[CentOS-virt] Network failure on KVM guest

I set up a KVM host a few months back with eight virtual machines running on it. Now, at least since yesterday, one of the guests (which apart from the MAC address is otherwise identical to six other guests) has lost its network connection. The other seven vms work fine.

More bizarre, even rekickstarting does not work due to this issue. I suspect some issue on the host, but don't really have an idea what to check.

Host and virtual machines all run CentOS6.3 plus all patches. The issue persists through a host reboot.