IPv4 3 transcript

Okay, we'll start with subnet mask. So what is a subnet mask? Consider 192 168 1.0/24. This is an IP address. Now every IP address has two parts. One is the network portion, another is the host portion. So any IP address that you bring, it has got two parts. One is the network portion, another is the host portion. Now please if you think that this is the network portion and this is the host portion this is completely wrong this is how or this is the host portion this is the network portion anyway this is not how it works okay so we will look which is the network portion and which is the host portion now every IP address has two parts network portion and host portion we don't know which is the network and we don't know which is the host leave it as it is every IP address is accompanied by a subnet mask now look at Okay, very carefully.

Every IP address is accompanied by a subnet mask. This is the subnet mask. So this is the IP address and this is the subnet mask. Subnet mask is a 32-bit number. Now look at here very carefully. IP address is also 32bit. Subnet mask is also 32bit. But here if you look at here it looks like an IP address but it doesn't look like an IP address. We'll come to that point later. Now, subnet mask is a 32-bit number that helps you to separate the network portion from the host portion.

So, if I say this is the IP address 192 168 1.0, it has a network portion and it has a host portion. This /24 which I say is the subnet mask will help me to identify the network portion and the host portion. Now very important to understand here there is something something called subnet mask and there is something called cider value. Now if you write /24 this is called cider value and this /24 can be written as 255.255.255.0 and if you write like this way it is called subnet mask.

So if you write /24 that is cider value. If you write subnet mask it is 255 255 255.0. Now they both represent the same thing. They have the same meaning. This is just a different way of writing. But that is why when we say 32 bits the subnet mask if you look at here this is 32bit. It looks like an IP address. Okay. It helps to identify the network portion and the host portion. Okay. Now look at here very carefully. It can be written in two ways.

If you write like this way, we call it cider. It is easy to write. And if you write like this way, we call it a subnet mask. If you write like this way, we call it a subnet mask. Now let us consider this number 192 168 1.0. Okay, it is important to remember. It is important to understand the slash value represents the number of ones. So if you see here / 24 that means there are 24 ones. So 1 1 1 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 and look at here 8 + 8 16 + 8 24 and rest of them are 1 2 3 4 5 6 7 8 zeros.

Okay. So that is why you get here 24 255 255 255 and zero. In the same way if you see slash8 /8 means there are 8 1's 8 once is equivalent to 255. If you convert 8 ones in binary to decimal you will find 255 and rest of them are zero. So slash means the number of ones that you have. Okay. And you cannot have more than eight ones in one in one octed. So you have you divide them you put them as an octed and that is how you get the subnet mask.

Okay. Um I think it should be fine here. Okay. So if you look at here what it says uh when the subnet mask is converted to binary the once denoted the network portion while the zeros denoted the host portion. Now look at here very carefully the ones denoted the network portion and the zeros denoted the host portion. Let us consider this one. So if you look at here the cider for this um subnet mask is slash8. So if I do here 10.0.0.08 0/8.

So that means there are eight ones 2 3 4 5 6 7 8 which is equivalent to 255. So you've got 255 and rest of them are zeros. Now again if you convert them into binary it will be eight ones and rest of them will be zeros. Zeros zeros. what it says when the subnet mask is converted to binary the ones denoted the network portion while the zeros denoted the host portion. So if I consider this an example then what's going to happen?

This is the network portion. This is the network portion. I will write it as N. And this is the this is the host portion and I will write it as H. Okay. So this is the network the network portion is the network portion is always on the left hand side and the host portion is always on the right hand side. Very important to understand network portion ends host portion starts. Okay. So you will never have a combination of network host network host or something like that.

So network portion will be always on the right hand side. The network portion ends. It can end at any point and from there the host portion starts and it will finish the number. Okay? So you'll never see that one. The first eight bits are made up of ones and that that is the network portion. Hence the notation 10.008 the number after the slash indicates the network portion. So if you look at here very carefully we have slash8 that means we have eight binary ones [snorts] and this is the equivalent to and this is the network portion.

So slash8 the number after the slash indicates the network portion. So you know that this is the network portion. This is the network portion and this is the host portion. Now let me go a little bit to make it more clear. So if you look at here very carefully, what I'll do here is what I will do here is let's uh let's put this binary here. 1 2 3 4 5 6 7 8 and 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 Now look at here very carefully. 10 dot 0 dot 0.0.

So this is the network portion. Whatever number instead of 10 you could have let's say 128 you could have here 171 doesn't matter whatever is the number this portion this octed is a network portion and this octed is the host portion these three octets are the host portion host portion host portion network portion you cannot change the network portion it is always fixed the host portion is up to the user how the user wants it to be used.

