isdn router does not work any more with dynamic IP

Hi together,

in the past I set up a little ISDN Router with 2 passiv ISDN Cards based on KNOPPIX 3.4.
Everything worked fine till last Friday. After a reboot there ist the following situation.
All dynamic IP connections get the ip Adress from eth0. The connection is there and stabel, but based on this IP the partner does not accept the packages from the private network (192.168.30.0).
Has any body an idea what goes wron her now?
By the way, the one connection with a static IP works still fine.