Port 1601 — The registered middle ground

Port 1601 belongs to the registered port range (1024-49151), the middle tier of the Internet's port system. These ports aren't as privileged as well-known ports (0-1023), but they're more structured than the ephemeral range (49152-65535) that your operating system assigns randomly.

What the Registered Range Means

When an organization develops network software, they can request a registered port from IANA¹. The process is lighter than claiming a well-known port—no RFC required, just a registration form. The port gets assigned, documented in IANA's registry, and theoretically reserved for that application.

In practice, most registered ports sit quiet. The software that claimed them may have never been widely deployed, or it faded into obsolescence. The number remains listed, but nobody's listening.

The Port 1601 Mystery

Port 1601 demonstrates the messiness of port documentation. Some third-party port databases claim it's associated with HP JetDirect print servers for SNMP management². But HP's official documentation doesn't list port 1601 anywhere³. The standard JetDirect ports are well-documented:

• Port 9100 — Raw printing (the main JetDirect port)
• Port 161 — SNMP for printer management
• Port 515 — LPD printing protocol
• Port 631 — IPP (Internet Printing Protocol)

Port 1601 doesn't appear in that list. This is common in port databases—information gets copied between sources without verification, creating ghost assignments that may have never been real or may represent someone's misconfiguration that got documented as fact.

What Might Be Listening

If you find something on port 1601, it's likely:

1. Custom software — An application that chose this port arbitrarily
2. Malware — Attackers sometimes use registered ports hoping to blend in
3. Misconfiguration — Software running on the wrong port
4. Nothing — The most common case

Checking What's Actually There

On Linux or macOS:

# See what's listening on port 1601
sudo lsof -i :1601

# Or using netstat
netstat -an | grep 1601

On Windows:

# Check listening ports
netstat -an | findstr 1601

If nothing returns, the port is closed—which is the expected state for most machines.

Why Unassigned Ports Matter

The registered range contains 48,127 port numbers. Most of them will never have anything listening. And that's fine. They exist as possibility space—numbers available when software needs a semi-permanent home that won't conflict with system services.

Port 1601 is one of thousands in this liminal space. Not special enough to be well-known, not random enough to be ephemeral. Just a number in the registry, waiting for software that may never arrive.

Security Note

Any port can be exploited if something malicious is listening on it. The fact that port 1601 doesn't have a widely-known service makes it neither more nor less dangerous—it just means you can't assume what's there based on the port number alone.

If you find unexpected traffic on port 1601, investigate it. Check what process is using it. Verify it's something you installed deliberately.