auto eth0
 iface eth0 inet dhcp
    bond-master bond0
    bond-primary wlan0
    bond-mode active-backup

 auto wlan0
 iface wlan0 inet dhcp
    wpa-conf /etc/network/wpa1.conf
    bond-master bond0
    bond-primary wlan0
    bond-mode active-backup

 auto wlan1
 iface wlan1 inet dhcp
    wpa-conf /etc/network/wpa1.conf
    bond-master bond0
    bond-primary wlan0
    bond-mode active-backup

 auto bond0
 iface bond0 inet dhcp
    bond-slaves none
    bond-give-a-chance 20
    bond-mode active-backup
    bond-miimon 100