Just installed 2 pack of Deco M5 AC1300 v3.8 to replace the router on Netgear C3700 cable modem/router. Got fully configured and then turned off routing on the Netgear.
Modem --> Deco router port 1 (initially got IP from Netgear router on 192.168.0.x with gateway at 192.168.0.1 but goal is to replace that router with mesh)
Deco router (192.168.68.1) --> 2nd Deco mesh AP (192.168.68.103) + wifi devices (all get 192.168.68.x)
+ Deco router port 2 --> 5 port TP-Link switch port 1 for wired devices
Switch --> 1 Linux computer, 1 other monitoring device, + back link to Netgear modem 2nd port for management (Netgear management is at 192.168.100.1)
Once I turned off the Netgear routing (bridge mode) and plugged Deco's 2nd port into switch port 1, Deco took the modem IP of 173.29.x.x (formerly held by the Netgear) and wired devices, now serviced from the Deco, got addresses from the Deco with it's normal 192.168.68.x addresses, like the wireless. They showed in the Deco app and web interface. I could print to the wireless printer from wired and wireless. And I could get to the Netgear management interface at 192.168.100.1.
After a few hours later the internet dropped. So I began troubleshooting and found that no wired devices were getting addresses. I could not get to the Netgear unless I reverted the Netgear to feed the wired devices and put it back in router mode.
So for now the Netgear routing is back on, but wireless is disabled. Deco wireless works. Wired devices (including the Deco) are being served by the Netgear router again with 192.168.0.x addresses. This includes the Deco.
In the Netgear there is a LAN Setup setting toggle called "Use Gateway as DHCP Server". Don't see anything equivalent in the Deco.
Timing is suspicious, in that it worked fine until it didn't. That sounds like setting timeouts. AARP table maybe? Restarting any and all devices did not help.
At some point after getting everything working originally I added the 2nd Deco. Firmware needed updating. I did not check wired devices specifically after that so don't know if there is a relationship.
Why would it affect only wired DHCP?