To reduce the load on root nameservers caused by the reverse DNS lookups of these IP addresses , a system of `` black-hole '' nameservers is provided by anycast network AS112 . Private networks often do not properly configure DNS services for addresses used internally and attempt reverse DNS lookups for these addresses , causing extra traffic to the Internet root nameservers . The AS112 project attempted to mitigate this load by providing special blackhole anycast nameservers for private address ranges which only return negative result codes ( not found ) for these queries .