Port 62: ACA Services — A Reservation Without a Story

A Port with a Name and No Story

Port 62 is assigned. It has a service name: acas. It has a description: ACA Services. It has a contact: E. Wald. And that is nearly everything the public record has to say about it.

This port has been in the IANA registry since at least March 1990, when it appeared in RFC 1060, the "Assigned Numbers" document maintained by Jon Postel and Joyce Reynolds at the Information Sciences Institute¹. It was carried forward through RFC 1340 in 1992² and RFC 1700 in 1994³. The registration has never been revoked. The port remains reserved for both TCP and UDP.

But what ACA Services actually is, what software spoke this protocol, what problem E. Wald was solving: that has slipped through the cracks of Internet history.

What We Know

The name: acas, listed as "ACA Services." The acronym "ACA" was never publicly expanded in any RFC or IANA document that survives in searchable form.

The registrant: E. Wald, listed in RFC 1700's contact section with the identifier [EXW]. In the early days of port registration, IANA kept records informal. A name, sometimes an email address, and a one-line description were often all that was required to claim a well-known port number.

The era: Port 62 was assigned during a period when the well-known port range (0-1023) was being filled in rapidly. Many of these early assignments went to protocols and services that were significant within specific organizations or research communities but never achieved widespread adoption.

The classification: Port 62 sits in the System Ports range (0-1023), which means it was assigned through IETF Review or IESG Approval processes⁴. On Unix-like systems, binding to a port in this range requires superuser privileges. This is the most exclusive neighborhood in the port number space.

The Well-Known Port Range

Port 62 belongs to the well-known ports (0-1023). These are the Internet's reserved addresses, controlled by IANA and typically requiring root privileges to use. This range contains the protocols that built the Internet: HTTP on 80, SMTP on 25, DNS on 53, SSH on 22.

Port 62 sits among these foundational services. Its neighbors include some of the most important protocols ever written. Port 53 carries every DNS query. Port 67 and 68 handle DHCP. Port 80 serves the web. And port 62 sits quietly between them, holding its reservation, running nothing that anyone can identify with certainty.

Security Considerations

Port 62 has been flagged in some security databases as historically associated with Trojan or malware communication⁵. This does not mean the port is inherently dangerous. It means that at some point, malicious software chose this port precisely because it is obscure: an open port that firewalls might not specifically block and that network administrators might not specifically monitor.

This is the paradox of unused well-known ports. Their obscurity makes them attractive to malware authors looking for ports that fly under the radar.

How to Check What Is Listening on Port 62

Linux:

sudo ss -tlnp | grep :62
sudo lsof -i :62

macOS:

sudo lsof -i :62
netstat -an | grep '\.62 '

Windows:

netstat -an | findstr :62

If something is listening on port 62 and you did not put it there, investigate immediately.

Why Unassigned and Obscure Ports Matter

The Internet's port system has 65,535 numbered ports. Of these, only about 1,024 are "well-known," and only a fraction of those carry protocols that most people would recognize. Ports like 62 represent the vast majority: assigned but quiet, reserved but unused, holding space in a registry that has been maintained continuously since the 1980s.

These ports matter because the port registry is a historical document. It records who was building what, and when. Every assignment tells you something about what people thought the Internet needed at a particular moment in time. Port 62 tells us that in the late 1980s or early 1990s, someone named E. Wald needed a well-known port for something called ACA Services, and Jon Postel's team at ISI said yes.

The fact that we cannot reconstruct what that service did is itself a kind of data. Not everything that was built on the early Internet was documented for posterity. Some of it was built for a specific need, served that need, and faded when the need passed.