Apparently a bad Ethernet cable can cause the other ports to fail on the back of a UCG-Ultra.
I am running a Unifi Gateway Ultra running Unifi OS v4.0.6. This device has 5 ports on the back. One for WAN and 4 for normal LAN traffic. In Port 1 I have a “US-8-60W” switch. Ports 2-4 I have 3 other Linux devices.
Yesterday, according to my logs, I encountered an issue where around 1:06pm one of those 3 devices disconnected. To minutes later, another device disconnected. And 20 minutes later, the last device disconnected. I didn’t catch this until later in the evening when I was trying to access one of these devices and started going through the logs.
I restarted the UCG-Ultra and devices came back but then disconnected. No alerts or anything so this was odd behavior. I also verified that I didn’t have any crazy VLAN rules on those ports.
I have a US-8-60W that is connected and not failing on Port 1. I had some open ports so I decided to connect the 3 devices that were attached to the UCG-Ultra to the US-8-60W. 2 of the devices connected, however, one of these, after connecting, I saw a warning message in the web app I was logged into:
Blocked by Spanning Tree Protocol to prevent a network loop. This port will be automatically re-enabled when the loop is no longer detected.I had no idea what that meant, but the fact that the Ethernet cable was attached to an older Linux device, I just assumed the Linux device went bad so before I went down that rabbit hole, I decided to replace the Ethernet cable. It worked! The device reconnected!!!
That said, I think it was the Ethernet cable but I’m curious why it was causing the other devices on the UCG-Ultra to fail except for the US-8-60W switch but I was looking for anyone else in the community that might provide me with an answer to this issue or to help someone out in the future if they suddenly lost all their devices on the UCG-Ultra to test out the Ethernet cables and see if one of them is bad. I then reconnected everything back to the UCG-Ultra that I had temporarily moved to the network switch and verified I had connectivity again to those original 3 devices.
To summarize my debugging:
- Noticed Unifi Gateway Ultra (UCG-Ultra) didn’t detect traffic on ports 2-4 but port 1 was still active and connected to a network switch (US-8-60W)
- Restarted the UCG-Ultra but nothing changed. Devices on ports 2-4 were not accessible.
- Moved devices from ports 2-4 to ports on the network switch.
- After doing that, received an error on one of the ports.
- Replaced the Ethernet cable on that port back to the device which resolved the issue.
- To verify it was the Ethernet cable, I moved all the devices back to the UCG-Ultra and I confirmed I had connection to those devices again.
TIL
Make sure you are careful with your Ethernet cables! Apparently they can go bad! Writing this out because I’m 75% sure that it’s an Ethernet cable issue but I’m not completely convinced, and at minimum I’m not sure why I get an error when connected to a switch but no error when the Ethernet cable was connected to the Unifi Gateway Ultra (UCG-Ultra).
I originally posted this to the Ubiquiti forum: https://community.ui.com/questions/Cloud-Gateway-Ultra-UCG-Ultra-Ports-failing-due-to-Bad-Ethernet-Cable/75765775-5391-4ae3-b066-1f42a9c7fcd8