Port 636 (TCP) — LDAPS

Check if port 636 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':636 '

From another machine, test reachability:

nc -zv your-server.example.com 636

Block port 636 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 636

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=636/tcp && sudo firewall-cmd --reload

← All common ports