Direct cable NIC to NIC

[hosselausso]

Is there a way to emulate a direct crossover cable connection from one NIC of a VM to another NIC of a second VM?

[Perryg]

Select the internal network adapter for both machines and make sure they both use the same "name" adapter.

[hosselausso]

Isn't that like connecting both interfaces to a internal network with a bridge/switch?

[mpack]

With a switch yes. What's the difference? A "crossover cable" is logically just a switch, except it can only have two connections. The things that make a cable different from a switch are not relevant to something not made of physical wires.

Ps. If I'm not mistaken, ethernet cables are balanced pair transmission lines, so you don't ever cross them over.

[hosselausso]

That makes sense. Thank you!

[socratis]

Ps. If I'm not mistaken, ethernet cables are balanced pair transmission lines, so you don't ever cross them over.

You used to have to, otherwise they wouldn't work. The NICs couldn't figure out the pairing. We used to have specially labelled, handmade cables that were used for PC-to-PC/instrument connections. The "normal" ones wouldn't work. I've made several of them...

If I'm not mistaken the first computer that I encountered that could figure the pairing was my first MacBook, way too many years ago...

[mpack]

I've never needed to study the Ethernet cabling standards, but it certainly has all the hallmarks of a balanced pair, i.e. only two wires for a start (not two wires plus ground), and line terminators, and the distance they can go. Perhaps there's some reason why you'd want to distinguish between the nominal + and the nominal -, for idle/carrier detection perhaps.

Edit:  Or perhaps there are pullups/pulldowns that need to observe the correct polarity.

[socratis]

I was about to reply "I vaguely remember something about orange and green" (not the red/blue that you see on the movies), when I decided to search for a reference. And lo and behold, my memory is still functioning
https://en.wikipedia.org/wiki/Ethernet_ ... le_pinouts

[Martin]

...and if you look a few lines up in your Wikipedia link you will see that crossover cabling is no longer relevant with gigabit Ethernet / 1000Base-T because of Auto MDI-X

[mpack]

Weird. Am I totally imagining having ever seen Ethernet carried over coax? In which case it couldn't possibly have more than two cores, and maybe a shield. I'm probably remembering something ancient.

[socratis]

Am I totally imagining having ever seen Ethernet carried over coax?

Not at all! I remember those too from my student years, 8086/80286 era. https://en.wikipedia.org/wiki/Ethernet_over_coax

I'm probably remembering something ancient.

That would be correct; 80's. Look at the history section in the link above...

[Perryg]

Ah the good old days. I have strung miles of coax and still have the scars on my fingers from putting the ends on. Neat concept that is still in use today only in a larger concept ( think cable companies ). In the old days 10Mb was the best you could get and was limited in the amount of machines and distance, but for small offices it worked flawlessly. There is still one protocol that is older though.

[socratis]

In the old days 10Mb was the best you could get

You're one lucky man. I was getting errors at 2400 bps! (remember those?)

There is still one protocol that is older though.

ARCnet maybe? Other than that is snail mail and of course... pigeons!

[Perryg]

Yeah I do remember and sold/installed my share of modems, but the first network I built used rs232 and you were lucky if you could sustain anywhere near 2400bps but it did allow for connectivity and better than a floppy for getting data between various machines. Don't even get me started with tty machines. I totally hated them.