New to this, confused about CAT5e crossover wiring

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aalcoo

Commendable
Apr 23, 2016
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Hi,
I just started studying networking and we made CAT5e RJ45 cables at school. I searched the Internet to try to understand everything better. But when I made a crossover cable almost every guide on the Internet only swapped the green and orange wires while the instruction I got from the teacher said to also swap the brown and blue wires. This is what confuses me, which one is right?
 
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Someone Somewhere
Green and orange pairs (so you're also swapping green/white with orange/white) are the only ones you swap.

If you look up the pinouts, you'll see that a crossover cable is a cable where one end is wired 568A, and the other 568B.

Note that for modern gear, you don't need to worry about crossover cables. Almost every gigabit NIC and the vast majority of 100Mb/s NICs supports 'Auto MDI/MDI-X', which means it auto-detects.

The only exception is 1000 BASE-TX, which was basically stillborn. 1000-BASE T (almost every commercial NIC available) transmits and receives simultaneously on all four pairs; a crossover cable is pointless.

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Someone Somewhere

Someone Somewhere

Titan
Sep 23, 2012
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Green and orange pairs (so you're also swapping green/white with orange/white) are the only ones you swap.

If you look up the pinouts, you'll see that a crossover cable is a cable where one end is wired 568A, and the other 568B.

Note that for modern gear, you don't need to worry about crossover cables. Almost every gigabit NIC and the vast majority of 100Mb/s NICs supports 'Auto MDI/MDI-X', which means it auto-detects.

The only exception is 1000 BASE-TX, which was basically stillborn. 1000-BASE T (almost every commercial NIC available) transmits and receives simultaneously on all four pairs; a crossover cable is pointless.



That cable will blow up a lot of PoE devices. You're swapping the negatives and positives over, not swapping transmit/receive.

All ethernet-compliant devices that transmit on pairs 1 & 4 are 1000 BASE-T, so don't need a crossover.

For non ethernet-compliant devices, don't assume any cable will work. Always check the specs.
 
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