Apex domains cannot have CNAME records.
Question and response
Question
dig gpool.oss-core.net. NS
Answer
gpool.oss-core.net. 5 NS melcoregtm01.gpool.oss-core.net.
gpool.oss-core.net. 5 NS sydcoregtm01.gpool.oss-core.net.
Authority
The response has no authority records.
Additional
melcoregtm01.gpool.oss-core.net. 5 A 203.134.65.68
sydcoregtm01.gpool.oss-core.net. 5 A 203.134.64.68
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0