Interesting trace down to stale ARP entries. It gets worse when the switches are running mac address filtering and they get out of date. We had that issue with some Blade G8052 top of rack switches with their upstream 10G ports. They sometimes "forget" which upstream port has the MAC address that they are switching too, and those packets just spew out messily into the data center leaving a mess. The "fix" it to force the switch to ping up through a specific upstream port periodically to the center switch's management IP address. Sigh.