The gigabit Ethernet standard requires that all pins be connected.
So this is an example of a crossover cable for gigabit using the T568B standard.
Notice all pins are configured in a crossover fashion
all 4 pairs of wires are used in this example.
Now in the past you’d have to know when to use a straight through or crossover cable.
Any of these implementations would use a straight through cable.
So router to switch, PC to switch, PC to bridge or PC to hub.
Any of these implementations would use a crossover cable.
So router to router, switch to switch, PC to PC or hub to hub
or bridge to switch, PC to server, hub to switch and once again
router to router, all require crossover cables.
However today automatic crossover or auto MDIX is widely used.
Auto MDIX was introduced in 1998
and it made to the requirements for crossover cables obsolete
MDI devices are typically routers or PCs
MDIX devices are typically switches or hubs.
So they are Medium Dependent Interface crossover devices.
And in the past you would need to connect an MDI device
such as a PC to switch or hub.
In the old days once again, certain ports would have a button to flip the roll
from MDIX to MDI which would allow you to connect a switch to a switch
using a straight through cable.
However today in a lot of cases, auto MDI/MDIX
allows for automatic switching once the cable is connected.
The devices can auto detect the cable type
so there’s no need to worry as much about cable types today.
The straight through cable as an example
could be used between hubs or between switches.
So in the past, you used to have to use a crossover cable
between 2 switches but that’s not necessarily required today.
Straight through cables could be used
and devices would work out which side is MDI and which side is MDIX.
However be careful that’s not always true.
When on sites you may encounter an older Cisco switch
that doesn’t support auto MDI/MDIX.
So you may have to use the correct cabling type between all the devices.