Port 3239: appareNet User Interface — A Registered Port with a Vanished Owner

What This Port Is

Port 3239 is a registered port — the middle tier of the port numbering system, spanning 1024 to 49151. IANA maintains a registry for this range, and applications or vendors can request assignments. Registered doesn't mean required: software can use any port in this range, assigned or not.

IANA's registry lists port 3239 as apparenet-ui — the "appareNet User Interface" service, registered in February 2002 over both TCP and UDP.¹ Its neighbor, port 3238, holds the "appareNet Analysis Server."

appareNet appears to have been a network analysis product. Evidence of the company or software is nearly absent from the modern web — no active website, no documentation, no community presence. The registration remains in the IANA registry; the product does not appear to remain anywhere else. The port now sits like an empty desk with someone's name still on it.

Who Actually Uses Port 3239 Today

In practice, port 3239 is most likely to appear in Citrix environments using Framehawk.

Framehawk is Citrix's display transport protocol for virtual desktops over lossy or high-latency networks — think a hospital worker on WiFi connecting to a remote Windows desktop. By default, Framehawk allocates UDP ports in the range 3224 to 3324, assigning one port per concurrent session.² Port 3239 is squarely inside that range.

If you see UDP traffic on port 3239 in a corporate network, Citrix Framehawk is a reasonable first hypothesis.

How to Check What's Using Port 3239

On Linux or macOS:

# Show what process is listening on port 3239
sudo lsof -i :3239

# Or with ss (Linux)
ss -tulnp | grep 3239

On Windows:

netstat -ano | findstr :3239

The PID returned by netstat can be matched to a process in Task Manager or with tasklist /fi "PID eq <pid>".

Why Unassigned (and Dormant) Ports Matter

The registered port range exists to reduce collisions — two pieces of software trying to use the same port on the same machine. In practice, the registry has accumulated decades of entries for products that no longer exist, companies that were acquired, and protocols that never shipped.

Port 3239 is a minor example of this. The IANA entry is accurate as a historical record. It's not accurate as a guide to what you'll find running on this port today.

When investigating unknown traffic on any registered port, treat the IANA name as a starting point, not a conclusion. Check what's actually running.