Port 1899: Unassigned — One Below Famous

Port 1899 belongs to the registered port range (1024-49151). IANA has not assigned any official service to this port on either TCP or UDP.

What the Registered Range Means

Ports 1024-49151 are available for applications to register with IANA for specific, named services. Registration doesn't happen automatically — software vendors apply, IANA reviews, and if approved, the port gets a service name in the official registry.

Port 1899 never went through that process. No vendor claimed it. It sits in the registry as a blank line.

This is more common than it sounds. The registered range has over 48,000 possible ports. Most are unassigned.

The Neighborhood

Port 1899's immediate neighbor is port 1900, which carries SSDP — the Simple Service Discovery Protocol. SSDP is how your phone discovers your smart TV, how your laptop finds the printer, how UPnP devices announce themselves on a local network. Millions of devices listen on port 1900.

Port 1899 is one number away from all of that activity, and has no official tenant. That combination — registered range, no owner, proximity to active protocols — makes it occasionally attractive to software that needs a port and doesn't want to conflict with anything well-known.

Observed Unofficial Uses

Two things have been observed on port 1899 over the years:

MC2Studios — Some sources identify this port with mc2studios software, a media content development platform. This is an informal use, not an IANA registration. ¹

Malware — Security databases flag port 1899 as having historical trojan associations. Unassigned ports in the registered range are occasionally chosen by malware authors precisely because they're unlikely to be blocked by default and don't conflict with expected traffic. The fact that a port appears in a trojan list doesn't mean traffic on that port is malicious — it means you should know what's using it. ²

How to Check What's Using Port 1899

If you see traffic on port 1899 and want to know what's responsible:

On macOS or Linux:

sudo lsof -i :1899

On Windows:

netstat -ano | findstr :1899

This shows the process ID. You can then look up the process name to identify what's listening or connecting.

With nmap (to check a remote host):

nmap -p 1899 <target-ip>

Why Unassigned Ports Matter

The port numbering system only works if assignments are stable and trustworthy. When you see traffic on port 443, you know what it probably is. When you see traffic on port 1899, you don't — because nothing is supposed to be there.

That ambiguity isn't a flaw in the design. The registered range was always intended to accommodate future protocols. Port 1899 is simply a slot that hasn't been spoken for yet. Whether something legitimate lives there or something malicious does, the answer is the same: check.