So guys, next we will going to discuss the hierarchical nature of a DNS system.
Now, DNS system by its design is highly hierarchical in nature.
Right now we know that there is one special DNS server called Root DNS Server.
This root DNS server is at the apex of DNS hierarchical system.
The other type of DNS servers are called top level domain DNS servers.
Now there are about 20 to 30 top level domain DNS servers, among which I have shown you the important
ones.
So this edu.
Com in arpa.
Org net.
ET cetera.
Are actually top level domain dns servers.
We can also call them as TLD servers.
That is short form of top level domain DNS servers.
Now, as I said, that DNS system is highly hierarchical system.
That is, there has to be a parent child relationship between these DNS servers.
So that parent child relationship is shown with the help of this dotted line, right?
So you can see that in this DNS system, the root DNS server is actually at the apex of the hierarchical
system, whereas these top level domain DNS servers are at the first level of this DNS hierarchy.
So top level DNS servers are actually the children of root DNS servers.
Now please note that the root DNS server, together with this top level domain DNS servers, comes under
the control of central authority.
This central authority is actually responsible for maintenance and protection of root DNS servers and
top level domain DNS servers, which are distributed all across the globe.
So this central authority is actually a body or a committee or and you can say an organization which
actually looks after the root DNS servers as well as top level domain DNS servers, which are distributed
all over the world.
Right now going to the second property of this DNS hierarchical system that the DNS servers, which
are higher in the hierarchy, only knows how to reach directly lower ones in the hierarchy.
So you can see that in this DNS hierarchy, the root DNS server actually has a database called DNS database.
In this database, the root DNS servers knows the IP address of all the top level domain DNS servers.
Now, top level domain DNS servers are the direct children of root DNS server.
Therefore, root DNS server is supposed to know only the IP address of DNS servers, which are its direct
children.
So you can see in this DNS database the IP address of each of the top level domain DNS servers is stored.
Similarly, the DNS servers, which are one level below the root DNS servers.
That is, let us say for example.
Com.
DNS server will also have its own database called DNS database.
And in its DNS database it will going to store the IP address of DNS servers, which are at second level
of this DNS hierarchy.
So you can see that in the DNS database of com top level domain DNS server, you have an entry for Microsoft
DNS server and Google DNS server.
Right now.
What does that mean?
It means that Microsoft Corporation is running its own DNS server, and the name of that DNS server
is Microsoft DNS Server, and that Microsoft DNS server is registered under.
Com DNS server.
Right.
So Microsoft must have paid to this central authority in order to have their entry of IP address in
the DNS database of.
Com DNS server.
Right.
And same is true with Google DNS server.
So you can see that this is a DNS server for Microsoft.
This is a DNS server for Google.
So each DNS server has a name that is Google's DNS server has a name, Google.
The Microsoft DNS server has a name called Microsoft, and the top level domain name servers has a name
like.com like.edu.n.arpa.org.
ET cetera.
Now, one thing to note here is that now one thing to note here is that the root DNS server, along
with the top level domain DNS servers, are under the supervision of some central authority.
But what about Microsoft and Google DNS servers?
Of course, because it's a Microsoft DNS server, the Microsoft is responsible to look after their own
DNS servers, right?
Similarly, Google will be responsible to look after its own Google DNS servers.
The central authority has nothing to do with the management or control over the.
Organization specific DNS servers.
So Microsoft or Google DNS servers are the DNS servers, which are under the authority of their respective
organization.
Right.
So Microsoft, that is Microsoft is a DNS server for Microsoft.
Now, it is very much possible that Microsoft can maintain its another DNS server, which is actually
a direct children of its parent DNS server.
So in this example, you can see that Microsoft has installed another DNS server called Support.
And because this DNS server is actually a children of another Microsoft DNS server, therefore support
DNS server is called subdomain DNS server.
And as I said, that coming to this point, that is every DNS server, which is higher in the hierarchy,
only knows how to reach the directly lower ones in the hierarchy.
So you can see that in Microsoft DNS servers, DNS database, there is an entry for support DNS server.
Right.
So Microsoft DNS servers know how to reach the support DNS server because in its DNS database it has
an IP address.
And this IP address is the IP address of support DNS server.
So same is true with Google.
That is, Google has also launched its another sub domain DNS server called mail.
So you can see that how DNS system is highly hierarchical system by design.
And coming to the last point, that is the DNS servers which are at the leaf of the DNS tree, right.
Those DNS servers contains the IP address of the servers, which actually provides the service.
So you can see in this diagram that what are the DNS servers which are at the leaves of the tree.
Those DNS servers are supported DNS server and mail.
DNS server.
Now, if you look at the DNS database of support, DNS server, the DNS database of support, DNS server
stores, the IP address of server, whose name is customer.
So within the Microsoft network there will exist a server called Customer whose IP address is 212.1
32 .1.2.
And it is this customer server which actually provides a service.
Now that service could be an access to the Microsoft website.
So note that that customer is not a DNS server, it's a normal server which actually provides a service
to the end user.
Whereas all other black boxes that you can see on this slide are actually domain name servers.
Also one thing to note that that these dotted lines are actually not a physical length, but they are
logical links.
Now, logical links means that, for example, the.com DNS server can reach the Microsoft DNS server
or Google DNS server through L-3 Network.
That is the com and Microsoft or Google DNS server could be geographically located anywhere in the world.
They need not be placed together and they need not be connected via physical link.
So now, having understood the hierarchical nature of this DNS system, now I ask you one question.
What you have to do in order to have your own website launched publicly and you want the rest of the
world to be able to access your own website through your website domain name.
So let us discuss that in the next slide that what actually are supposed to do in order to make your
website accessible through its domain name.