Problem: Bridge Interface Disconnected after Update

Problem

After an Update the bridged interface got disconnected. No virtual machine (VM) has any network connection.

$ brctl show
bridge name     bridge id               STP enabled     interfaces
br0             8000.000f3d57bde7       no

Solution

Re-attach the bridge interface to the correct main interfaces.

$ brctl addif br0 vnet0
$ brctl show
bridge name     bridge id               STP enabled     interfaces
br0             8000.000f3d57bde7       no              vnet0