Had an interesting issue where vMotion was failing between 2 ESXi 5 servers. No matter what I did they just wouldn’t respond.
I couldn’t ping between the 2 VMkernel ports despite them being on the same subnet etc.
After some digging around it transpires that the MAC addresses for both VMKernel ports was the same.
It transpires that the end user who set them up had cloned the ESXi servers.
The MAC addresses for VMkernel ports are generated from the underlying OS so it was always generating the same MAC address.
Once the 2nd server was rebuilt from scratch it was all good and both addresses different.
To verify what MAC addresses are assigned use the command
esxcfg-vmknic -l