/sbin/ip rule add from $IP1 lookup nic1
/sbin/ip rule add from $IP2 lookup nic2
/sbin/ip rule add from $IP3 lookup nic3

/sbin/ip rule add to $IP1 lookup nic1
/sbin/ip rule add to $IP2 lookup nic2
/sbin/ip rule add to $IP3 lookup nic3

/sbin/ip route flush table nic1
/sbin/ip route flush table nic2
/sbin/ip route flush table nic3

/sbin/ip route add $IP1 dev $IF1 scope link table nic1
/sbin/ip route add $IP2 dev $IF2 scope link table nic2
/sbin/ip route add $IP3 dev $IF3 scope link table nic3

/sbin/ip route add $NETMASK1 dev $IF1 proto kernel scope link src $IP1 table nic1
/sbin/ip route add $NETMASK2 dev $IF2 proto kernel scope link src $IP2 table nic2
/sbin/ip route add $NETMASK3 dev $IF3 proto kernel scope link src $IP3 table nic3

/sbin/ip route add default via $GATEYWAY1 dev $IF1 table nic1
/sbin/ip route add default via $GATEYWAY2 dev $IF2 table nic2
/sbin/ip route add default via $GATEYWAY3 dev $IF3 table nic3