Apex domains cannot have CNAME records.
Question and response
Question
dig 092.209.pools.vodafone-ip.de. NS
Answer
092.209.pools.vodafone-ip.de. 5 NS ns3.arcor-ip.de.
092.209.pools.vodafone-ip.de. 5 NS ns2.arcor-ip.de.
092.209.pools.vodafone-ip.de. 5 NS ns1.arcor-ip.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0