回复：你应该讲出你的router及modem的型号

there is possibility that your modem and router works, the problem is that do you know if your modem has a router inside, in that case you do not need another router. you must find out if it has a router inside.
you can connect as more routers as you want, but you can only use one DHCP of them, and disable the rest.

你的router上的modem接口应叫做wan 接口，就是用哪一接口接你邻居的任一 lin（1-4） 接口。