Cache Poisoning
Cache Poisoning is the insertion of false data into recursive Name Server, which remember previous lookups.
Overview
The attacker sends fake DNS answers in response to a query and tricks it into thinking the wrong data is correct for a given domain. The server remembers the wrong answer in its cache and provides that wrong answer in future lookups.[1]
History
Mitigation
Use a randomized source port to reduce the risk of a cache poisoning attack instead of using the same source port number for every DNS query.