Once even sometimes three times per day, one of our guests loses network connections. Our ping responds with "Host unreachable", even from the dom host. I am running an Essex environment in VLAN mode. For some reason, my instance cannot renew its IP address/lease and the dhclient fails. This issue is definitely not traffic or load related because nothing is running. We have a dedicated nova network GW, KVM and we are running on OS Ubuntu 12.04.