Detecting a Misconfigured vSwitch

Years ago I received a call for help from someone setting up a vSphere host. The install had never worked right and the clients were upset at the upgrade. It sometimes took 30 seconds to connect to a server and their SQL applications would crash daily. My intuition told me there was something strange going on with the network. It was a very basic install with one Standard vSwitch doing management and virtual machine network traffic.