Unbound (DNS server)

Unbound is a validating, recursive, and caching DNS resolver product from NLnet Labs. It is distributed free of charge in open-source form under the BSD license.

Unbound

Screenshot of Unbound 1.22.0, showing version information, build configuration, and usage of unbound-host to check DNSSEC validation
Developer(s)	NLnet Labs
Initial release	February 19, 2007; 18 years ago (2007-02-19)
Stable release	1.23.0[1]  / 24 April 2025; 19 days ago (24 April 2025)
Repository	Unbound by NLnetLabs on GitHub
Written in	C
Operating system	Unix-like, Windows
Type	DNS server
License	BSD license
Website	unbound.net

Features

• Caching resolver with prefetching of popular items before they expire
• DNS over TLS forwarding and server, with domain-validation^[2]
• DNS over HTTPS^[3][4]
• DNS over QUIC^[5]
• Query Name Minimization^[6]
• Aggressive Use of DNSSEC-Validated Cache^[7]
• Authority zones, for a local copy of the root zone^[8]
• DNS64
• DNSCrypt^[9]
• DNSSEC validating
• EDNS Client Subnet

History

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.^[10]

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, macOS, and Linux, as well as Microsoft Windows.

Reception

Unbound has supplanted the Berkeley Internet Name Daemon (BIND) as the default, base-system name server in FreeBSD and OpenBSD, where it is perceived as smaller, more modern, and more secure for most applications.^[11][12]

See also

• NSD, an authoritative name server, also from NLnet Labs
• Comparison of DNS server software