You can have multiple routers. Sure, if your edge router is getting DDOS'd, you can't get to the internet, but your intranet services will still work.

I meant DNS.

I feel like I'm not following what you mean, but DNS can run on multiple routers as well

No, I think you're following me fine. I was, erm, rather unnerved by the recent DynDNS attack, which is a definite minority of the internet.

Exactly.