Port 687 sits in the well-known ports range (0-1023), the territory managed by the Internet Assigned Numbers Authority (IANA) for standardized services. But 687 was never assigned an official service. It's marked "Unassigned" in the registry.1
That didn't stop Apple from using it.
What Apple Did With It
Port 687 (TCP) was used by Server Admin, an administrative tool that shipped with macOS Server for managing server settings and services.23 This was part of Apple's server administration infrastructure, alongside port 660, which also served Server Admin functions.
Server Admin allowed administrators to configure and monitor macOS Server remotely—managing file sharing, web services, mail servers, and other server functions through a GUI or command-line interface.
The Problem: It's All Gone
macOS Server is discontinued. Apple stopped developing it years ago, stripping out most server features and eventually removing the product from the Mac App Store entirely. Server Admin went with it.
Port 687 remains listed in Apple's legacy documentation, a forwarding address for software that no longer exists.4 If you check what's listening on this port on a modern Mac, you'll likely find nothing.
Why Unassigned Ports Matter
The well-known range (0-1023) is supposed to be the authoritative list—the ports that mean the same thing everywhere. When a port is unassigned, it means IANA hasn't blessed any protocol to use it.
But "unassigned" doesn't mean "unused." Companies and developers sometimes claim unassigned ports for proprietary software, internal tools, or services that never get standardized. Apple did this with 687. It worked fine—until the software disappeared and left the port behind like an abandoned storefront.
This is the risk of informal port use. It works until it doesn't. The software changes, the company moves on, and the port becomes a historical footnote.
Checking What's Listening
If you want to see whether anything is actually using port 687 on your system:
On Linux or macOS:
On Windows:
Most likely, you'll find nothing. Server Admin is gone. Port 687 is a ghost.
The Range It Belongs To
Port 687 is in the well-known ports range (0-1023). These ports are assigned by IANA and require administrative privileges to bind to on Unix-like systems. They're meant for standardized services—HTTP on 80, HTTPS on 443, SSH on 22.
Being unassigned means 687 was reserved but never claimed. It's like a plot of land in a city that was set aside for a public building that was never built. Technically available, but nobody's moved in.
What This Port Carries Now
Nothing, most likely. Unless you're running very old macOS Server infrastructure—software that Apple itself has abandoned—port 687 is silent.
It's a reminder that even in the well-known range, not every port has a story that ends with widespread adoption. Some ports are just footnotes. Some are ghosts.
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