So you can change number from this portion. You cannot change anything from the network portion. Never ever you cannot change anything from the network portion. It is always fixed. And um the host portion is there. Now look at here very carefully. We need both of them. Why we need both of them? Just think like this way. If you want to go to someone else's house, let's say this is a house. Okay? This is a house. You need the road number at least and also the house number.

Okay. And also the house number. Okay. Now um so with one of them you cannot work simply. Okay. So think like this way. You need both the network portion and the host portion. Okay. Uh why? We will come to that point later. I think uh you understood this one. There is no more questions with this one. Okay, let's move on to another example. We have 192 168 1.0/24. Now / 24 which is means 24 ones. 24 ones and which will be 255255255.0.

Now look at here very carefully. The decimal is 255 255 255 0. The binary is 24 ones, 24 ones and 8 zeros. Okay. Now look at here. 24 1's 8 zeros. So if you add 24 + 8 which is equals to 32 bits. Okay. This is the binary portion. Now this is the binary. So if you look at here 24 ones and eight zeros, the first 24 bits are ones and it is the network portion. So anytime you see slash8 there is eight there is eight bits and this is the network portion that means 8 bits network portion.

If you see / 16 that means there are 16 bits network portion. If you see / 24 that means there are 24 bits network portion. Hence the notation is / 24. 8 bits are made up of zeros and that's the host portion. Network portion you cannot touch it. Host portion you can play with it. You can change the number and you can assign you assign IP address from the host portion but the network portion remains the same. The network portion cannot be changed.

Now if you remember we have we will be working mostly with three classes class A, class B, class C. If it is class A by default if nothing is given you consider /8 is the default subnet mask. If nothing is given by default you consider for class B the uh the subnet mask is SL16 and for class C the cider is SL24 okay or the subnet is SL24 okay this is what is the default value if nothing is given but if something is given that is different okay but if nothing is given then we consider these are the default values and they have to be memorized they have to be memorized and if you use logical like you see 8 16 24 A B and see the total number of possible hosts.

Now if someone gives you um a network okay how can you find how many hosts you can accommodate okay because based on these values the number of hosts will differ the total number of possible host IP address on a network is 2 to the^ 8 okay so what is 2 to the power a h 2 to the^ h is the number of host bits okay so look at here very carefully 2 to the^ h is the number of host bits Now look at here very carefully. If I'm taking class C which the default cider is / 24 that means you have 24 network bits and you have eight host bits according to the formula is 2 ^ 8 h.

So get 2 ^ 8 which is 256 IP addresses. So you can produce 256 IPs from the class C address. That is the max IPs that you can produce. You cannot produce more than that. Now look at here very carefully. H represents the number of host bits zeros in the sub mask. So if it is class B is the same thing which is /6. So you will have two 16 network bits plus 16 host bits. So you have 2 ^ 16. Okay, it will be something uh you need to do the calculation that is the what is the value of 2 ^ 16 will be the maximum IPS then that you can produce from from a class B with class A is the same thing.

Okay, but um with class A it is /8. So you have eight network bits that means 24 host bits. So you will be able to produce 2 ^ 24. Imagine 2 to the^ 24 IPs. What will be the value is the max IPS you can produce from here. Now I will erase B and C sorry B and A because I need to discuss two things from here as well. Now even though it produces 256 IP addresses however you need to subtract two IPs. So you can assign only 254 IPs.

You can assign 254 IPs usable. Why 254 IP usable? Because you deducted two. Now the question is why did I deducted two? Because there are two numbers there are two addresses that you cannot assign to anyone. One is the network address. Another is the broadcast address. Okay. Now what is the network address? It will be all host bits zeros. that is the network address. In other words, the first address of the first address.

Okay. Now, if I can give you an example, think like this way. Let me take a class C 192 168.1. This is class C. We don't have any problem with that one. And the slash value is /24. When I say slash24 your So if I if I u if I can write this one here. Just give me a second. 192 will be one. 1 1 1 2 3 4 5 6. 168 would be something 1 Z um 128 0. Then um 64 32 1 2 3 4 1 5 and then one will be 1 2 3 4 5 6 7 8 and the other one will be same. 1 2 3 4 5 6 7 8.

This is this one. And what's the subnet mask is SL24. So it will be 1 one one one one 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8. Rest of them will be 2 3 4 5 6 7 8. Now look at here very carefully. According to the formula, this is the network portion. So and this is the this is the network portion and this is the host portion. You cannot change anything in the network portion. So I will type here 192.168.1. I cannot change anything in the network portion.

Okay. So let me just write it like this way. one I cannot change anything in the network portion. According to the formula all host bits zeros. So if you put all host bits zeros it will be the zero. Okay. So this is the network address. Now look at here very carefully. Isn't it the first address? Because you cannot go below zero. Right? So all host bit zeros whatever address comes that will be the network address and usually it will be the first address.

So network address is used to identify a network. So if you think about a road number like a road name or something like that that cannot be assigned to any house because that is to identify the road. Now what is the broadcast address? Broadcast address is all host bits once. Usually it will be the last address. Usually it will be the last address. Now look at here very carefully. Think about this one. So if you bring this one, it will be 192.

I am I'm trying to I'm trying to write in decimal and binary format and it will be 168 and it will be one. This is this is where I'm writing in decimal format. Okay. Now think about the host portion and this is where I'm writing in decimal format and here I will write in the binary format okay because I want to save the space what did I say all host bits once so if you bring this host portion let's bring it here and you need to make all the host bits once then what is going to happen 1 2 3 4 5 6 7 8 that means you will get something like 255 So it will be 192.168 1.255.

This is the broadcast address and usually it will be the last address of the network. In the same way if you look at here the first address or the last address of the network for this particular one that is the network address and this is the broadcast address usually. But the most correct way of saying is all host bits zeros. All host bits zeros. All host bits ones. Okay. Now again if you come here the total number of hosts since the first and the last address are not usable.

Now look at here how many number of IP address that you can produce. Okay, the total IP address is 2 ^ H for class C because here we have an example for class C is 2 ^ 8 which is 256. However, if you look at here the total number of usable IP address is 2 ^ minus 2. That means y2 one is the network address another is the broadcast address that you cannot assign it to anyone else. Okay. So, um what is the broadcast address?

The broadcast address is an address that is for everyone in the network. So, imagine if you have 100 computers and u 100 PCs and you want to send the same packet to 100 PCs, you will use the broadcast address. Okay? So, you will use the broadcast address and it will go to all the PCs. So that is why you cannot have that address to a particular that is why you cannot have that address to any particular PCs. Okay. But IP address like 19681 maybe the IP address of PC1 19268.50 maybe the IP address of PC 50.

So if you look at here so you need to subtract two. So the usable IP address is 254. So you need to always make sure that you need to subtract two. Okay? Regardless whatever addresses you have over there. Now let's try to understand why we need subnetting. Let's consider an IP address. So think like this is uh can you tell me whether it's a network uh it's a public or private? It's a private it's a public IP address.

Now look at here very carefully. It has got eight bits. That means uh eight network bits 24 host bits. So you can produce 16 777214. Okay. 167777 214 IP addresses. Now do like how many companies need um the the these number of IP addresses and imagine if you have a house with a lot of doors that means you need to provide more security you need to check all the doors and that creates more issues. No one wants to buy a house with 100 doors.

Okay. So if you don't need any IP address like if you like if you need let's say 1,000 IP addresses and getting these number of IP addresses is huge. So most organization don't need such large network and it will be difficult to manage especially if it is broadcast that means it will be sent to all the IP addresses okay it will be huge. So subnetting will help you breaking the large networks into small networks so that it is much more manageable.

So if I ask you to carry 50 kilo at a time it will be very hard for you. But if I ask you to break it into break it into 10 break it into five parts 10 kilos 10 kilos 10 kilos 10 kilos in this way it becomes much more manageable. So that is the part of subnetting. Okay. Let us consider a scenario. You have a router here and it is connected to another router here. So how many IP addresses do you need when you have two routers connected?

One IP addresses, two IP addresses. Now if I say which class can give me the lowest number of IP addresses? C. Because you have 2 ^ 8 which is 2 ^ 8 that means 2 ^ hus 2 which is 254 IP addresses. If you go to class B it will be 2 ^ 16. If you go to class A it will be 2 ^ 24. Now looking into those things now you can understand C can only give me the lowest IP addresses and how many usable IP address 254. But how many IP addresses do I need?

Two. what will be the total number of wastage? It will be 252 wastage. Why? And it is a problem because these IP addresses can be used by the hackers as well. So you don't want to you don't have want to have extra IP addresses. So that is that is why the problem happens. Now how to solve this problem? Now let's come here. Look at here very carefully. Instead of slash 24 where you get 2 to the power with slash 24 you have eight you have 24 network bits and you have eight host bits.

So 2 ^ 8 - 2 is equals to 254 usable IP addresses. However if I make it /30 then you have 30 network bits and you will have two host bits. So which will make 2 ^ 2 - 2 is equals to two IP addresses. So consider the above scenario where I need just two IP addresses. Isn't it better to have /30 instead of having /24 which doesn't make any sense. Okay. So this is how subnetting subnetting allows efficient use of IP addresses.

This is how subnetting allows efficient use of IP addresses.