Re: Realtek NICs don't like either other
I would try to remove the auto negociation and force A, B, C to Full/1 Gbps speed. Since you are using a gigabit switch, make sure to force all ports to Full/1 Gbps.
Also, i would try with or without jumbo frames support from both A and C nics.
If it still doesnt work i would connect A to C, bypassing the switch.
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