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I've got an HP 2510G-24 and Intel Pro/1000 PT Quad Port NIC in a 4x LACP trunk. When I cool at the switch's "Status and Counters - Port status" page, I see an inconsistency between ports of the same trunk. I would expect them to be identical.

So, my questions:

  • What is MDI and MDIX?
  • Do I need to be concerned about the inconsistency?
  • If so, how to resolve?

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1 Answer

up vote 4 down vote accepted

Take a look here. Basically, MDIX is when a "cross ethernet cable" is connected, MDI when a "straight ethernet cable" is connected. Should not be a concern.

Indeed this is not a concern, but do not assume that just because it says MDIX that it means that you are using a crossover cable.

Used to be that devices couldn't negotiate what between each other what pins to use on a cable, and you had to run either a straight through or a crossover depending on what you are trying to link up.

Nowadays most decent switches can negotiate with the devices, and depending on what the other device is and what cable you've used it'll set the mode on its own interface.

An example:

Computer ==> Straight through cable ==> Switch

The devices will test the connection and decide what mode to use.

In this case the mode chosen on each end will be different. What is chosen on each end will be seemingly random, you need to see the mode set on each end to see what's going on.

If you used a cross over cable they'd be the same.

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What was bugging me was the seemingly random distribution of which port was MDI and which was MDIX. It seems that this is because both the card and the switch are auto-sensing, and settling on one, regardless of whether it is crossover or not. –  Stu Thompson Jul 24 '10 at 8:59
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