Port 574 is assigned to ftp-agent, the FTP Software Agent System. Both TCP and UDP protocols use this port.
The name is confusing—this has nothing to do with File Transfer Protocol. FTP Software was a company. And their story is the story of the early commercial Internet.
What Ran on This Port
The FTP Software Agent System was part of PC/TCP, a suite of networking software that gave DOS-based IBM PCs the ability to communicate on TCP/IP networks. In 1986, when FTP Software incorporated, this was revolutionary. Most PCs couldn't talk to mainframes. Most PCs couldn't speak TCP/IP at all.
Port 574 carried the agent communications—the background system that managed network operations for PC/TCP applications. The technical details are lost to time. The software is obsolete. But the port registration remains.
The Company Behind the Port
FTP Software started at MIT in the mid-1980s.1 Five students wrote a version of TCP/IP that allowed DOS-based IBM PCs to communicate with mainframe computers. They called it PC/IP, later PC/TCP. The core development began in 1982 as the PC/IP project.2
They incorporated in January 1986 and built a business around something that seems obvious now: connecting PCs to networks. By the early 1990s, they were the dominant supplier of TCP stacks for x86-based machines.3
Then Windows 95 shipped with a TCP/IP stack built in. Free. Part of the operating system.
FTP Software's revenue collapsed. In 1998, they were acquired by rival NetManage.4 The company that pioneered commercial TCP/IP for PCs was destroyed by the thing they proved people needed.
Why This Port Matters
Port 574 is a monument to the weird economics of protocol implementation.
In 1986, you couldn't get your PC on a TCP/IP network without buying software from companies like FTP Software or the Wollongong Group.5 The protocols were public and standardized. The implementations were proprietary and expensive.
This created a strange world where the Internet was "free and open" in theory, but in practice you paid FTP Software for the privilege of accessing it from a DOS machine. They registered port 574 for their agent system because they were doing real work, solving real problems, building real infrastructure.
And then Microsoft bundled a TCP stack with Windows and the entire business model evaporated overnight.
Current Status
Port 574 still appears in the IANA registry as assigned to ftp-agent.6 The service hasn't existed for decades. The company doesn't exist anymore. But ports, once assigned, tend to stay assigned.
If you see traffic on port 574 today, it's either:
- Legacy systems still running ancient PC/TCP installations (unlikely)
- Something else repurposing an assigned-but-unused port (possible)
- Malware using an obscure port for covert communications (the usual suspect for old registered ports)7
To check what's listening on port 574 on your system:
The Lesson
Port 574 exists because someone had to build TCP/IP for PCs before operating systems did it for them. FTP Software built it so well that everyone wanted it. Then everyone got it for free, and the company died.
This is the paradox of infrastructure: the better you solve a fundamental problem, the more likely your solution becomes a commodity, and the less likely you can sustain a business around it.
Port 574 is what remains—a two-byte reminder in every port registry of a company that succeeded itself out of existence.
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