ns5.166.com has no CNAME records.
Question and response
Question
dig ns5.166.com. NS
Answer
The response has no answer records.
Authority
166.com. 6 SOA ns4.166.com. admin.166.com. 991188 36000 3000 3600000 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0