Domain Name System (DNS) in Computer Networks Explained transcript

Hello friends. Welcome to Engineering Funda family. In this video I am going to explain you DNS Domain name system and to understand DNS, let me show you how many things that I am going to cover in this video. See first I will be discussing about basics of DNS. Here I will give you one practical example in which I will show you in my computer with the use of Wireshark software, in which I will show you how DNS that is used to get IP address from domain names.

Right after that I will explain you how domain names are. They're like generic domain and country domains. That is how two general categories are there. Then I will be discussing about hierarchical access to domain name that I will explain you by one practical example, like how hierarchical approach is there with domain name. Then I'll be showing you how DNS database organization is there and how DNS entries are provided.

So both of these things that I'll be showing you by one practical scenario. And at last I'll be showing you two methods for address resolution. So address resolutions using iterative method and address resolution using recursive method that I am going to discuss that in this video along with one practical scenario. So let us try to understand first how basics are there with Domain Name System. So domain Name System that we use it to get IP address from domain names.

So first of all you should know what is IP address. There are two types of IP address IPv4 and IPv6. Right. And with the use of IP address only one can communicate with another computer. Without IP address we cannot communicate on computer network. Right. So to get IP from domain name we will be using DNS. So what is domain name. Domain name means google.com. That is one domain name. So to have a communication with Google you should be having IP of Google to get IP of Google, we will be using DNS right.

So when you write www.google.com you are writing domain name over here on web browser, right? You don't have IP of Google, but to get IP of Google first DNS frame that is getting forwarded and then DNS reply will come by, which user will get to know IP of Google. And now user can communicate with Google. So before communication user should be having IP address to get IP address DNS is used right DNS is using UDP protocol.

So let me show you that by one practical scenario. So that will give you more clarity. So let me take you to my computer screen here on my computer screen. You see here I'll be showing you DNS protocol frame. You see this is first one and this is second one. First one is request and second one is reply. Right. First one is request. You can say query and second one is reply. Now see what I was doing? I was trying to search something on Grammarly.

Now I was not having I was not having IP of Grammarly. Right. So you see, to access Grammarly, I just need to have IP to get IP. I am forwarding query. So this is my IP and this is IP of my router right. So I am sending frame to my router. Obviously I can communicate with router only right. My router is communicating to the internet. Now see this. My IP is sending request to my router regarding IP of Grammarly. That is DNS query you see here domain Name system query that is written over here.

Right. And see this domain name system that is implemented over UDP. And UDP is implemented here over IPv4. And that is implemented over Ethernet over here. Right. And then we are having frame. So this is my request. You see here query or request that you can say that is first frame. After that you see. This IP which is my IP that is destination IP means now my router's IP which is source IP. Now that is forwarding frame to me that is DMs, that is DMs response.

So by this DMs response. Now I am getting IP of Grammarly. Right now I am getting IP of Grammarly. Now once I am having. IP of Grammarly I can communicate with Grammarly. Right? So see to get IP of Grammarly I am sending. Frame that is DNS frame that is implemented over UDP protocol. Remember this right? So now I think you are having idea about what. What is that which we are doing. Right. So practically DNS protocol that we use it to get.

IP address from domain name, right from domain name. You will be trying to get IP address right. Once you have IP address you can communicate. So you can have your own domain name. As my website is there, you should know that website name is www.engineeringfunda.co.in So this is my domain name right now. As if you want to access this website. First you will be forwarding DNS frame along with DNS protocol. So that will be request.

Then you will get reply. In that reply you will be getting IP of my website. Once you have IP of my website, you can communicate on my website means you can access my website, right? See, IP addresses are dynamic. You should know that dynamic means with respect to time, IP will change. Before two days. When I was watching my IP of my computer, that was different compared to today, right? So IP address will change with respect to time, right?

IP addresses are dynamic that will change with respect to time. Recently accessed domains are stored in entries for faster access to the domain. So recently accessed domains are stored on your system, right? And based on that you can have faster access. The reason is every time you cannot ask for domain name and all those things, right. The domain name that you are having. But every time you cannot ask for IP address, one time you can ask IP address.

