Primary DNS server settings that do not comply with RFC standards
When enabling Secondary DNS, you must ensure that the primary DNS server settings comply with RFC standards. For settings that do not comply with RFC standards, the Secondary DNS handles them as follows:
The range of the serial number value in the SOA record is 1~2^32-1. If the serial number value in the SOA of the primary DNS server exceeds this range, the Secondary DNS will stop synchronizing resource records from the primary DNS server.
The range of the refresh time value in the SOA record is 30-2^32-1. If the refresh time in the SOA of the primary DNS server exceeds this range, the system will modify it to 30 minutes by default.
Currently, Secondary DNS can synchronize up to 10,000 resource records from the primary DNS server. If the primary DNS server has more than 10,000 resource records, the synchronization operation of the Secondary DNS will be invalidated.
If your settings do not comply with RFC standards, the Secondary DNS will discard these non-compliant setting parameters when synchronizing resource records from the primary DNS server.
To ensure smooth connection between primary and secondary DNS servers, you should open TCP port 53.
Limitations and impact description of primary DNS server
When using Secondary DNS, please note the following limitations and impacts on the primary DNS server:
If you have multiple primary DNS servers, you need to ensure data synchronization between each server. Otherwise, inconsistencies between primary and secondary DNS data may occur. If all primary DNS servers cannot be connected, the system will determine that the primary DNS connection is broken and decide whether to trigger SMS notification based on your settings.
For the resource records in the primary DNS server, please ensure they comply with the requirements for resource records in Cloud DNS. There should not be conflicting records. For more information, see Resource record conflict rules.