Port 1522: Oracle's alternate listener — The port that lives one number away from the default

Port 1522 occupies an interesting position in the registered port range: it has no official IANA assignment, yet it has a clear, well-established purpose in Oracle database deployments worldwide.

What Runs on Port 1522

Port 1522 is most commonly used for Oracle TNS (Transparent Network Substrate) listeners—the service that allows client applications to connect to Oracle databases. While Oracle's default listener port is 1521, port 1522 frequently serves as the alternate when:

• Multiple Oracle database instances run on the same server
• Port 1521 is already occupied by another service
• Organizations want to move away from the well-known default for security reasons
• Oracle RAC (Real Application Clusters) deployments need additional listeners

The choice of 1522 isn't mandated by Oracle documentation. It's a convention that emerged from the simple logic of "the default is 1521, so let's use 1522 for the second one."¹

The Registered Port Range

Port 1522 sits in the registered port range (1024-49151). Ports in this range can be registered with IANA for specific services, but registration isn't required to use them. This is different from well-known ports (0-1023), which require root privileges to bind on Unix-like systems.

The registered range exists as middle ground—less restricted than well-known ports, more organized than ephemeral ports (49152-65535). Services can claim ports here through IANA, but in practice, many ports in this range are used by convention rather than official assignment.

Why This Port Matters

Port 1522 illustrates something honest about how the Internet actually works: official assignments matter less than actual deployment. No RFC defines 1522 as "the second Oracle listener port." IANA's registry doesn't assign it to Oracle. Yet thousands of production databases listen on this port because:

1. DBAs needed a second listener port
2. "1521 + 1" felt natural
3. It worked
4. The convention spread

This is how many ports in the registered range operate—not through formal specification, but through shared practice that solidifies into de facto standards.

Security Considerations

Using port 1522 for Oracle listeners provides minimal security benefit over 1521. Attackers scanning for Oracle databases will check both ports (and often the entire 1521-1529 range). Port scanners looking for Oracle instances specifically target this range.²

Real security for Oracle listeners comes from:

• Proper authentication and access controls
• Network segmentation (databases shouldn't be Internet-accessible)
• Keeping Oracle software patched
• Monitoring listener logs for unauthorized access attempts

Changing the port number is security through obscurity—it might slow down automated scans slightly, but it won't stop a determined attacker.

How to Check What's Listening

On Linux or macOS:

# See what's listening on port 1522
sudo lsof -i :1522

# Or using netstat
netstat -an | grep 1522

On Windows:

# Check port 1522
netstat -an | findstr 1522

If you find Oracle listening on this port, you can often identify which database instance by checking the Oracle listener configuration file (listener.ora), typically found in $ORACLE_HOME/network/admin/.

Related Ports

• Port 1521 — Oracle's default TNS listener port
• Ports 1523-1529 — Additional ports commonly used for Oracle listeners in multi-instance environments
• Port 2483 — Oracle database SSL connections (encrypted TNS)
• Port 2484 — Oracle database SSL with server authentication

The range 1521-1529 has become informally associated with Oracle deployments, even though only some of these ports have any official Oracle documentation.³