configuring linux system as router

echo 1 > /proc/sys/net/ipv4/ip_forward

/etc/sysctl.conf:

net.ipv4.ip_forward = 1

configure A for NAT

Now that we have a connection from A to B, we can tell A to share internet connection with B.

• Go to computer A and share its internet connection with B by typing the two commands :

modprobe iptable_nat
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth1 -j ACCEPT

Now you do a ping test from remote system

ping 8.8.8.8  [ should be working ]

then check ping www.google.com   [ if not working then check for /etc/resolve.conf ]

• Run this script on the host A :

#!/usr/bin/env bash
modprobe iptable_nat
echo 1 > /proc/sys/net/ipv4/ip_forward
ifconfig eth1 192.168.0.1 netmask 255.255.255.0
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth1 -j ACCEPT

• Run this script on the host B where xx.xx.xx.xx is your dns server :

#!/usr/bin/env bash
ifconfig eth0 down
ifconfig eth0 192.168.0.2 netmask 255.255.255.0
route del -net default 2>/dev/null
route add default gw 192.168.0.1 2>/dev/null
echo "nameserver xx.xx.xx.xx" > /etc/resolv.conf

few more links:

http://how-to.wikia.com/wiki/How_to_set_up_a_NAT_router_on_a_Linux-based_computer

http://martybugs.net/wireless/router.cgi

http://gohgarry.wordpress.com/2010/04/16/how-to-setup-linux-os-as-router/

http://forum.codecall.net/topic/48438-configuring-your-linux-server-as-a-router/#axzz2J0AHaM3O

http://glonek.co.uk/linux-router/basic-linux-router/