@db215 

TP-Link calls that feature "Smart DHCP." They promised to give option to turn it off in firmware 1.6, which should be right around the corner according to TP-Link.

You can also check your router documentation to see if it has configuration setting with the following functionality: "Start DHCP server even if another DHCP server is already present on the network." If such setting does exist in your router, enable it.

Deco in AP mode will stop serving DHCP requests as soon as your router's DHCP server is running.

@Alexandre. Thanks, that is helpful. This "feature" is very aggressive given my home router reboots is less than 60 seconds. I've enabled the suggested option on my home router, but that won't prevent clients from getting an incorrect address (wrong subnet).

@db215 

There are ways to mitigate this. Set router DHCP lease time to at least few hours, to reduce number of devices that will request IP address when router is down. 

Device that gets IP address from Deco will have DHCP lease time of 1-2 minutes, meaning as soon as your router DHCP is up devices should get proper IP address from it.

Do not reboot Deco when router is down - Deco remembers your home network IP range and actually gives IP addresses in that range. I found that when I tested how "Smart DHCP" feature works.

Only when you reboot Decos while router is down, Main Deco will forget your home network IP range and will start giving IP addresses from 192.168.68.*

By the way, you may have found another not documented Deco feature, which is mesh resiliency. Do you know why you had to power off and on all three of your wired Deco units instead of just Main Deco? It is because when you have more than one wired Deco and Main Deco goes down, another wired Deco will automatically take the role of Main Deco.

Which means, losing Main Deco in setup like yours will still keep Deco mesh alive with two remaining units.

@TP-Link 

Hi,

I understand you are planning a new firmware with option to disable 'smart dhcp'.

So, what is the status on this?

I have deco m9 plus in ap mode, and when the router reboots, the 'smart dhcp' is kicking in giving wrong subnet/gateway to clients.

And to make things worse, my main router disables its own dhcp server permanently when it detects deco's server.

So i actually have ro reset my router to factory and configure it before turning on all the decos again. Puh...

I spent hours learning about dhcp and wireshark before i realized that it was the deco ap causing the problems on my home network.

I was sure it was something wrong with the dhcp server in the main router.

Also, is it ok to place M9 plus upside down to better get rid of the heat?