What is VLSM?

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All right. So what is the lesson learning all that vlsm stands for variable length subnet masking. Okay. That is the reality now. I use pop up public networks, but private networks as examples when I do this, because we're not used to really looking at public networks. We're kind of, you know, we get confused when we look at it.

So I use private networks. That's where we're used to, but vlsm was really, it's really used for public networks. Why did they invent Why did they came up or come up with this particular mechanism? to slow down the death, the imminent death of ipv4, Yoast 2.4 billion addresses is just not going to be enough. Especially when you need 1000 networks or 10,000 networks or whatever the case may be. I need 10,000 IPS, no problem.

We'll give you a Class A with a salary You have 16 million IPS available to you. What? No mean? Whoa. So that's how we did not mean I wasn't around. Alright.

So now that'll Ah, they just gave people out whatever, you know, blocks. They said, Okay, here's all a whole 11 hour, here's a whole 12 No, we're all 13 or we're or whatever the B and the C, all right, they'll give them more than what they needed. That's why we wasted so they came up with like, Hey, we need to scroll this down. vlsm that means I networks don't know how to say Santa mask. Exactly. They don't have the same some of the math This was called class less routing, classless routing, all routing protocols support this reversion to ribbon G, another ribbon g really this matters because of ipv6 but Ei GRP right.

So forces or pf all routing protocol support, variable length subnet masking or classless routing. Okay? rules Oh, there are rules to vlsm there are rules, you must start with zero network, you must start from the zero network because the whole point is not to waste any of the IPS. So start from zero. Okay? Start from the highest number of hosts.

There's a million ways people are going to show you out there, how to do this. Okay? The way that I'm going to show you is the way that is supposed to that it should be I'll say that way. Because I have done the comparisons between the way that I'm doing it and the way others do it. And this way, you save the most IPS. Okay, you save the most IPS but detach yourself, alright.

And it should be in contiguous order. Your network should be contiguous. Not No. It should should But it's not going to be alright. And when you go take your test, they do that they give you this contiguous network, that's fine. Our routing protocol support this contiguous networks.

Not a big deal. All right, but according to the rules, or the standards and all this, they should be in a particular order, but the ones you really need to follow is the zero network, start from the highest number. And as you'll see, when we start actually calculating that you'll go from the last available network and then you go to the next one last available, then you go to the next and so forth, okay, but you'll see when we get into a lab, but I just wanted to show you a visual. Alright, you can see that this is a cider 27 and comments by 32 so what's the next network 64 but you have a different host there on here. You don't need so many hosts that are 27 holes, you need only host the 26 holes, but you had to go to the next network 64 Okay, so from 64 the next network is 128 But you really need another 25 because you need more holes.

And that's the way it is. Okay, they vary in length. But again, next network, next network next network, okay, or next IP. Alright, and here you can see it up here, you see this continuous? It's not gonna take us. All right 10 114, we didn't use a zero.

All right, a 30. These are 30 because only two IP addresses, and then the next network 832 IP address. So this is a visualization. But let's go ahead and go into a lab, which really is going to focus on the concepts that I just spoke about suicide. Alright, welcome to the vlsm Lab. And really, this is understanding what we just talked about.

So as rules and concepts and things like that will be listen does, we looked at a network. Well, here's another example. Here we have a little you know, three router network, and one has 3500 nodes won't have 725 nodes and one's 100 Hundreds, then obviously in between these routers need IP address as well, we have two, two nodes or two IPS, each. And this is the address that we've been given to work with. So we start from the highest number of nodes, and then work our way down from 3500 to 725 to 100, and then Tu Tu, Tu Tu doesn't matter which ones, right? So what you do is the first two octets, obviously, are not going to be used at all.

They're not going to be used at all. So we leave them alone. That's why you see them there. And great. Hopefully you see him right. All right, and you can see I put a little details here, you'll be you all give you this, you can see how you'll be proved to this.

I'll sum that up for you. All the numbers in yellow are network increments. So when we count for 3500 nodes from right to left, you can see 248 1632 blah, blah, blah, blah, boom, we come to here we draw a line, right, that line is our new mask. So we then our increments is 16. Now the rules Hall says we must start from zero. So we start 172 20 00.

So we have our increment is 16. All right? Well, we really don't really care about much about that right now. We use it out to double check. Vital now 00. So what's our broadcast?

