NS record mr1.mydomain.com. cannot be resolved to an IP address

Virtualmin
1

Hi,
Centos 7, I installed virtualmin. I have only one NS server.
I create virtual server and everything is ok.
When I create another server as mydomain2.com in DNS record I get
Warning - errors were found in this domain’s DNS records : NS record mr1.mydomain.com. cannot be resolved to an IP address

$ttl
Default Cache Time 38400

mydomain2.com SOA - Start Of Domain mr1.mydomain.com. root.mr1.mydomain.com. 1482925093 10800 3600 604800 38400

mydomain2.com
NS - Name Server mr1.mydomain.com.

mydomain2.com
NS - Name Server ns2.mydomain.com.

mydomain2.com
A - IPv4 Address 172.20.15.83

www
A - IPv4 Address 172.20.15.83

ftp
A - IPv4 Address 172.20.15.83

m
A - IPv4 Address 172.20.15.83

localhost
A - IPv4 Address 127.0.0.1

mail
A - IPv4 Address 172.20.15.83

mydomain2.com SPF - Sender Permitted From v=spf1 a mx a:mydomain2.com ip4:172.20.15.83 ?all
2

If DNS is hosted on your server it means you are missing A/NS records for your nameserver(s).

Zone file example:
@ IN NS ns1.domain.com.
@ IN NS ns2.domain.com.
ns1.domain.com. IN A xxx.xxx.xxx.xxx
ns2.domain.com. IN A xxx.xxx.xxx.xxx

3

I have the same issue. What is this file and location?
/etc/hosts ?
/etc/resolv.conf ?
/var/named/domain.tld.hosts ?