IDS can't detect fragmented packet and passed firewall

[ehsanaskari]

hello all,
i'd configured IDS and enabled it. also download rules and adding some rules for IP Flag protocol. unfortunately, packet with ip.flags=0x04(Reserved), ip.flags=0x02(Don't fragment), ip.flags=0x01(More fragments)  passed firewall and i receive it. 
would i ask you to help me?  actually, need to specific configurations?
thanks