Port 804 occupies a peculiar position in the Internet's addressing system. It sits in the well-known ports range (0-1023)—the prestigious addresses reserved for fundamental Internet services—yet IANA's official registry lists it as unassigned1. No RFC defines what should run here. No standards body has claimed it.
But if you scan corporate networks running Sparx Systems' Enterprise Architect, you'll find port 804 very much occupied.
What Lives Here (Unofficially)
Enterprise Architect's WebConfig uses port 804 for HTTP traffic by default2. When administrators need to configure their modeling repositories, their browsers connect to port 804, where the WebConfig interface answers. Port 805 handles the HTTPS variant.
This isn't an IANA-approved assignment. It's a vendor choosing an empty port number and shipping software configured to use it. The official registry still says "unassigned," but practically speaking, thousands of installations consider port 804 home.
The Well-Known Range
Ports 0-1023 were meant to be special. IANA controls this range. The idea was simple: if you see traffic on port 80, it's HTTP. Port 443, it's HTTPS. Port 22, it's SSH. The well-known ports would be a universal language for the Internet.
But there are 1,024 slots and far fewer truly universal protocols. So gaps exist. Port 804 is one of them—technically available for official assignment, practically claimed by software that needed a port and didn't wait for permission.
Why Unassigned Ports Matter
When a port sits unassigned in the well-known range, it represents potential. IANA could assign it tomorrow to a new protocol that needs universal recognition. But the longer a port stays "unassigned" while software uses it unofficially, the harder it becomes to reclaim.
If IANA assigned port 804 to something else, every Enterprise Architect installation would suddenly conflict with the official service. The unofficial use creates a kind of adverse possession—not legally binding, but practically sticky.
Historical Context
The well-known ports range originated in the early Internet, when the port number list fit on a single page and Jon Postel maintained it personally. As the Internet grew, IANA formalized the assignment process through RFC 63353. But between the need for official assignments and the reality of software shipping with default port configurations, gaps emerged.
Port 804 represents that gap. The system says "available." The network says "occupied."
What This Means for You
If you encounter traffic on port 804, it's likely Enterprise Architect's WebConfig. But "likely" isn't "certain"—because the port is unassigned, any application could theoretically use it. There's no guarantee.
To check what's actually listening on port 804 on your system:
On Linux/macOS:
On Windows:
The output will show the process ID and program name using the port.
The Larger Pattern
Port 804's story repeats across the port number space. Official assignments exist alongside unofficial uses. The registry says one thing, the network does another. The Internet built standards, then built around them.
This isn't chaos—it's how distributed systems actually work. No central authority can control what millions of network administrators configure. The official registry documents what should happen. Network traffic reveals what does happen.
Port 804 sits at that intersection: officially available, practically claimed, perpetually unassigned in the records while very much assigned in reality.
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