cleanup () {
    for br in $(sudo ovs-vsctl list-br); do
        sudo ovs-vsctl del-br $br
    done
    IFS=$'\n';
    for i in  $(sudo ip netns list); do

        NS=$(echo $i | cut -d ' ' -f1)
        sudo ip netns delete $NS;
        # Sometimes the veth-$NS is not deleted.
        sudo ip link delete veth-$NS;
    done
}
