i woudl like to say, as politely as i know how, that a NAT TABLE of 400 entries is INSANELY small...
Having done tech support for an ISP, i can tell You from FIRST hand knowledge/experience...
We CONSTANTLY get calls from people who are "DOWN" (think they are), and ALWAYS assume their ISP is the problem...
Just ONE web browser open to Facebook, running FARMVILLE can open OVER 1000 connections. Now imagine a family of people, Mom, Dad, 2 kids (or more), all trying to play farmville?? 4000+ NAT TABLE entries...
and ISP have to do all of the router manufacturers tech support for them...
and when we refer them to the router manufacturer, the router manufacturers, deny their router's are at fault... they try to CHARGE their customers MONEY to help them... then the tech support at the router manufg. doesn't even help them solve their problem... they just blame the isp... at the ISP we can see what's happening...
It might sound ridiculous, but modern routers need to support MANY MANY MANY more times the number of NAT table entries... either that, or give the end user access to setting the timeout on the connections to a much lower time interval...