What Port 2425 Is
Port 2425 sits in the registered ports range (1024–49151). These ports are assigned by IANA to specific applications — not reserved like the well-known ports below 1024, but officially recognized and recorded.
The official registrant for port 2425 is Fujitsu App Manager (fjitsuappmgr), registered by Hiroyuki Kawabuchi of Fujitsu. What exactly Fujitsu App Manager does is... not well documented. It's an enterprise application used internally within Fujitsu's software ecosystem, and it's not something most network operators will ever encounter.
What they will encounter is something else entirely.
The Real Tenant: IP Messenger
IP Messenger (IPMsg) is a LAN instant messaging protocol created by Shinya Shirouzu. It's been around since the late 1990s and remains actively used — particularly in Japan and China, where it became a workplace standard long before Slack or Teams existed.
The design philosophy is deliberately minimal: no server, no accounts, no Internet required. You join a network, and the software announces itself to everyone on the subnet via UDP broadcast. Other instances respond. Suddenly you have a contact list of everyone currently online. Disconnect, and you disappear.
- UDP 2425 — peer discovery, presence broadcasts, message delivery
- TCP 2425 — file and image transfers
The protocol specification is public.1 The reference implementation is open source.2 Clients exist for Windows, macOS, and Linux.
This is why you might see port 2425 active on machines in an Asian corporate network or university lab even though nothing there has anything to do with Fujitsu App Manager. The port was in use by IP Messenger before or regardless of the IANA registration, and the software community simply kept using it.
The Gap Between Registration and Reality
This situation — an official IANA registrant and a completely different dominant real-world user — is more common than the registry suggests. IANA assigns ports to whoever asks first with a plausible application. Adoption follows its own logic.
For port 2425: if you see it active on a machine, Fujitsu App Manager is the less likely explanation. Check whether IP Messenger is running.
How to Check What's Listening on Port 2425
On Linux or macOS:
On Windows:
The process ID in the output can be looked up in Task Manager (Windows) or via ps (Unix) to identify the application.
Check both TCP and UDP — IP Messenger uses both, and netstat may not show UDP listeners by default without the -u flag on Linux.
Security Notes
Port 2425 has appeared in scan logs associated with opportunistic probing. In 2017, researchers observed SYN flood traffic originating from Chinese IP space targeting port 2425 on Fujitsu RAID controller interfaces — suggesting that known port registrations are sometimes used to fingerprint exposed enterprise hardware.3
IP Messenger itself is plaintext. Messages, file transfers, and presence broadcasts on UDP 2425 are visible to anyone on the same network segment. It was designed for trusted LAN environments. Treat it accordingly.
Frequently Asked Questions
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