Unraid 7.3.1 Network Issue – GUI moved to a different IP address, shim-br0 taking the original address.

I recently upgraded my Unraid server from 7.2.5 to 7.3.1 and ran into a confusing networking issue that took some investigation to resolve. I am posting my findings here in case it helps someone else.

Symptoms

Before the upgrade:

• The Unraid GUI and Docker containers were accessible through the same IP address.

• The server obtained its IP address via DHCP.

• My router provided a DHCP reservation based on the server's MAC address.
  

After upgrading to 7.3.1:

• The interface called shim-br0 has taken the IP address associated with eth0 interface, that was bridged to br0 even though it's MAC address did not match the router configuration.

• The Unraid GUI was no longer reachable on its original IP address.

• The router still showed the original IP address assigned to the server, but to a different MAC address than specified in the reservation.

• Docker containers continued to work normally and were accessible on the old IP address.

• The Unraid GUI became reachable on a different IP address.
  

When investigating the interfaces, I found:

• br0 had the original MAC address that was configured in my router's DHCP reservation.

• shim-br0 had a different MAC address.

• br0 and shim-br0 were using different IP addresses.
  

This resulted in a situation where the original reserved IP address was no longer being used by the Unraid GUI and any system services like smb.

Solution

1. Disable Docker

Navigate to:

Settings → Docker

Set:

• Enable Docker = No

2. Disable Host Network Access

While Docker was disabled, I also disabled:

• Host Network Access

3. Reboot the Server

After rebooting:

• The shim-br0 interface disappeared.

• Only the normal br0 interface remained.

4. Change Unraid from DHCP to a Static IP

Navigate to: Settings → Network Settings

Change: IPv4 Assignment Method from DHCP to Static

Then manually configure the IP address that you want Unraid to use (in my case, the original IP address).

Save the settings and reboot the server.

5. Verify Connectivity

After rebooting:

• The Unraid GUI was again reachable on the desired/original IP address.

• The br0 interface was correctly using that address.

• Everything appeared to function normally.

6. Re-enable Host Network Access and Docker

Finally, I re-enabled:

1. Host Network Access

2. Docker

Result

After Docker started again:

• The shim-br0 interface was recreated automatically.

• However, the previous issue did not return.

• The Unraid GUI and services remained reachable on the configured static IP address.

• Docker containers continued to work correctly.

• Both br0 and shim-br0 now show the same IP address.

Conclusion

It appears that after upgrading to Unraid 7.3.1, the interaction between DHCP, Docker networking, and the shim-br0 interface caused the host network identity to become inconsistent.

Switching Unraid from DHCP to a static IP while Docker and Host Network Access were temporarily disabled completely resolved the issue. Once Docker and Host Network Access were re-enabled, the system continued to operate normally and the shim-br0 interface no longer caused any IP address confusion.

Hopefully this helps anyone else who encounters a similar issue after upgrading to 7.3.x.