FwxGetHostByAddrEvent structure

Applies to: desktop apps only

The FwxGetHostByAddrEvent structure contains parameters for an event of the fwx_GetHostByAddr type, as defined in the FwxFirewallEventType enumerated type.

An event of this type event is a notification of a Forefront TMG Client or Firewall Client operation that uses the Winsock gethostbyaddr function, which requests the host information corresponding to a specific network address. Such an event allows the filter to modify or block a name resolution request generated by gethostbyaddr by calling the IFWXGetXByY::SetResult or IFWXGetXByY::Deny method. Two events are generated, one before and one after the actual name resolution.


typedef struct _tagFwxGetHostByAddrEvent {
  BYTE            *Address;
  DWORD           AddressLength;
  INT             AddressType;
  LPHOSTENT       Hostent;
  DWORD           HostentLength;
  BOOL            fBeforeAction;
  FwxFilterAccess FilterAccess;
  IFWXGetXByY     *piGetXByY;
} FwxGetHostByAddrEvent;


  • Address
    Pointer to the network address passed to the gethostbyaddr function in network byte order.

  • AddressLength
    Length, in bytes, of the data pointed to by the Address member.

  • AddressType
    Type of address, such as the AF_INET address family type (defined as TCP, UDP, and other associated Internet protocols). Address family types and their corresponding values are defined in Winsock2.h.

  • Hostent
    Pointer to a hostent structure. This member points to a valid hostent structure if the fBeforeAction member is FALSE. Otherwise, the value of this member is undefined.

  • HostentLength
    Length, in bytes, of the data pointed to by the hostent member.

  • fBeforeAction
    Before-action flag. The value of this flag is TRUE if the event is generated before name resolution is performed, and FALSE if the event is generated after name resolution is performed.

  • FilterAccess
    Value from the FwxFilterAccess enumerated type that indicates the type of access permission granted for the event. This member is used internally by the Microsoft Firewall service and should not be modified or relied upon by application filters.

  • piGetXByY
    Pointer to an IFWXGetXByY interface that contains methods for controlling the outcome of the name query.


The events for which this structure is used are generated only for Forefront TMG Client and Firewall Client computers (sources of type fwxSourceWSP, as defined in the FwxFirewallEventSource enumerated type). They are not generated for SecureNAT clients.


Minimum supported client

None supported

Minimum supported server

Windows Server 2008 R2, Windows Server 2008 with SP2 (64-bit only)


Forefront Threat Management Gateway (TMG) 2010



See also





Build date: 7/12/2010