91 has no CNAME records.
Question and response
Question
dig 91. NS
Answer
The response has no answer records.
Authority
. 85379 SOA a.root-servers.net. nstld.verisign-grs.com. 2026030301 1800 900 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0