@Rainman4500 

Hi, when the internet is down, is the ISP modem still powered on and the first main Deco remained physically connected to the modem via Ethernet cable?

And Can I have a picture or diagram of your network topology?

Wait for your reply and best regards.

  @Rainman4500 

Hi, Thanks a lot for the network plan. On the Deco M5, the Ethernet ports are WAN/LAN auto-sensing. When the physical connection of the previous WAN is broken, Deco will take both Ethernet ports as potential WAN ports to seek for IP assignment, Which might explain why the desktop from the main Deco is no longer getting IP address from Deco. But the rest of the wired devices, like the Apple TV and NAC remain accessible in the LAN network.

Here is a key trigger that the physical connection between the ISP modem and the first main Deco was cut off. In other words, if the modem just had no internet service but still properly powered on, the WAN port on the Deco would remain unchanged.

So is the ISP modem still powered on when the internet was down?

Thank you very much and best regards.