enabling ip_forward, slow my network rate

[Manuel Mely <mmelyp@gmail.com>]

Hi,

After some years using iptables as a firewall, i never have seen this. 
If i enable ip_forward, my download rate is ~865Kbits (on a 100Mbit 
Ethernet enviroment), if i disable ip_forward i get ~10Mbits.
Unloading iptables rules doesn't change the sympthoms.