rare gold pack <| sep |> Is this a quiz or are you actually asking ? In either case , it ' s basically just port forwarding . It ' s probably called reverse because it ' s actually setting up a reverse proxy in which a http server running on your phone accepts connections on a port and wires them to your computer . Or vice versa . The port is specified twice because you have the ability to control the listening port on both sides of the proxy . When the RN packager is running , there is an active web server accessible in your browser at 127 . 0 . 0 . 18081 . It ' s from this server that the JS bundle for your application is served and refreshed as you make changes . Without the reverse proxy , your phone wouldn ' t be able to connect to that address . Hopefully that helps . I would include some referential links but mobile is a pain .