I'm offering my Internet to somebody living in another apartment and used an Airport Express to extend my Airport Extreme signal. Since the Aiport Express only extends the "main" network, the other person is using the main network whereas I'm using the "guest" network myself.
I recently got an external hard drive and connected it to the Airport Extreme's USB port because I want to use Time Machine to automatically backup my MBA.
However, the hard drive is automatically connecting itself to the "main" network. Is there a way for me to access the hard drive through the "guest" network instead?