[scurvy]

No, they don't. Transit providers acting in a pure transit manner do not null route destination networks that they're not responsible for. Provider B, providing transit from AS A to AS C, will not block traffic bound for C or beyond. They might block some things bound for AS B or a customer of AS B, but they're not acting in a pure transit capacity there.

Content and eyeball networks are free to do whatever they want with regards to routing and blocking. Transit providers? No, they just provide transit. That's the business they want to be in. They're not in the blocking business.

Thanks for the NANOG tip though. I'm a member and active participant. See you in Seattle.

The main NANOG threads are about detecting the NTP traffic and blocking malicious requests in content and eyeball networks -- not transit. There's also the OpenNTP project discussion -- http://openntpproject.org/