No it is not mandatory.
You may have both DNS servers configured at domain registrar pointing to the same IP
ns1.domain.com → 123.123.123.123
ns2.domain.com → 123.123.123.123
However this is not compliant with the standard.
Have a look here:
No it is not mandatory.
You may have both DNS servers configured at domain registrar pointing to the same IP
ns1.domain.com → 123.123.123.123
ns2.domain.com → 123.123.123.123
However this is not compliant with the standard.
Have a look here: