How To Masquerade On Linux (Internet Connection Sharing)  

It's very simple to masquerade (internet connection sharing in Windows language ) on Linux with a few lines of iptables and ip_forward commands.

First of all you have to flush and delete existing firewall rules.

So flush rules by typing in terminal:

iptables -F
iptables -t nat -F
iptables -t mangle -F

Now delete these chains:

iptables -X
iptables -t nat -X
iptables -t mangle -X

Now it's time to save the iptables rules so type:

service iptables save
service iptables restart

Now all rules and chains have been cleared!

Check it in /etc/sysconfig/iptables which has all default rules set to accept.

Now open /etc/rc.d/rc.local and insert the line:

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

And then save and close the file.

Now asuming that your internet interface is eth0, type:

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
service iptables save
service iptables restart

Note: check if iptables is set to start during boot up.

Or check the status of your iptables service:

chkconfig –list iptables

If level 5 is on then it's ok othewise start the service at level 5 or level 2345.

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