I connect a 3550-12T and a 2950T-24 through 1000base-T port. Regarding to the CCO document, the crossover cable should be 1,2 to 3,6 and 4,5 to 7,8. I realised that it is still working fine if 4,5 and 7,8 is not crossed. The case is the same as b.yan...