citadel.verisign.net has no NS records.
NS records for this zone are defined at verisign.net.
NS records for this zone are defined at verisign.net.
Question and response
Question
dig citadel.verisign.net. NS
Answer
The response has no answer records.
Authority
verisign.net. 86400 SOA av1.nstld.com. mdnshelp.verisign.com. 1773533959 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0