"Your nameservers are on the same Class C IP range"

[Fli]

Hello, i got message "Your nameservers are on the same Class C IP range. This is very bad if you want to be found in the case of outage, or even worst, problems!" from this domain checker: http://www.dnsqueries.com/en/domain_check.php

Im curious how one can have nameservers with different C class IP, meaning in another GEO location? It means i need to somehow mirror/sync one webserver with another? It sounds difficult..