Re: Kicked in immediately
Cloudflare (as an example) seem to disagree with you. I don't believe they are using BGP to do that - given the global distributed network they use and that you don't have to apply it to all services on your netblock.
I'm not affiliated to Cloudflare,but have seen traffic flipped to them quickly when another customer had similar issues.
My point on the original post was that preparation is key here, get DoS protection in place for WHEN you get targeted, not when you realise you are no longer on the Internet.