Port 2616: AppSwitch-EMP — A Registered Ghost

What Port 2616 Is

Port 2616 sits in the registered port range (1024–49151). These ports are assigned by IANA on request — any organization building a product or protocol can apply, stake a claim, and get a port number recorded in the global registry.

IANA lists port 2616 as belonging to a service named appswitch-emp, registered on both TCP and UDP. The contact on file is Ted Ross at toplayer.com.

The Story Behind the Name

Top Layer Networks was a network security and switching company active in the late 1990s and early 2000s. Their flagship product line was the AppSwitch — an application-layer switching appliance that operated at Layer 7, routing traffic based on the actual content of packets rather than just IP addresses. It was early-era deep packet inspection hardware, the kind of thing enterprises deployed to prioritize business-critical applications.

EMP likely stands for Enterprise Management Protocol — the proprietary channel used to manage and communicate with AppSwitch hardware.

Top Layer Networks eventually pivoted to network security (becoming Top Layer Security), and the company has since faded from the market. The appliances are gone. The protocol is unused. But the port registration lives on in the IANA registry, a small fossil from a company that does not appear to have shipped relevant products in well over a decade.

What This Means in Practice

If you see traffic on port 2616 today, it is almost certainly not an AppSwitch appliance. Possibilities include:

• Ephemeral port collision — operating systems sometimes use registered ports as temporary outbound ports for unrelated connections
• Custom application — developers occasionally pick ports from the registered range without checking IANA assignments
• Scanner or probe traffic — security scanners sweep all ports; seeing a probe on 2616 is unremarkable

No documented malware is associated with this port.¹

How to Check What's Using This Port

On Linux or macOS:

# Show what process is listening on port 2616
sudo ss -tlnp | grep 2616

# Or with lsof
sudo lsof -i :2616

On Windows:

netstat -ano | findstr :2616

Then cross-reference the PID with Task Manager or tasklist to identify the process.

Why Unassigned (and Ghost-Registered) Ports Matter

The registered port range exists so that well-known services don't collide. When two applications independently decide to use the same port, you get conflicts — connections fail, services can't start, firewalls behave unexpectedly.

Port 2616 is technically "assigned," but assigned to something that no longer exists in practice. This is common in the middle of the registered range: the port numbers from the 1990s and 2000s are littered with registrations for proprietary protocols of companies that were acquired, pivoted, or shut down. The registry is part living standard, part archaeology.