featuring Dynamic DNS update support. PowerDNS PowerDNS is a free software DNS server with a variety of data storage back-ends and load balancing features. Authoritative and recursive server functions are implemented as separate applications. Secure64 DNS DNS Authority is commercial authoritative name server software from Secure64, the company that built Genuinely Secure DNS applications and operating system and completely automated the deployment of DNSSEC. DNS Cache is scalable, highly secure recursive DNS software from Secure64 which provides built-in protection against high-volume denial of service attacks, including Pseudo Random Sub Domain (PRSD) attacks. Simple DNS Plus Simple DNS Plus is a commercial DNS server product that runs under Microsoft Windows with an emphasis on a simple-to-use GUI. Maintenance of the software appears to have slackened in recent years. Unbound Unbound is a validating, recursive and caching DNS server designed for high performance. It was released on May 20, 2008 (version 1.0.0) as free software licensed under the BSD license by NLnet Labs. It is installed as part of the base system in FreeBSD starting with version 10.0, and in NetBSD with version 8.0. A version is also available in OpenBSD version 5.6 and beyond. (Previous versions of FreeBSD shipped with BIND.) YADIFA YADIFA is a BSD-licensed, memory-efficient DNS server written in C. The acronym YADIFA stands for Yet Another DNS Implementation For All. It was created by EURid, which operates the .eu top-level domain. Features Some DNS features are relevant only to recursive servers, or to authoritative servers. As a result, a feature matrix such as the one in this article cannot by itself represent the effectiveness or maturity of a given implementation. Another important qualifier is the server architecture. Some DNS servers provide support for both server roles in a single, "monolithic" program. Others are divided into smaller programs, each implementing a subsystem of the server. As in the classic Computer Science microkernel debate, the importance and utility of this distinction is hotly debated. The feature matrix in this article does not discuss whether DNS features are provided in a single program or several, so long as those features are provided with the base server package and not with third-party add-on software. Explanation of features Authoritative A major category of DNS server functionality, see above. Recursive A major category of DNS server functionality, see above. Recursion Access Control Servers with this feature provide control over which hosts are permitted DNS