root 11:45:18 : ~ # cat /etc/network/interfaces
auto lo
iface lo inet loopback

# Network to Test-Desktop, TFTP/NFS
auto eth0
iface eth0 inet static
        address 172.21.0.31
        netmask 255.255.255.0
        gateway 172.21.0.1

# Network per USB-to-Ethernet HUB
auto eth1
iface eth1 inet static
        address 192.168.0.31
        netmask 255.255.255.0
        gateway 192.168.0.1

# Network per USB-to-WLAN
hotplug wlan0
iface wlan0 inet static
        address 152.21.0.31
        netmask 255.255.255.0
        broadcast 152.21.0.255
        up systemctl start wlan.target
        down systemctl stop wlan.target