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Notice you will require two NICs (Network Interface Cards) for the computer acting as a NAT (Network Address Translation) router. The first NIC will connect your Cable/DSL modem to your Linux box, and the second would connect to a HUB or another computer on your LAN.
On your Linux computer, you will need to set up the two NICs, that is, load the drivers/modules, configure the IP address if necessary.
First, enable IP forwarding. This can be done when compiling the kernel or through sysctl. To do so through sysctl type:
echo 1 > /proc/sys/net/ipv4/ip_forwardNow for those using Linux 2.0.x kernels or ipfwadm use:
/sbin/ipfwadm -F -p denyFor those using Linux 2.2.x kernels or ipchains use:
/sbin/ipchains -P forward DENYAdditional information about IPFWADM or IPChains can be found here.
For those using 2.4.x or Netfilter/iptables use:
/sbin/iptables -P FORWARD DROPMore information about Netfilter/IPTables can be found here.