Apex domains cannot have CNAME records.
Question and response
Question
dig 25.130.45.rev.airmob.eu. NS
Answer
25.130.45.rev.airmob.eu. 5 NS rdns1.airmob.eu.
25.130.45.rev.airmob.eu. 5 NS rdns2.airmob.eu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0