a23.verisigndns.com has no CNAME records.
Question and response
Question
dig a23.verisigndns.com. NS
Answer
The response has no answer records.
Authority
verisigndns.com. 15339 SOA av1.nstld.com. dnssupport.verisign-grs.com. 1772756367 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0