What Is A Zone File?

Date First Published: 15th April 2022

Topic: Computer Networking

Topic: Network Identifiers

Article Type: Computer Terms & Definitions

Difficulty Level: 9/10

Learn more about what a zone file is in this article.

In DNS, a zone file, also known as a master file, is a text file that contains information about all the resources for a domain name, such as the DNS records, the admin email address, the nameservers, the IP address to domain name mappings, the reverse lookup of an IP address to other domains, and more. Because zone files are text files with the .zone file extension, they are portable and can easily be edited with text editors, such as Notepad. In the event that unauthorised users gained access to the zone file and made modifications to it, it could cause websites to fail to respond or even point to the wrong web server. Because of this, it is important to keep zone files safe and keep regular backups of them.

An example of a zone file can be seen in the image above.

Note:

They are called zone files because they define the zone that the nameserver manages.

Each line of text is known as a resource record (RR). These define the forwards lookup of the domain name to the IP address as well as the reverse lookups of the IP address to the domain name. Additional records can be added to a zone file. Once the additional records have been added, it is necessary for them to be separated with a full stop. Semicolons can be used to add comments to a zone file and multiline comments can be added by brackets. Multiline comments are ended with a bracket placed on a single line.

History

Zone files have been around since 1987. They were developed by the ISI (USC Information Sciences Institute). The format of a zone file is defined in RFC 1035 and RFC 1034, which was originally used by the Berkeley Internet Name Domain software package.