Emulate a crossover cable

[Joban]

I was thinking the other day. The thoughts were mostly irrelevant, but one of them caught my attention. Could I use one of my many spare lan cables as a crossover cable?

That would allow me to double the size of my network...

Is it possible?

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Sure..... in a properly-wired cable swap the orange and green pairs
(solid for solid, stripe for stripe). You'll need a crimper and a new
end for your cable, though. Crimpers can be expensive.... rj45 ends are
really cheap.

Good luck.





Joban wrote:
> I was thinking the other day. The thoughts were mostly irrelevant, but
> one of them caught my attention. Could I use one of my many spare lan
> cables as a crossover cable?
>
> That would allow me to double the size of my network...
>
> Is it possible?
>
>
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[Joban]

Wow, that was a speedy reply!

How's about doing it with software rather than playing with the physical cables. I want to spend exactly $0 on this, and I wish to waste as much time as possible trying

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Hmmm.......... I'm not quite that good w/ifconfig or the 'ip' command...
'fraid I can't really help you there. If possible it may be a quick
hack, but I'd be inclined to just crimp a new end (if I could borrow
crimpers and spend $0.10 on a connection) or buy a crossover cable as
cheaply as possible.

Good luck.





Joban wrote:
> Wow, that was a speedy reply!
>
> How's about doing it with software rather than playing with the
> physical cables. I want to spend exactly $0 on this, and I wish to waste
> as much time as possible trying
>
>
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[ken_yap]

Ready-made crossover cables start at $2 to $3 for short lengths. You can even get them at variety stores now. How much is your time worth?

[Joban]

I just thought it would be fun to give a go, but I have no idea where to start, as I really don't know much about how networks work (I mean sure I can set up a home/office network, but I have no idea how they actually WORK). I also thought it could be an interesting learning curve.

That said, I don't know if it is even possible, and if it is a driver-level hack, I won't have a chance.

[ken_yap]

It's a hardware thing. A crossover cable swaps the transmit and receive pairs so that the NIC1's transmit pair is connected to NIC2's receive pair, and similarly for the other two pairs. There's no way a software driver can compensate for a transmit pair going into a transmit pair and a receive pair going into a receive pair. There would simply be no communication.

Having said that, lots of Ethernet switches autosense the polarity and handle both straight through and crossover. But that's for switches. Unless specifically stated, NICs generally don't have this capability. See here:

Medium dependent interface - Wikipedia, the free encyclopedia

[Joban]

Bah. That's a shame. At least I did learn something though!

Cheers all.

Joban schrieb:
> How's about doing it with software rather than playing with the
> physical cables.

Nope. Not possible. Software cannot rewire hardware if the
hardware hasn't been designed for that.

There are autosensing switches which can automatically swap
the wires if they detect two ports being connected by a straight
cable where a crossover cable should have been used. But that's
hardware, too. If it isn't there, it cannot be called into
existence by software.

HTH
T.

--
Tilman Schmidt
Phoenix Software GmbH
Bonn, Germany

[cjcox]

On Tue, 2008-08-26 at 00:46 +0000, Joban wrote:
> Wow, that was a speedy reply!
>
> How's about doing it with software rather than playing with the
> physical cables. I want to spend exactly $0 on this, and I wish to waste
> as much time as possible trying

The answer is NO. Choices...

1. Buy a crossover cable.
2. Buy a crossover adapter.
3. Switch to gigabit and be free!
4. etc...