Status: Unassigned
Range: Registered Ports (1024-49151)
Common unofficial use: Microsoft SQL Server RPC (dynamic allocation)
What This Port Is
Port 1572 has no official service assigned to it by IANA. It sits in the registered ports range—the middle territory between well-known ports (0-1023) and the dynamic/ephemeral range (49152-65535).
The registered ports range contains over 48,000 possible port numbers. IANA has officially assigned perhaps a quarter of them to specific services. The rest remain unassigned—not reserved, not claimed, just... available.
Port 1572 is one of those unclaimed ports. No RFC defines what should run here. No protocol specification claims it. No company registered it for their service.
The Registered Ports Range
Ports 1024-49151 are called registered ports because organizations can request IANA to assign them for specific services. To get a port officially assigned, you submit an application to IANA explaining what service will use it and why.
But most ports in this range remain unassigned. They're available for use, just not officially claimed.
Unofficial Use: SQL Server RPC
While port 1572 has no official assignment, it's been observed in use by Microsoft SQL Server for remote procedure calls (RPC).12
SQL Server doesn't specifically target port 1572—it uses dynamic port allocation for certain RPC functions. When Windows allocates a dynamic port for SQL Server's RPC service, it might land on 1572. Or it might land on 1573, or 2847, or any other available port in the dynamic range.
This is different from SQL Server's main listening port (default 1433), which is officially assigned and typically static. The RPC functionality uses whatever port the operating system provides at the time.
Why Unassigned Ports Matter
Unassigned ports serve several purposes:
Flexibility — Applications can use them without conflict as long as nothing else on that system is already listening.
Dynamic allocation — Operating systems draw from unassigned port ranges when applications request ephemeral ports for temporary connections.
Future assignment — When new protocols emerge and need a permanent home, IANA can assign them an official port number from the unassigned pool.
Testing and development — Developers can run services on unassigned ports during development without worrying about conflicting with standard services.
How to Check What's Listening on Port 1572
On Linux or macOS:
On Windows:
If you see something listening on port 1572, it's not running a standard assigned service—it's either SQL Server's dynamic RPC allocation, another application that chose this port, or potentially something that shouldn't be there.
The Reality of Unassigned Ports
The port number system has 65,535 possible ports. Only a fraction are officially assigned. The rest exist in this liminal state—unclaimed but available, empty but usable.
Port 1572 is one of approximately 40,000 unassigned ports in the registered range. It might stay empty on your system forever. It might get borrowed by SQL Server for a few minutes during a connection. It might be chosen by a developer testing new software.
Unassigned doesn't mean unused. It means unclaimed. The difference matters when you're trying to understand what's actually happening on your network.
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