Stick to the Basics–vMotion fails at 21%

I was working with a client recently and after doing a memory upgrade and vSphere upgrade from 5.x to 6.0, my vMotion activity began to fail when moving VMs back to the host.

The vMotion migrations failed because the ESX hosts were not able to connect over the vMotion network

The error above popped into vCenter when trying to preform a vMotion.  It would stall at exactly 21%.  This being a client environment that I couldn’t be 100% sure of, I went to basic troubleshooting.  After inspecting the connected vNics and looking carefully at the CDP information provided, we noticed that one of the vNics had been connected to an incorrect switch.
Every time you get the above 21% error, check the physical connections.  I’m sure you will find your misconfiguration there.
Physically flipped it back to the right switch and vMotions were moving along without issue.