Some of my domains run using two different IPs for each ns property in their DNS records, e.g.:
ns1.example-1.com 18.104.22.168 ns2.example-1.com 22.214.171.124
and some of my domains have the same IP for all, e.g.:
ns1.example-2.com 126.96.36.199 ns2.example-2.com 188.8.131.52
Despite of the fact that the examples above work identically well, if I check-mark Test DNS Servers at registar's domain manager using same IP for each ns1 and ns2 (see example-2.com), then the error is returned, requiring to have two different IPs for each ns property? (see example-1.com)
My question is straightforward:
Why do you need two different IPs for each ns record in order to run DNS Servers' Test but at the same time if you just set records without testing procedure, then the registar adds them as it is with no problem?