Four people in the university dormitory share a wireless router, and a roommate's mobile phone is connected to wifi. As soon as he got out of the dormitory, the network in the dormitory was cut off. Why? First of all, make sure your friend won't spoof you, because the router can bind the dynamic domain name, and he can access this dynamic domain name anywhere with his mobile phone, 2G or 3G network, and directly enter the router to disconnect the router.

Or an excuse that the switch of the superior equipment connected to your dormitory by your network cable was unplugged.

If not, you can consider the router problem.

Otherwise, this phenomenon will not occur.