Unbound is a validating, recursive, and caching DNS resolver.

The C implementation of Unbound is developed and maintained by NLnet Labs. It is based on ideas and algorithms taken from a java prototype developed by Verisign labs, Nominet, Kirei and ep.net.

Unbound is designed as a set of modular components, so that also DNSSEC (secure DNS) validation and stub-resolvers (that do not run as a server, but are linked into an application) are easily possible.