Port 339 is unassigned. It exists as a number within the well-known ports range (0-1023) but carries no officially designated protocol or service.
What "Unassigned" Means
The Internet Assigned Numbers Authority (IANA) maintains the official registry of port numbers. Within the well-known ports range (0-1023), ports can be in one of three states:1
- Assigned — Allocated to a specific service or protocol
- Reserved — Held by IANA for special purposes (like boundary markers or future range extensions)
- Unassigned — Available for assignment but not currently allocated
Port 339 falls into the third category. Ports 334-343 are collectively marked as "Unassigned" in the IANA registry.2
The Well-Known Ports Range
Well-known ports (0-1023) are the oldest and most protected tier of the port system. These numbers require IETF Review or IESG Approval for assignment—the strictest assignment process in the registry.3
The range is densely populated with fundamental Internet protocols: port 22 for SSH, port 25 for SMTP, port 80 for HTTP, port 443 for HTTPS. But not every number in this range has been claimed. Some remain unassigned, gaps in the addressing system.
Port 339 is one of these gaps.
Why Unassigned Ports Matter
The existence of unassigned ports within the well-known range serves several purposes:
Future allocation space — New protocols still emerge. Unassigned ports provide room for future Internet standards that may need well-known port numbers.
Deliberate gaps — IANA doesn't assign ports speculatively. A port remains unassigned until a legitimate protocol with broad utility requests it through the proper channels.
Registry hygiene — Keeping ports unassigned until needed prevents namespace pollution and ensures only protocols with genuine requirements occupy the protected well-known range.
No Unofficial Use
Unlike some unassigned ports that develop informal uses, port 339 has no documented unofficial services or applications. It doesn't appear in malware databases, exploit toolkits, or alternative service registries. It's genuinely empty.
Checking What's Listening
If you encounter traffic on port 339, it's worth investigating. While the port has no official assignment, any service can technically bind to it.
On Linux or macOS:
On Windows:
These commands show whether any process is listening on port 339 and what that process is.
The Space Between
Port 339 is a number with no story yet. It sits in the well-known range, protected by the strictest assignment requirements, waiting. Most ports in this range were claimed decades ago—SSH in 1995, HTTPS in 2000, even HTTP in 1992. Port 339 has remained empty through all of it.
Maybe a protocol will emerge that needs this specific number. Maybe it will remain unassigned indefinitely, a permanent gap in the Internet's addressing system. For now, it's a space holder—a reminder that not every number has a purpose, and that's okay.
The Internet has 65,536 port numbers. Not all of them need to carry something.
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