Is it possible to create a route on your internet router which routes traffic unknown to null. So you basically dont even let traffic route into your firewall unless its approved? Can this help detour the ICMP pings which take down your circit?
The problem with some kind of DDoS attacks isn't what happens to traffic. The problem is the existence of the traffic itself on the link. At some point, your link will just be too full for your router to be able to handle the requests (dropping or null-routing). You see, it doesn't matter what the server/router/firewall is doing, the hose is just too congested.
You defend against this kind of DDoS either by having more links than your attackers can fill (using big service providers like CloudFlare or Akamai, they take the hit for you) or just take your connection/server down.
To answer your question, yes, null routes can be added to your router to help mitigate a DoS attack.