When you enable the secondary DNS, make sure the settings of your primary DNS comply with RFC protocols. The secondary DNS takes the following measures when settings that fail to comply with RFC protocols are found.
- The range of the serial number in the SOA record is 1 to 2^32-1. If the serial number in the SOA record of the primary DNS exceeds this range, the secondary DNS stops synchronizing the resource records from the primary DNS.
- The range of the refresh interval in the SOA record is 30 to 2^32-1. If the refresh interval in the SOA record of the primary DNS exceeds this range, the system defaults the interval to 30 minutes.
- The secondary DNS can synchronize a maximum of 10,000 resource records from the primary DNS. The synchronization fails when the number of resource records exceeds 10,000.
- When the secondary DNS synchronizes the resource records, parameter settings that do not comply with RFC protocols are discarded.
- To ensure the connection between the primary and secondary DNS, you must enable port 53 on TCP.
When you use Secondary DNS, note the following restrictions and impacts on the primary DNS:
If you have more than one primary DNS server, make sure the data is synchronized across multiple primary servers. Otherwise, data inconsistency may occur between the primary and secondary DNS. If the secondary DNS fails to connect to your primary DNS servers, the system detects an interrupted connection to the primary DNS and sends SMS message notifications depending on your settings.
Make sure the resource records on your primary DNS conform with the rules and do not conflict with each other. For more information, see Rules on DNS resource records.