Comparison of DNS server software

This article is a comparison of DNS server software, comparing the features, platform support, and packaging of independent implementations of DNS.

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 master server, either via a DNS mechanism, or by other data store synchronization mechanisms.

• Recursive Servers: 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 as well, usually, caching 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 sites such as www.google.com.

BIND

The de facto standard open-source DNS server. BIND ships on most Unix platforms, where it is most often also referred to as named (name daemon) and is the most widely deployed DNS server. Historically, there were three major versions of BIND, each with significantly different architectures: BIND4, BIND8, and BIND9. The first two of these are now technically obsolete. This page refers to BIND9, a ground-up rewrite of BIND featuring full DNSSEC support.

Microsoft DNS

The DNS server provided with Windows Server, a key component of Microsoft's Active Directory, and therefore one of the most widely deployed implementations of the DNS.

djbdns

Djbdns is a collection of DNS applications, including tinydns, the second most popular open-source DNS server. It was designed by Daniel J. Bernstein, author of qmail, with an emphasis on security considerations. According to his own website, the author offers a still unclaimed $1000 prize to be awarded to the first person finding a security hole in djbdns. With a modular, light-weight design, djbdns components are considered faster than their BIND counterpart, but feature several uncommon installation and configuration methods. Djbdns code is not actively maintained and was released into the public domain in 2007.

Dnsmasq

Dnsmasq is a lightweight, easy to configure, DNS forwarder and local resolver (and DHCP server) and is usually integrated in home networking routers.

Simple DNS Plus

A popular Windows DNS server product with emphasis on a simple-to-use GUI.

NSD

A popular open-source authoritative server provided by NLNet Labs. NSD is a test-bed server for DNSSEC; new DNSSEC protocol features are often prototyped using the NSD code base. NSD hosts several top-level domains, and operates three of the root nameservers.

PowerDNS

An open-source DNS server with a variety of data storage back-ends and load balancing features. Authoritative and recursive server functions are implemented as separate applications. It is the DNS implementation relied upon by Wikipedia.

MaraDNS

An open source DNS server by Sam Trenholme that claims a good security history and ease of use.

ANS

A commercial authoritative server from Nominum, a company founded by Paul Mockapetris, the inventor of the DNS. ANS was designed to meet the needs of top level domain servers.

CNS

A high-performance commercial recursive caching server from Nominum, intended as a secure alternative to BIND for enterprises.

Posadis

An open source DNS server, written in C++, featuring Dynamic DNS update support.

Secure64 DNS

A security-hardened commercial DNS appliance, deployed on a proprietary 64-bit operating system running on Intel Itanium hardware.

Unbound

Unbound is a validating, recursive and caching DNS server designed for high-performance. It was released May 20, 2008 (version 1.0.0) in form of open source software licensed under the BSD license by NLnet Labs, Verisign Inc., Nominet, and Kirei.

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 recursive lookups. This is useful for load balancing and service protection.

Slave Mode

Authoritative servers can publish content that originates from primary data storage (such as zone files or databases connected to business administration processes)--such servers are also called 'master' servers--or can be slave or secondary servers, republishing content fetched from and synchronized with such master servers. Servers with a "slave mode" feature have a built-in capability to retrieve and republish content from other servers. This is typically, though not always, provided using the AXFR DNS protocol.

Caching

Servers with this feature provide recursive services for applications, and cache the results so that future requests for the same name can be answered quickly, without a full DNS lookup. This is an important performance feature, as it significantly reduces the latency of DNS requests.

DNSSEC

Servers with this feature implement some variant of the DNSSEC protocols. They may publish names with resource record signatures (providing a "secure authority service"), and may validate those signatures during recursive lookups (providing a "secure resolver"). DNSSEC is not widespread, and has not been adopted by the most popular sites on the Internet. Its value and feasibility has been the subject of debate. However, the presence of DNSSEC features is a notable characteristic of a DNS server.

TSIG

Servers with this feature typically provide DNSSEC services. In addition, they support the TSIG protocol, which allows DNS clients to establish a secure session with the server to publish Dynamic DNS records or to request secure DNS lookups without incurring the cost and complexity of full DNSSEC support.

