linuxhost.iassys.com has no CNAME records.
Question and response
Question
dig linuxhost.iassys.com. NS
Answer
The response has no answer records.
Authority
iassys.com. 3352 SOA DNS101.REGISTER.com. root.REGISTER.com. 125080511 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0