Something we learned the hard way recently while upgrading from ESX 3.5 to 4.0 Update 1 is that the Intel 82571EB dual port network adapter does not work with the default ESX 4.0 settings. The network connections simply don't function in any capacity and Cisco Discovery Protocol is also broken. I almost immediately found the following KB: http://kb.vmware.com/kb/1010313 However I didn't even try the fix because we're not using iSCSI and the error the KB article references messages being in the vmkernel log was not in ours. After opening a case with VMware and scouring forums, I thought I'd try the fix in the above referenced KB article and it worked! Surprisingly VMware support didn't have the answer either even after having the case open for two days.
One thing to note -- if you have four network ports or less with your Intel 82571EB's, run the command "esxcfg-module -s IntMode=0,0,0,0 e1000e" If you have eight or less, then run the command "esxcfg-module -s IntMode=0,0,0,0,0,0,0,0 e1000e"
I hope this saves someone else the many hours I wasted.
