Port 850 is officially unassigned by IANA. It sits in the well-known ports range (0-1023), but it has no standard service, no RFC defining its use, no official protocol.
It's a gap in the Internet's numbering system. A space that exists but serves no defined purpose.
What the Well-Known Ports Range Means
Ports 0-1023 are called well-known ports or system ports. They're managed directly by IANA, the Internet Assigned Numbers Authority. Getting a port in this range requires formal approval—an RFC, a standardized protocol, a legitimate reason.
Port 22 is SSH. Port 80 is HTTP. Port 443 is HTTPS. These are the foundation. The ports everyone knows.
Port 850 is none of these. It's officially unassigned, which means IANA has not allocated it to any protocol or service.1
Why Unassigned Ports Matter
Unassigned doesn't mean unused. It means there's no official owner.
Software can listen on port 850. Applications can bind to it. Nothing in the TCP/IP stack prevents it. But there's no guarantee. No standard that says "this port does this thing."
Historically, Apple used the range 600-1023 for RPC-based services in Mac OS X, including tools like NetInfo.2 Port 850 falls within this range, but there's no evidence it was ever formally assigned to a specific Apple service.
The gap exists because standardization is slow. Protocols get proposed, debated, sometimes abandoned. Ports get reserved during development and never released. The well-known range isn't perfectly packed—it has holes.
Checking What's Listening
If you want to see if anything is using port 850 on your system:
On Linux or macOS:
On Windows:
Using netstat (cross-platform):
If nothing returns, port 850 is closed. If something does, you've found software using an unassigned port—either legitimately for internal purposes, or potentially something that shouldn't be there.
The Reality of Unassigned Ports
Port 850 exists on every device connected to the Internet. It's addressable. Packets can be sent to it. But it has no meaning.
This is the reality of the port system. Not every number has a purpose. Some are just... there. Waiting for a protocol that may never come, or serving purposes too niche to standardize.
The well-known ports range is supposed to be the organized part of the Internet. But even in the most structured spaces, there are gaps.
Port 850 is one of them.
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