20 Aug 09 Linux NAT Masquerading HOWTO

Here’s a really quick rundown on setting up masquerading. You’d use this to share one internet connection between multiple local network machines. It’s what most regular ‘routers’ that your ISP sends out do and it’s really easy to set up under Linux in it’s most simplest form

modprobe ipt_MASQUERADE
iptables -F; iptables -t nat -F; iptables -t mangle -F
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward

eth0 should be your external interface. You can use ppp0 or any other registed netwrk interface. For security you might want to stop anything in the forward chain except that originating from your own local network, e.g.:

iptables -P FORWARD DROP
iptables -A FORWARD -s 192.168.1.0/24 -j ACCEPT

Tags: iptables, ip_forward, Linux, masquerade, masquerading, modprobe, nat, postrouting

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