why can't use connlimit ??

[Buddy wu <ejournal4me@gmail.com>]

   I want to use connlimit to set the connections of each person to a
certain number, but when I add a rule using iptables, error occured
like these:

[root@server1 linux]# /sbin/iptables -A INPUT -m connlimit
--connlimit-above 6 -j DROP
iptables: No chain/target/match by that name

   I have searched for this problem, someone said it maybe need to
load the ipt_connlimit module. I tried it, but it can not work. I
doubted that I have the wrong command.
   first I use '/sbin/modprobe ipt_connlimit' command ,and then I
reaceive the error 'FATAL: Module ipt_connlimit not found.'
   second, I use '/sbin/modprobe /lib/iptables/libipt_connlimit.so'
and then error comes again 'FATAL: Module
/lib/iptables/libipt_connlimit.so not found.'

   How to make it work ? I'm almost mad

Thank for your advise