What is a zone (DNS zone)?

A DNS zone is a part of the domain name space for which a specific DNS server is responsible and in which DNS records are stored.

In simpler terms: a DNS zone is the area of responsibility of a DNS server.

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#Why a DNS zone is needed

DNS is a large distributed system. To make it manageable, it is divided into zones.

A DNS zone makes it possible to:

• distribute responsibility across servers
• manage domains independently
• scale DNS without a single "main" server

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#A domain and a zone are not the same thing

This is a common interview question.

#Domain

• a logical name in DNS
• part of the naming hierarchy Example: example.com

#DNS zone

• a set of DNS records
• stored on specific DNS servers
• describes how the domain is served

Usually a domain and a zone coincide, but technically they are different concepts.

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#An example for understanding

There is a domain:

example.com

The example.com DNS zone may contain records for:

• the site's IP
• the mail server's IP
• subdomains (www, mail, api)

And this zone is stored and served by an authoritative DNS server.

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#What is stored in a DNS zone

A zone holds DNS records, for example:

• A: domain -> IPv4
• AAAA: domain -> IPv6
• MX: mail servers
• NS: DNS servers for the zone
• TXT: service information

All of this together is the content of the DNS zone.

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#Types of DNS zones (very briefly)

For general understanding:

• Primary (master): the main zone, where records are edited
• Secondary (slave): a copy of the zone for fault tolerance
• Reverse zone: a zone for reverse lookup (IP -> name)

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#A real-life analogy

A DNS zone is like:

• a folder of documents
• for which a specific employee is responsible

The folder's name is the domain, the contents are the DNS records, the person in charge is the DNS server.

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#Short interview answer

Remember this formulation:

A DNS zone is a part of the domain name space for which a specific DNS server is responsible and in which DNS records describing the domain and its subdomains are stored.