@tm450 

Hi, Is your Arris CM8200B P2 like the product on this link:

https://www.commscope.com/globalassets/digizuite/62379-touchstone-cm8200-data-sheet.pdf

Since the Arris CM8200B P2 is a bridge cable modem, normally the network switch is supposed to connect behind the wireless router;

So I think the correct network diagram should be:

Arris CM8200B P2---Deco M9 plus--- Dahua 10 port POA unmanaged switch--other satellite Deco units;

While considering it is a pure cable modem, are you sure that there is a web interface for the cable modem?

Please feel free to let me know if there is any mistakes;

Thank you very much.

@tm450 

Hi, May I know why do you want to turn off the multi-cast on the Deco?

If you checked on the web UI of the Deco M9 Plus, the IGMP feature on the Deco M9 plus is disabled by default;