Pinout for crossover cable plz

Flashie · April 25, 2017

Hey.
I was asked by a friend to make a crossover cable for him, but a quick google image search shows various results and combinations in odd orders. Does anybody have a link for me to a legitimate crossover cable pinout albeit it literally "OW - O - GW - B" (and please specify if your pinout has the clip facing down and the pins facing up)

Tx

mariushm · April 25, 2017

Gigabit network cards have auto-detection of pair order, so you can use a plain network cable (like the one you use between computer and router) and make the connection between two gigabit network cards.

Crossover cable is only required if one of the cards is not capable of 1 gbps or if for some reason (buggy drivers, buggy chip) it can't automatically detect the pair order.

There's two ways to wire a connector : T568A (the one that starts with green, on the right) and T568B (the one that starts with orange) :

For a regular cable, you use same version on both ends (either T568A - T568A or T568B-T568B) , for crossover cable one end must have T568A and the other end must have T568B (like in the picture above).

brwainer · April 25, 2017

1 hour ago, mariushm said:

Gigabit network cards have auto-detection of pair order, so you can use a plain network cable (like the one you use between computer and router) and make the connection between two gigabit network cards.

Crossover cable is only required if one of the cards is not capable of 1 gbps or if for some reason (buggy drivers, buggy chip) it can't automatically detect the pair order.

There's two ways to wire a connector : T568A (the one that starts with green, on the right) and T568B (the one that starts with orange) :

For a regular cable, you use same version on both ends (either T568A - T568A or T568B-T568B) , for crossover cable one end must have T568A and the other end must have T568B (like in the picture above).

I know that you see this all over the place, but it is WRONG. You do not get a proper crossover cable by using T568a on one end and T568B on the other. It should be clear why if you look at the colors- only green/orange are getting flipped, blue/brown are staying the same. This means that the resulting cable is partially crossover, and partially straight. The only reason this "advice" exists is because if you are only using 100Mb equipment, they will happily use this as a crossover cable. But if one or both ends are 1Gb capable, they will take longer to negotiate a link, and when they do, they might end up with something weird, like 100Mb half duplex. The spec for negotiation that came out with 1Gb ethernet doesn't say how to handle a cable like this. Even NICs that are capable of Auto-MDIX often get confused by this, because most of them can't flip only half of the pins.

mariushm · April 25, 2017

Like I said ... gigabit network cards have auto detection of pairs.

If one of the network card is 100 mbps, then only two pairs are used, so it's perfectly fine to wire the two connectors like this because the other 4 wires don't matter.

If you really want all pairs crossed 1 gbps crossover cable, use this:

Cross over patch for 1 Gb Ethernet
	T568B
Name		NIC1	Color		NIC2		Name
(BI_DA+)	Pair2.1	1	White/Orange	White/Green	3	Pair3.1	(BI_DB+)
(BI_DA-)	Pair2.2	2	Orange	Green	6	Pair3.2	(BI_DB-)
(BI_DB+)	Pair3.1	3	White/Green	White/Orange	1	Pair2.1	(BI_DA+)
(BI_DC+)	Pair1.2	4	Blue	White/Brown	7	Pair4.1	(BI_DD+)
(BI_DC-)	Pair1.1	5	White/Blue	Brown	8	Pair4.2	(BI_DD-)
(BI_DB-)	Pair3.2	6	Green	Orange	2	Pair2.2	(BI_DA-)
(BI_DD+)	Pair4.1	7	White/Brown	Blue	4	Pair1.2	(BI_DC+)
(BI_DD-)	Pair4.2	8	Brown	White/Blue	5	Pair1.1	(BI_DC-)

brwainer · April 25, 2017

22 minutes ago, mariushm said:

Like I said ... gigabit network cards have auto detection of pairs.

And like I said, most cards with Auto-MDIX (auto detection of whether it needs to flip TX and RX) can only do so for all the pairs together, not for individual pairs. Meaning that they either flip all the TX and RX, or none of them.

22 minutes ago, mariushm said:

If one of the network card is 100 mbps, then only two pairs are used, so it's perfectly fine to wire the two connectors like this because the other 4 wires don't matter

It's thinking like this that has perpetuated the myth of crossover just being one end T568A and the other T568B. Sure it works for FE, but if you're custom terminating a cable, why wouldn't you want to make it a proper one that isn't limited to FE just because you pushed in the wires wrong?

Flashie · April 25, 2017

2 hours ago, brwainer said:

I know that you see this all over the place, but it is WRONG. You do not get a proper crossover cable by using T568a on one end and T568B on the other. It should be clear why if you look at the colors- only green/orange are getting flipped, blue/brown are staying the same. This means that the resulting cable is partially crossover, and partially straight. The only reason this "advice" exists is because if you are only using 100Mb equipment, they will happily use this as a crossover cable. But if one or both ends are 1Gb capable, they will take longer to negotiate a link, and when they do, they might end up with something weird, like 100Mb half duplex. The spec for negotiation that came out with 1Gb ethernet doesn't say how to handle a cable like this. Even NICs that are capable of Auto-MDIX often get confused by this, because most of them can't flip only half of the pins.

2 hours ago, brwainer said:

And like I said, most cards with Auto-MDIX (auto detection of whether it needs to flip TX and RX) can only do so for all the pairs together, not for individual pairs. Meaning that they either flip all the TX and RX, or none of them.

It's thinking like this that has perpetuated the myth of crossover just being one end T568A and the other T568B. Sure it works for FE, but if you're custom terminating a cable, why wouldn't you want to make it a proper one that isn't limited to FE just because you pushed in the wires wrong?

The first post's video is the exact same pinout as the one in the picture on the second post that was being discussed (from what i could make out atleast).

Long story short, i paused the video in at its start and followed that pinout; and the result was great. I could LAN between the two test-computers Amazing. Thanks guys.