I have used Ubiquiti UniFi equipment for quite a few years both at work and at home. I have used DHCP reservations (Ubiquiti calls this "Fixed IP Address") within my configuration to ensure that some client devices are assigned the same IP address by my Ubiquiti Dream Machine.

Several weeks ago, I wanted to access the web management portal for one of my IoT devices. Normally, this would be just https://ipofdevice:port, in this case, https://192.168.1.20:8080, however my browser told me that it couldn’t connect as the server didn’t respond. I knew the device was online, I could see it was, not only that, but it had also sent me several email alert messages.

After some brief troubleshooting, I quickly realised the device wasn’t using 192.168.1.20, it had been assigned a different address via DHCP. I was able to confirm this in the UniFi Network Application as well, more importantly, the reservation was gone.

Perplexed, but happy to find the issue, I tried to set the reservation back to 192.168.1.20, only to be told: "This fallback IP cannot be assigned since it's reserved for resolving connectivity issues". This caught me by surprise, this device has long since used 192.168.1.20, why had things suddenly changed?

Ubiquiti (and others) have long used 192.168.1.20 as a fallback address, but they previously didn’t prevent you from assigning it to a client. This all changed with the release of Unifi Network Application 7.4. With this new release, they reserved 192.168.1.20 and prevented its reservation for client devices.

Unfortunately, there isn’t a possibility to disable this application-level reservation of 192.168.1.20. This leaves us to:

1. Use a different IP address for the clients DHCP reservation, or,
2. Change the DHCP start range to be at least 192.168.1.21 and then assign a static IP address within your client (assuming you can do this).

Sorry I couldn’t provide any better alternatives, however I wanted to ensure that there were more details for the next person who runs into this issue.