Protection for Lame Delegation (Dangling NS records)

a cat of MEXT 
   bousai.mext.go.jp.	300 IN NS ns-173.awsdns-21.com.
   bousai.mext.go.jp.	300 IN NS ns-686.awsdns-21.net.
   bousai.mext.go.jp.	300 IN NS ns-1407.awsdns-47.org.
   bousai.mext.go.jp.	300 IN NS ns-1711.awsdns-21.co.uk.

from Jan 12 3:00 by tss @ suzuki.sist.chukyo-u.ac.jp