#!/bin/bash

# enable packet forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward

# create the routing tables
TABLE1="T1"
TABLE2="T2"

echo "201 $TABLE1" >> /etc/iproute2/rt_tables
echo "202 $TABLE2" >> /etc/iproute2/rt_tables

# establish default gateways for the tables
DEV1="eth1"
DEV2="eth2"
GW1="192.168.1.1"
GW2="192.168.2.1"

ip route add default via $GW1 dev $DEV1 table $TABLE1
ip route add default via $GW2 dev $DEV2 table $TABLE2

# redirect marked packets to the tables
ip rule add fwmark 0x1 table $TABLE1
ip rule add fwmark 0x2 table $TABLE2

# mark packets before routing
iptables -t mangle -A PREROUTING -s 192.168.3.2 -j MARK --set-mark 0x1
iptables -t mangle -A PREROUTING -s 192.168.3.3 -j MARK --set-mark 0x2

# enable NAT for outgoing packets (tcp/udp/icmp)
iptables -t nat -o $DEV1 -A POSTROUTING -p tcp -j MASQUERADE
iptables -t nat -o $DEV2 -A POSTROUTING -p tcp -j MASQUERADE
iptables -t nat -o $DEV1 -A POSTROUTING -p udp -j MASQUERADE
iptables -t nat -o $DEV2 -A POSTROUTING -p udp -j MASQUERADE
iptables -t nat -o $DEV1 -A POSTROUTING -p icmp -j MASQUERADE
iptables -t nat -o $DEV2 -A POSTROUTING -p icmp -j MASQUERADE