(Should Be) Basic Networking Problem

[awakening]

Hi guys, im trying to setup a very basic network with both linux and windows machines. What i have is a server running debian linux with two nics and i want a cable from my modem (internet) to come in one and out of the other i want to be able to share my connection with a switch or hub to which other windows computers are connected. Heres a Diagram of what i want

(Internet)_________LINUX SERVER____________SWITCH_________WIN PC

WWW---------NIC1(ETH0)--NIC2(ETH1)---------SWITCH---------pc1 pc2 pc3

Any help on how i would set this up is appreciated as right now none of my windows pcs can access the internet.
THANKS A LOT FOR YOUR HELP!

[KenJackson]

You need to do three things on your Linux PC: 1) enable routing in the kernel, 2) setup iptables for network address translation or NAT, and 3) setup the routing table.

To enable routing, edit /etc/sysctl.conf and add or uncomment this line:

net.ipv4.ip_forward  = 1

That will set it up the next time you start up, but to enable it immediately, run this:

echo 1>/proc/sys/net/ip_forward

You need to select a local address range for your PCs. The most popular local address range seems to be 192.168.1.0/24. That is, the 254 IP addresses from 192.168.1.1 to 192.168.1.254.

Your Linux PC has two NICs so it will have two IP addresses. The one connected to the modem get's a real IP address assigned by your ISP. You must assign the other one--the one that connects to your local network. Traditionally, the gateway/server/router is assigned the lowest IP address in the range.

Setting up iptables will take some trial and error. It's best to read a little about setting up NAT. There is a lot of material available, including the documentation at netfilter.

Hang in there. It takes a little effort to get everything setup like you want, but it's fun, and doing it gives you very valuable insight into a lot of networking issues.