Conditional forwarder no longer resolving partner domain

Question

We have a conditional forwarder configured for a partner company's DNS domain, but it stopped resolving names after they made changes to their DNS infrastructure.

I would like to understand the recommended process for verifying the current forwarder configuration, confirming connectivity to the partner's DNS servers, and re-establishing reliable name resolution.

Answer 1

Hi Rohan,

You can follow the steps and will require Network Engineer to work on this with you

1. Port 53 open: Your firewall must allow traffic from your local DNS server to the external DNS IP over port 53 (both UDP and TCP).
2. Direct IP routing: The local DNS server must have a valid network path (via WAN or VPN/ExpressRoute) to reach the target external IP.

You can try telnet or port query to the target DNS Server on port 53.

Hope this helps.

JS

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Answer 2

Hello Rohan Joshi

Thank you for contacting Microsoft Q&A.

Based on the information provided, it appears that the issue may be related to the conditional forwarder configuration or connectivity to the partner's DNS servers following recent changes in their DNS environment.

As a next step, could you please help verify the following:

• Confirm the current DNS server IP addresses provided by the partner for the affected domain.
• Verify connectivity from your DNS server to the partner's DNS servers on port 53 (DNS).
• Test name resolution directly against the partner's DNS servers using tools such as nslookup or Resolve-DnsName.
• Check whether the conditional forwarder configuration is still pointing to the correct DNS servers.
• Review the DNS Server event logs for any timeout, SERVFAIL, or connectivity-related errors.

If the partner has recently migrated or replaced their DNS servers, the conditional forwarder may need to be updated with the new DNS server addresses.

Please let us know the results of the above checks, and we will be happy to assist you.

Hope you found something helpful here. Please let me know if you need further assistance.

If this answer could solve the issue, it's appreciated to accept the answer.

Thank you again for your patience and support!

Ivy Bui