BIND is open source software that implements the Domain Name System
(DNS) protocols for the Internet. It is a reference implementation
of those protocols, but it is also production-grade software,
suitable for use in high-volume and high-reliability applications.

The optional "ratelimit" flavour builds BIND9 with the experimental
patches to add rate limits for authoritative servers, information about
how to use this is available at http://www.redbarn.org/dns/ratelimits