Port 137: NetBIOS name service
Legacy Windows name lookups.
- Port
- 137
- Protocol
- UDP
- Service
- NetBIOS name service
- Exposure
- Do not expose to the internet
What is port 137 used for?
Old Windows networking.
Is it safe to expose port 137 to the internet?
Never expose. Disable NetBIOS over TCP/IP where you can.
If port 137 seems closed or unreachable
- Check that the NetBIOS name service service is running and listening on port 137, not only on 127.0.0.1.
- Check the firewall on the host itself (Windows Defender Firewall, iptables, nftables, ufw) for a rule that allows UDP 137.
- If the host is behind a router, confirm the forwarding rule points to the correct internal address and that your internet provider does not use carrier-grade NAT.
- Test from outside your own network. A port can be open locally and blocked at the edge, or the other way round.
Using port 137 safely
Treat port 137 as an internal-only service. Reach it through a VPN or an SSH tunnel, restrict it by source address, and keep the software that listens on it patched.
Check whether port 137 is open on your host
The check connects from our server, so it shows what the internet can reach.
Open the port checker