Port 2599: Unassigned — A Registered Port with No Official Tenant

What Range This Port Belongs To

Port 2599 is a registered port — part of the range from 1024 to 49151 that IANA manages for assigned services. Unlike the well-known ports below 1024 (which require root privileges to bind and carry names everyone recognizes — 80 for HTTP, 443 for HTTPS, 22 for SSH), registered ports are open to any application that files for an assignment. ¹

The system works on the honor principle. IANA maintains a registry. Developers request assignments. Most comply. But IANA can't enforce anything, and plenty of software just picks a number in this range and uses it without asking.

Port 2599 was never formally claimed. IANA shows it as unassigned. ¹

Known Unofficial Uses

Despite having no official tenant, port 2599 shows up in a few places:

SonicWALL Anti-Spam is the most documented use. SonicWALL's security appliances use port 2599 for communication between the Remote Analyzer (RA) and the Control Center (CC) in their anti-spam architecture — internal traffic between components that monitor and filter email threats. ²

"Snap Discovery" appears in several informal port databases as an association with 2599, though this predates the Ubuntu Snap package system and likely refers to something older. The connection is murky enough to treat with skepticism. ²

Meridian Data is listed in SANS historical records as another association. Meridian Data made CD-ROM networking software in the 1990s. Whether they actually used this port or it was just catalogued alongside their products is unclear. ²

Malware has historically used port 2599 for command-and-control traffic. This doesn't make the port dangerous on its own — malware uses whatever port is convenient — but it means security tools sometimes flag it. ³

How to Check What's Listening on This Port

If you see traffic on port 2599 and want to know what's using it:

On Linux or macOS:

# Show what process has port 2599 open
sudo ss -tlnp | grep 2599
# or
sudo lsof -i :2599

On Windows:

netstat -ano | findstr :2599
# Then look up the PID:
tasklist | findstr <PID>

If nothing shows up, nothing is listening. If something shows up and you don't recognize it, that's worth investigating — especially on a server.

Why Unassigned Ports Matter

The registered port range has about 48,000 slots. Thousands are assigned. Thousands are in use without assignment. And thousands, like 2599, are officially empty but occasionally squatted on.

This matters for two reasons. First, firewall rules: if you're locking down a system, you need to know what's actually running, not just what IANA says should be running. An unassigned port that has traffic is worth understanding. Second, conflict: if you're writing software and need a port, picking an unassigned one is reasonable — but check whether anything in your environment already uses it. The registry tells you what's official. netstat tells you what's real.