How to become gateway using a linux OS

From old notes..

Describe namran/how to become gateway here. sometime we have only one internet access but would like to have more than one device / computer/ laptop to share that same connection.

assume the one that will become gateway is a linux. kernel 2.6.* above.

enable ip forward. as root.

echo 1 > /proc/sys/net/ipv4/ip_forward

if want permanent change in /etc/sysctl.conf

and change the line that says net.ipv4.ip_forward = 0 to

net.ipv4.ip_forward = 1.

and..

using iptables ..

export OUT=ppp0
export IN=eth0
/sbin/iptables -t nat -A POSTROUTING -o $OUT -j MASQUERADE
/sbin/iptables -A FORWARD -i $OUT -o $IN -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -A FORWARD -i $IN -o $OUT -j ACCEPT

and from the other pc.. define the gateway ip.. as in eth0 in this case.

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