Are you saying that the same device that runs CC can connect to calibre using a browser on that very same device? That would be strange.
The full test is to connect to the OPDS part of the content server using the browser on the device running CC. If I am reading your post correctly then that would be
http://192.168.1.21:8080/opds. If that works but CC doesn't then more debug work is needed. If that doesn't work then something on your network is preventing the connection. My guess would be wireless isolation or guest mode in the router, or a firewall on the machine running calibre. If you are running some kind of reverse proxy then that could be the problem.