You may have wondered what steps you need to follow when you want to configure a Slave (Secondary) DNS zone and keep it synchronized with an existing Primary DNS server. The good news is that the setup is quite straightforward. In this article, we will guide you through the process step by step and show you how to configure the Secondary zone correctly.
First, of course, you need to have a Slave DNS zone created. We assume this step is already completed, but we still want to provide a reference to the relevant article and setup instructions in case you are not familiar with the process.
After creating your Slave DNS zone, open its management page and click the second button, called "Primary Settings". There, you will see several IP addresses that need to be allowed on your Primary DNS server. For the secondary zone to operate properly, these IP addresses must be permitted both for notifications using also-notify and for zone transfers using allow-transfer.
Make sure that TCP port 53 is open and accessible on your Primary DNS server. AXFR zone transfers are performed over TCP, so ClouDNS must be able to establish a connection to this port in order to retrieve the zone data successfully.
Make sure that your firewall does not block any of the ClouDNS IP addresses listed under Primary Settings. These IP addresses must be able to reach your Primary DNS server without restrictions so that zone transfers and synchronization can work correctly.
You should also make sure that UDP port 53 is accessible from the listed ClouDNS IP addresses. This may be required for DNS queries such as SOA queries, which are used to check the current zone serial and determine whether an update is needed. If you have any firewall rules, packet filtering, or UDP rejection policies in place, make sure they do not block these requests.