@johntong 

Hi, the cisco switch is an unmanaged switch or managed switch? if the switch is only used to provide more LAN ports, and your client devices only need internet access, no additional settings required, they should work that way, just make sure there is no IP conflict. For example, the default LAN IP address of MR6400 is 192.168.1.1, then the switch IP address should not be 192.168.1.1, it could be 192.168.1.2 etc.