Port 137 — NetBIOS-NS

UDP · Port 137/UDP is used for NetBIOS Name Service (NBNS) queries, which help devices on a network discover and identify each other. This service is critical for Windows-based networks to function properly. It's also a common target for reconnaissance attacks.

Port Number: 137
Service Name: NetBIOS-NS
Protocol: UDP
Common Software: Samba, Windows

Security Notes

Review IANA registry for port 137 usage. Apply principle of least privilege - only open ports that are required.

FAQ

What is port 137 used for?

Port 137 is used for NetBIOS-NS. Port 137/UDP is used for NetBIOS Name Service (NBNS) queries, which help devices on a network discover and identify each other. This service is critical for Windows-based networks to function properly. It's also a common target for reconnaissance attacks. Common software: Samba, Windows.

Is port 137 dangerous to leave open?

Review IANA registry for port 137 usage. Apply principle of least privilege - only open ports that are required.

How do I check if port 137 is open?

Use nmap: nmap -p 137 <target> or check locally: ss -tlnp | rg 137