IPv6

Servers with this feature are capable of publishing or handling DNS records that refer to IPv6 addresses. In addition to be fully IPv6 capable they must implement IPv6 transport protocol for queries and zone transfers in slave/master relationships and forwarder functions.

Wildcard

Servers with this feature can publish information for wildcard records, which provide data about DNS names in DNS zones that are not specifically listed in the zone.

Split horizon

Servers with the split-horizon DNS feature can give different answers depending on what IP/subnet the query is coming from.

Feature Matrix

1. ^  A BIND configuration module is available for Webmin in many Linux distributions.
2. ^  djbdns provides facilities to transfer zones; after completing the zone transfer, djbdns can act as an authoritative server for that zone. Consult the axfr-get documentation for further information.
3. ^  This is not the same as views in bind. But it is a solution with comparable capabilities. See: section of tinydns-data.
4. ^  dnsmasq has limited authoritative support, intended for internal network use rather than public Internet use. A records are supported via /etc/hosts, and there is some MX record support via the command line.
5. ^  MaraDNS cannot directly provide slave support. Instead, a zone transfer is needed, after which MaraDNS will act as an authoritative server for that zone. See DNS Slave for further information.
6. ^  DNSSEC functionality must be manually activated in the registry. It is not enabled by default, and is only available in Windows Server 2003. Additionally, the DNSSEC support is sufficient to act as a slave/secondary server for a signed zone, but not sufficient to create a signed zone (lack of key generation and signing utilities).
7. ^  IPv6 functionality in the Microsoft DNS server is only available on Windows Server 2003 and newer.
8. ^  Simple DNS Plus does not have "views" in the same way as BIND, but has a "NAT IP Alias" feature which allows host records to resolve to different IP addresses depending on where the DNS request comes from.
9. ^  It is possible to support the concept of views in PowerDNS by either running two copies of PowerDNS in parallel (on the same machine), or by writing a custom backend which serves different data based on the client who is querying. See here for the original answer regarding this topic by the author of PowerDNS.
10. ^  IPv6 support in PowerDNS is incomplete. Zone transfers in master/slave replication are only functional with IPv4 transport.
11. ^  DNSSEC support in PowerDNS is currently restricted to being able to serve DNSSEC-related RRs. No further DNSSEC processing takes place.

Platforms

The operating systems or virtual machines the DNS server are designed to run on without emulation; there are several possibilities:

• No indicates that it does not exist or was never released.

• Partial indicates that while it works, the server lacks important functionality compared to versions for other OSs; it is still being developed however.

• Beta indicates that while a version is fully functional and has been released, it is still in development (e.g. for stability).

• Yes indicates that it has been officially released in a fully functional, stable version.

• Included indicates that the server comes pre-packaged with or has been integrated into the operating system.

• Software Appliance indicates that the server has the operating system built in as Just enough operating system (JeOS)

Please note that the list is not exhaustive, but rather reflects the most common platforms today.

1. ^  BIND is available for Windows NT-based systems (including Windows 2000, XP, and Server 2003) in a port known as ntbind.
2. ^  The functionality available with the Microsoft DNS server varies depending on the version of the underlying operating system; such as most Windows Server components, it is upgraded only with the rest of the operating system. Certain functionality, such as DNSSEC and IPv6 support, is only available in the Windows Server 2000-2003 version. Windows 2000 Server includes TSIG support. The Microsoft DNS Server is not available on Windows client operating systems such as Windows XP.
3. ^  Most well-known Linux distributions come with BIND either installed as default or with the option of only installing a caching-only configuration. Distributions installed as a typical server configuration will have the former and distributions installed as a desktop or workstation configuration will have the latter.^{[citation needed]}
4. ^  Secure64 DNS runs exclusively on SourceT, a micro operating system developed by Secure64.

Packaging

See also

• DNS management software

External links

• Don Moore's May 2004 DNS Internet survey
• The Measurement Factory DNS Survey Summary: April & June 2005
• Beehive/CoDoNS DNS Survey: July 2004
• ITU ccTLD DNS Survey