What does NTSTATUS 0xC0220009 (STATUS_FWP_ALREADY_EXISTS) mean?

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A WFP object with the supplied GUID or LUID already exists.

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STATUS_FWP_NOT_FOUND	STATUS_FWP_IN_USE

STATUS_FWP_ALREADY_EXISTS

The identifier collides with an existing filtering-engine object

STATUS_FWP_ALREADY_EXISTS is returned when an add operation supplies a GUID or a locally unique identifier that is already present for the relevant WFP object class. This is an identity collision in the Base Filtering Engine (BFE), not evidence that a packet matched an existing rule.

Keep the persistent object key, the runtime ID returned by BFE, and the installation scope separate in diagnostics. A filter combines conditions, action, weight, optional context, and sublayer; recreating it with a new identifier can leave the old rule active and alter arbitration unexpectedly.

What to compare before changing policy

The called Fwpm*Add0 API and object class: filter, provider, sublayer, callout, or context.
The supplied GUID or LUID, the current object owner/provider, and the target layer or sublayer.
Whether a previous installation completed, retried after a partial failure, or left persistent policy behind.
The effective existing object, rather than only its display name.

References

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