Subnetting

8. Subnetting Large Networks Part 1

Until this point, we've done several examples of subnetting class C networks, and hopefully you've got a good handle on that. Now in this lecture, we're going to take it on stage by subnetting larger networks, so we're going to look at subnetting our class and our class B networks. So let's say, for our first example, that we've been allocated to class B. The IP address is 155.15. That's our network address, and if we subnet that into 29 subnets, we're going to have three bits for host addressing because we've got 32 bits in the address 32 -29.That gives us our three bits, and that will allow us six hosts per network because the power of three is two. Four. Eight minus R two gives us six hosts, so A slash 29. That's going to give us six available hosts per network, whether we're using a class A, B, or C. It's going to be the same for all of them because we were allocated a class B 16 range. We're going to have 13 bits for the network address if it was a class C. We would only have five bits for the network address because it's 24 to 29, a difference of five. That would give us five bits with a class B. We've got those extra eight bits, so five plus eight gives us the 13 bits, and that is going to allow a total of 8192 subnets. Let's count that up as well. So two to the power of 13 two, 4816, 32, 64, 128 two, five, 65, 12, 10, 24, 20, 48, 40, 96and finally 13 8192 for the IP address one, 3515, ten, 138, 29 What would be the network address, the broadcast address, and the range of valid IP addresses? You know the drill by now. Please pause the video, figure that out, and we'll be back with the answer Okay, here's the answer: The question then became whether the IP address was one of 3515, ten, 138, or 29. What's the network address, the broadcast address, and the range of valid IP addresses? We'll write this out the same way as usual, so we're out the IP address and the subnet mask. We put the line in after the 29 and the line is going in after the 8. You can see here if you look up at the top right that we've got one under the one. Two. Eight and eight, so we add those two together. Two. Eight plus eight is 136, so the network address must be 1351. 510.136. The line is after the eight, so we add eight to one. Three.Six, the next network address would be one of 3515. 10.144 and if the next network address is one. Four. Four. Then the broadcast address must be one of 3515. Ten. One. Four. Three and the valid addresses for our hosts fall between the network address and the broadcast address, so that's one P 515. Ten. One. Another popular method of calculating the network address is three.seven up to 1420. The broadcast address and the host address are by using the magic number method. You'll see this being cited in quite a few places on the Internet. This one is very handy if you've been given the subnet mask in dotted decimal notation rather than with a slash. In that case, you can usually figure it out in your head. So 29, if we wrote that out in a decimal notation, it's two 5525-525-5248. And what you do with the magic number is take the value in the octet that is being subneted. So 248. In this case, you take that away from two, five, and six. So two five six minus two four eight gives you eight. And you know that the network addresses are going to go up in blocks of eight. In our example, our address is one of 3515, ten, and 138. So we find which block of eight is closest to that. So, ten times eight is 80. Another five times eight would be 40. At the 80 and the 40 together, that gives us 120. The difference between 120 and 138 is 18. So two times eight is 16, which would give us one three six.That's the closest value we get here. So the network address must be one, three, six. And then we add the eight to the one threesix to get the one four-four again and we know that that is the next address block. Okay, that's the magic number method. The magic number method is just whatever the subnetmask is, you subtract that from two fivesix and that gives you your address blocks. It's pretty similar to the way that I was doing it previously. The way I normally do it is the option that is being subneted on. I'll write that out as 12844, 3216, and so on. And then I will figure out what the bit pattern is and then I can put the line in and see where the address block is at. But play around with this a bit. Fine. Try out the different methods of doing it and figure out which one you're most comfortable with, and that's the one that you can use in practise and the one that you're going to use on exam day. Okay, let's move on to another example. So in this example now we'll do a class A where we're going to subnet on the fourth of the previous examples. We justdid a class B on the fourth octet. This is going to be a class A on the fourth of October. And here we've been allocated 68. If you apply the subnet mask, the answer to the first question is 2552-552-5524 A. So it's the same style of question but a different mask here. How many subnets do we have and how many hosts per network? So, as usual, stop the video and I'll see you back in a second to give you the answer. Okay, so this example here, you see, the other examples we've been given the subnet maskas slash notation on the exam. Maybe you'll be given a slash notation. Maybe you'll be given it in dot a decimal. Here we were given it in dot adecimal, and we can figure out that 255-252-5524A is the same as subnetmaskov 28th. If you're not sure, you can just write it down. The more practise you get with these, the faster you'll get at doing it. If you look at the last octet, thereone two eight plus 64 is one nine. Two plus 32 is two. Two four plus 16 is two four eight plus eight, and two four eight plus four is two five. Two plus two is two and a half, and plus one is two five five.You see, I was able to do that without even thinking about it. Once you practise this a little bit,you'll be doing exactly the same thing. So for our example, we had a slash 28. We put the line in and we can see that we've got four bits for our host addressing. So that's two. 4816 minus two gives us 14 hosts per network. And now, because we were allocated a class A, we're going to have 20 bits for network addresses because the difference between the default eight and the 28 that we're using is 20 bits. So two to the power of 20 worksout a little over 1 million subnets. Hopefully, you won't have to figure out a number as big as that on the exam, but if you have to, you'd still be able to do it again. You just start at two and just keep doubling all the way until you've done it 20 times. As usual, we've got part two of the question. So for the IP addresses 1615, 1075, and 28,what is the network address, the broadcast address,and the range of valid IP addresses? Pause the video and I'll see you back here with the answer. Okay, for this example, the line is at 16 when we draw it out. So the network address is going to go up in multiples of 16. I can see by looking at the last octet of the address that I've got a one under the 64, and that's all. So the network address is going to be 6015, 1064. And if I add 16 to that, the next network address will be 60, 15, 10, 80. So our broadcast address here must be 6015, 1079. And the range of valid host addresses falls between the network address and the broadcast address. 60, 15, 10, 65, up to 78. Another way you can do it is by using the magic number. And you can do it in your head quite quickly, especially if you were given the subnet mask in dot decimal notation rather than slash notation. But even if you have been given in slashnotation, you can still do it this way. You'll just need to convert it to a decimal first. So our example was a slash 28 and a slash 28. The subnet mask is going to be 255-25-5255, or 248. We can figure that out by adding up the numbers. So a 28 is going to use the first four bits in the last octet. So four bits is going to be one two eight plus 64, which is one nine. Two plus 32 is two. Two hundred forty-four plus sixteen equals 248. Then what we do with the magic number is we take that number away from two, five, six. So, if the subnetting number is 240, then two-four A subtracted from 256 equals 16. So we know that the address blocks go up in multiples of 16. And with our example, it's asked us to figure out the network address for 6015. Dot 10, dot 75. So we just go up in multiple poles of 16 until we get to the closest subnet. So that would be 16, then 32. We can double that to 64. The next one would be 80. So 75 is between 64 and 80. So the network address must be 16, 15, 10, or 64. We know that the next block starts at 80, so the broadcast address must be 79. And a valid host would be 65 to 78.

