Apex domains cannot have CNAME records.
Question and response
Question
dig 80-87.76.111.217.in-addr.arpa. NS
Answer
80-87.76.111.217.in-addr.arpa. 5 NS ns8.colt.net.
80-87.76.111.217.in-addr.arpa. 5 NS ns2.syzygy.de.
Authority
The response has no authority records.
Additional
ns2.syzygy.de. 5 A 46.28.184.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0