Unbound is a validating, recursive, and caching DNS server software product from NLnet Labs, VeriSign Inc., Nominet, and Kirei. It is distributed free of charge in open source form under the BSD license.
Originally designed by Jakob Schlyter of Kirei and Roy Arends of Nominet in 2004, funding was provided by VeriSign and ep.net to develop a prototype written in Java (David Blacka and Matt Larson, VeriSign). In 2006, the prototype was re-written for high-performance in the C programming language by NLnet Labs.
Unbound is designed as a set of modular components that incorporate modern features, such as enhanced security (DNSSEC) validation, Internet Protocol Version 6 (IPv6), and a client resolver application programming interface library as an integral part of the architecture. Originally written for POSIX-compatible Unix-like operating system, it runs on FreeBSD, OpenBSD, NetBSD, OS X, and Linux, as well as Microsoft Windows.
Reception
Unbound has supplanted the Berkeley Internet Name Domain (BIND) as the default, base-system name server in several open source projects, where it is perceived as smaller, more modern, and more secure for most applications.