In NXDOMAIN attacks, hackers overwhelm a target DNS server with invalid DNS record requests. DNS resolvers suffer the most from NXDOMAIN attacks.
In NXDOMAIN attacks, hackers try to engage authoritative DNS servers and DNS proxy servers with invalid requests. At a big enough scale, such a cyberattack generates NXDOMAIN error responses and the DNS server experiences latency issues. In the end, the sheer amount of invalid requests sent to the target DNS server leads to significant performance issues. The DNS requests themselves point to non-existing domains, which also causes problems like DNS recursion.