Well, the some of these right, here's right here. 15. So 15 in the third octet, plus the zero and the third octet gives us 15 here. And then the last octet we add all these bit vowels together to the five to the five, plus buzz for doctor here, now users to 35. So we get one cent to 20 1525, which is our broadcast. That's what we came up with that.

And then we find out the range or what's after 0001 what before 1525 feet into the floor, just like we were so many, but we have a new mask. We Have a new mask. Now a cider 20 no longer 16. Now we start off with 21 234 by 16. That's 20. So that is our new mass.

Now with vlsm, we look at the last IP address that we use, which is the broadcast and we say, okay, what's the next available IP address? Well, the next available IP address, it has the maximum, then we go to 16 dot zero. This is the maximum value here. reset to zero brings us to 1616 dot zero. Now we can use that increment all we increment by 1616, zero 16. So we're good.

So this will be our next starting point. And you can see right here, that's what I said this is the next available IP address. The next starting point, okay, so we say okay, we now say 125. So we count four holes again, blah, blah, blah, to get to the need for 725 which is going to stop the line right there. Okay, so I know where the anchorman is for. Alright, and then To calculate the broadcast on the third octet, we add these two numbers, that's three does you see that up there?

Well, three, plus 16, that's 19. And then the fourth octet, we add all these bits right here together that used to be 50225. We get 19. To define what's in between, what's after 16, zero 16. One was after 19. Two, I mean, what's after what's before 1925 1924 with a new math because we had to move the line two bits over.

So we had 20, before we move the line to more bits, that makes it a cider 22. Right? So we can do this. And then we know we get these network IDs with these new masks to the administrators. Okay, this is what you got to work with. We submit it do with it what you will this is your space that you can work with.

This is your range, resubmitted if you like daughters you need okay. So again, we come to The next one, which is 100 nodes, and what is after 19 to 3529? Zero? Well, we're incremented by four, four and 16 is 20. So we use as a double check. All right, so we're still good to go.

All right. 20 dot zero is our next starting point right here. So how many knows we need 100. So we counted for 100 nodes from right to left, and it stops right here. Okay, so we draw our line. Alrighty, so we want to calculate for broadcast.

So we're in the fourth octet now, now we're in the fourth octet. That means we need the third octet alone, so it's 172 2020. And then, where does that give you? 60 or 127. I'm sorry, 127 127 01 27. That's what we have here.

So our broadcast is once every through 2021 27 was in between point one before 2126. What's our new math? Well, if our little red line is right here, that means we added three more bits, which makes it 25. Okay, see how that works. Now again, we started with a next available IP address what's actually 127 128. As you can see, I didn't change the 20 because we're working on the fourth octet.

We're working on the fourth octet. So this is our starting point now. Now we need to knows well, the count for two. Because in hosts, we also try to, okay, and then Okay, so we come here, and we see we increment, we increment by four, but it's three to calculate for broadcast. So three plus 128 is 131. What's in between 2930 and the two is pretty simple as that and we got to control the way down.

Our increment is four you can see it says four and 121 32 4132 136 All right, we know that it's always going to be three. So you have 32132. Yeah. 130 531 36 is 139. And then whatever is in between, and you can see we have the same mass, which is three, that is a vlsm. Network.

That is the concept of how you would do it. Okay. We will be doing a lab. Okay, and I'll be showing you exactly how to do it. But I want you to understand the rules. We started with the zero network.

We use, we started from the highest number of nodes to the lowest number of nodes. And we it's contiguous. It's contiguous that way. You do not waste any IP addresses. And like I said previously, this is the whole point of the lesson not to waste IP addresses. This is where they came up with this public IP even though I use private IPS as an example.

But it's really public IPs that we do not want to waste. Because before like I said, again, I said it before. Bye In a day, if you had 1000 employees that will give you a 16 or 16 with a Class B, why is it I have 65,000 addresses Hello, I'll need 1000. So then now I'm wasting 64,535 or 36 addresses. So that's the whole reason. One of the things with the IP version four, the demise of it was just that we were very wasteful when assigning.

And this is one of the mechanisms that was invented, which was vlsm. To do so. But in order to do so you have to follow certain rules again, and you see how they work what they are. Start with a zero is the lowest and then keep it continuous. And this is the best method for not so you don't waste a whole bunch of IPS Will you waste of course, because you can never be exact. Okay, but very little, very little.

So there's the question concept behind a vlsm network. Okay, and when we go to the next lecture, I will show you exactly how we do that. I'll see you in the next

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