That used to require a crossover cable; I've done precisely that (with a crossover cable) back before https://en.wikipedia.org/wiki/Medium-dependent_interface#Aut... became widespread. With a straight-through cable, you'd be connecting the Transmit (TX) pin of one adapter to the TX pin of the other one, and the Receive (RX) pin of one to the RX pin of the other — and neither device would "hear" the messages the other one was sending. A crossover cable flipped those wires, so each device's TX pin was connected to the RX pin on the other end, and both devices could "hear" each other.

But with auto MDI-X, each device would notice "hey, I'm sending but not receiving anything," and would try flipping its Transmit and Receive functions around (transmitting on the RX pin and receiving on the TX pin). Since each device waited a random period before doing that, it was very unlikely (nigh-impossible) that they would both flip at the exact same moment. And if they did, the second interval would most likely not be identical either.

I'm simplifying a bit in the explanation above, but that's the broad strokes. And that's how my carefully-labeled crossover cables started gathering dust. (And then I realized "hey wait, I can just use these as normal cables now", and pulled them back out of storage and mixed them with my normal patch cables).

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soundworlds 3 hours ago | parent | next [-]

That wasn't that long ago was it..?

/looks longingly out the window, and catch my aging face in the reflection

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abrookewood 2 hours ago | parent [-]

Yup ... still have some old 'xover' cables lying around - all of which are RED in colour to explicitly declare their usage

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valleyer 2 hours ago | parent [-]

Interesting. I don't remember my crossover cables being marked that way; you had to read the dot-matrix printing along the side to know. Color would have been way more handy.

	▲	zeristor 4 minutes ago \| parent \| next [-]
		I seem to recall crossover cables being yellow.
	▲	rmunn an hour ago \| parent \| prev \| next [-]
		I added labels (just a piece of paper under some clear tape) saying "CROSSOVER" at both ends of the cables, so that if I ever plugged a crossover cable into a place where I needed a straight-through, the label would be right there next to the plug.
	▲	tedeh 2 hours ago \| parent \| prev \| next [-]
		Well I have to add that was interesting too. Because I remember you had to hold the ends up next to each other and compare the order of the colored wires. Same order left-to-right, not cross-over. Anything else, cross-over.
	▲	jalk 2 hours ago \| parent \| prev [-]
		I had quite a few cables with a yellow crimp "jackets" just behind the RJ45. IIRC they came with DSL modems / routers

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rootsudo 2 hours ago | parent | prev [-]

Basically beat me to writing this, but I wouldn’t have made it so eloquent of an explanation.