What Port 3103 Does
Port 3103 is registered with IANA for the Autocue SMI Protocol — a control and scripting protocol used by Autocue's professional teleprompter and broadcast systems.1
Autocue is a British company that has been making teleprompting equipment since 1955. Their systems are standard infrastructure in broadcast studios worldwide: the scrolling text that news anchors read, the invisible words behind political speeches, the script a presenter sees while looking directly into the camera. SMI (Script Management Interface) is the protocol layer that lets studio software talk to prompter hardware and manage script flow over a network.
Port 3103 sits in the registered port range (1024–49151). IANA maintains this range for applications and services that have formally requested a port assignment. The registration doesn't mean every network will use it — most installations exist only within broadcast facilities — but it does mean another application shouldn't claim this number by default.
The Registered Port Range
Ports 1024–49151 are registered, not reserved. Unlike the well-known ports below 1024 (which require root/administrator privileges to bind on Unix-like systems), registered ports are informational. IANA records who asked for the number. Nothing prevents another application from using it.
This means port 3103 might appear on a system that has never heard of Autocue. The number is available, and software developers sometimes pick ports in this range without checking the registry.
The Pigeon Server Incident
In 2004, a vulnerability was discovered in Pigeon Server 3.02.0143 — a now-defunct Windows messaging product that also used port 3103.2 An attacker could send a crafted login request with an excessively long username, triggering an infinite loop that consumed all available CPU. The server would hang until restarted.
This vulnerability was assigned CVE-2004-1688. Pigeon Server is long abandoned, but the CVE is worth knowing: it illustrates how applications in this port range come and go, sometimes leaving security debt behind.
Checking What Is Listening on Port 3103
If you see activity on port 3103 and you're not running broadcast equipment, it's worth investigating.
On Linux or macOS:
On Windows:
The process ID in the output can be cross-referenced in Task Manager or with:
If nothing you recognize is listening, and you're not in a broadcast facility, the port should be closed.
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