Hi, I'm trying to write an Online Firewall creator but I have one problem.

This will fix Masq and Forwarding

echo '1'> /proc/sys/net/ipv4/ip_forward
/sbin/iptables --table nat --append POSTROUTING -o eth1 -j MASQUERADE
/sbin/iptables --append FORWARD --in-interface eth0 -j ACCEPT


But problem is that anything from eth1(LAN) will be accepted
out to Internet.

I want to enable Masq and Forwarding AND by default deny everything from eth1.

And then I want to open upp some selected ports, udp and tcp.

I have been reading some docs but can't figure it out

Does anyone have a clue ?

Set your default policy on the forward chain to DROP - then you'll have to specifically allow any forwarding, as in your 3rd line