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FWP_E_ALREADY_EXISTS
FWP_E_ALREADY_EXISTS means that WFP already contains an object with the GUID or LUID supplied by the caller. The important question is not simply whether to ignore the error, but whether the existing object is the same policy object that this version of the product expects.
Why blind retries are unsafe
A duplicate may be the result of a successful prior install, a partially completed install, a concurrent update, or a different component that accidentally reused an identifier. Treating all duplicates as success can preserve an outdated filter action, layer, provider, or security descriptor.
Idempotent deployment pattern
- Read the existing object by stable key and compare its meaningful configuration with the desired definition.
- Update or replace it only within the product’s defined ownership boundary.
- Use explicit transactions for related adds and deletes so a failure does not leave a half-created policy graph.
Microsoft: WFP error codes · Microsoft: WFP sessions and transactions · Microsoft: explicit transactions for related changes
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