tools like Responder. Always block this port at the firewall perimeter.

NetBIOS-NS

NetBIOS name resolution on Windows networks

Port

137

Protocol

UDP

Service

NetBIOS-NS

Security

Dangerous

Full name: NetBIOS Name Service

What is port 137?

UDP port 137 is used by Windows for NetBIOS name resolution — mapping computer names (e.g., MYPC) to IP addresses. In modern networks it has been replaced by DNS. When exposed to the internet it can leak hostnames and domain information, and is exploited in NBNS poisoning attacks using tools like Responder. Always block this port at the firewall perimeter.

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