client-backup-1.sk.eserver.net has no CNAME records.
Question and response
Question
dig client-backup-1.sk.eserver.net. NS
Answer
The response has no answer records.
Authority
sk.eserver.net. 1588 SOA ns1.eserver.net. hostmaster.eserver.sk. 2025102801 7200 3600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0