With all due respect, over the past fifteen years of trying to secure corporate networks, we've learned the hard way that this simply isn't a realistic goal. Having a hard outer shell and a squishy center just leaves the entire network vulnerable, because it's simply not possible to isolate yourself from the badness of the outside world. As soon as you let anyone in who's ever spoken to the hostile outside world, they bring the hostile outside world in with them.

We can't keep pretending that we can keep home networks isolated from the rest of the world when many of the computers in those networks move freely between the global Internet and the private home intranet. All connected devices are part of the global Internet whether or not we want them to be, and whether or not their connections are persistent.