Port 83: MIT ML Device — A Ghost in the Port Registry

Port 83 is officially assigned to "MIT ML Device" in the IANA registry. No standard protocol runs on it. No modern service claims it. To understand what port 83 is, you have to understand what "ML" meant at MIT in 1971, and it's not what you think.

The Machine Called ML

In the early 1970s, MIT's Artificial Intelligence Laboratory had several PDP-10 computers, each with its own name.¹ There was AI (serial #8), the original, online since 1968. There was DM (serial #144), for Dynamic Modeling. And there was ML (serial #198), which stood for Mathlab.²

ML was a DEC KA10 that ran the Incompatible Timesharing System (ITS), the famously open operating system that rejected the security-first philosophy of Multics.³ The Mathlab machine was home to Macsyma, one of the first computer algebra systems ever built, a program that could perform symbolic integration, simplify equations, and solve problems that would take a human mathematician hours to work through by hand.²

Port 83 was reserved so that devices on the network could communicate with this machine. The contact listed in the IANA registry is David Reed, the MIT computer scientist who would go on to design UDP and co-author the foundational paper on the end-to-end principle.⁴

ML ran from 1971 to 1984. Then it was turned off. The port assignment was never reclaimed.

What Runs on Port 83 Today

Nothing, officially. But port 83 hasn't gone entirely unnoticed.

The SANS Internet Storm Center published a diary entry titled "What is going on with Port 83?" after observing unexplained spikes in scanning activity.⁵ Their investigation found that some Apache and PHP configurations use ports 81 through 83 as alternatives to port 80, which means the traffic was likely automated scanners probing for web servers on non-standard ports.

This is the modern life of port 83: not a protocol, not a service, but a target for scanners hoping to find a web server that someone tried to hide by moving it one door over from the standard.

A Well-Known Port with Nothing to Say

Port 83 sits in the well-known range (0 through 1023), which means on most Unix-like systems, only privileged processes can bind to it.⁶ This range was originally meant for protocols important enough to need system-level protection. Port 83 earned its place not through protocol significance but through institutional significance. MIT's AI Lab was one of the most important nodes on the early ARPANET, and when they needed a port for their machines, they got one.

Port 85 is also assigned to "MIT ML Device" under the same contact, David Reed.⁷ Two ports, one machine, both still reserved decades after the machine was decommissioned.

How to Check What's Listening on Port 83

If you want to see whether anything on your system is using port 83:

# macOS / Linux
sudo lsof -i :83

# Windows
netstat -an | findstr :83

# Network scan
nmap -p 83 target_host

If something is listening on port 83, it's not the MIT ML Device. It's either an alternative web server, a misconfigured service, or something worth investigating.

Why Unassigned Ports Matter

The port registry is not just a technical directory. It's a historical document. Ports like 83 preserve the names of machines and institutions that shaped the Internet. The fact that IANA hasn't reassigned port 83 to a modern service tells you something about how the registry works: assignments are rarely revoked, even when the original purpose has been obsolete for decades.

Every unassigned well-known port is a small monument. Port 83 is a monument to a KA10 in a lab at 545 Technology Square in Cambridge, Massachusetts, where hackers built computer algebra systems and refused to put passwords on their operating system.