DNS/delegation/親子でのNSレコードを一致させるについて、ここに記述してください。

DNS/RFC/1034/4.2#A13 より

As the last installation step, the delegation NS RRs and glue RRs
necessary to make the delegation effective should be added to the parent zone. 
The administrators of both zones should insure that the NS and
glue RRs which mark both sides of the cut are consistent and remain so.