Port 758: nlogin — A ghost from the early Internet

Port 758 sits in the well-known ports range (0-1023), officially assigned to a protocol called "nlogin" for both TCP and UDP. But if you search for what nlogin actually does, you'll find almost nothing. This is a ghost port—assigned decades ago, barely documented even then, and largely forgotten now.

What We Know

Port 758 appears in RFC 1060 (Assigned Numbers, March 1990) and its successor RFC 1340 (July 1992) with the simple designation "nlogin" for both TCP and UDP.¹ That's it. No specification. No detailed RFC explaining the protocol. Just a name in a list.

Some sources mention that port 758 was used by Mac OS X RPC-based services, particularly NetInfo—Apple's now-defunct directory and network configuration system that existed in NeXTSTEP and early Mac OS X versions.² NetInfo was completely removed from Mac OS X Leopard (10.5), taking whatever use port 758 had with it.

The Well-Known Range

Port 758 belongs to the well-known ports range (0-1023), which means it was assigned by IANA and theoretically reserved for system-level services that require root privileges to bind. These ports represent the Internet's original infrastructure—the services deemed important enough in the 1980s and early 1990s to receive permanent assignments.

But importance in 1990 doesn't guarantee relevance in 2026. The well-known range is full of ports like 758—officially assigned, rarely used, sometimes completely forgotten.

What Probably Happened

The most likely story: someone needed a port number for a network login service in the late 1980s. They requested an assignment from IANA. They got port 758. The protocol either never gained adoption, was absorbed into other services, or simply faded as better alternatives emerged.

The name "nlogin" suggests network login functionality—possibly a remote authentication or login service for Unix systems. But without specification documents or surviving implementations, we're left guessing.

Checking What's Actually Using Port 758

If you want to see if anything is listening on port 758 on your system:

# Linux/macOS - check what's listening
sudo lsof -i :758
sudo netstat -tulpn | grep :758

# Scan a remote host with nmap
nmap -sV -p 758 target-host

On modern systems, you'll almost certainly find nothing. Port 758 is assigned, but unused.

Why Ghost Ports Matter

Ports like 758 reveal something true about the Internet: it carries history in its structure. The well-known ports range is a fossil record of what mattered in networking's early decades. Some of those assignments—like port 80 for HTTP or port 25 for SMTP—became fundamental to how the Internet works. Others, like port 758, became footnotes.

The port remains assigned because removing port assignments is harder than making them. Once a number is given, it stays given—even if no one remembers why.

Security Considerations

An unused assigned port is actually safer than an active one. There's no service to exploit, no protocol to attack. The only risk would be if malware chose to use port 758 precisely because it's supposed to be empty—hiding in plain sight among the forgotten assignments.

If you find something listening on port 758 on your network and you didn't configure it, investigate. Legitimate use in 2026 is unlikely.

Related Ports

Other authentication and login services occupy nearby territory:

• Port 513: rlogin (remote login, also largely obsolete)
• Port 22: SSH (the modern replacement for insecure remote login protocols)
• Port 389: LDAP (directory services, which may have absorbed whatever nlogin was meant to do)