Once you have it, you just store it in entries. It will not change immediately, right? It will take some time. So how entries are stored. Let me show you that over here. See first there will be domain name. Domain name means you can have Google, Amazon or my website. That is domain name that we are storing with respect to IP address and that IP address that we get it with the use of DNS protocol. And along with IP there will be validity.

Or you can say TTL field. So that TTL field that will show you for how much time this IP and domain name are validated with each other. After this time, both of these entries that will get invalid. Remember this right? See, one more command is there that is known as lookup, by which you can get to know like how we can get IP address and see this Nslookup that is inherently using DNS protocol, right. Let me show you that on my computer screen.

So that will gives you more clarity. So here if you observe this is command prompt in which I have written nslookup space google.com. So see this server means my WiFi is my WiFi is initiating that communication which is asking for IP address of Google. So you see now name that is google.com that is having IP address. That is this. This is IPv6 address and this is IPv4 address. Let me show you one more example. nslookup space.

If I write yahoo.com. Now you see how many how many IPs are available with this. So that many IPv6 addresses are available with Yahoo and these are IPv4 addresses are available with Yahoo with which my computer can communicate to yahoo.com. And to get this IP DNS protocol that we are using. Right. So this is how things are there. So I think now you are having idea about how Nslookup is there and how DNS that is working right now.

Let me give bit clarity about how domain names are classified. See, in general you can say generic domain and country domain. That is how it is classified. These are main domains that you can see right? Generic means.com. .org .edu .net .mil That is how generic domains are there. .com that is used for commercial domains. .org is used for organizations. .edu that is used for educational institutions. .net initially that was used for internet service provider only.

But nowadays some companies are even using this .mil that is used for military organizations nowadays, probably with rare use. That is their right. Country domains are their country domains like with India. .co.in is their like my website. .co.in So last at last dot in is their that belongs to country India. At last if .jp is there that belongs to Japan. At last. if.uk is there that belongs to United Kingdom at last.

If .de is there, that belongs to Germany, right? So that is how country domains are. Their generic domains are there, right? Now let me explain you how hierarchical access that is there with domain. So first thing that you need to understand that is this dot. This dot explains root domain this dot that explains root domain. Then top level domain will be there at second level means after root domain there will be top level domain. top level domains are like .in .org .edu .com .net .uk right.

So those are top level domains. Right after that there will be second level domains. Second level domains are like.co.ac. You might have seen that even right. Like my website that is .co.in. There can be .ac.in. So these are second level domain. Wikipedia is also second level domain. And then there will be sub domain. Sub domain could be like en example. Let me show you one practical example. So that will give you more clarity right.

Like you see if I write engineering funda if I write engineering funda. So that is my that is my sub domain. The reason is I am taking it from GoDaddy. Right. So GoDaddy have provided this sub domain to me. And then there is .co so .co that is second level domain. And then there is . in right. So see this is my in total domain name where this dot this first dot that is domain root. Then dot in is there. That is top level domain. then .co is there.

That is second level domain and then sub domain. That is engineeringfunda Let me give you one another example. See in another example. What I'll be doing is I'll be writing en.wikipedia.org. Right. So now if you observe here this first dot, this first dot that is root domain, then .org that is top level domain. And then see Wikipedia that is second level domain. And then en en stands for English. So that is my sub domain with Wikipedia.

And then one can communicate with host system right. So see this is how this is how two examples that I have conveyed to you. So you should know how hierarchical access that is happening right. So root domain is there after that top level domain. That is how this top level domains are there. Then second level domain like .co.ac. Those are second level domain. And then en. An example. That is how some subdomains are there right.

Sometimes like my website is subdomain. So sometimes what happens you know like in competitive examination they may give you uh that domain name. And in domain name there can be question like what is subdomain with that domain name. What is second level domain with that domain name. What is top level domain with that domain name. See that kind of questions may come in competitive examination. So for that you should be ready right.

I think now these two examples are sufficient to understand that. Now let me explain you how DNS database organization is there. See there are three levels of organization that is distributed database approach that you should know right. First of all you need to remember these three names. That is quite easy one see root DNS server. After that the name server. And after that host server. That is how it is the right root DNS server.

