Local NS Matches Parent
Checks that the authoritative name servers and their parent have matching records.
When looking up a DNS record for a domain, the request starts with the Root DNS servers. There are 13 of these that are essentially hard coded into the internet. This initial query will almost certainly not get a complete answer because the Root DNS servers do not hold all the answers. Instead, they will look up the top level domain (TLD) and give you the next DNS server to ask. If we were to personify the Root DNS server, it would say something like "Oh, you are looking for a .org domain name? Go ask Chris, they are in charge of the .org domains."
With this referral, a new request is made. That may return an answer, or it may return another referral. Recursive requests are made in this manner until an authoritative answer is received.
This test will do the entire recursive DNS query until it finds an authoritative answer for the name servers for a domain. It will then compare this answer to the previous answer one level above it in the recursive chain. If the name servers do not match (parent does not match local), this test will indicate that there is a problem.