The Internet uses the Domain Name System (DNS) to associate numeric computer IP addresses with human readable names. The top level of the domain name hierarchy, the DNS root, contains the top-level domains that appear as the suffixes of all Internet domain names. The most widely used (and first) DNS root is administered by the Internet Corporation for Assigned Names and Numbers (ICANN). In addition, several organizations operate alternative DNS roots, often referred to as alt roots. These alternative domain name systems operate their own root nameservers and administer their own specific name spaces consisting of custom top-level domains.
The Internet Architecture Board (IAB) has spoken out strongly against alternate roots in RFC 2826.
The DNS root zone consists of pointers to the authoritative domain name servers for all TLDs (top-level domains). The root zone is hosted on a collection of root servers operated by several organizations around the world that all use a specific, approved list of domains that is managed by ICANN. By contrast, alternative roots typically include pointers to all of the TLD servers for domains delegated by ICANN, as well as name servers for other, custom top-level domains that are not sanctioned by ICANN. Some alternate roots are operated by the organizations that manage these alternative TLDs.
Zach Bastick proposes that alternative DNS roots have allowed for more democratic control of the Internet:
"The implementation of alternative gTLDs predates any significant debate on name space extension by official actors, and this exemplifies how democratising the DNS alters the pace of developing Internet policy, the nature of decisions that justify that policy development, and political dynamics and user autonomy in the network infrastructure." (p.103)
Unless one specifically changes their DNS resolution settings, alternative DNS top level domains are generally unreachable, and very few Internet service providers provide this configuration by default.
Some organizations provide alternate DNS root services, such as additional Top Level Domains.
Emercoin provides the top level domains .coin, .emc, .lib, and .bazar via a blockchain-based DNS resolution service. Resolution is also provided by OpenNIC.
Namecoin supports the alternative top-level domain .bit. The alternative domain .bit is resolved by any computer running a namecoin full node and bridging software such as, nmcontrol, ncdns, and the freespeechme browser plugin. A centralized server which bridges DNS and Namecoin can also be used, meaning that users who use the centralized server do not benefit from Namecoin's decentralized and secure nature. Alternatively, its resolution is also provided by OpenNIC.
New Nations provides domains to nation-states that aren't listed in the ISO 3166-1 standard and therefore do not have their own ccTLD delegated to them. For example: .ko (Kosovo), .ku (Kurdish people), .te (Tamil Eelam), .ti (Tibet), and .uu (Uyghur people). Domain name resolution is provided by a peering agreement with OpenNIC or New Nations' own DNS resolvers.
OpenNIC is a user owned and controlled alternative to InterNIC and ICANN providing a non-national democratic alternative to traditional domain registries. OpenNIC servers are able to resolve all ICANN top-level domains, some OpenNIC original top-level domains, and the resolution of other Alternate DNS Roots with which they have reached peering agreements.
eDNS (Enhanced Domain Name Service) was founded by a coalition of ISPs led by Karl Denninger of the Chicago-area MCSNet. It ceased operation in 1998. It served the following domains: biz (general business use), corp (corporations), fam (for and about family), k12 (for and about children), npo (non-profit organizations), per (personal domains), web (web-based sites, Web pages).
One of the notable challengers to ICANN's control of the DNS namespace was Open RSC (Open Root Server Confederation), a group that grew out of private discussions and developed into a public mailing list. It grew large enough that the group decided to submit an application to the United States government to run the DNS.
The organization posted bylaws and articles of incorporation outlining ORSC's position following extensive public discussion regarding the manner in which the DNS was operated.
ICANN chairwoman Esther Dyson acknowledged adopting features such as membership from ORSC in her response to the United States Department of Commerce.
ORSC publishes a root zone containing additional top level domains not found in the ICANN root zone.
Microsoft offered the RealNames service on its Internet Explorer browser address bar. RealNames, to users of Internet Explorer, was in effect a domain registry. RealNames shut down operations in 2002 following a decision by Microsoft to redirect the 1 billion page views per calendar quarter that RealNames was resolving from the browser address bar into its MSN search engine.