Port 3118: PKAgent — Assigned but Absent

What Port 3118 Is

Port 3118 sits in the registered port range (1024–49151). These are ports that applications can request IANA formally assign to them, distinguishing their service from the chaos of uncoordinated port usage.

IANA lists port 3118 as assigned to PKAgent on both TCP and UDP.¹ But here's the honest reality: PKAgent has almost no documented presence. The name appears in port databases that mirror IANA's registry, and there's a small GitHub repository from a company called Versal that describes a "PubKey Agent" daemon — a process that connects to a messaging system and triggers agent runs.² Whether that project is the one that claimed the IANA assignment is unclear. There's no RFC, no protocol specification, and no significant real-world deployment visible in the public record.

PKWARE, the company behind ZIP encryption technology, also uses "PK" branding in its products, but there's no documented connection to this port assignment.³

In practical terms: if you see something listening on port 3118, it almost certainly isn't PKAgent.

The Registered Range and What It Means

Ports 1024–49151 are registered, not reserved. Anyone can submit an application to IANA requesting a port assignment for their service. Once assigned, the name appears in the official registry — but IANA doesn't enforce usage. A registered port is a claim, not a lock.

The result is a long list of ports assigned to services that launched, faded, or never shipped. Port 3118 appears to be one of these. The assignment is real. The service is a ghost.

What's Actually Listening on Port 3118

If you find port 3118 open on a machine, it's almost certainly something other than PKAgent. Common causes:

• An application that picked the port arbitrarily
• A game (some shooters use dynamic ports in the 3000–3200 range)
• A developer running a local service on a non-standard port
• Malware, which happily ignores IANA assignments

To see what's actually using it:

macOS / Linux:

# Show the process listening on port 3118
lsof -i :3118

# Or with ss (Linux)
ss -tlnp sport = :3118

Windows:

# Show listening processes
netstat -ano | findstr :3118

# Then look up the PID
Get-Process -Id <PID>

Why Unassigned (or Nominally Assigned) Ports Matter

The port system depends on coordination. When a service reliably runs on a known port, firewalls can make decisions, administrators know what to expect, and security tools can flag anomalies. A port with a ghost assignment — technically claimed, practically empty — is still useful: it signals that traffic here is unexpected and worth investigating.

If port 3118 shows up in your firewall logs or a network scan, it's worth a second look. Not because PKAgent is likely running, but because something is — and it probably didn't announce itself.