When configuring an application that creates vlans by using
vconfig add, I discovered that it was adding a vlan device to something that was already a vlan device. Effectively, what happened was:
# vconfig add bond0 168 ... # vconfig add bond0.168 100
The vlan100 interface was then attached to a bridge which connects to a KVM instance:
# brctl addbr br100 ... # brctl addif br100 vlan100
Here's what the bridges look like:
# brctl show bridge name bridge id STP enabled interfaces br100 8000.02163e4fc8db no vlan100 vnet0 virbr0 8000.000000000000 yes
Oddly enough, everything seemed to work, I was able to ssh to my KVM instance.
What happens when you add a vlan-device to an interface that is already a vlan device? In particular, what VLAN tag do the ethernet frames have that go to the VM instance?