Welcome to the ITFreeTraining video on DNS namespace. This video will show how the DNS
namespace is broken up and stored on different servers allowing decentralized administration
while still allowing centralized control. All this is important in order to keep control
on the internet while still allowing flexibility to individual administrators.
When looking at the DNS namespace it is important to understand the term fully qualified domain
name. A fully qualified domain name is essentially a complete Domain name. Some examples of fully
qualified domain names are given. Remember that DNS is a system that allows
a client to translate a friendly name like example.com into an IP address. To do this,
DNS uses a hierarchy of servers in order to determine the IP address of a fully qualified
domain name. Once DNS has resolved the name, it is returned to the client.
It is hard to estimate how many domain names are currently in use on the internet at any
one time, but estimates indicates there are over 200 million domains currently in use.
With so many domain names in use, the namespace needs to be divided up for administration
and performance reasons. Without dividing up the namespace, DNS would be difficult to
implement and difficult for there to be decentralized control.
So how does DNS divide up the namespace? At the top of the namespace is the root domain
which is represented by a dot. This forms the top of the hierarchy. On the internet
there are over 300 root servers which start the resolving process.
The root server's job is to provide help to resolve the next part of the address. When
looking at the DNS name they are resolved from right to left. All DNS namespaces end
with a dot even though you do not need to put the dot at the end when resolving DNS.
The DNS sever will add the dot automatically. The next part of the address is referred to
as the top level domain. This contains the next part of the address, which can be com,
net or country codes like UK or AU just to name a few.
The next level is the second level domain. These can be registered by individuals or
companies. This is where the administrator gains some control over the DNS namespace.
Once a second level domain is registered, the administrator is then free to create any
child level domains that they wish. These child domains are referred to as third level
domains, but the administrator is free to also create fourth and fifth level domains
if they require. The administrator effectively has control of the DNS namespace after the
second level domain and can add as many or few child domains as they require. This includes
additional child domain like www or ftp. Let's consider an example of how a client
would go about resolving a DNS name ITFreeTraining.com. Firstly, the client would send a request to
its DNS server for the IP address of ITFreeTraining.com. The server would look in its cache for the
IP Address. If the IP address for ITFreeTraining was not in the cache, the DNS server would
need to locate a DNS server on the network that knows the IP Address.
Remember that DNS is hierarchy based and administrators are at the second level domain, which means
they have control over the DNS name. For example, if they wanted to change the IP address pointed
to by the DNS name they could do so at any time.
So how does the DNS server know which DNS servers on the internet have information about
ITFreeTraining and how does it know this information can be considered correct? A DNS server that
contains records about a DNS domain is considered to be what is called authoritative. An authoritative
DNS Server means that information on this server is considered to come for the source
or, in other words, come from the administrator of that DNS domain.
So the question arises, how does the DNS server find an authoritative DNS server in order
to get the correct answer? First of all, the DNS Server will contact a root hint server
to obtain the IP Address of a DNS server that can resolve dot com addresses. The address
of some root hint servers are pre-configured in the DNS Server and thus this is how the
DNS Server knows where to start the process. Once the DNS server has the IP address of
a DNS Server that can resolve dot com addresses, it will then contact the dot com DNS server.
This dot com DNS server will return the IP Address of a DNS server that can resolve the
domain name ITFreeTraining. With this information, the DNS server can
now contact the ITFreeTraining DNS server and obtain the most up to date record for
IP addresses associated with ITFreeTraining.com Once the DNS request has been resolved, the
result will be stored in the cache for the DNS server. Also the IP Address of the root
hint server and the dot com DNS server will be stored in the cache.
In the real world, the root hint server will often also have top level domains like dot
com stored on it as well, but I am sure that you get the idea how each part of the DNS
name is looked at and broken down. Using this method means DNS can have centralized control
but still allow administrators to make their own changes to domain names that they register.
The good news with root hints is that they are configured by default and normally there
is no need to change them. In some rare cases on an internal network an administrator may
disabled the root hints servers or create their own root hints servers. This is however
is rare and only done in special circumstances. The majority of administrators will never
need to make changes to the root hints servers or disable them. Most companies will forward
DNS requests to their ISP DNS server. Since their ISP's DNS server resolves a lot more
requests than the company, there is a good chance the ISP's DNS server has already
resolved the DNS request. This is a much more efficient way of resolving DNS names rather
than the company DNS server having to resolve each DNS request itself. When a DNS server
is configured to forward DNS requests to another DNS server, the root hints values will not
be used. Thanks for watching this video on the DNS
Namespace. More videos to come including demonstration videos on how to configure DNS to meet the
needs of your organization. Thanks for watching and see you in the next video.