I guess i already found it
fe-0/0/7 { flexible-vlan-tagging; native-vlan-id 1; unit 0 { vlan-id 1; family inet { address 192.168.0.254/24; } } unit 30 { vlan-id 30; family inet { address 192.168.30.1/24; } } }
Because i set the native-vlan-id to 1 i guess this vlan is accessible from any vlan even if it has no vlan tag