ns.second-ns.com has no CNAME records.
Question and response
Question
dig ns.second-ns.com. NS
Answer
The response has no answer records.
Authority
second-ns.com. 1422 SOA ns1.your-server.de. postmaster.your-server.de. 2025120200 86400 10800 3600000 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0