Port 2836 is a registered port with an unusual distinction: it has a name and almost nothing else.
Some IANA-derived databases list this port as assigned to a service called "catalyst" on both TCP and UDP. But there is no RFC defining it, no documentation describing what it does, no company that claims it, and no software known to use it. The name exists. The service does not — or at least, not in any way that left a record.
What Range This Port Belongs To
Port 2836 sits in the registered ports range (1024–49151). This range is managed by IANA and intended for services that have applied for an official assignment — distinguishing them from the well-known ports (0–1023) used by fundamental protocols like HTTP, SSH, and DNS.
Registration is supposed to mean something: a specific service, an RFC or technical specification, a point of contact. In practice, the registry is imperfect. Ports get registered and abandoned. Names get attached without implementations following. Port 2836 appears to be one of these — a placeholder that never became a protocol.
What "Catalyst" Might Mean
The name "catalyst" is generic enough to belong to almost anything. It could have been intended for a proprietary enterprise tool, an internal Cisco application (given Cisco's "Catalyst" product line), or simply an application that never shipped. Without a registrant on record and no RFC citation, there is no way to know.
This is not unusual. The registered port space has thousands of similar entries — names that were claimed, then abandoned, then forgotten.
Checking What's Actually Using This Port
If you see port 2836 active on a system, it's almost certainly custom software, a misconfigured application, or something proprietary. To find out what's there:
On Linux/macOS:
On Windows:
The process ID from these commands will tell you what application claimed the port. From there, the application itself is your best source of documentation.
Why Empty Registrations Matter
The port registry exists to prevent collisions — to ensure two services don't accidentally claim the same port and confuse each other on shared networks. When ports get registered and then abandoned, they leave gaps. Those gaps are not wasted, exactly, but they are a form of entropy in the system.
Port 2836 is a minor example of a real pattern: the registry reflects intent more than reality. What was registered decades ago may bear no relationship to what actually runs on a network today. Trust lsof more than the registry.
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