For some reason you got more then 2 modem router and you like to make all you LAN be able to access Internet and access to each other over LAN. This is somehow silly but this is what happened to me.

scanario 1: 1 modem router (with no switch) + 1 AP+router+4 port switch ( with no Modem)

scnario 2: both modem router with switch and you would like to use 1 as modem+router+switch and another 1 only switch

Here is the quick setup:

1. Pick the modem unit - make sure all the internet setting is correct ( username/password, DNS server - by ISP )
2. Turn on DHCP server over the router modem, I assume most of the modem router do have this feature.
3. Login to the other devices other then the modem unit ( AP / switch / modem ) , make sure all these units’ DHCP server are turn off.
4. Check your modem is connection to internet , make sure connection over your connected pc / laptop are able to connect LAN and internet.
5. ( optional ) If you have have server need to set port forwarding / DMZ , login to the modem unit to make the setting..