Port 767: Phonebook — The forgotten directory service

Port 767 sits in the well-known ports range (0-1023), officially assigned to a service called "phonebook." But if you search for documentation about what this service actually did, you'll find almost nothing. This is one of the Internet's ghost ports—claimed in the registry, but forgotten by history.

What Was Phonebook?

The name tells you something: it was meant to be a directory service. Some kind of lookup protocol, probably for finding people or systems on a network. The assignment appears in RFC 1340 from 1992, labeled simply as "phone" or "phonebook" for both TCP and UDP.¹

But that's where the trail goes cold. No protocol specification. No implementation guide. No evidence that anyone actually used it. Just a name in a list, registered to IBM, and then silence.²

The Well-Known Ports Range

Port 767 falls in the range from 0 to 1023, the well-known ports that IANA assigns for standard services. Getting a port number in this range meant something in the early Internet—it meant your protocol was important enough to deserve universal recognition.

But importance at the time of assignment doesn't guarantee survival. The Internet is littered with protocols that seemed essential in 1992 but are completely forgotten by 2026.

What Happened?

Directory services evolved in different directions. LDAP (Lightweight Directory Access Protocol) on port 389 became the standard for organizational directories. DNS on port 53 became the phonebook for domain names. Finger on port 79 let you look up users on Unix systems (until privacy concerns killed it).

Phonebook on port 767 apparently lost this evolutionary race. The service was assigned, perhaps implemented somewhere, and then abandoned before it gained traction. Now it's just a number in the registry that no modern system expects to find anything listening on.

Should You Care About Port 767?

Only if you're curious about what didn't survive. Port 767 is unassigned in practice—no legitimate service uses it today, and you won't find software listening on it unless something is badly misconfigured or deliberately hiding there.

Security scanners sometimes flag port 767 because unassigned well-known ports occasionally get used by malware precisely because no one expects traffic there. But there's nothing inherently dangerous about the port itself. It's just empty space in the numbering system.

Checking What's Listening

If you want to see whether anything is using port 767 on your system:

# Linux/macOS
sudo lsof -i :767
sudo netstat -tulpn | grep :767

# Windows
netstat -ano | findstr :767

You'll almost certainly find nothing. That's normal. Port 767 is a relic.

Why Unassigned Ports Matter

The phonebook service is a reminder that port assignments aren't permanent truths—they're historical decisions that sometimes outlive their purpose. IANA's registry contains hundreds of ports like this: officially assigned, practically unused, kept in the list out of bureaucratic inertia.

These ghost ports serve a purpose in their absence. They show that the Internet isn't just what works now—it's also what was tried and abandoned, what seemed important once and turned out not to be, what someone thought was worth standardizing before anyone actually used it.

Port 767 was supposed to be a phonebook. Instead, it became a footnote.