Well you could get hold of the routing tables and filter out unallocated space. But thats not going to help much as there are still 64 low end bits to guess, so

Well you could get hold of the routing tables and filter out unallocated space. But thats not going to help much as there are still 64 low end bits to guess, some people use xxx::1 and ::2 but others use mac address based IPs (and random ones). So we are probably at the best point to portscan before the possibility goes away again...