What does Windows error code 9001 (DNS_ERROR_RCODE_FORMAT_ERROR) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The DNS server could not interpret the format of the DNS request.

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ERROR_DS_VALUE_KEY_NOT_UNIQUE	DNS_ERROR_RCODE_SERVER_FAILURE

DNS_ERROR_RCODE_FORMAT_ERROR

DNS_ERROR_RCODE_FORMAT_ERROR represents DNS RCODE FORMERR. The receiving server could not interpret the request format. It normally points to a malformed query, an incompatible DNS extension, or a device modifying DNS traffic rather than to a missing DNS record.

What to check

Repeat the lookup against the same server with a standard DNS client to determine whether the failure is specific to one application or query format.
Check whether DNS inspection, a proxy, VPN, firewall, or custom client is changing packets before they reach the server.
Enable DNS diagnostics for a short capture window and correlate the malformed request with its client address and query type.

Resolve-DnsName -Name "example.com" -Server "dns-server" -DnsOnly

Microsoft: DNS system error codes

Microsoft: DNS logging and diagnostics

Microsoft: DnsServer PowerShell module

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