Port 766: Phonebook — A ghost from the NeXT era

Port 766 is a ghost port. Officially assigned by IANA to the "phonebook" service, it once carried the nervous system of Mac OS X—but the service it served has been dead for nearly two decades.¹

What Ran Here

Port 766 was used by Mac OS X RPC-based services, particularly NetInfo—Apple's distributed directory database.² NetInfo stored everything that made a Mac OS X system work:

• User accounts and passwords
• Network configurations
• Printer settings
• NFS mounts
• Email configurations
• Computer and resource information

Every time the system needed to know "who is this user?" or "where is this printer?" it consulted NetInfo. And NetInfo used ports in the 600-1023 range, including port 766, to communicate across the network.³

The NeXT Connection

NetInfo wasn't originally an Apple creation. It came from NeXTSTEP—the operating system Steve Jobs built at NeXT Computer after leaving Apple in 1985. NeXTSTEP introduced NetInfo in version 0.9 in 1988 as a centralized directory service.⁴

When Apple acquired NeXT in 1997 and built Mac OS X on top of NeXTSTEP's foundation, NetInfo came along for the ride. For years, it was the authoritative source for system configuration on every Mac running OS X.

The End

Mac OS X Server 10.2 Jaguar (2002) introduced Open Directory, Apple's standards-based replacement for NetInfo. But NetInfo lingered. It wasn't until Mac OS X Leopard (10.5) in 2007 that Apple completely removed NetInfo, replacing it with property list files in /var/db/dslocal/.⁵

Port 766 outlived its purpose. The "phonebook" service assignment remains in IANA's registry, but the protocol that used it is gone. If you see traffic on port 766 today, it's either legacy equipment that nobody updated or something else entirely using a forgotten port number.

Why Ghost Ports Matter

The Internet is full of ports like 766—officially assigned to services that no longer exist or were never widely adopted. They're archaeological layers. Evidence of protocols that seemed important enough to deserve a well-known port number but didn't survive the evolution of the Internet.

Ghost ports remind us that the Internet isn't static. Protocols die. Services get replaced. Port assignments become historical artifacts.

How to Check This Port

To see if anything is listening on port 766 on your system:

On Linux/Mac:

sudo lsof -i :766
# or
sudo netstat -tuln | grep 766

On Windows:

netstat -ano | findstr :766

You'll almost certainly find nothing. NetInfo has been gone since 2007. Port 766 is a monument to a protocol that once mattered and now doesn't.