Port 2372: LanMessenger — The Office Chat That Needed Nothing

Port 2372 is officially assigned to LanMessenger, a serverless instant messaging application for local area networks, registered with IANA on February 1, 2008 by Garrett Padera. It uses both TCP and UDP.¹

What It Does

LanMessenger solves a problem that sounds simple but used to be genuinely hard: how do people on the same office network chat with each other without setting up a server?

The answer: don't use a server. When you open LanMessenger, it broadcasts over the local network asking who else is running the application. Anyone who answers appears in your contact list. You can then send private messages, share files, or broadcast to everyone at once. No Internet required. No accounts to create. No IT department needed to stand up infrastructure.

This was practical and elegant in 2008. Before Slack, before Teams, before cloud everything, many offices ran on exactly this kind of tool.

How It Works

LanMessenger uses UDP for discovery — broadcasting to the local network to find other instances — and TCP for actual message delivery. It encrypts messages using AES with RSA as the key exchange mechanism, which was thoughtful for software of its era.²

The key insight is the absence of a central authority. Every client is also its own server. When you're on the same LAN as someone else running LanMessenger, you can talk directly. When you leave the network, they disappear from your list. It's the network as the source of truth.

Port Range

Port 2372 sits in the registered port range (1024–49151). These are ports that applications can officially register with IANA to signal their intended use — not reserved by the operating system like the well-known ports below 1024, but not ad hoc either. A registered port is a handshake with the broader Internet ecosystem: "this is where our thing lives."³

Checking What's on This Port

To see if anything is using port 2372 on your machine:

macOS / Linux:

# Check for listeners on port 2372
lsof -i :2372

# Or with netstat
netstat -an | grep 2372

Windows:

netstat -ano | findstr :2372

If you find something unexpected listening on 2372, it's almost certainly not LanMessenger — that software has largely faded from use. More likely it's another application that happened to choose this port, or something worth investigating.

Why Unassigned-Feeling Ports Matter

Registered ports like 2372 occupy a useful middle ground. Below 1024, ports are guarded — you need administrative privileges to bind to them, and they're assigned to foundational protocols (HTTP, HTTPS, SSH, DNS). Above 49151, ports are ephemeral — handed out temporarily when your computer makes outgoing connections.

The registered range is where applications live. Thousands of services have claimed a spot here, from major databases to niche enterprise software to small open-source projects like LanMessenger. The range is large enough that most legitimate applications find a home; the registry exists so they don't collide.

What Happened to LanMessenger

LanMessenger represents a category of software that Slack and Microsoft Teams largely displaced. When work moved to the cloud and teams spread across offices, cities, and continents, the local-network messenger lost its context. You can't broadcast to a LAN that your colleagues aren't on.

But in its moment, it solved the problem exactly right: zero configuration, zero infrastructure, just people on the same network being able to reach each other. The principle survives in modern tools. The serverless, broadcast-for-discovery pattern shows up in everything from AirDrop to Bonjour to certain IoT protocols. LanMessenger just did it in 2008 for office chat.