istanbul.ns.korpcloud.com has no CNAME records.
Question and response
Question
dig istanbul.ns.korpcloud.com. NS
Answer
The response has no answer records.
Authority
korpcloud.com. 1555 SOA aarav.ns.cloudflare.com. dns.cloudflare.com. 2398427516 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0