FwpsInjectForwardAsync0 function

The FwpsInjectForwardAsync0 function injects packet data into the forwarding data path.

Note  FwpsInjectForwardAsync0 is a specific version of FwpsInjectForwardAsync. See WFP Version-Independent Names and Targeting Specific Versions of Windows for more information.


NTSTATUS FwpsInjectForwardAsync0(
  HANDLE                injectionHandle,
  HANDLE                injectionContext,
  UINT32                flags,
  ADDRESS_FAMILY        addressFamily,
  COMPARTMENT_ID        compartmentId,
  IF_INDEX              interfaceIndex,
  NET_BUFFER_LIST       *netBufferList,
  HANDLE                completionContext



An injection handle that was previously created by a call to the FwpsInjectionHandleCreate0 function.


An optional handle to the injection context. If specified, it can be obtained by calling the FwpsQueryPacketInjectionState0 function when the packet injection state FWPS_PACKET_INJECTION_STATE is FWPS_PACKET_INJECTED_BY_SELF or FWPS_PACKET_PREVIOUSLY_INJECTED_BY_SELF.


Reserved. Callout drivers must set this parameter to zero.


One of the following address families:


The IPv4 address family.


The IPv6 address family.


The identifier of the routing compartment into which the packet data is injected, specified as a COMPARTMENT_ID type. This identifier is provided to a callout through the compartmentId member of the FWPS_INCOMING_METADATA_VALUES0 structure that is passed to the callout driver's classifyFn callout function. If the compartmentId member is available to callouts, FWPS_METADATA_FIELD_COMPARTMENT_ID will be set in the currentMetadataValues member. Otherwise, set this parameter to UNSPECIFIED_COMPARTMENT_ID.


The index of the destination interface (on which the packet data is to be sent). The index is a 32-bit value. A callout driver should use the value of the interface index that is passed as one of the incoming data values to its classifyFn callout function for this parameter if the packet is to be injected into the same interface where the original packet was indicated.


A pointer to a NET_BUFFER_LIST structure that describes the packet data that is being injected. A callout driver allocates a NET_BUFFER_LIST structure to inject packet data by calling either the FwpsAllocateCloneNetBufferList0 function or the FwpsAllocateNetBufferAndNetBufferList0 function. The NET_BUFFER_LIST structure must begin with an IP header.


A pointer to a completionFn callout function provided by the callout driver. The filter engine calls this function after the packet data, described by the netBufferList parameter, has been injected into the network stack.


A pointer to a callout driver-provided context that is passed to the callout function pointed to by the completionFn parameter. This parameter is optional and can be NULL.

Return Value

The FwpsInjectForwardAsync0 function returns one of the following NTSTATUS codes.

Return code Description
The packet data injection was initiated successfully. The filter engine will call the completion function after the filter engine has completed injecting the packet data into the network stack, or when an error occurred subsequently, in which case the Status member of the completed NET_BUFFER_LIST structure will indicate the reason for failure.
The TCP/IP network stack is not ready to accept injection of packet data.
The injection handle is being closed.
Other status codes
An error occurred.


A callout driver calls the FwpsInjectForwardAsync0 function to inject packet data or a packet fragment into the forwarding data path.

This function can execute asynchronously. Callout drivers normally inject data into the network stack when modifying packet data. For more information about how a callout driver can modify packet data, see Callout Driver Operations.

A packet or packet fragment injected with this function will not be indicated to any WFP layer for filtering.

If the return value is not STATUS_SUCCESS, the completion function will not be called. In this case, the net buffer list pointed to by netBufferList must be freed by a call to FwpsFreeNetBufferList0 or FwpsFreeCloneNetBufferList0.

IP packets or fragments can be cloned, modified, and injected back into the network stack. However, a fragment group must be reassembled by the callout driver as a single NET_BUFFER_LIST before it can be reinjected.

Forward-injected packets do not reenter the forwarding layer. Therefore, they will not be reclassified.


Minimum supported client Available starting with Windows Vista.
Target Platform Universal
Header fwpsk.h (include Fwpsk.h)
Library Fwpkclnt.lib

See Also

FWPS_INCOMING_METADATA_VALUES0 FwpsAllocateCloneNetBufferList0 FwpsAllocateNetBufferAndNetBufferList0




Packet Injection Functions