CA                                        MA
          |---------------|                         |--------------|
(LAN)-eth0| ---  br0 ---  |tap0  <----------->  tap0| --- br0 ---  |eth0-(LAN)
          | 10.12.12.x/22 |                         | 10.12.12.1/22|
          |---------------|                         |--------------|

          br0 == (eth0 + tap0), on each side