Port 3624: dist-upgrade — A Name Without a Protocol

What This Port Is

Port 3624 sits in the registered port range (1024-49151). These are ports that individuals, companies, and projects can formally claim through IANA, the organization that coordinates Internet numbering resources.

Port 3624 is registered — on both TCP and UDP — under the service name dist-upgrade, short for "Distributed Upgrade Port." The assignee is Jason Schoon, who registered it in October 2002.¹

Beyond the name and the date, there is essentially nothing. No RFC. No protocol specification. No software that announces itself on port 3624. The registration exists in every port database on the Internet, and the thing it names does not.

What the Registered Port Range Means

The port space is divided into three ranges:

• Well-known ports (0-1023): Reserved for major protocols. HTTP, HTTPS, SSH, DNS. These are tightly controlled by IANA and assigned only to established, widely-used services.
• Registered ports (1024-49151): Anyone can apply. IANA reviews requests and records them, but the bar is lower. A registration doesn't mean the software succeeded — or that it was ever finished.
• Dynamic/ephemeral ports (49152-65535): Not assigned to any service. Used temporarily by operating systems for outgoing connections.

Port 3624 is solidly in the middle tier. The registration means someone went through the process. It says nothing about adoption.

The Ghost Registration Problem

The registered port range is full of these: ports with names and dates and assignees, attached to projects that stalled, pivoted, or simply never shipped. "Distributed Upgrade Port" sounds like it belonged to a software distribution system — perhaps something for pushing updates across a corporate network, or a peer-to-peer upgrade mechanism that seemed promising in 2002.

We don't know. The registration is the only artifact.

This matters for one practical reason: if you see traffic on port 3624 on your network, it's almost certainly not the registered service. It's something else — a custom application, a misconfigured service, or something worth investigating.

How to Check What's Using This Port

If port 3624 shows up in your environment, these commands will tell you what's actually listening:

Linux/macOS:

# Show what process is listening on port 3624
ss -tlnp | grep 3624

# Or with lsof
lsof -i :3624

Windows:

# Show listening port with process ID
netstat -ano | findstr :3624

# Map process ID to application
tasklist | findstr <PID>

Network-wide (with nmap):

nmap -p 3624 <target-host>

The output will tell you the actual process. That's the ground truth — not what IANA's registry says, but what's running on your machine right now.