This article presents a comparison of the features, platform support, and packaging of many independent implementations of Domain Name System (DNS) name server software. Servers compared Each of these DNS servers is an independent implementation of the DNS protocols, capable of resolving DNS names for other computers, publishing the DNS names of computers, or both. Excluded from consideration are single-feature DNS tools (such as proxies, filters, and firewalls) and redistributions of servers listed here (many products repackage BIND, for instance, with proprietary user interfaces). DNS servers are grouped into several categories of specialization of servicing domain name system queries. The two principal roles, which may be implemented either uniquely or combined in a given product are: Authoritative server: authoritative name servers publish DNS mappings for domains under their authoritative control. Typically, a company (e.g. "Acme Example Widgets") would provide its own authority services to respond to address queries, or for other DNS information, for www.example.int. These servers are listed as being at the top of the authority chain for their respective domains, and are capable of providing a definitive answer. Authoritative name servers can be primary name servers, also known as master servers, i.e. they contain the original set of data, or they can be secondary or slave name servers, containing data copies usually obtained from synchronization directly with the primary server, either via a DNS mechanism, or by other data store synchronization mechanisms. Recursive server: recursive servers (sometimes called "DNS caches", "caching-only name servers") provide DNS name resolution for applications, by relaying the requests of the client application to the chain of authoritative name servers to fully resolve a network name. They also (typically) cache the result to answer potential future queries within a certain expiration (time-to-live) period. Most Internet users access a recursive server provided by their internet service provider to locate internet hosts such as www.example.com. BIG-IP DNS F5 Networks product offers DNS as an authoritative server, recursive and adds additional security measures. Key advantage is to use the same application delivery controller to support DNS and application acceleration. BIND BIND is the de facto standard DNS server. It is a free software product and is distributed with most Unix and Linux platforms, where it is most often also referred to as named (name daemon). It is the most widely deployed DNS server. Historically, BIND underwent three major revisions, each with significantly different architectures: BIND4, BIND8, and