Hi,
According to your description, it seems that it is an AD-integrated zone.
An AD Integrated is stored in the AD database, and the zone will replicate to other domain controllers within the same replication scope automatically as part of the
AD replication process. By default, AD integrated zones are configured to not allow zone transfers. Allowing zone transfers is an option provided to support non-DC DNS servers, BIND or any other name brand DNS server that you want to allow zone transfers to
a secondary on those servers.
In your case, if you want to make the Windows Server 2003 as an additional DC, then zone transfer is not needed. If not, you can configure zone transfer and add the
IP address of the Windows Server 2003 to the zone transfer tab in the properties of the zone in DNS console.

Best regards,
Susie
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