This page shows you how to configure a Multi-homed Linux Box with 2 Network Interfaces to connect to the internet properly.
Step 1 – Update /etc/iproute2/rt_tables
echo 1 NET100 >> /etc/iproute2/rt_tables
echo 2 NET200 >> /etc/iproute2/rt_tables
Step 2 – Update the Routing Table
ip route add default via 192.168.100.1 dev eth1 table NET100
ip rule add from 192.168.100.0/24 table NET100
ip route add default via 192.168.200.1 dev eth0 table NET200
ip rule add from 192.168.200.0/24 table NET200