Port 748: Russell Info Sci Calendar Manager — A forgotten reservation

The Service Nobody Remembers

Port 748 is officially assigned to Russell Info Sci Calendar Manager (ris-cm), a calendar management service from the early days of networked computing.¹ Both TCP and UDP protocols are registered for this port.

If you've never heard of it, you're not alone. This is one of those port assignments that exists in the official registry but disappeared from practical use decades ago.

What the Well-Known Range Means

Port 748 sits in the well-known ports range (0-1023), which is reserved for system services and requires privileged access to bind to. These ports are assigned by IANA and were meant for services important enough to deserve universal recognition.

The well-known range was established when the Internet was much smaller and the assumption was that services assigned these ports would become standard parts of networked systems. Some did—HTTP on 80, SMTP on 25, DNS on 53. Others, like port 748, were reserved but never achieved widespread adoption.

The Reality of Forgotten Ports

Port 748 represents something honest about Internet infrastructure: not every reservation became essential. In the 1980s and 1990s, IANA assigned well-known ports to services that seemed important at the time. Some became foundational. Others faded away as better solutions emerged or as the companies behind them disappeared.

Russell Info Sci Calendar Manager is one of the ghosts—a service that got its port number, had its moment, and then vanished while the Internet moved on.

Checking What's Actually Running

If you want to see whether anything is actually listening on port 748 on your system:

Linux/macOS:

sudo lsof -i :748
netstat -an | grep 748

Windows:

netstat -ano | findstr :748

Chances are you'll find nothing. This port is assigned, but it's not used.

Why Keep It?

You might wonder why IANA doesn't reclaim ports like this. The answer is stability. Once a port is assigned, removing it creates risk—even if the risk is tiny, even if the service is forgotten. Somewhere, someone might still be running legacy software that expects port 748 to be ris-cm. Changing the assignment could break that system.

So port 748 stays reserved, a permanent monument to a calendar service that history forgot.

Related Ports

Other calendar and scheduling services found homes in different port ranges:

• Port 2049 - Network File System (NFS), which often carried calendar data
• Various ephemeral ports - Modern calendar services (CalDAV, etc.) typically run over HTTP/HTTPS