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I recently found something very odd. Traditionally connecting two pc's directly via an ethernet cable from one nic to another required a special wiring pin out that was also used to connect network hubs that didn't have a specialized port for such.

In the office about a week ago I connected two machines with a cable wired for such and they didn't see each other... as a joke I connected them with a standard pin out cable. They started talking... this should not have worked.

While upgrading software at a clients site this week, I went to connect two machines directly together to take an old 10mbs hub out of the picture (there were only two machines anyway) hoping to get a hundred megabit connection. Neither the standard pin out nor the hub to hub pin out worked. The one machine was brand new (replaced an older one) with onboard nic, the other was an older machine running a 500mhz processor. I didn't really look to closely at the older machine but I'm assuming it was a generation or so behind current technology. While it is possible the machine was not capable of a hundred megabit connection, it still should have worked at ten megabit.

The only thing I can think of at this point is that hardware manufactuers may have made a standarized change to nic architecture to allow the use of standard cable pin outs for machine to machine connections. If this is the case I need to figure out the pin outs that will allow older nics to talk with newer ones directly.

when you go from a layer 2, to a layer 3 device, you need straight ethernet

when you connect a layer3, to layer 3 (or 2 to 2) you need a rollover cable


unless the device is smart enough(a lot of new ones are) to sense the fact they're being connected to a like device, then they'll roll the pins internally, in software


so chances are, you have an old machine that's not smart enough to roll the pins, but 1 smart one that is trying to roll the pins

Thanks Tikker,

I didn't consider that the sofware roll was being done due to device layer detection, rather I was thinking the wire signals was used in determination, and that pretty much explains it.

So I get to do some homework and try and figure out pinouts to counter the pin roll when going between a machine that does and one that does not. Otherwise this will be tripping me up to no end I'm sure.

I was always told that I needed a null modem or something like that so I deemed the task too fucking complicated and yanked the hard drive out.

We are talking about Ethernet Cabels between network cards. A null modem cable would be something completely different, and generally used to allow two computers to communicate via serial ports.

I know. Just figured my experience with trying to connect two computers would be slightly humorous. =) I think at the time I was attempting it with parallel ports but can't remember now. Don't go getting all Lyion-esque on me.

There was nothing funny about null modem cables... it was only a slight step above sneaker net, I prefer not to remember those dark days .