unwanted dial-out

[Caspar von Seckendorff]

Hi,

I am using a Linux Unix system as my gateway to the internet. When a user requests information from the internet it auomatically establishes an ISDN connection to the ISP. Now there some computers that should'nt be allowed to use the internet. So I installed a firewall with masquerading excluding these IP-numbers.
You cannot access the Interenet from these machines, but when there is a request from one of these computers my gateway still estalishes an ISDN connection.
Why is that?

		Caspar