Port 343 is unassigned. According to IANA's Service Name and Transport Protocol Port Number Registry, ports 334 through 343 have no official service assignments.1 This port exists as reserved but unclaimed space in the Internet's addressing system.
What "Unassigned" Means
Port 343 sits in the well-known ports range (0-1023), which is controlled by the Internet Assigned Numbers Authority. Ports in this range require IANA approval for assignment and are typically reserved for system services and widely used protocols.2
Being unassigned means:
- No official protocol or service is registered to use this port
- IANA could assign it to a future protocol or service
- Applications could technically use it, though this would be non-standard
- It has no documented history of assignment or de-assignment
The Context: Reserved Space
Port 333 (just before this range) is assigned to "Texar Security Port." Port 344 (just after) is assigned to PDAP (Prospero Data Access Protocol). Between them, ports 334-343 remain blank—ten consecutive unassigned ports in a range where most numbers carry something.
This isn't unusual. The well-known ports range contains several gaps where IANA has reserved space but never assigned services. These gaps exist as room for future protocols, for needs we haven't encountered yet, or simply because the services that might have used them never materialized.
No Documented Unofficial Uses
Unlike some unassigned ports that get repurposed by applications or exploited by malware, port 343 has no documented unofficial uses. Security databases tracking trojan ports don't list it. Application documentation doesn't reference it. It appears to be genuinely unused in practice.
Checking What's Listening
Even though port 343 has no official assignment, something could theoretically be listening on it on your system. To check:
On Linux or macOS:
On Windows:
If nothing returns, nothing is listening. If something is, you've found a non-standard use—an application that chose this unassigned port for its own purposes.
Why Unassigned Ports Matter
The existence of unassigned ports is part of how the Internet's addressing system works. Not every number needs a purpose immediately. IANA maintains this registry carefully, preserving space for future protocols while documenting the history of ports that have been assigned and later freed.
Port 343's emptiness is functional. It's available space. If someone designs a new protocol tomorrow that needs a well-known port, 343 is one of the options. The Internet's addressing system isn't full—there's still room for things we haven't built yet.
The Range Above
If you need a port for a custom application, don't use port 343. The well-known range is reserved for IANA-assigned services. Use the dynamic/ephemeral ports range (49152-65535) instead, which is specifically designated for temporary and private use.
Port 343 waits. Not for your application, but for a protocol important enough to warrant IANA assignment. Until then, it remains what it is: a number, reserved, carrying nothing.
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