NotifyRouteChange2 function (netioapi.h)

The NotifyRouteChange2 function registers to be notified for changes to IP route entries on a local computer.


  [in]      ADDRESS_FAMILY             AddressFamily,
  [in]      PVOID                      CallerContext,
  [in]      BOOLEAN                    InitialNotification,
  [in, out] HANDLE                     *NotificationHandle


[in] AddressFamily

The address family on which to register for change notifications.

Possible values for the address family are listed in the Winsock2.h header file. Note that the values for the AF_ address family and PF_ protocol family constants are identical (for example, AF_INET and PF_INET), so either constant can be used.

On the Windows SDK released for Windows Vista and later, the organization of header files has changed and possible values for this member are defined in the Ws2def.h header file. Note that the Ws2def.h header file is automatically included in Winsock2.h, and should never be used directly.

The values currently supported are AF_INET, AF_INET6, and AF_UNSPEC.

Value Meaning
Register for only IPv4 route change notifications.
Register for only IPv6 route change notifications.
Register for both IPv4 and IPv6 route change notifications.

[in] Callback

A pointer to the function to call when a change occurs. This function will be invoked when an IP route notification is received.

[in] CallerContext

A user context passed to the callback function specified in the Callback parameter when an IP route notification is received.

[in] InitialNotification

A value that indicates whether the callback should be invoked immediately after registration for change notification completes. This initial notification does not indicate a change occurred to an IP route entry. The purpose of this parameter to provide confirmation that the callback is registered.

[in, out] NotificationHandle

A pointer used to return a handle that can be later used to deregister the change notification. On success, a notification handle is returned in this parameter. If an error occurs, NULL is returned.

Return value

If the function succeeds, the return value is NO_ERROR.

If the function fails, the return value is one of the following error codes.

Return code Description
An internal error occurred where an invalid handle was encountered.
An invalid parameter was passed to the function. This error is returned if the Family parameter was not either AF_INET, AF_INET6, or AF_UNSPEC.
There was insufficient memory.
Use FormatMessage to obtain the message string for the returned error.


The NotifyRouteChange2 function is defined on Windows Vista and later.

The Family parameter must be set to either AF_INET, AF_INET6, or AF_UNSPEC.

The invocation of the callback function specified in the Callback parameter is serialized. The callback function should be defined as a function of type VOID. The parameters passed to the callback function include the following:

Parameter Description
IN PVOID CallerContext The CallerContext parameter passed to the NotifyRouteChange2 function when registering for notifications.
IN PMIB_IPFORWARD_ROW2 Row OPTIONAL A pointer to the MIB_IPFORWARD_ROW2 entry for the IP route entry that was changed. This parameter is a NULL pointer when the MIB_NOTIFICATION_TYPE value passed in the NotificationType parameter to the callback function is set to MibInitialNotification. This can only occur if the InitialNotification parameter passed to NotifyRouteChange2 was set to TRUE when registering for notifications.
IN MIB_NOTIFICATION_TYPE NotificationType The notification type. This member can be one of the values from the MIB_NOTIFICATION_TYPE enumeration type defined in the Netioapi.h header file.

The callback function specified in the Callback parameter must be implemented in the same process as the application calling the NotifyRouteChange2 function. If the callback function is in a separate DLL, then the DLL should be loaded before calling the NotifyRouteChange2 function to register for change notifications.

When the callback function is received when a change occurs and the Row parameter is not NULL, the pointer to the MIB_IPFORWARD_ROW2 structure passed in the Row parameter contains incomplete data. The information returned in the MIB_IPFORWARD_ROW2 structure is only enough information that an application can call the GetIpForwardEntry2 function to query complete information on the IP route that changed. When the callback function is received, an application should allocate a MIB_IPFORWARD_ROW2 structure and initialize it with the DestinationPrefix, NextHop, InterfaceLuid and InterfaceIndex members in the MIB_IPFORWARD_ROW2 structure pointed to by the Row parameter received. A pointer to this newly initialized MIB_IPFORWARD_ROW2 structure should be passed to the GetIpForwardEntry2 function to retrieve complete information on the IP route that was changed.

The memory pointed to by the Row parameter used in the callback indications is managed by the operating system. An application that receives a notification should never attempt to free the memory pointed to by the Row parameter.

Once the NotifyRouteChange2 function is called to register for change notifications, these notifications will continue to be sent until the application deregisters for change notifications or the application terminates. If the application terminates, the system will automatically deregister any registration for change notifications. It is still recommended that an application explicitly deregister for change notifications before it terminates.

Any registration for change notifications does not persist if the system is shutdown or rebooted.

To deregister for change notifications, call the CancelMibChangeNotify2 function passing the NotificationHandle parameter returned by NotifyRouteChange2.

An application cannot make a call to the CancelMibChangeNotify2 function from the context of the thread which is currently executing the notification callback function for the same NotificationHandle parameter. Otherwise, the thread executing that callback will result in deadlock. So the CancelMibChangeNotify2 function must not be called directly as part of the notification callback routine. In a more general situation, a thread that executes the CancelMibChangeNotify2 function cannot own a resource on which the thread that executes a notification callback operation would wait because it would result in a similar deadlock. The CancelMibChangeNotify2 function should be called from a different thread, on which the thread that receives the notification callback doesn’t have dependencies on.


Requirement Value
Minimum supported client Windows Vista [desktop apps only]
Minimum supported server Windows Server 2008 [desktop apps only]
Target Platform Windows
Header netioapi.h (include Iphlpapi.h)
Library Iphlpapi.lib
DLL Iphlpapi.dll

See also