I have a quad node C6100 XS23-TY3. They are setup in a ESXi 5.0U1 cluster and have the two onboard nics as the management, vmotion, and production vm network as well as a half-height intel PCIE dual port nic in the expansion bay that serves as a round robin iSCSI controller. Nodes 1 and 2 work fine while both are powered on and have been that way for some time. Nodes 3 and 4 cannot be on at the same time and maintain a consistent ping to the management network. If either one are powered off the other functions perfectly. I have been pulling my hair out trying to figure out what is different and why they are doing this. Please let me know any information that would be helpful in troubleshooting this and I will be happy to provide it.
I was actually able to resolve my own issue. It appears that the blade i replaced was not identical to the one before and the esxi install attempted to use the same mac addressing as the previous blade, which was causing flapping on the switch. A fresh install of esxi took care of it and everybody is happy now.