Why do I use crossover lines for the same device connections?

Most people know that crossover lines are used to connect the same devices, but straight lines are needed to connect different devices. But why? Knowing it but knowing why, it increases a lot when you come to chat with others. All right, cut the crap and get to the point.

First, let's see how the Nic interface corresponds to the network cable sequence:

Network card: 1

two

three

four

five

six

seven

eight

Net wire sequence white orange white green blue white blue green

White brown

White orange corresponds to 1 / 2 and white, green and green corresponds to 3 / 6 is received. Other interfaces have no data transfer function. A straight-through line is the same line sequence at both ends of the network cable. The network card interface of the same device sends and receives the same. Look at the following picture:

Device 1 Network Card Interface 1 2 (send)

3 6 (receive)

One end of white-orange-white-green-green straight-through line white-orange-white-green-green equipment 2 network card interface 1 2 (send) 3 6 (receive)

Connecting with a straight-through line is equal to connecting the sending interface of the same device to the sending interface of another same device, and the receiving interface corresponding to the receiving interface cannot be interconnected.

By the way, the four white, blue, blue, white and brown wires in the network cable do not transmit data, and twisted together with other lines at a certain angle is mainly to reduce electromagnetic interference.