9. Subnetting Large Networks Part 2

Do another example. So the previous example was class A on the fourth oct. This time we're going to do a class A on the third octet, and this one can get a little bit confusing. She might need to pay attention to this one again. So in our example, we've allocated classA 16, dot, dot, dot eight. If we subnet it into 19 networks, how many subnets do we have and how many hosts per subnet? So pause the video again and figure out the answer,and I'll see you back here with the answer. OK, 19 is the line that is going to be after three bits on the third octet. So that leaves us 13 bits for the host; eight in the last octet, and then five on the righthand side of the third octet. So to figure out how many hosts each network is going to support, it's two to the power of 13 minus two. So that's two, 4816, 326-412-8256, 512, one, two,eight, then 204-8496, and 8192 minus two, giving us 8190 hosts per network. And because we were allocated the class aeight range, the difference between eight and a19 is going to be eleven bits. So we figure out how many networks we have. It's two to the power of eleven. So we already know that two to the power of ten is 1024. So we'll double that again. That gives us 2048 subnets. As usual, we've got the second part of the question. So for the IP addresses 6015, 1070, 519,what's the network address, the broadcast address, and the range of valid IP addresses? Please pause the video as usual, and I'll see you back with the answer. Okay, in this example we are subnetting on the third octet. The other examples we've beensubnetting on the fourth octet are The line is after the 32 on the third octet. So the network block addresses are still going to go up in multiples of 32, but it's just going to be on the third octet rather than the fourth octet. Our network address is 16150 now. You can see it if you write out the whole IP address. Also, we're 60, or 1510. We're going up in the middle of 32. So, obviously ten is less than 32, so the network address must be 6015 dot dot o. The next network address would be 60, 15320. So the broadcast address is going to be one less than that on the third octet and 255 on the fourth octet. So the broadcast address is 16, 1531, two, five,five, and the valid host addresses will be between the networking address and the broadcast address. So that's 600, one up on t061-53-1254. Okay, so the value in the fourth octet is the lower range is going to be a one, the higher range is going to be a two, five, four for the hosts. The subnetting is done in the third Octet. If the subnet mask is anything between 16 and 24, We can use the magic number method for that example. Again, it was a 19. So 19 is three bits on the third octet. So that is 12819 two and then two, two, four. We subtract two and four from two five and six, which gives us 32, so that we know that the addressblock is going up in values of 32. Again, it's on the third octet rather than the fourth octet here. So we can figure out, as we did in the previous slide, that it must be a network address of 6015, because our value in the third set is ten. The broadcast address is one less than that. 60, 1531 dot, two, five, five, valid host, 61 up to 60, 1531 dot, 25, four. OK, review this example again if you're not sure about what to do on the third octet. Remember, we figured it out exactly the same way as we did when we were doing it on the fourth of October. So the address block is figured out exactly the same way. