The difference between RJ45 connector and RJ11 connector

The RJ45 interface is typically used for data transfer, the most common being the NIC interface. There are two types of wires that use RJ45 connectors: straight-through wires and cross wires. There are two types of common RJ45 interfaces: DTE type for Ethernet network cards, routers, Ethernet interfaces, etc., and DCE type for switches.

The RJ11 interface is similar to the RJ45 interface, but has only 4 pins (8 for the RJ45). In computer systems, RJ11 is mainly used to connect modem modems. The RJ11 usually refers to a 6-position (6-pin) modular jack or plug. This connector has no international standard and is mentioned in the general cabling standard

The difference between RJ45 connector and RJ11 connector
Different standards, different sizes (RJ11 has 6P6C, 6P4C, 4P4C, 4P2C, where C represents the number of gold needles in the crystal head; RJ45 has 8P8C)
Due to the different sizes of the two (RJ11 is 4 or 6 pins, RJ45 is an 8-pin connector), the RJ45 connector cannot be inserted into the RJ11 connector. The reverse is physically feasible (the RJ11 connector is smaller than the RJ45 connector), which makes people mistakenly think that the two can work together. This is actually not the case. It is highly recommended not to use the RJ11 plug for the RJ45 connector.