What This Port Is
Port 60904 is part of the dynamic and/or private ports range (49152–65535), also called ephemeral ports. 1 This range is intentionally left unassigned by IANA. No authority owns these ports. They exist to be borrowed.
The Range and What It Means
The IANA designates 49152–65535 for temporary, short-lived uses. 2 When your web browser connects to a server, your operating system doesn't use a well-known port like 443 or 80 for the return traffic. It grabs an ephemeral port from this range—maybe 52431, maybe 58219, maybe 60904—uses it for the connection, and releases it when done. The next application that needs a temporary port will grab another one.
This range exists specifically because there are only 65,535 ports total. Well-known services (1–1023) and registered services (1024–49151) claim their fixed addresses. Everything else—every temporary client connection, every internal service, every short-lived daemon—lives in this unstable range.
Known Uses
Port 60904 has no official IANA assignment. 3 However, some research suggests it may be used by Apple's Xsan filesystem in certain environments. 4 Xsan is Apple's storage area network (SAN) clustering system, and it allocates client connections across the dynamic port range (49152–65535). 5 If you see port 60904 in your logs or network traffic, it's likely either:
- A temporary client connection to something (the kernel grabbed it for you)
- Part of Xsan filesystem activity on a Mac or Xserve system
But these are guesses. Port 60904 itself has no legal claim.
How to Check What's On This Port
On macOS/Linux:
On Windows:
On any system with nmap:
If nothing appears, the port is idle. That's the normal state. An ephemeral port is only "in use" during the microseconds of an active connection.
Why Ephemeral Ports Matter
Ephemeral ports are how the Internet solves a fundamental problem: how do you support millions of simultaneous client connections when you only have 65,535 port numbers?
The answer: ports are time-shared. A well-known service listens on a fixed port (443 for HTTPS, 22 for SSH). The client connects from an ephemeral port that the OS assigns on the fly. When the connection closes, the port goes back into the pool. This is why your laptop can have thousands of active connections even though most ports are unassigned.
Port 60904 is one of these temporary addresses. Most of the time it sits empty. Occasionally some application will use it for a few seconds. Then it's gone again.
That's not a bug. That's the design.
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