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If you are seen duplicated packets it is because you are a loop in the network, and if you are running openstack on VM, it is most likely that the loop is a software generated, not in you physical network. When you send a brodcast packet (arp/dhcp), the packet get restransmited over all ports, physical and virtual. In VMware i had to set the vswitch ports to use promiscous mode for the VM, with two uplink. The second uplink generate a loop just for broadcast packets. This generates update in the bridge/mac/portID table, wich you dont wont. Example: if you follow the broadcast packet (tcpdump -i at every involved interface, bridge and tap), you will see it first in the TAP/PortID=1, then at the Bridge going out, then it will enter again the same packet, so the bridge will assoiate the MAC to the PortID2, then you will see the actual reply wich will be redirected to PortID2, and your VM was on PortID1.

On the next brodcast it will repeat, so your VM MAC will be jumping from portID1 to 2. As the packets flow, but it will never gets to the VM, because at that moment, the MAC will be associated to the wrong port.

Check the vswitch, it has to has only one external port.

Another way to check, is by ussing the command brctl showmac (ml2)

hope it helps