FAQ's

route del default

route add -net 0.0.0.0 netmask 0.0.0.0 gw 192.168.0.1 dev eth0 metric 100
route add -net 0.0.0.0 netmask 0.0.0.0 gw 192.168.10.1 dev eth1 metric 200
route add -net 0.0.0.0 netmask 0.0.0.0 gw 192.168.20.1 dev eth2 metric 300

ip route add default scope global nexthop via 192.168.0.1 dev eth0 weight 1 nexthop via 192.168.10.1 dev eth1 weight 2 nexthop via 192.168.20.1 dev eth2 weight 3

ip route flush cache

ping -I eth0 www.google.es
ping -I eth1 www.google.es
ping -I eth2 www.google.es