For this tutorial, we are using a modern linux os with IPTables, on a computer with two ethernet cards.
All commands run should be done with root privs
[The Phyical Setup]Connect to the first ethernet card (eth0) the line that gets this computer connected to the internet.
Connect to the second ethernet card (eth1) to a hub/switch
Connect all clients to be NAT'ed to the hub/switch.
Logical Setup The NAT'ed network will be 192.168.0.0/24
And the NAT'ing computer will be 192.168.0.1 on eth1
On the NAT'ing computer:
ifconfig eth1 192.168.0.1 netmask 255.255.255.0 Enabling IP Forwarding in the KernelCheck and see if your computer is already doing forwarding with:
sysctl net.ipv4.ip_forward If what it returns is 0, its off
if what it return is 1 then its already enabled.
Turn it on now by running:
sysctl -w net.ipv4.ip_forward=1and to enable it at boot, add this line to your /etc/sysctl.conf:
net.ipv4.ip_forward = 1 Now restart your networking:
/etc/init.d/networking restart Forwarding Rules in IPTablesCODE
iptables -A FORWARD -i eth1 -o eth0 -s 192.168.0.0/24 -m state --state NEW -j ACCEPT
iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A POSTROUTING -t nat -j MASQUERADE
Finally setup you clients to have a 192.168.0.0/24 address, with the gateway as 192.168.0.1
Setting Up NAT, Network Address Translation
9 Aug, 2006 - 09:27 AM
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