Knowledge Base - How to install VMXNET network adapter and driver for VM’s in ESX Server
http://networkadminkb.com/kb/Knowledge%20Base/VMWare/How%20to%20install%20VMXNET%20network%20adapter%20and%20driver%20for%20VM%92s%20in%20ESX%20Server.aspx by default vmware installs “pcnet32” network card which is a software emulation of 100MB card; most ppl switch