DNS check

Check that all defined nameservers for a domain do reply to queries for that domain. 

dom=example.com
rec=SOA

for serv in $(dig -t NS $dom +short); do
    echo $(dig @$serv -t $rec $dom +short) from $serv
done

or on one line: 

dom=example.com; rec=SOA; for serv in $(dig -t NS $dom +short); do echo $(dig @$serv -t $rec $dom +short) from $serv; done

Output for this example: 

outputelliott.ns.cloudflare.com. dns.cloudflare.com. 2397268091 10000 2400 604800 1800 from hera.ns.cloudflare.com.
elliott.ns.cloudflare.com. dns.cloudflare.com. 2397268091 10000 2400 604800 1800 from elliott.ns.cloudflare.com.

This can also be done, in a more comprehensive way, through various online services. For example: