Port137— NetBIOS Name Service
UDP 137 is the NetBIOS Name Service (NBNS) from the legacy Windows stack — it resolves computer names to IPs. UDP 138 (datagram) and TCP 139 (session) complete the trio. Modern Windows networks rely on DNS plus SMB over 445, leaving 137 as legacy.
Registry assignments, software defaults and local listeners are different things. A port number alone does not identify or secure a service.
Configuration and troubleshooting
For Samba/Windows share issues: check 445 (SMB) and DNS resolution first — 137/138 only matter for legacy browsing and device discovery. Samba disables it with `disable netbios = yes`; modern deployments should turn it off and rely on DNS.
Important limitations
NetBIOS is a classic worm and recon target — 137 leaks hostnames and workgroup info even when 445 carries the actual exploit traffic. Never expose 137/138/139/445 to the internet; use a VPN for cross-network access.
Read-only checks: run on the server host
Choose the commands for your OS. Check TCP and UDP separately. No result is not a lasting availability guarantee; inspect host and container separately.
Linux
sudo ss -lunp 'sport = :137'macOS
sudo lsof -nP -iUDP:137Windows PowerShell
Get-NetUDPEndpoint -LocalPort 137Sources and review
Sources checked on:
This review covers the explanations and sources on this page, not your device or every community software entry below.
Software Using This Port (3 software)
Community software entries: links are references, not individual verification.
Windows NetBIOS
WindowsNetBIOSService
NetBIOS Name Service
NetBIOSService
Usage Suggestions
- Before using port 137, please confirm it is not occupied by other services
- If you encounter port conflicts, consider using other ports or stopping the occupying service
Frequently asked questions
What is port 137 used for?
Port 137 sits in the System category. This page lists the registered purpose and the software commonly associated with it; to see what is actually listening on a specific machine, check the process with ss/netstat.
Is port 137 TCP or UDP?
The registered protocol on this page is UDP. The same number behaves independently on each protocol: TCP may be listening while UDP is idle, so check them separately.
How do I check if port 137 is in use?
On Linux: sudo ss -tlnp 'sport = :137' for an exact port match. On macOS: sudo lsof -nP -iTCP:137 -sTCP:LISTEN. On Windows PowerShell: Get-NetTCPConnection -LocalPort 137 -State Listen. A listener counts as confirmed only when you can see the bind address and process name; without root/admin you will not see other users' processes.
Is port 137 secure? Should I open it in my firewall?
A port number has no inherent security — it depends on whether the listening service is correctly configured and whether it needs exposure at all. Keep loopback/internal-only services firewalled; where public access is required, pair it with source restrictions, VPN or authentication. The caution section on this page lists port-specific risks.
Quick Info
- Port
- 137
- Protocol
- UDP
- Categories
- System
- Usage Status
- 3 software in use
Related Ports
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