Then name server and then host server. There are 13 root servers that is available in the world. And why? There are 13 root servers. The reason is single point failure is not allowed. Right. Like you might have seen tsunami have came to Japan. Now if root DNS server that is there in Japan and if single point failure is happening, then the entire world's internet will go down. So to avoid those situations, right now there are 13 root level servers that is available in the globe.

So single point failure will not happen. Right now root DNS server. After that there will be name server. Name server is like.com.in.org .net right. So those are name servers. After that there will be host servers. Host servers are like YouTube servers. Maybe they're Google servers, maybe they're Yahoo server, maybe they're Amazon server, maybe they're so those are host servers right. So DNS database organization that is happening like this root DNS server name server and host server.

Always remember this sequence. The reason is always DNS is DNS is fetching IP in this hierarchy only. Right. I will show you that by one practical example. But right now consider this hierarchy. See DNS entry that I have already told you. Once you take IP address from DNS, there will be entry. That entry will be as per domain name, then IP address, and then validity. Validity means TTL. That explains you for this much duration only this IP and this domain name, those are actively attached to each other.

After that that will get invalid. Right. So that is how DNS entries that is getting stored. And based on that only we are communicating on computer network. Now very interesting what that I am going to explain you. That is address resolution means how computer is taking IP address with the use of DNS. You see here one computer that I have shown. Now this computer is requesting for let us say any website. Right. So obviously to access website with the use of DNS first what we will be taking IP address of that website.

Right. But how. There are two ways. One is iterative and second is recursive. Let me explain you first iterative method. See what we do is this computer is requesting for website that will go to this router. Like I am having my computer in front of me that is connected with my router. So obviously I can request to my router only now my router will request it to a exterior environment. Right. So this is local server, which is my router, which is connected to root DNS server.

Now you see this router will be requesting root DNS server regarding regarding IP. So this root DNS server is saying what root DNS server is saying you should go to name server. How this root DNS server that will give this IP this IP in feedback. You see this IP in feedback. So now this IP that is there with this local server. So it will send request to this name server. Now this name server will give this IP to this local router.

So now this IP. Now that came to this local router. Now it will request to host server. Now host server will say okay this is my IP. Only you can communicate with me over here right. So if you observe here we are having iteration three. Iterations are there. First iteration that have happened with root DNS server. Root DNS server have given address of name server like see root DNS server that is having that is having database of everything right.

Like root DNS server is saying you should go to .com. so .com that is there with name server. I have told you see this name server that is that could be .com .in .org .net. Right. So root DNS server that is giving approach to name server. So name server again is giving approach to host server. So in iterations that is happening. That is one way by which this DNS will give IP of website to host. Right now. Second approach is quite interesting.

You see what is happening when this host is requesting for website's IP with the use of DNS at that time, this local server is requesting this DNS server. Now this DNS server is not having idea about what is the IP. So what it does is now it will not give feedback directly over here. What it does is it will ask to name server then name server will ask it to it to host server. Now host server will deliver exact IP to name server.

Now name server will deliver that IP to root DNS. Now that IP will come over here. So here local server is not doing iterations like this. Local server is just asking it to root DNS server. Root DNS server is approaching in this hierarchy. And it is taking that IP from host server. And it is giving it to this local server. Now this local server will give it to this host right. So this is recursive method right. So in recursive method local server that will approach once only while in in iterative method local server will approach is many times.

That depends on how many iterations are happening. Here I have shown you three level hierarchy right. There can be five level hierarchy. Obviously that is always possible. Right? So that is that that is possible over here in iterative method. So this is how address resolution that is happening. In short you just need to understand one thing as if this computer is writing google.com then this is domain. Now this computer wants IP.

So this request will be given to local server. Now it will request like this. Or it may request like this. Right. That depends on the approach. There can be iterative method or there can be recursive method. Right. At last this computer will get what it will get this IP right at last. But how much time how long it will take. That depends on which method that we use in iterative method. It will take bit more time. In recursive method it will take bit less time.

That is how things are there. If anything that would like to share, please note it down in comment section. I'll be happy to help you. Thank you so much for watching this video.