network performance problems with SuSEfirewall2 and multiple interfaces

Hi everyone, I've a machine with 3 real and 15 virtual interfaces under SuSE 9.0 with SuSEfirewall2. Resulting from this I've also a lot of iptable-rules (iptables-save | wc -l gives me 1068 lines). After some weeks the machine slows down network-traffic, although everything else seems to run quite well (low CPU-load, low memory-usage), so I have to reboot it (restarting SuSEfirewall2 does not help). I wounder if anybody else has experienced something similar, if anything of that kind is known and if anybody has an idea, where the problem may lay. Greetings, Ralf