The adsl-router is connected direct to the externel device (eth1) of the server. The internel device (eth0) is connect to a switch. The same configuration was running on an ohter server with SuSE Linux 7.0 (Kernel 2.2) and SuSEfirewall1.

do you have a routerdaemon up and running, listening and shouting on udp-port 520? ('netstat -anp | grep 0.0.0.0:520') if so, you can either configure your routerdaemon not to shout on both interfaces or you disable the logging of these messages. regards, stefan