Apex domains cannot have CNAME records.
Question and response
Question
dig de.colt.net. NS
Answer
de.colt.net. 5 NS ns1.de.colt.net.
de.colt.net. 5 NS ns0.de.colt.net.
Authority
The response has no authority records.
Additional
ns0.de.colt.net. 5 A 212.74.78.55
ns1.de.colt.net. 5 A 212.74.77.55
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0