What Range This Port Belongs To
Port 3548 sits in the registered port range (1024–49151), also called the user ports range. This middle tier of the port space is managed by IANA, which accepts registrations from software vendors and standards bodies. Unlike the well-known ports (0–1023), registered ports don't require administrative privileges to bind on most systems, and they carry no guarantee of widespread recognition. A registered port means someone filed paperwork — not that anything is listening.
The IANA Assignment
IANA's registry lists port 3548 as assigned to a service called "interworld" on both TCP and UDP, registered in July 2002.1
That's where the trail ends. There is no RFC defining the Interworld protocol. No open-source implementation. No documentation from whatever company or project filed the registration over two decades ago. The name suggests something ambitious — inter-world communication of some kind — but the substance didn't survive. It's an orphaned registration: the paperwork exists, the protocol doesn't.
This is more common than you'd expect. The early 2000s saw a wave of port registrations from startups and software projects that no longer exist. IANA doesn't reclaim ports when a company dissolves, so the registry carries these fossils indefinitely.
Known Unofficial Uses
None documented. Port 3548 doesn't appear in any firewall guidance, security advisories, or network monitoring references as a port associated with active software.
If you see traffic on port 3548, it is not a recognized protocol — it could be custom software, a misconfigured application, or something you should look at more closely.
How to Check What's Listening on This Port
On Linux or macOS:
On Windows:
These commands show you the process ID (PID) holding the port open. Cross-reference that PID with your process list to identify what's actually running.
From outside the machine:
A response of open means something is listening. closed means nothing is — but the host is reachable. filtered means a firewall is in the way.
Why Unassigned and Orphaned Ports Matter
The registered port space is a commons with 48,127 slots. Many are actively used. Many are registered and forgotten. And many were never registered at all.
This matters for two reasons. First, if you deploy software that uses port 3548, you're technically not in conflict with any active protocol — but you're also not following an established standard. Second, any unexpected traffic on an unassigned port is worth investigating. There's no legitimate "Interworld" software out there expecting a connection.
The IANA registry was meant to bring order to port allocation. For ports like 3548, it mostly records the ambitions of organizations that no longer exist.
Frequently Asked Questions
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