Port 2591: Unassigned — A Name Without a Protocol

What Range This Port Belongs To

Port 2591 falls in the registered port range (1024–49151), sometimes called the "user ports." This range was designed with a specific contract in mind: software vendors and developers could request a port number from IANA, get it officially assigned to their application, and everyone else would know to leave it alone.

The well-known ports (0–1023) are reserved for foundational protocols: HTTP at 80, HTTPS at 443, SSH at 22. The registered range extends that organized territory to thousands of applications that needed a stable home.¹

Port 2591 has no home. IANA lists it as unassigned.

The "Maytag Shuffle" Mystery

Several third-party port databases — the kind that aggregate old protocol lists from across the Internet — list port 2591 under the name "Maytag Shuffle" (service name: maytagshuffle).²

There is no RFC for it. There is no known software that uses it. There is no documentation explaining what problem it was meant to solve or who submitted it. The name appears to be a historical artifact: an entry that propagated from one port list to another without anyone verifying whether the protocol actually existed.

It's the port equivalent of a citation that no one can trace back to a primary source.

What Might Actually Be on This Port

Because port 2591 is unassigned, any application can use it for any purpose. In practice, if you see traffic on this port, it's likely one of three things:

• A custom application that picked an unassigned port to avoid conflicts
• Malware or a backdoor — unassigned ports are attractive because they don't trigger immediate recognition
• Ephemeral traffic from your own OS using it as a temporary outbound source port

Some older security databases flagged this port as having been used by malware in the past, though no specific, active threat is currently documented.³

How to Check What's Listening

To see if anything is using port 2591 on your system:

macOS / Linux:

lsof -i :2591

Windows (PowerShell):

netstat -ano | findstr :2591

If something is listening, the output will show the process ID. Cross-reference that with your running processes to identify what it is.

Why Unassigned Ports Matter

The registered range only works if applications actually register. When they don't — when software squats on unassigned ports, or when ghost entries like "Maytag Shuffle" occupy namespace without serving any protocol — it erodes the system that makes network configuration predictable.

An assigned port is a promise: this port does this thing, and you can count on it. An unassigned port is open space. Sometimes that's fine. Sometimes it's where things hide.