There should only be one set of DNS servers that are responsible (authoritative) for directing Internet traffic for your domain name. These should be the DNS servers that are held in the Domain Name Registry database against your domain name. For example, the domain name yourname.co.nz is delegated to the DNS servers ns1.eziweb.net.nz and ns2.eziweb.net.nz in the NZ Registry database, therefore these two DNS servers are ‘authoritative’ for yourname.co.nz.