DNS/qname-minimisation/RFCについて、ここに記述してください。

https://tools.ietf.org/html/rfc7816  [[/Appendix A]]

3.  Possible Issues

Some broken name servers do not react properly to QTYPE=NS requests.

For instance, some authoritative name servers embedded in load balancers 
reply properly to A queries but send REFUSED to NS queries.

   This behaviour is a protocol violation, and there is no need to stop
   improving the DNS because of such behaviour.  
However, QNAME minimisation may still work with such domains,
   since they are only leaf domains (no need to send them NS requests).

Such a setup breaks more than just QNAME minimisation.
   It breaks negative answers, since
   the servers don't return the correct SOA, and it also breaks anything
   dependent upon NS and SOA records existing at the top of the zone.

Another way to deal with such incorrect name servers would be to try
   with QTYPE=A requests (A being chosen because it is the most common
   and hence a QTYPE that will always be accepted, while a QTYPE NS may
   ruffle the feathers of some middleboxes). 

Instead of querying name servers with a query "NS example.com",
   we could use "A _.example.com" and see if we get a referral.