That brings the picture clearer.
There is NO WAY you want your NAS boxes sitting on a public IP address! Most of the time, multiple public IP addresses don't have file sharing capability between them anyway, not that anyone in their right mind would enable it if they did! That would be a security hole that you can drive a tractor trailer through!
I suspect you need to rethink the whole network topology, it sounds like somewhat of a kludge right now. It also sounds like security is nonexistent. I think a network diagram would probably be a good start to understanding exactly what you have now.
If you'd like to discuss this further, I'd suggest a more appropriate location. I spend a lot of time at www.techguy.org, and we have some crackerjack networking folks in our Network forums. I don't see the support forums for the DNS-323 as the ideal location.
