Now, guys, let us try to understand the system architecture.
The honor system is nothing, but it is a group of servers called DNS Servers, which works in collaboration
with each other in order to implement the functionality.
So there are certain group of machines which works in collaboration with each other.
Those machines are called DNS servers.
So DNS system is nothing, but it is a group of DNS servers.
These DNS server machines are distributed all across the globe and these machines are distributed with
sufficient redundancy.
We will come back to this point later.
Machines are monitored and managed by central authority.
Right.
So global DNS server machines, which comes under central authority, works at two levels.
The first level is a root level.
DNS servers, which works at root level are called root DNS servers.
So you can see here it's a root DNS server.
The second type of DNS servers are called top level DNS servers.
These are the DNS servers which works at top level are called top level DNS servers.
So you can see in this diagram that below the root DNS server comes the top level DNS servers.
So you can see that there are only a handful of top level DNS servers.
The some of the examples I have shown here, Edu is a top level DNS server.
Similarly com in Arpa, org and Nat, these are all top level DNS servers.
The top level DNS servers works at one level below the root DNS server.
So you can see that DNS system is actually kind of tree like system.
It's a hierarchical system.
The root of this tree is the root DNS server, whereas the DNS servers, which works at one level below
the root DNS server, are top level DNS servers.
And remember root DNS server, along with top level DNS server are managed and controlled and look after
by the central authority.
Now let us discuss this point that what is meant by sufficient redundancy.
Now let's come to the DNS server.
Geographical distribution.
The DNS servers, that is the root DNS server and top level DNS servers are distributed across the globe.
So redundancy means that a same DNS server has been replicated at various geographical locations.
Around the globe.
For example, in this diagram, you can see that route DNS server has been replicated at these many
places.
It is done for the sake of fault tolerance and load balancing.
That is, if root DNS server, say K fails, then I will take the responsibility of route DNS server
K.
Whenever you access a website, the root DNS server is always used in order to map the website name
with the IP address.
Now there are hundreds of millions of peoples who are accessing the website all around the globe.
So one root DNS server cannot sustain such a great load of website requests.
So it is for this reason that load balancing is required and we need to maintain n number of root DNS
servers across the globe.
So here I have shown you the example of redundancy of root DNS server.
Not only root DNS servers are replicated, but also top level domain name servers are also replicated
in the same way.
So we do the redundancy of DNS servers for two purpose that is fault tolerance as well as load balancing.
In this map, I have shown you the distribution of root DNS server all around the globe.
In a similar way, the top level domain name servers are also replicated all around the globe.
However, I don't think it is required to show you the geographical locations of the distribution of
top level domain name servers.
But top level domain name servers are also distributed and replicated in the same way as root level
domain name servers are.