iptables command

as you can see here
http://www.netfilter.org/documentation/HOWTO/netfilter-extensions-HOWTO-3.html#ss3.5

iplimit is not already implemented on the mayority of kernels. you should patch a kernel so you can have this math in iptables (it also requires you an up-to-date iptables)

here you have some info in how to compile extensions for iptables:
http://www.netfilter.org/documentation/HOWTO/netfilter-extensions-HOWTO.html

howver, I'm seeing that debian has this patch, so maybe you need to load the module in order to use it:
modprobe ipt_iplimit

if you get an error modprobing the module, then you do not have iplimit compiled in the kernel. if you get nothing but the command line again, then try your rule again =)

# somthing like:
iptables -I FORWARD -p tcp --dport 80 -d IP   --syn -m dstlimit --dstlimit-mode srcipdstip-dstport --dstlimit 1/sec -j ACCEPT
iptables -A FORWARD -p tcp --dport 80 -d IP ! --syn -j ACCEPT
iptables -A FORWARD -p tcp --dport 80 -d IP   --syn -j DROP
# allows an average of 1 syn/sec and max. 5 syns in a burst.

error:
iptables -I FORWARD -p tcp --dport 80 -d IP   --syn -m dst                                                                             limit --dstlimit-mode srcipdstip-dstport --dstlimit 1/sec -j ACCEPT
iptables v1.2.11: Couldn't load match `dstlimit':/lib/iptables/libipt_dstlimit.s                                                                             o: cannot open shared object file: No such file or directory

Try `iptables -h' or 'iptables --help' for more information.

try with haslimit insetad dstlimit, since is deprecated:
http://www.netfilter.org/patch-o-matic/pom-obsolete.html

of course, your linux distribution should have patch-o-match included (this includes a patched kernel) so you need to try and check if it works

if not, then add the patch-o-matic (need to read the documentation):
http://www.netfilter.org/patch-o-matic/

i'm running iptables v1.2.8
how can i fix for use this command?

thanks