Port 6443 (TCP) — Kubernetes API

Check if port 6443 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':6443 '

From another machine, test reachability:

nc -zv your-server.example.com 6443

Block port 6443 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 6443

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=6443/tcp && sudo firewall-cmd --reload

← All common ports