ns.plsspb.ru has no CNAME records.
Question and response
Question
dig ns.plsspb.ru. NS
Answer
The response has no answer records.
Authority
plsspb.ru. 10800 SOA plsspb.ru. admin.plsspb.ru. 20 604800 86400 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0