How to do NAT on my linuxbox

[capsmon]

I have done all the correct physical connection n setup the ip,subnet n gateway for my eth0 (to internet) n eth1 (to private network).

But i don't understand the iptables part.Can anyone guide me on the iptables part.

using Linux kernel 2.6.9-5.Elsmp...can anyone guide me on this.

[libregeek]

STEP 1:
Configure the two network interfaces according to the network
ifcfg-eth0
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.102.50
NETMASK=255.255.255.0
ifcfg-eth1:
DEVICE=eth1
ONBOOT=yes
BOOTPROTO=dhcp
HWADDR=00:E0:4D:02:60:30

STEP 2:
Enable the IPV4 Routing (both static and dynamic)
static :
Edit /etc/sysctl.conf
change "net.ipv4.ip_forward = 0" to "net.ipv4.ip_forward = 1"

Run the following command:
# echo 1 > /proc/sys/net/ipv4/ip_forward

STEP 3:
Configure the IP tables

3.1 Flush all the current rules:
# iptables -F -t nat

3.2 Set the Masquerading
# iptables -A POSTROUTING -t nat -o eth1 -j MASQUERADE

CAUTION :
The above set up doesn't uses any firewalls. If you need firewalls to be implemented then either visit www.netfilter.org or www.tldp.org.
other resources(preferred):
http://www.linuxforum.com/linux_tutorials/5/1.php
http://www.linuxforum.com/linux_tutorials/6/1.php

regards
libregeek

[capsmon]

According to your step 1,i have some confusion on it.Do i need to set an ip like 192.168.0.1 for the eth1 n eth1's gateway is equivalent to eth0's ip address? Do u have any comment on this?

[libregeek]

There is no need to give GATEWAY in the router configuration. You need the GATEWAY in the client's ifcfg-ethX file. Only thing is that yiou should enable IP forwarding in your linux machine