zone vs domain

[Chris Buxton]

On Nov 30, 2009, at 9:43 PM, Mark Andrews wrote:
> In message <402431.44413.qm at web112611.mail.gq1.yahoo.com>, 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?
> 
> example.net.	SOA ns.example.net. hostmaster.example.net.  (
> 		    1 3600 1200 3600000 1200 )
> example.net.	NS ns.example.net.
> ns.example.net. A  1.2.3.4
> www.example.net. A 1.2.3.5
> 
> All the above form a zone which would be called example.net.
> 
> example.net, ns.example.net and www.example.net 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:

sub.example.net.  NS  ns.sub.example.net.

Now the "example.net" 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)
com.
example.com.
www.example.com.

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 "www.example.com." is a member of each of these domains, but only one of these zones (example.com.). That's because the zone "example.com." 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