[svandamme]

private adresses all have the same range, 192.168.1.x

this range never get's routed to other pc's , hence they can be used for Network Adress Translation

eg , you get one public adress from your isp 234.234.234.234 , and yoru router translates that to and from your pc's in the 192.168.1 range...

it's also a good security measure , since your pc's are not accessible to the internet, just your router is...

as for blocking ip adresses, that works as long as the ip adress of the offender doesn't change to often, like on dial up modem... in those cases mods can ban a complete range , such as 234.234.234.x , or even wider 234.234.x.x but that has the disadvantage of banning everybody on the same network as the offender...