What is port 1521 used for?
The Oracle TNS listener.
Should port 1521 be open?
Don’t expose to the internet. Keep this port on private networks and reach it through a VPN or SSH tunnel. Keep database listeners on private networks only.
See what is listening on port 1521
# Linux
sudo ss -tlnp | grep ':1521 '
# macOS
sudo lsof -nP -i TCP:1521 -sTCP:LISTEN
# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1521 -State ListenOpen or block port 1521 in a firewall
# Ubuntu / Debian (ufw)
sudo ufw allow 1521/tcp
sudo ufw deny 1521/tcp
# Windows (PowerShell, as administrator)
New-NetFirewallRule -DisplayName "Port 1521" -Direction Inbound -Protocol TCP -LocalPort 1521 -Action AllowOn cloud servers, also open the port in the provider’s security group or network firewall. At home, a service behind a router needs a port-forwarding rule to the device’s local IP.
Test it from outside
A port can be open on the server but blocked upstream. The Port Checker connects from the internet, so it shows what the world sees. From your own machine, use nc -vz example.com 1521 (macOS/Linux) or Test-NetConnection example.com -Port 1521 (Windows).
Port CheckerTest whether a server accepts connections on specific ports — web (80/443), mail (25/587/993), SSH, databases or remote desktop — and see which are open, closed or filtered by a firewall.
Open the tool Frequently asked questions
What is port 1521?
The Oracle TNS listener.
Is it safe to open port 1521?
Don’t expose to the internet. Keep this port on private networks and reach it through a VPN or SSH tunnel.
How do I check if port 1521 is open?
Enter your domain or public IP in the Port Checker with port 1521. It tries a TCP connection from the internet and reports open, closed or filtered.