NETBIOS Name Service

NETBIOS-NS (NetBIOS Name Service) operates on port 137 and is essential for name resolution and registration in Windows-based networks. It allows devices to identify and communicate with each other by resolving NetBIOS names to IP addresses. This service is crucial for the proper functioning of networked applications and services in a Windows environment.

What is NETBIOS Name Service

NETBIOS-NS (NetBIOS Name Service) is a protocol used primarily in Windows networks for name resolution and registration. Operating on port 137, it plays a critical role in allowing devices to identify and communicate with each other by resolving NetBIOS names to IP addresses. This service is essential for the proper functioning of networked applications and services in a Windows environment.

Historically, NetBIOS was developed in the early 1980s to support network communication over IBM PC networks. It was later adopted by Microsoft for its Windows operating systems, becoming a fundamental component of Windows networking. NETBIOS-NS is one of the three core NetBIOS services, alongside NetBIOS Datagram Service (port 138) and NetBIOS Session Service (port 139).

In modern networks, NETBIOS-NS is often used in conjunction with other name resolution services like DNS (Domain Name System). While DNS has largely supplanted NetBIOS for name resolution on the internet, NETBIOS-NS remains relevant in local area networks (LANs) where legacy systems and applications still rely on it. Network administrators must ensure that NETBIOS-NS is properly configured to avoid conflicts and ensure seamless communication between devices.

NETBIOS Name Service runs on TCP and UDP port 137 and is official IANA port.

Security risk

If port 137 is open and the NETBIOS-NS service is running, it can expose the network to various security risks, including information leakage and potential exploitation by attackers. Unauthorized users could gather information about network devices and their names, which could be used for further attacks. It is crucial to secure this port and limit its exposure to trusted networks only.

In our UFW tutorial you can follow instructions how you can configure UFW to close port 137. Use StackChanges to monitor if the NETBIOS Name Service port is closed and stays closed. StackChanges will send an alert if port 137 is open again.