Hello,
Thank you for posting in Q&A forum.
To further troubleshoot this issue, please kindly try below steps:
1.Open CMD window and run ping or telnet command on primary DNS Server to secondary DNS server to make sure the network connectivity is okay.
2.Make sure the firewall settings on both sides are whitelisting the UDP Port 53 traffic.
3.Check the DNS server configuration and make sure the secondary DNS server is correctly configured to accept zone transfers.
I hope the information above is helpful.
If you have any questions or concerns, please feel free to let us know.
Best regards,
Jill Zhou
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