ok I am missing something here. On MX4300 I have:
native-vlan-id 10;
unit 0 {
family ethernet-switching {
interface-mode trunk;
vlan {
members all;
}
on MX port I have: type trunk ; native vlan 10; allowed vlans 10
This kills my whole network ..... 
}
}
EX4300 v10 = 192.168.168.2/24 and v10 on MX = 192.168.168.1/24
This look like a STP loop becase I use this as second connection bewteen EX4300 and MX. I am doing something wrong here.