two different hypervisors. That is, <code>active</code> means that
this <ref column="external_ids" key="iface-id"/> is the active
instance within a single hypervisor, not in a broader scope.
+ There is one exception: some hypervisors support ``migration'' from a
+ given hypervisor to itself (most often for test purposes). During
+ such a ``migration,'' two instances of a single <ref
+ column="external_ids" key="iface-id"/> might both be briefly marked
+ <code>active</code> on a single hypervisor.
</p>
</column>