Apex domains cannot have CNAME records.
Question and response
Question
dig fwd.linkedin.com. NS
Answer
fwd.linkedin.com. 2 NS dns4.p09.nsone.net.
fwd.linkedin.com. 2 NS dns2.p09.nsone.net.
fwd.linkedin.com. 2 NS ns4-43.azure-dns.info.
fwd.linkedin.com. 2 NS ns2-43.azure-dns.net.
fwd.linkedin.com. 2 NS dns3.p09.nsone.net.
fwd.linkedin.com. 2 NS ns1-43.azure-dns.com.
fwd.linkedin.com. 2 NS dns1.p09.nsone.net.
fwd.linkedin.com. 2 NS ns3-43.azure-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0