Wow, that's a really good question. Thinking about this a bit, I don't think authoritative servers pose as big of a problem in practice. DNS amplification att

Wow, that's a really good question. Thinking about this a bit, I don't think authoritative servers pose as big of a problem in practice. DNS amplification attacks require that the size of the response be much larger than the size of the query (which is why it's an "amplification" attack). Right now amplification attacks query for the same large response via lots of different open resolvers. However, I suspect the majority of authoritative servers out there only ever return small responses, which would limit the number of servers an attacker could use in an amplification attack. Furthermore, the attacker would need to tailor a specific query for each server rather than using the same query for all of them, making the attack more difficult to pull off.