 I am working as a student professor in computer science and engineering department at Walton Institute of Technology, Solaapur. Today, I am going to give the lecture on DNS, DNS is domain name system. Now, let us see the learning outcomes of DNS. At the end of this session, the students will be able to explain the concept of DNS protocol. Second one is students will be able to explain the types of DNS protocol. These are the different topics I am going to cover in this lecture that are need for DNS, namespace, domain namespace, distribution of namespace. About DNS, domain name system is a hierarchical decentralized naming system for computers, services or other resources connected to the internet or private network. The domain name system delegates the responsibility of assigning domain names and mapping those names to internet resources by designing authoritative names servers for each domain. This is a purpose of why we have to use DNS. In this diagram, I am going to explain how the client can send the request and then how the server can assign some IP address to the client request. This user, this is a user, this user can send the host name to the file transfer client. This file transfer client can collect the information from the user, then it can send it to the DNS client that is host name whatever the host name, how issued from the user can send it to the DNS client, the DNS client can search the information in the store data that can DNS host name can send it to the DNS server in the form of query. After receiving this query in the DNS server side, it can assign some IP address to the DNS client query and then in the form of response it can send it to the DNS client. DNS client can after receiving the response from the DNS server it can check the IP address assigned to this host name then that assigned IP address instead of sending the host name it can send the IP address to the file transfer client and then the file transfer client can access that assigned IP address outside I mean in the transport layer. Name space, name space to be unambiguous the names assigned to machines must be carefully selected from a name space with complete control over the binding between the names and IP addresses. In other words the names must be unique because the addresses are unique. The name space that maps each address to unique name can be organized in two ways that are flat name space and hierarchical name space. Now what is flat name space? The flat name space a name in this name space is a sequence of characters without structure. Name may be or may not have a common section. It has no meaning, it cannot be used in internet because in the flat name space there is no proper structure for finding the path name or domain name. If the user want to find out the proper structure then they can go to the hierarchical name space. In the hierarchical name space the first part defines the nature of organization, second part can define the name of organization, third part can define departments in the organization and so on. The central authority assign only the first two parts the name space the rest of the parts are assigned organization itself. The organization can add prefix or suffix to the name to define its host or resources. This is a domain name space when we have a hierarchical name space domain name space to be designed in that the three names are defined in an inverted tree with one or root at the top. The tree can have a only 128 levels and level 0 is a root to level 127. This is a block diagram this can indicates the root and then this part this whole line is in level 1, the second line is a level 2, level 2, level 3, level 4 until we have to select 127 levels. This is a root it is a null string. Now what is level? Each node in the tree has a level which is a string with a maximum of 63 characters. The root label is a null string, second one is domain name. A full domain name is sequence of labels separated by dots. The domain names are always read from the node up to the root. Finally it ends with the null or root. For example, this is a good example for domain name space. This is a root and this is a leaf level. It should auto starts from leaf level to the root. A label 0, 1, 2, 3, 4 like this it will go. That is first is challenger, ATC, FSDA, EDU. These are the labels and we can also call it as domain names. The full path name is challenger dot ATC dot FSDA dot EDU. This is a full path name. Then we have to start from leaf to the root. Based on this one they have given two DNS parts that are PQDN, FQ end with the root. Now let us see FQDN. Partially qualified domain name is the complete domain name for the specific computer or host or internet. FQDN, the PQDN partially qualified domain name. If a label is not terminated by null string, it is called PQDN. I mean in this example, this is fully qualified domain name. These are the partially qualified domain names. Domain name space. Domain is a subtree of the domain name space. The name of the domain is the domain name of the node at the top of the subtree. This is an example. This is a diagram can contains a different domains. This is a root server. These are the different domain. Two domains are there dot EDU, then dot dot com dot EDU, commercial educational. This is a full one domain is there. Under EDU, one more sub domain is there. That is this green part can indicates a separate domain. Here is also three domains are there. This one is separate domain. This one is also separate domain. And this is also separate domain. Subdomains are there under main domain. Main domains are dot com dot EDU. Think and write. This session can contains one question that is list the difference between FQDN and PQDN. Now pass the video and answer the question. Now let us see the answer for the above question. FQDN, fully qualified domain name. FQDN is the complete domain name for a specific computer or host, a host or on the internet. FQDN consisting of two parts, a host name and domain name. If the label is terminated by null string, it is called FQDN. For example, challenges dot ATC dot FHDA dot EDU. Then partially qualified domain name. If the label is not terminated by null string, it is called partial PQDN. It starts from the node and but it does not reach the root. Here the resolver can supply the missing part called suffix to create an FQDN. For example, challenges dot ATC dot FHDA. Here this is a challenges one separate and I have given the comma and then ATC dot FHDA dot EDU. This one is an example one more one more example and null is another example. These are three examples for partially qualified domain name. Distribution of namespace. To store the huge amount of data in a single system, it is a user may face the problem. For that we have to use distribution of namespace concept. The information contained in the domain name, domain namespace must be stored. It is inefficient also unreliable. It means to store huge amount of data in a single system after storing the huge amount of data in a single system. If the user want to assign that work or the data to some other users, then that time the user may face the problem for searching the required data. For that purpose, the domain name system we have to use in the internet also. The hierarchy of based on that only they have given hierarchy of name server. First one is root server. Here we have to use root and zone also root server. Root server is a server whose zone consisting of the whole tree. Root server usually does not store any information but authority to other servers. Based on that only they have given two servers that are primary server, secondary server, primary server. Primary server have an authority to store the file about the zone, responsibility for creating, maintaining and updating the zone files. Then secondary server that transfer the complete information about a zone from another server and stores the file on its local disk. Here both primary and secondary server have an equal authority for maintaining server. These are the references I use for preparing the above PPT. Thank you.