Port 2784 is unassigned. No RFC defines it. No IANA record claims it. By every official measure, it is an empty slot in the registered port range, waiting for a purpose that never came.
Except it had one once. A significant one.
The Web's Original Port
In the early days of the World Wide Web, before there was a standard, before there was a port 80, Tim Berners-Lee needed somewhere to run HTTP. He chose 2784.
In January 1992, Berners-Lee sent a note to the www-talk mailing list:
"During development, the default HTTP TCP port number is 2784 — this will change when an official port number is allocated."1
It did change. Port 80 was officially designated for HTTP, and the web moved there. But buried inside the source code of the original WorldWideWeb browser, there remains a single line that names port 2784 as OLD_TCP_PORT.2
The web was invented on this port. Then it moved on, and the port was left empty.
What Range It Belongs To
Port 2784 sits in the registered port range (1024–49151). These ports require IANA registration for official use, but "unassigned" means no service has claimed this one. The range exists to give applications a stable, predictable address — not on the famous low ground of well-known ports (0–1023), but not in the ephemeral chaos of dynamic ports (49152–65535) either.
An unassigned registered port is a reserved seat with no ticket holder.
Unofficial Uses
Security databases flag 2784 as having been used by malware in the past — which is unsurprising. Unassigned ports are attractive to trojans and backdoors precisely because no legitimate service occupies them, making anomalous traffic harder to detect at a glance.3
No widely used legitimate application claims 2784 today.
What's Listening on Your Machine
To see if anything is using port 2784 on your system:
macOS / Linux:
Windows:
If nothing returns, the port is idle. If something does, that warrants investigation — especially since no standard service should be there.
Why Unassigned Ports Matter
The port space isn't just infrastructure — it's history. The gaps between assigned ports are fossils of decisions made and paths not taken. Port 2784 is one of the more interesting gaps: a port that carried the first HTTP requests across a university network in Geneva, before anyone knew what the web would become.
The OLD_TCP_PORT comment still sits in old source code. The web grew up and moved to port 80. Port 2784 stayed behind, empty, holding the shape of where something enormous began.
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