When I tether my mobile network to laptop with Hotspot on iPhone and test for Reachability's currentReachabilityStatus it reports ReachableViaWiFi where neither Wifi is open nor is it sharing mobile network via Wifi. I know even with this, it shows correct information on internet connectivity but the nature of my app requires exact information on whether Wi-fi is connected or not so its not the issue to determine internet connectivity but more of Wi-fi reachability.
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Infact it fails if there is no device connected on USB. Only reports ReachableViaWiFi when a machine is using its internet via USB.