Why do we need the blackhole servers?
A4: Strictly speaking, we don’t need the blackhole servers. However, DNS clients will sometimes remember the results from previous queries (that is, “good” answers to queries are cached), and the blackhole servers are configured to return answers that DNS clients can cache. This allows the clients to rely on their cached answers, instead of sending another query, which in turn reduces the overall amount of traffic on the Internet. Since the RFC 1918 addresses should never be used on the public Internet, there should be no names in the public DNS that refer to them. Hence, an inverse lookup on one of these addresses should never work. The IANA blackhole servers respond to these inverse queries, and always return an answer that says, authoritatively, that “this address does not exist”. Because of the caching noted above, this is far better than simply not responding at all, so the blackhole servers are provided as a public service.
