Actually contrary to what A-Live said Reachability IS a part of AFNetworking. It's implemented inAFHTTPClient.hhere. You have to have the correct imports in your .pch file as discussed here in order to use it.
To use it you'll probably want to have a subclass of AFHTTPClient so you can usesetReachabilityStatusChangeBlock defined here. Here's a simple example without using a subclass.
If you don't like how this reachability setup works I would recommand Tony Million's fork of Apple's Reachability. Simple example: