Just to say,
We ( an ISP among others ;) )are now running a Linux Box with IPNat and Masquerading. Thanks to it, we can masquerade all our network connexions for people to access the Net, and translate some IPs from out private network to public IPs ( needed for some Mail servers ). The box is actually the *head* of our privates networks. It supports about 20 privates networks, with 19 translated IPs. Before using IPNat/Linux we used a DOS tool called ipnat, I've got to say the network speed has now increased about 40%.
The configuration is :
A K6-2 / 350 machine 3 ethernet ( 10/100 ) cards ( one for each network ) Linux 2.0.36 kernel patched whith IPchains & IPnat
Thanks for all people !