Windows error 9975 (DNS_ERROR_CLIENT_SUBNET_IS

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The client subnet cannot be removed because a DNS policy currently references it.

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DNS_ERROR_POLICY_INVALID_SETTINGS	DNS_ERROR_CLIENT_SUBNET_DOES_NOT_EXIST

DNS_ERROR_CLIENT_SUBNET_IS_ACCESSED

DNS_ERROR_CLIENT_SUBNET_IS_ACCESSED protects a client-subnet definition that is still referenced by a DNS policy. Removing it would leave the policy with a broken match criterion.

What to do

Find every server-level and zone-level policy that references the client subnet.
Update or remove those policy references as a planned configuration change before removing the subnet.
Verify the effective answer path for affected clients after the change, especially for split-brain or geo-location policies.

Get-DnsServerQueryResolutionPolicy
Get-DnsServerQueryResolutionPolicy -ZoneName "example.com"
Get-DnsServerClientSubnet

Microsoft: Get-DnsServerQueryResolutionPolicy

Microsoft: Get-DnsServerClientSubnet

Microsoft: Add-DnsServerClientSubnet

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