What does Windows error code 9978 (DNS_ERROR_SUBNET_DOES_NOT_EXIST) mean?

DNS_ERROR_SUBNET_DOES_NOT_EXIST

DNS_ERROR_SUBNET_DOES_NOT_EXIST means the operation refers to an IPv4 or IPv6 prefix that is not part of the named DNS client-subnet definition.

What to check for DNS_ERROR_SUBNET_DOES_NOT_EXIST

• Inspect the exact address and prefix length; a host address and a network prefix are not interchangeable.
• Check whether the prefix belongs to a different client-subnet name.
• When modifying a definition, preserve any existing prefixes that are still needed by policy matching.

Get-DnsServerClientSubnet

Microsoft: Get-DnsServerClientSubnet

Microsoft: Set-DnsServerClientSubnet

Microsoft: Add-DnsServerClientSubnet

Where the result is returned

This result is Win32 system error 9978 (0x000026FA) from winerror.h. AllStat describes it as “The IP subnet specified does not exist in the client subnet.”. The code is useful only together with the API that failed, because multiple Windows components can reuse system-error values while imposing different retry and cleanup rules.

Diagnostic sequence

• Call GetLastError immediately after the failing API and save this result, the function name, all relevant flags, and the target path, handle, service, device, account, or policy object.
• Capture the component log that owns the dns / subnet / does / exist operation and retain the original numeric value before a framework converts it to an HRESULT or exception.
• compare preconditions with the API documentation and reproduce with a minimal request before changing system-wide configuration.

Retry this result only after the resource or state named in “The IP subnet specified does not exist in the client subnet.” has changed. For invalid parameters, unsupported formats, missing objects, policy restrictions, and access failures, correct the input or configuration instead of immediately repeating the same call.

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