Recently I was working on an issue where a VM with a load balancing function would lose network connectivity consistently every 10-15mins for approx. 5-10mins.
I traced the mac address entry back to the core which consisted of a set of 6500 switches.
The ARP table on the core showed an Incomplete hardware address. This generally occurs for one of two reasons – the host doesn’t exist or the switch is receiving packets for that IP address on another interface.
To get this to work I had to set a static ARP entry on the core with the configured IP address and the hardware address for the VM load balancer.