I was just reviewing a server heartbeat (HB) cable that was failing because it had only 2 pairs (1,2,3,6) and was crossed over in the typical way:
https://ciscoccvp.files.wordpress.com/2009/06/img_3738.jpg
like this above. this cable was missing the brown and blue pairs - because it didn't need them on 10 and 100 Mbps. Someone used an old cable in this instance!
This got me thinking about my use of crossover cables in 1000Base-T setting. And the more I thought, the more I got confused.
I believe I have deployed some 1Gb crossovers that had only two pairs crossed over. And it seemed to work. But they had the brown and green pairs as well, but they were just not crossed over.
So now im wondering if all 1Gb applications requiring a crossover need all four pairs crossed or just the 1,2,3,6 conductor pairs (orange and green)?
And are there any physical variations of 1000 Base-T that only need 2 pairs to work? I suspect there might be a lot of folks that have made crossovers by just crossing the 1,2,3,6 pairs and expect it to work at 1Gbps speeds.
thx,
Will
