Linux network /etc/network/interfaces file to bond eth0 and wlan0 into one virtual interface bond0

interfaces

# Regardless of how our topology looks, we'll need the local interface
auto lo
iface lo inet loopback 

# Configuration basics taken from:
#   http://www.kernel.org/doc/Documentation/networking/bonding.txt
# Define the bonding master, which is ideally our only interface to the outside world
# - define slaves as none initially, this helps with booting faster
# - the primary line makes most sense here, but is not enough
# - set the interface check interval to 100ms
# - we activate 1 interface at a time for now, if one fails, the other takes over
auto bond0
iface bond0 inet dhcp
      bond-slaves none
      bond-mode active-backup
      bond-primary eth0
      bond-miimon 100

# Slave: wired ethernet connection port, typically our office connection
# - critical that the type is set to 'manual'
# - typically wired is the fasted connection, so make this the primary
# - the primary line seems redundant but is needed here
auto eth0
iface eth0 inet manual
       bond-master bond0
       bond-primary eth0

# Slave: the wireless connection interface
# - critical that the type is set to 'manual'
# - interface roams under control of wpa_supplicant
# - the primary line seems redundant but is needed here
# -  
# - tell the interface that packets come in over bond0 instead of wlan0
# - the wpa conf file contains network definitions and other settings.
auto wlan0
allow-hotplug wlan0
iface wlan0 inet manual
      bond-master bond0
      bond-give-a-chance 10
      bond-primary eth0
      wpa-bridge bond0
      wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

# TODO: configure the WAN interface as slave
# TODO: configure the Bluetooth interface as slave
# TODO: why use active-backup when we could combine interfaces and gain some speed if we can.