@Kelvin_Ng

Having a static reservation in the external DHCP server is frankly not a great solution unless TP-link can fix the firmware to keep trying dhcp renewal if you so insisting on only supporting DHCP in AP mode. The problem I constantly get into is after a power outage the decos boot up a lot faster than my dhcp server. When the main deco cannot get a least quickly, it falls back to a weird default address. The only fix is to wait for the dhcp server to fully recover then manually power-cycle the deco.

@xvi 

The ability to turn off "Smart DHCP" in Deco AP mode will come with firmware 1.6.

When Deco runs "Smart DHCP," it distributes IP addresses with very short lease time. In my tests dhcp lease time from Deco was under 3-4 minutes. Meaning, as soon as your dhcp server is up, Deco recognized it and ceased running "Smart DHCP," all your devices should request IP addresses from your dhcp server. In less than 5 minutes your home network should recover on its own, without need to power cycle Deco.

If you need to bounce Decos more than 5 minutes after power and your dhcp server recovery, there must be something else going on in your network.

If you'd like, you can run quite simple test: turn off your dhcp server, power cycle Main Deco and force one of devices that is connected to Deco mesh and can report DHCP lease time to request IP address. It should request it from Main Deco and that IP address will be from 192.168.68.* range. Then, check DHCP lease time of that IP address on your device which got it.

DHCP lease time should not be longer than few minutes.

I have ISP Router that runs as my DNS and DHCP server, with Deco in AP mode. I plugged ISP Router to uninterruptible power supply, and that is another workaround for brief power outages, till firmware 1.6 is released.

@Alexandre. I think the problem is with the deco itself, not the wireless clients it serves. When the AP deco cannot obtain an IP for itself, it appreantly assigns itself one and it's very different than the DHCP server's network space. That IP also sticks around forever until I reboot it. So while wireless clients can connect to the deco without my external dhpc server, it cannot go anywhere. I'm not sure how smart dhcp can help. Having the ability to set a static IP/mask/gateway/DNS for any TCP/IP device seems to be a fundamental thing but the deco does not allow.