Port 1523 lives in the gap between official assignment and real-world usage. IANA says it belongs to one service. Network administrators use it for another.
What Port 1523 Is Officially For
According to IANA's port registry, port 1523 is assigned to cichild-lm—a license manager service.1 The registration shows both TCP and UDP protocol support, registered by someone from cichlid.com.
That's what the official record says. Here's what actually happens.
What Port 1523 Actually Carries
In production environments, port 1523 is commonly used for Oracle database listener processes—despite Oracle's official port being 1521.2
Why? Because real networks are messy. When you have multiple Oracle database instances running on the same server, or when port 1521 is already occupied by another service, administrators reach for nearby available ports. Port 1523 is close enough to remember, far enough to avoid conflicts.
Oracle Enterprise Edition environments, particularly those running multiple listeners for load balancing or application segregation, frequently use ports 1522 through 1529.3 Port 1523 sits right in that range.
The Registered Port Range
Port 1523 belongs to the registered ports range (1024-49151). Unlike well-known ports (0-1023) which require root privileges and have strict assignments, registered ports are listed with IANA but not enforced. Any application can listen on them. Any administrator can repurpose them.
This is where the port system's idealism meets pragmatism. IANA maintains a registry hoping for order. Administrators configure what works.
How Oracle Uses Non-Standard Ports
When you configure an Oracle listener on port 1523 instead of 1521, you're making a deliberate choice. Maybe you're running Oracle E-Business Suite on 1523 while third-party applications use the default 1521.4 Maybe you're segregating development and production databases. Maybe port 1521 was taken and you needed the next available option.
The listener doesn't care. It accepts connections on whatever port you configure in listener.ora. The client connects to whatever port you specify in the connection string. The official assignment becomes irrelevant.
Checking What's Actually Listening
To see what's really using port 1523 on your system:
On Linux or macOS:
On Windows:
The output will show you the truth—whether it's the officially assigned cichild-lm service, an Oracle listener, or something else entirely.
Why This Matters
Port 1523 demonstrates something important about how the Internet actually works versus how we document it. IANA maintains a registry of 65,535 port numbers, carefully assigning each one to specific services. But outside the well-known range, those assignments are more suggestion than law.
The registered ports range exists in a middle ground. Services can register their ports to avoid conflicts. Administrators can check the registry before choosing ports. But nothing enforces it. Nothing prevents an Oracle DBA from using a port registered to a license manager service that may or may not still exist.
This flexibility is both strength and weakness. It lets networks adapt to real-world constraints. It also means documentation lies more often than we'd like to admit.
Security Considerations
If you're running Oracle on port 1523, secure it like you would any database listener:
- Restrict access with firewall rules
- Use encryption for connections (Oracle Native Network Encryption)
- Monitor for unauthorized connection attempts
- Keep the listener updated to patch known vulnerabilities
If you're actually running cichild-lm on port 1523, well—the same principles apply to any license server managing valuable software access.
Related Ports
- Port 1521 — Oracle's official default TNS listener port
- Port 1522-1529 — Commonly used for additional Oracle listeners
- Port 27000-27009 — FlexLM license manager (another license management range)
Sources:
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