What Port 3619 Is
Port 3619 sits in the registered port range (1024-49151), the middle tier of the port numbering system. IANA maintains this range to prevent collisions: if you build a networked application and want a permanent, named home for it, you register a port number.
In 2002, someone registered ports 3618 and 3619 under the names "AAIR-Network 1" and "AAIR-Network 2." That registration is the entirety of the public record. No RFC was ever written. No implementation was ever documented. The protocol, if it ever existed beyond an intent to build something, left no trace.
This happens more often than you'd expect. The registered port range has thousands of entries for projects that stalled, pivoted, or simply never shipped.
What This Means in Practice
The port is effectively unassigned. Any software could use port 3619 for any purpose without conflicting with a real, active protocol. Network scanners may flag traffic on this port as anomalous simply because there's nothing it's supposed to be.
If you see activity on port 3619 on a machine you manage, it's almost certainly something specific to that environment: a development service, a game server, a custom internal tool, or malware that chose an obscure port to avoid detection.
How to Check What's Listening
On Linux or macOS:
On Windows:
These commands will show you the process ID using the port. From there, look up the process by name to understand what it actually is.
Why Unassigned Ports Matter
The port numbering system only works if registrations mean something. When a name like "AAIR-Network 2" occupies a slot without a real protocol behind it, that slot becomes ambiguous. Security tools can't confidently classify the traffic. Firewall rules have nothing to key off. The port exists in a kind of liminal state: officially named, practically vacant.
The IANA registry is a registry, not a certification. Registration means someone filed the paperwork. It doesn't mean the protocol exists, that it's maintained, or that anyone uses it.
Port 3619 is a placeholder for something that never arrived.
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