Port 175: VMNET — A Reserved Port That History Forgot

Port 175 is officially assigned to VMNET¹ in the Internet Assigned Numbers Authority (IANA) registry. It's registered for both TCP and UDP protocols, with Christopher Tengi listed as the contact. But here's the strange part: this port sits mostly unused.

The Well-Known Ports Range

Port 175 falls within the well-known ports range (0-1023)², which are system ports that typically require privileged access to bind. These are the ports IANA traditionally reserves for standard Internet services. Getting a well-known port assignment means your protocol was considered important enough to warrant a permanent address in the Internet's namespace.

But importance and usage are different things.

The Name Collision

The confusing part is the name. When you search for "VMNET," you'll find extensive documentation about VMware's virtual networking³—but that's not what port 175 is for. VMware's VMnet refers to virtual network interfaces (vmnet0, vmnet1, vmnet8) that create bridged, host-only, and NAT networking modes for virtual machines. These virtual switches operate at the network interface level, not as a service listening on port 175.

The VMNET service registered on port 175 appears to be an earlier, unrelated protocol that shares an unfortunate naming similarity with VMware's later virtual networking technology.

What Actually Uses This Port

In practice, port 175 is rarely used. The official IANA assignment exists, but there's little evidence of active services binding to this port in modern networks. It's one of those early reservations that secured a spot in the well-known range but never became widely deployed.

Why Unused Ports Matter

Unused assigned ports like 175 tell us something about the history of the Internet. They're archaeological layers—evidence of protocols someone thought would matter, services that were planned but never widely deployed, or technologies that were superseded before they became standard.

Every assigned port represents a moment when someone believed they were solving an important problem. Port 175 is a reminder that not every solution finds adoption, even when it gets official recognition.

How to Check What's Listening

Even though port 175 is rarely used, you can check if anything is listening on it:

# On Linux or macOS
sudo lsof -i :175
sudo netstat -an | grep :175

# On Windows
netstat -an | findstr :175

If you find something listening on port 175, it's worth investigating what it is—because it's likely not the official VMNET service.

Security Considerations

Because port 175 is rarely used for its intended purpose, finding unexpected traffic on it can be a sign of misconfiguration or misuse. Any service choosing to use this port is either:

1. Legitimately using the VMNET protocol (extremely rare)
2. Repurposing an unused assigned port (poor practice)
3. Potentially malicious (worth investigating)

The obscurity of unused ports can make them attractive to attackers precisely because system administrators might not monitor them closely.

The Bigger Picture

Port 175 is a small footnote in the Internet's port registry, but it represents something larger: the gap between planning and reality, between assignment and adoption. The well-known ports range was designed when we thought we could predict which services would matter.

Some predictions were perfect: port 80 for HTTP, port 25 for SMTP, port 22 for SSH. Others, like port 175, secured their place in the registry but never found their purpose in the network.