Snort deadly quiet in the firewall.

["SW" <samwun () onebb net>]

Hello,

I install snort in a network with static public IP connected to the internet, it logged all scanned and frag packet.
But when snort installed in anotehr network on a dynamic public IP address, it goes silent, but sometimes do log some 
packet. It failed to log Frag attack, and all sort of scans. The logged packet are those like WEB-CGI, etc..
I launched the same attack on both network, but the snort with static IP does log the packet, while the snort with 
dynamic IP doesn't log the packet.

Does anyone know how to track down the problem? I am using OpenBSD 3.1 Current.

Thanks
Sam