I've been using Dell Poweredge c6100 L5520 model server and I ordered a few more from refurbishing company. However the BMC firmware was different version this time, the latest edition. Here's some info about the bios and firmware ver.
 - VBIOS 0.90.7a
 - AMIBIOS ver1.70(based v02.69) build date: 12/19/12
 - BMC Firmware (IPMI Firmware): 1.32

What I have used with no problem was like this
  - VBIOS 0.80.9a
  - AMBIOS ver 08.00.15(based v02.61) Build date: 11/06/09
  -BMC Firmware: 1.05

And now I can't set up IPMI at all. No input any IP. I did some googling and downloaded 1.32 firmware through dell website and tried reflashing, but it only results wiping out the entire firmware, and I've got MAC address :00:00:00:00:00 message now. Firmware version in Bios is shown normal, but it seems that firmware cannot cope with both input and output correctly with chip set. I think rollback the present Bios to the older version seems to be the only option here, which means downgrading the Bios to the one that worked well. So, please help me, how can I do that?