Urgent: IP masquerading in Debian 3.0
 

Do I need to re-compile the kernel?
Or, the kernel is already support the IP masquerading?

apt-get install ipmasq did the trick for me.

iptables or ipchains?
 

I prefer to use iptables. I've found it to be much easier to use and more flexible than ipchains. It's quite easy to set up..

Download a 2.4 kernel and compile it.
Here are the relevant options using 2.4.21 from .config. I've put them in a link because they are too long to include here.

After you recompile (don't forget to include all your other options!), use these two commands:

echo 1 > /proc/sys/net/ipv4/ip_forward
/sbin/iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

Where eth1 is your EXTERNAL interface. You may need to look at your routing tables (route -n) to make it work correctly.

Note that this is a WIDE OPEN configuration and provides
NO security. Beware! See the IP tables howto for information on a more secure setup.

Hope that helps...