There will be some RJ11 connectors in the household ADSL Modem, which is slightly smaller than the RJ45, mainly used to connect the phone line.123

It should be noted that the RJ11 interface is 4 or 6 pins, and the RJ45 is an 8-pin interface, so the RJ45 plug can not be inserted into the RJ11 interface,and the RJ11 plug can not be inserted into the RJ45 interface (though it is achievable on the physical interface) The actual use must be clearly distinguished