Internet Guide Logo

DNS Root Zone File

Last Edit: 27/03/17

The DNS root zone file is a small data set file - it is currently 2.12 MB (2,232,320 bytes) - and is edited / provided by the Internet Assigned Numbers Authority (IANA); who are overseen by ICANN. The DNS root zone file is located on 13 root zone servers - who are operated by 12 organisations / managers. The DNS root zone is the highest level in the hierarchy of namespace in the Domain Name System (DNS). The Domain Name System (DNS) is an Internet naming system that provides alphanumeric domain names and converts them into IP addresses; helping users more easily locate resources on the Internet. The DNS root zone is a nameless zone that contains information about the Top Level Domains (TLDs) in the Domain Name System (DNS).

The most well known TLDs are: com, org, edu, gov and net. The companies that administer these domains are named registries and they operate the authoritative name servers for these Top Level Domains. For example, Versign is the registry for the com Top Level Domain; over 100 million domains (Second Level Domains) have been registered in the com Top Level Domain, and over 900 accredited registrars register and manage these Second Level Domains in the com domain for end users. The oldest com domain name - registered in 1985 - is symbolics.com; other old domains, registered in 1985 are: think.com, xerox.com, and DEC.com. A full list of the TLD operators can be found at: iana.org/domains/root/db.

The root zone file contains the address of the authoritative name server for each Top Level Domain (TLD). The root zone file is currently available at the following addresses:

The root zone file is a data set file, therefore fairly incomprehensible for human readers, a snippet of the file is as follows:

ns1.dns.nic.aaa. 172800 IN A 156.154.144.2
ns1.dns.nic.aaa. 172800 IN AAAA 2610:a1:1071:0:0:0:0:2
ns2.dns.nic.aaa. 172800 IN A 156.154.145.2
ns2.dns.nic.aaa. 172800 IN AAAA 2610:a1:1072:0:0:0:0:2
ns3.dns.nic.aaa. 172800 IN A 156.154.159.2

The above snippet of the root zone file shows the following DNS record fields: Address Mapping records (A) and IP Version 6 Address records (AAAA).

The root zone file is the ultimate authority that DNS servers query to resolve a naming issue. It should be obvious that the root zone file - being only 2 megabytes - does not store all the information of the DNS in one place, the DNS is a distributed database, where multiple servers / locations process DNS queries. The burden of processing DNS queries is spread amongst these name servers, but the root zone servers (13 in total) are the ultimate resolver of a naming issue and these are the servers that publish the root zone file.

The data in the root zone file changes and the changes in the file are edited by the Internet Assigned Numbers Authority (IANA). Common reasons for editing the root zone file: if the address of an authoritative name server changes; a new Top Level Domain is created; or the registry for a Top Level Domain is changed. Therefore, it is recommended that DNS servers download the root zone file every 24-48 hours to ensure the DNS data set they are using is accurate.