Could you or someone else expand on this? How do you coordinate rtbh with your ISP? And how do you check for whether it's working? I'd love to learn more on this topic. Thanks!
How do you test it? Very simple. Announce an IP (or a few) as blackhole and test to make sure things don't work (from that IP).
Very simply could setup something to ping something on that provider's infrastructure from that IP and... if it starts to work, alert!
I imagine getting paged because of a DDOS is slightly easier when it's telling you it already null routed a few IPs so the rest of your network isn't screwed and you just have to identify how problematic those specific IPs being out of service is and whether you need to take action or wait for them to get bored.