Apex domains cannot have CNAME records.
Question and response
Question
dig colo.transip.net. NS
Answer
colo.transip.net. 5 NS ptr0.transip.nl.
colo.transip.net. 5 NS ptr2.transip.nl.
colo.transip.net. 5 NS ptr1.transip.nl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0