What This Port Is
Port 3105 is a registered port, meaning it falls in the 1024–49151 range and has a formal IANA assignment. The registered service is Cardbox — a document database management system that has been in continuous development since 1982.
When a Cardbox Server starts up, it listens on port 3105 by default. Clients connect to it there to read and write database records. Port 3106 is used for the Cardbox Licence Server, keeping the two services from stepping on each other.1
What Cardbox Is
Cardbox is a flexible, freeform document database for Windows. It's designed for things that don't fit neatly into rigid schemas: contact archives, museum catalogues, personnel records, research abstracts, photographic inventories, criminal investigation files. Over 100,000 users have run it across 40+ years, from individuals to United Nations agencies.2
It's not a mainstream name in 2026. But it's been quietly doing its job longer than most software anyone uses today has existed.
The Unexpected Tenant
Ubisoft's Settlers 4, Rainbow Six Vegas, and Splinter Cell: Conviction also use port 3105 for multiplayer connectivity.3 This wasn't coordinated with Cardbox. Games often reach for ports in the registered range opportunistically, and two very different pieces of software end up sharing the same number.
A spy game and a database for museum catalogues, using the same port. The Internet is full of small coincidences like this.
Checking What's on This Port
If port 3105 is open on a machine you manage and you're not running Cardbox or an old Ubisoft game, it's worth knowing what's there.
On Linux or macOS:
On Windows:
The process ID in the output maps to a running process. On Windows, cross-reference it in Task Manager under the Details tab.
Why Unassigned Ports Matter
The registered range (1024–49151) exists as a coordination layer. Software developers register their ports with IANA so two applications don't accidentally collide—at least in theory. In practice, IANA registration is voluntary, and plenty of software ignores it. The result is a port space that's partly organized and partly improvised.
Port 3105 landed on the organized side. Cardbox filed, IANA recorded it, and the assignment has held for decades. Most registered ports have a story like this: a developer, a problem they were solving, and a number they picked and kept.
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