Apex domains cannot have CNAME records.
Question and response
Question
dig ROUTER-OPEN.ru. NS
Answer
ROUTER-OPEN.ru. 5 NS ns1.vps1.net.
ROUTER-OPEN.ru. 5 NS ns2.vps1.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0