Port 2906: CALLER9 — A Name Without a Service

What Port 2906 Is

Port 2906 sits in the registered ports range (1024–49151) — the space IANA manages for services that have applied for an official assignment. Unlike the well-known ports below 1024 (HTTP, SSH, DNS), registered ports don't come with hardened protocols and decades of RFCs. They come with a name, a contact, and an intent.

Port 2906's name is CALLER9. Its contact is an AOL email address. Its documentation is nonexistent.

The IANA Registry and Ghost Registrations

When IANA opened port registration in the early Internet era, the process was relatively informal. Organizations and individuals could claim a port number for a service they planned to build. Many did. Some shipped software. Many didn't.

The result is that the registered ports range is full of entries like CALLER9 — a name that sounds purposeful, assigned to someone who may have had real plans in 1997, whose AOL inbox has long since stopped receiving mail. The registration persists in the registry. The service does not appear to exist in the wild.¹

This isn't a flaw in the system. It's what happens when you reserve namespace for a future that doesn't always arrive.

What's Actually Listening on Port 2906

Almost certainly nothing, unless something on your system put it there deliberately. The port has no known legitimate software actively using it. Security databases have occasionally flagged it in the context of malware port scans — not because CALLER9 is malicious, but because scanners probe unusual ports and anything listening in uncharted territory deserves attention.²

If you see traffic on port 2906, check what's actually using it:

# On Linux/macOS — show what process owns the port
sudo lsof -i :2906

# Or with ss (Linux)
sudo ss -tlnp sport = :2906

# On Windows
netstat -ano | findstr :2906
# Then match the PID: tasklist | findstr <PID>

If something is listening, find out what it is before assuming it's benign.

Why Unassigned-in-Practice Ports Matter

The registered ports range contains thousands of entries in various states of life and death. A port being "registered" with IANA doesn't mean anything is running on it — it means someone once asked for it. A port being "unassigned" doesn't mean nothing is running on it — plenty of software uses whatever port is convenient without registering anything.

Port 2906 is a small, honest example of how the port numbering system actually works: it's a registry maintained by humans, reflecting human projects, with all the entropy that implies. Some entries are SSH. Some are CALLER9.