How to block fragmented UDP packets

Thanks google i read that using u32 module i can stop fragmented udp
packets. I have router with nat and conntrack and I cannot manage
bandwidth of these packets so I decided to cut them.
I found the rule:
iptables -m u32 --u32 "3&0x20=0x20"
or
|iptables -m u32 --u32 "3&0x20>>5=1"
or
||"4&0x3FFF=1:0x3FFF"
but none works.
I have to add that these packets cannot be clasified using HTB rules
and filters.

Hello,

(E-Mail Removed) a écrit :
> Thanks google i read that using u32 module i can stop fragmented udp
> packets. I have router with nat and conntrack and I cannot manage
> bandwidth of these packets so I decided to cut them.

Conntrack does reassembly before the packet enters the PREROUTING
chains, so fragmentation should not be a problem. Packets may be
fragmented again after the FORWARD chains when the packet size is bigger
than the output interface MTU and reassembled again before the
nat/POSTROUTING chain (NAT needs to work on complete IP datagrams), so
you will see fragments only in the mangle/POSTROUTING chain.

> I found the rule:
> iptables -m u32 --u32 "3&0x20=0x20"
> or
> |iptables -m u32 --u32 "3&0x20>>5=1"
> or
> ||"4&0x3FFF=1:0x3FFF"
> but none works.

These are not valid iptables commands : no command, no chain.