WARNING: Not all of your nameservers are in different subnets

[Fli]

IntoDNS (http://www.intodns.com) tells me that my domain is pointed to nameservers in one IP subnet which is bad:

WARNING: Not all of your nameservers are in different subnets
WARNING: Single point of failure


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What does it mean? In my case my domain has these nameservers:

ns1.mydomain.tld -> 1.2.3.4
ns2.mydomain.tld -> 1.2.3.4

so it points to same IP which is bad, we need some redundancy i assume, so ns2 should point to some IP of server located in different city/country.

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What do You please suggest is the easiest way to create DNS record on some Linux server (so the server serving as an DNS)?

mydomain, ns2 (6.7.8.9) -> DNS record pointing to example: 6.5.4.3 (hosting server)
mydomain, ns1 (1.2.3.4) -> DNS record pointing to example: 6.5.4.3 (hosting server)

[24x7cloudservermanagement]

Not all of your nameservers are in different subnets -- this is a general error when you create private name servers on a same server.
the error tells you are in same subnet that means , if you have additional IPs assigned to your server e.g. 1.2.3.4 and 1.2.3.5 then 1.2.3 is the same subnet and you are using the same subnet for name servers and hence the error.

[Fli]

i already know that. i as a Linux newbie rather asking for help/solution on how to fix this in a clever way easily