Port 1521 — Oracle Database

TCP registered

What runs on port 1521

Oracle listener port.

Security considerations

Same rule — databases belong on a private network.

Checking whether something is listening

# Linux / macOS — what is bound to the port
sudo lsof -i :1521
sudo ss -lntp | grep :1521

# Windows
netstat -ano | findstr :1521
Get-NetTCPConnection -LocalPort 1521

# is it reachable from outside?
nc -zv example.com 1521
curl -v telnet://example.com:1521

Freeing the port

# find the process, then stop it
sudo lsof -ti :1521 | xargs kill        # Linux / macOS
netstat -ano | findstr :1521            # note the PID, then:
taskkill /PID <pid> /F                    # Windows

Should this port be open to the internet?

No. Port 1521 should never be reachable from a public address. Bind it to localhost or a private network, and reach it through a VPN or bastion host if remote access is genuinely needed. Internet-wide scanners find newly exposed instances of this service within minutes.

Quick reference

Frequently asked questions

Other common ports

• Port 20 — FTP data
• Port 21 — FTP control
• Port 22 — SSH / SFTP
• Port 23 — Telnet
• Port 25 — SMTP
• Port 53 — DNS
• Port 67 — DHCP server
• Port 68 — DHCP client
• Port 69 — TFTP
• Port 80 — HTTP
• Port 110 — POP3
• Port 123 — NTP
• Port 143 — IMAP
• Port 161 — SNMP
• Port 389 — LDAP
• Port 443 — HTTPS
• Port 445 — SMB
• Port 465 — SMTPS

All port numbers