Ubuntu eth0 unable to ping rtnetlink answers: file exists

Hot fix Ubuntu RTNETLINK anwers: File Exists or unable to ping.

1. disable default gateway on eth1 (make sure only 1 gateway)
   check /etc/network/interfaces
2. check route list
   route -n
   ip route
3. make sure default route through gateway IP
4. delete current default if its wrong route (should be via gateway IP NIC)
   ip route del default
   ip route add default via <ip gateway> dev <default nic>