zone vs domain

Chris Buxton cbuxton at
Tue Dec 1 06:06:49 UTC 2009

On Nov 30, 2009, at 9:43 PM, Mark Andrews wrote:
> In message <402431.44413.qm at>, gmspro writes:
>> What's the main difference between zone and domain?
>> It's confusing to me,I'm searching though,i got once,"zone is a portion of do
>> main".
>> Can someone give example to clear things up?
>	SOA  (
> 		    1 3600 1200 3600000 1200 )
>	NS
> A
> A
> All the above form a zone which would be called
>, and are individual domains
> within the zone.

While that's true assuming there are no other records in the zone, consider what happens if you add this record:  NS

Now the "" domain extends below the bottom of the zone.

Ahem... (puts on lecturer robes...)

The domain name system is structured as an inverted tree, with a root at the top and other nodes below. Each node has exactly one parent, except for the root node, which has none.

A "label" is the short name given to a particular node.

A "domain name" is the full name of a node. It is equal to the name of the node and all of its ancestors, in order from the node itself to the root, left to right, separated by dots.

A "domain" is a subtree of the namespace - a given node and any and all descendants. It is named for the node at the top (the "apex"). The entire namespace is a domain named "." (which is how we write the name of the root node). Every domain name corresponds to a domain, although possibly a domain containing just a single node.

A domain can be divided administratively into units called "zones". A zone, like a domain, has a single node at its apex. The difference is, there can be a cut in the namespace separating a child zone from its parent. That is, a zone is equal to a domain of the same name (i.e. having the same apex) minus any child zones.

For example, consider the following well-known domain names:

"." (the root)

Each of these domain names except the last is the apex of a zone. All of them are the apexes of domains. The node named "" is a member of each of these domains, but only one of these zones ( That's because the zone "" is delegated (separated by an administrative cut) from its parent, "com.", although it is still a member of the "com." domain.

Is it clear yet?

Chris Buxton
Men & Mice

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