Using Network Configuration Detection

The ISA Server 2004 network configuration detection (NCD) mechanism allows application filters to react to network configuration changes without restarting a service. It specifically applies to changes related to Plug and Play network devices. The ISA Server 2004 NCD mechanism issues notifications of network configuration changes, and application filters can register to receive those notifications. This mechanism also maintains a consistent view of network information in a single location.

Network Configuration Detection Mechanism

When the NCD mechanism is initialized, it constructs an initial view of the relevant network configuration information. A view of the network configuration at a single point in time is referred to as a snapshot. When changes occur in the network configuration, the NCD mechanism undergoes a synchronization, at which time a new snapshot is created.

NCD clients such as application filters register with the NCD mechanism and provide a sink interface for NCD notifications. NCD sends notifications of any changes in the network configuration to all its clients. Each client handles the notifications that it is interested in.

Note  When a client registers, the NCD mechanism sends a series of notifications that creates a picture of the current network configuration, in a logical order.

Network Configuration Detection Interfaces

The NCD interfaces provided in the SDK file Wspfwext.idl are:

• IFWXNetConfigDetector, which can be retrieved using the IFWXFirewall2::GetNetConfigDetector method. This interface includes methods for registering and unregistering for NCD notifications. During registration, the client receives a handle specific to that registration operation.
• IFWXNetworkAddress, which represents an IP address. Each IP address is associated with an ISA Server network represented by an IFWXNetworkElement interface.
• IFWXNetworkAdapter, which represents a network adapter.
• IFWXNetworkElement, which represents a network defined in the stored ISA Server administration COM configuration. Each network can be part of a network set represented by an IFWXNetworkSet interface.
• IFWXNetworkSet, which represents a network set.
• IFWXNetConfigDetectionNotification, which is the notification interface that should be implemented by each NCD client.
• IFWXNetConfigDetectionSnapshot, which represents a snapshot of the complete network configuration.

Network Configuration Detection Configuration Events

The FwxNcdEvent structure defines types of NCD network configuration events, such as the addition or removal of a network adapter.

NCD Approaches

There are two ways to use the NCD mechanism:

• Response to incremental notifications.
• Response to a synchronization notification using a snapshot of the network configuration.

Use the incremental approach when the NCD client has to perform an action as a response to a single notification, and this action is not dependent on future notifications. To use the incremental approach, use the GetContext and SetContext methods of the applicable network configuration interface (such as IFWXNetworkAddress) to get and set the information and act appropriately when receiving a notification.

Use the synchronization approach when the NCD client has to examine a complete and consistent picture of the network configuration to perform an action. When you receive an incremental notification that you are interested in, set a flag. When you receive a synchronization notification (fwx_ncd_SyncConfig) indicating that an updated snapshot is available, examine your flags and examine the snapshot (IFWXNetConfigDetectionSnapshot), to determine how to act.