RHEL6: Can't communicate between guest VMs using ixgbe Virtual Function and guest VMs using a bridge

Issue

• A RHEL host contains (at least) two KVM guests
  • guest0 uses an SR-IOV Virtual Function of an Intel NIC (ixgbe driver) via PCI passthrough
  • guest1 uses a virtio or emulated NIC, bridged via br0 to the Intel NIC's Physical Function
• Both guest0 and guest1 can communicate with with hosts elsewhere on the physical network, but cannot communicate with each other