The NetworkReachability programming interface allows an application to determine the status of a system's current network configuration and the reachability of a target host. A remote host is considered reachable when a data packet, sent by an application into the network stack, can leave the local device. Reachability does not guarantee that the data packet will actually be received by the host.

The NetworkReachability programming interface supports a synchronous and an asynchronous model. In the synchronous model, you get the reachability status by calling the TryGetFlags function. In the asynchronous model, you can schedule the NetworkReachability object on the CFRunLoop of a client object’s thread. The client implements a callback function (SetNotification) to receive notifications when the reachability status of a given remote host changes.