Port 137 (NetBIOS Name)
UDPNetBIOS Name Service — NetBIOS Name listens on port 137 by default.
What is Port 137?
Port 137 is used by the NetBIOS Name Service, a component of the NetBIOS over TCP/IP (NBT) protocol suite. It provides name registration and resolution services for Windows networking, allowing computers to find each other by name on a local network.
NetBIOS Name Service on port 137 uses UDP for name queries and registrations. When a Windows computer starts up, it registers its NetBIOS name on port 137. Other computers query this port to resolve NetBIOS names to IP addresses before establishing connections.
Modern Windows networks have largely replaced NetBIOS name resolution with DNS, but port 137 remains active for backward compatibility. It should be blocked at the firewall perimeter as it can leak internal network information.
Port 137 Security
NetBIOS Name on port 137 should be secured with appropriate access controls and monitoring. Ensure the service is only accessible from trusted networks by configuring firewall rules to restrict access. If the protocol supports encryption, enable TLS/SSL to protect data in transit.
Regularly update NetBIOS Name to the latest version to patch known vulnerabilities. Monitor port 137 for unauthorized access attempts and implement rate limiting where possible. Follow the principle of least privilege when configuring access permissions.
How to Check Port 137
To check if port 137 is open on a remote host, use nmap: 'nmap -p 137 hostname'. For a quick TCP connection test, use: 'telnet hostname 137' or 'nc -zv hostname 137'. On Windows PowerShell, use: 'Test-NetConnection -ComputerName hostname -Port 137'.
To check if port 137 is listening on your local machine, use: 'netstat -tlnp | grep 137' on Linux, or 'ss -tlnp | grep 137'. On Windows, use: 'netstat -an | findstr 137'. For a comprehensive scan, use: 'nmap -sV -p 137 hostname' to detect the service version running on the port.
Related Ports
Frequently Asked Questions
What is port 137 used for?
Port 137 is the default port for NetBIOS Name Service (NetBIOS Name). It is used for netbios name communication using the UDP protocol.
Is port 137 TCP or UDP?
Port 137 uses UDP. UDP is used because netbios name requires fast, low-overhead communication.
Should port 137 be open?
Port 137 should only be open if you are actively running NetBIOS Name. Close unused ports to reduce your attack surface. If needed, restrict access to trusted IP addresses using firewall rules.
How do I check if port 137 is open?
Use 'nmap -p 137 hostname' to scan remotely, or 'netstat -tlnp | grep 137' to check locally on Linux. On Windows, use 'Test-NetConnection -Port 137 hostname' in PowerShell.
How do I secure port 137?
Secure port 137 by restricting access with firewall rules, using encryption (TLS/SSL) where supported, keeping NetBIOS Name updated, using strong authentication, and monitoring for unauthorized access attempts.
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