ns4.eserver.net has no CNAME records.
Question and response
Question
dig ns4.eserver.net. NS
Answer
The response has no answer records.
Authority
eserver.net. 962 SOA ns1.eserver.net. hostmaster.eserver.sk. 2026012901 7200 3600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0