You installed ChatLAN on two PCs, both are plugged into the same office network, and yet neither one shows up in the other’s chat list. This is almost always one of four causes, and all four are fixable in a few minutes without calling in outside help.
Step One: Run the Built-In Diagnostics
Before manually checking anything, open ☰ → Network diagnostics inside ChatLAN. It automatically checks your IP address, whether the firewall rule was created successfully, and whether your gateway is reachable — which narrows down which of the causes below you’re actually dealing with, instead of guessing.
Cause 1: The Two PCs Are on Different Subnets or VLANs
Device discovery in ChatLAN relies on broadcasting a small “hello” packet across the local network segment. If PC A is on 192.168.1.x and PC B is on 192.168.2.x — a different subnet — that broadcast never reaches it, even though both machines can technically ping the same router.
This is common in offices with managed switches that split departments into separate VLANs for security reasons. The fix is either to have your network admin bridge the two segments (if that’s acceptable for your security policy), or to connect manually by IP address from the ☰ menu instead of relying on automatic discovery.
Cause 2: Wi-Fi “AP/Client Isolation” Is Enabled
Most consumer and small-business Wi-Fi routers ship with a setting often labeled AP Isolation, Client Isolation, or Guest Network Isolation. It’s designed to stop devices connected to the same Wi-Fi from talking to each other directly — useful for a coffee shop’s guest network, actively harmful for an office trying to chat over that same Wi-Fi.
Check your router’s admin panel (usually under Wireless or Advanced settings) and turn this off for the network your office PCs use. If it’s a guest network specifically meant to be isolated, move your work PCs to the main network instead.
Cause 3: The Firewall Is Blocking the App
ChatLAN’s installer adds a Windows Firewall rule automatically during setup, but in a locked-down office environment, group policy can sometimes override or remove custom firewall rules after the fact. Open Windows Firewall → Allowed apps and confirm ChatLAN is listed and enabled for both Private and Public network types. If it’s missing, re-running the installer will recreate the rule, or you can add it manually.
Cause 4: The Network Is Set to “Public” Instead of “Private”
Windows treats Public and Private networks differently for discovery purposes — Public networks are more locked down by default, on the assumption you’re on an untrusted network like a café. If your office network is set to Public in Windows’ network settings, some discovery traffic gets blocked at the OS level regardless of the app’s own firewall rule. Switch it to Private under Settings → Network & Internet for your office Wi-Fi or Ethernet connection.
The Fallback: Connect Manually by IP
If none of the above resolves it immediately — or you just need it working right now — every version of ChatLAN supports connecting directly to a known IP address from the ☰ menu. It’s a two-second workaround while you sort out the underlying network configuration.
When to Loop In Your Network Admin
If you’ve checked all four causes and it’s still not working, the most likely remaining explanation is a managed switch or firewall appliance actively blocking broadcast traffic between specific ports — something only whoever manages that hardware can adjust. At that point, the diagnostics screen’s IP/gateway/firewall summary is exactly the information they’ll need to track it down quickly.
For everything else about how ChatLAN’s discovery and security model works, the FAQ covers the most common questions in more depth. If you haven’t installed it yet, the download page has the full setup guide and system requirements.