Ubuntu : Bonding interfaces eth1 eth2 eth3 into one logical bond0

Bonding interfaces 

 In the file /etc/network/interfaces 

 # Bonding 
up /sbin/modprobe -o bonding_ext1 bonding mode=4 miimon=500 updelay=0 xmit_hash_policy=layer3+4
up /sbin/ifenslave bond0 eth1 eth2 eth3

Checking if/which interfaces were bonded 
cat /proc/net/bonding/bond0