I came across a pretty interesting issue while troubleshooting a network issue in a new ESXi 4.1 environment. It seems that the default installation of ESXi will hard code the Speed and Duplex to 1000 Full for Gigabit networks. I’ve been told countless times by networking professionals that AutoNegotiate is the proper setting for 1GB connections and higher. This is because Auto Negotiation in Gigabit Ethernet includes negotiation for not only speed and duplex, but flow control, backpressure, inter-frame packet timing, etc.
The fix for this is pretty straight forward. Either run a quick PowerShell Script or use the GUI or Service console command line. You can find the HowTo on VMware’s KB.
I’m not sure if this was a design decision by VMware for the new 4.1 ESX build or if this was a bug that slipped through and will be corrected in a future patch.