What Port 3404 Is
Port 3404 is a registered port — one of the 48,128 ports in the range 1024–49151 that IANA oversees through a formal registration process. Unlike the well-known ports below 1024 (which require root/administrator privileges to bind), registered ports can be used by any application. Organizations can apply to IANA to reserve a specific number for their service.
Port 3404 has no current assignment. IANA lists it as unassigned.
A Brief, Forgotten History
Port 3404 wasn't always empty. At some point before May 2002, it was registered to a service called Bekkoame — both TCP and UDP. Then IANA removed the entry. The registry simply notes: "Removed, modified: 2002-05-01."1
What was Bekkoame? The name is associated with Bekkoame Internet, one of Japan's early independent ISPs, active in the 1990s. Whatever protocol or service was registered under this port number, it didn't outlast the registration. The slot has been vacant for over twenty years.
Most unassigned ports have no history at all. Port 3404 had one moment in the registry, then was quietly erased.
No Known Unofficial Uses
Unlike some unassigned ports that attract ad hoc uses (gaming clients, developer tools, IoT devices), port 3404 has no documented unofficial applications. Security databases don't flag it for malware associations. Port scanners don't find it hosting anything recognizable.
It is genuinely empty.
What Might Be Listening Here
If you see activity on port 3404, it's one of three things:
- An application you installed that chose this port arbitrarily
- A developer's local service during testing or development
- Something you didn't install — which warrants investigation
How to Check
On macOS or Linux:
On Linux (alternative):
On Windows:
The output will show you the process name and PID. From there, you can confirm whether you recognize what's running.
Why Unassigned Ports Matter
The registered port range exists because informal port usage creates conflict. Two applications reaching for the same number on the same machine means one of them fails. Registration is voluntary — IANA can't enforce exclusivity — but it creates a public record that helps developers avoid collisions.
Port 3404's vacancy isn't a problem. The registered range has thousands of unassigned slots, and that's intentional. Applications that need a stable, well-known port can apply; the rest pick from the dynamic range (49152–65535) and move on.
An unassigned registered port is simply an address where nobody has moved in yet. Some of them used to have tenants. Port 3404 did, briefly, in the late 1990s — then the tenant left, IANA cleared the mailbox, and the slot has been quiet ever since.
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