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Lesson 5 Zones
Objective Define the Concept of Zones as used in the DNS Namespace.

Concept of Zones as used in the DNS Namespace

A branch of the DNS namespace under the administrative control of some entity is called a zone. A company that registers the domain name company.com gains administrative control of the company.com zone. However, it also gains administrative control of other zones. At the very least, it gains control of the in-addr.arpa zones corresponding to its network addresses. For example, suppose that company.com has two Class C network addresses ( and Then company.com will have control over the company.com zone, and the two reverse zones 14.132.197.in-addr.arpa and 15.132.197.in-addr.arpa.

The entire collection of DNS administrative domains throughout the world are organized in a hierarchy called the DNS namespace. This section shows how the namespace organization affects both local domains and the Internet.
Like the UNIX file system, DNS domains are organized as a set of descending branches similar to the roots of a tree. Each branch is a domain, each subbranch is a subdomain. The terms domain and subdomain are relative. A given domain is a subdomain relative to those domains above it in the hierarchy, and a parent domain to the subdomains below it.

Name Hierarchy

  1. Unique domain suffix is assigned by Internet Authority
  2. The domain administrator has complete control over the domain
  3. No limit on number of subdomains or number of levels
  4. computer.site.division.company.com
  5. computer.site.subdivision.division.company.com
  6. Domains within an organization do not have to be uniform in number of subdomains or levels Name space is not related to physical interconnection, for example, math.ohio-state and cis.ohio-state could be on the same floor or in different cities
  7. Geographical hierarchy is also allowed
  8. A name could be a subdomain or an individual object

Domains and Subdomains

DNS namespace hierarchy
DNS namespace hierarchy