I recently ran into a not so obvious problem. One of our virtual MOSX servers that was cloned from another ESXi host to a new one started to behave strangely network-wise. Mostly the network didn't work at all and ifconfig on command line and the GUI tool in System Preferences wasn't agreeing on the state of the network interfaces and such.
The cause of the problem showed to be that there were two active physical network interfaces in ESXI but only one was assigned any network (see picture below).
Once we remove the unused interface from ESXi and rebooted the weirdly behaving machine everything went back to normal. We have several Mac Minis of very similar model where both the builtin network card/port and a Thunderbolt adapter is used and that hasn't caused this kind of problem but on those machines both interfaces are active in ESXi and assigned to a network.I don't know if this is specific for the combination of ESXi 5.5 and Mac OS 10.9 or if it also would apply to other versions of Mac OS 10 or Linux/Windows virtualised in ESXi.
