Believe me, i've been searching not only through this Forum, but also on the net (thanks for the link by the way - looks like i could learn a lot there).
I can see that this issue has been discussed before, but i'm afraid to say that i don't understand much of it.
Now - when i open the file /etc/init.d/masq, i get a LOT of information, all of it about ipchains. I don't feel i have any chance to guess where to edit the file. Another thing is, that the document starts with the text:
DO NOT MODIFY THIS FILE! It is updated automatically by the e-smith server and gateway software. Instead, modify the source template in the /etc/e-smith/templates directory.
...ok - a newbee like me get VERY nervous when i see this message, and to browse into /etc/e-smith/templates doesn't make me more comfortable.
I'm the first to admit it - i have a loooong way to go before i will be known as a Linux-geek, but i wish deeply that i could understand just a bit about this ipchains and port handeling.