When a UniFi device shows as disconnected or offline in the UniFi Network application, it doesn’t always mean the users connected to that device are experiencing internet issues. Understanding the root cause is key to fixing the problem and preventing future outages.
Table of Contents
Does “Disconnected” Mean the Internet is Down?
Not always. A disconnected device simply means it cannot communicate with the UniFi Network Controller. Users may still have uninterrupted internet access if the disruption is only in the communication channel between the device and the controller.
Example:
- If the controller is unreachable but the gateway is online, users still have internet access.
- If the device is truly offline (e.g., lost power or internet), user connectivity is impacted.
Common Causes of UniFi Device Disconnection
Here are the most likely scenarios:
| Cause | Description |
|---|---|
| Power outage | The device rebooted or lost power, causing loss of connection. |
| ISP outage | The internet connection is down at the site. |
| Device-to-server connectivity issue | Local network issues prevent the device from reaching the controller. |
| Server-to-device connectivity issue | The UniFi Controller cannot reach the device due to a firewall, routing, or DNS issue. |
How to Diagnose the Disconnection Cause
1. Check Device Uptime
Run the uptime command via SSH or inspect uptime in the UniFi controller.
- Low uptime = Device recently rebooted → Likely a power issue
- High uptime but still disconnected = Communication issue
2. Scope of the Problem
Determine how widespread the disconnection is:
| Scenario | Most Likely Cause |
|---|---|
| One or two devices offline | Cable issue, port problem, local power issue |
| All devices at one site offline | Power outage or ISP outage at that site |
| All devices across nearby sites offline | Regional ISP issue |
| All devices across all sites offline | Controller issue, cloud firewall block, DNS failure |
Troubleshooting Steps
✅ Power Issues
- Verify power supply is working.
- Check for tripped breakers or disconnected PoE injectors/switch ports.
- Consider adding a UPS (Uninterruptible Power Supply) or redundant PoE source for critical infrastructure.
✅ Connectivity Between Device and Controller
- Check physical Ethernet connection and uplink.
- Test local DNS resolution: the device must resolve the hostname of the UniFi Controller.
- Check firewall logs to ensure no ports are blocked. The controller uses TCP port 8080, 8443, 8880, and 3478 UDP.
- Ping the controller from another local host to ensure it’s reachable.
✅ ISP Issues
- Verify modem status and WAN link.
- Check logs or contact the ISP for known outages.
- Use tools like downdetector.com for regional outages.
✅ Controller-Side Issues
- If using a cloud-based controller, make sure it’s online and responsive.
- Check system resources (CPU, memory, disk).
- Restart the UniFi service or host server if necessary.
- Verify the inform URL is correct:
SSH into the device and run: bashCopyEditinfo
Bonus Tips
- Enable alerts: Use UniFi’s email or webhook alerts to be notified immediately when a device disconnects.
- Check logs: Review UniFi controller logs under Settings > System > Event Logs for context.
- Use a static inform URL: Especially for remote or multi-site deployments, ensure the device is pointed at a stable FQDN, not a local IP that might change.
Final Thoughts
A disconnected UniFi device doesn’t always mean downtime for users. By methodically checking power, ISP, LAN connectivity, and controller status, you can quickly isolate the issue and restore normal operation. Logging, alerting, and proactive monitoring go a long way in reducing future disruptions.
