Hi again.
Following my previous post regarding Supermicro with Tylersburg chipset, stupid IPMI behavior.
I just want to add that this behaviour is fixed on IPMI firmware level.
There is an check-box added in the Configuration -> LAN Select, where one can choose whether to use the dedicated IPMI LAN or On-Board LAN. However still a little crippled menu, because you can not choose which Onboard port to use.