cat /etc/network/interfaces
auto lo
iface lo inet loopback

# The primary network interface
auto em1.100
iface em1.100 inet static
    address 192.168.42.11
    netmask 255.255.255.240
    gateway 192.168.42.1
    dns-nameservers 8.8.8.8 8.8.4.4
    dns-domain lab.example.org

# Public network
auto cloudbr0
iface cloudbr0 inet manual
    bridge_ports em1.200
    bridge_fd 5
    bridge_stp off
    bridge_maxwait 1

# Private network
auto cloudbr1
iface cloudbr1 inet manual
    bridge_ports em1.300
    bridge_fd 5
    bridge_stp off
    bridge_maxwait 1

reboot  ==> then lost network connection.