Hi @schluchti
The DHCP server log message seems to me to possibly be indicating a mismatch between what you have on the WUI screen and what is in the dhcpd.conf and possibly what is still in the leases file.
Have a look in /var/ipfire/dhcp/dhcpd.conf to see if the fixed entries match up with your entries in the WUI and also the same for the dynamic range definitions.
Have a look in /var/state/dhcp/dhcpd.leases to see if 192.168.1.20 is present in there or not.
If you don’t find any differences between what is in the WUI and what is in the dhcpd.conf and dhcpd.leases files then I have no idea what is causing the message.
The best way to make the WUI and the dhcpd.conf and leases file match up is to disable the Green and Blue entries and save the screen. Wait a few seconds and then re-enable the Green and Blue entries and save again. Depending on how production critical IPFire is for you, this may need to wait for an appropriate time slot.
If you find a mismatch between any of your fixed leases between what is on the WUI and what is in dhcpd.conf then disabling that fixed lease removes it from the conf file and re-enabling it recreates it.
Disabling and saving will effectively clear the dynamic and global options parts of the dhcpd.conf file and clear all leases from the leases file and re-enabling and saving creates the dynamic and global options parts of dhcp.conf anew from the WUI entries.
Then we can wait and see if the error message returns. Hopefully not.
I run with VLAN tagging as you describe and I have no messages like yours in my logs with either Core Update 153 or 154 so if the messages return after the above steps we will need to have a further think.