Port 1521 (TCP) — Oracle DB

Check if port 1521 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':1521 '

From another machine, test reachability:

nc -zv your-server.example.com 1521

Block port 1521 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 1521

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=1521/tcp && sudo firewall-cmd --reload

← All common ports