Name server poisoning also happened occasionally on accident, due to responding accidently with an incremented query id, possibly poisoning some later random request. Also, if a DNS has DNS level blocking taking place, and it is treated like an authoritative DNS server in https://www.theemailshop.co.uk/secured-server-colocation/ it may 'black hole' your request. As in, send you an IP that is invalid and leads no where. This happened to google servers a while back when they accidentally had china servers listed as authoritative, which was causing global traffic to get black holed due to china censorship.
Name server poisoning also happened occasionally on accident, due to responding accidently with an incremented query id, possibly poisoning some later random request. Also, if a DNS has DNS level blocking taking place, and it is treated like an authoritative DNS server in https://www.theemailshop.co.uk/secured-server-colocation/ it may 'black hole' your request. As in, send you an IP that is invalid and leads no where. This happened to google servers a while back when they accidentally had china servers listed as authoritative, which was causing global traffic to get black holed due to china censorship.