Port 137 (UDP) — NetBIOS name

Check if port 137 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':137 '

From another machine, test reachability:

nc -zv your-server.example.com 137

Block port 137 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 137

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=137/udp && sudo firewall-cmd --reload

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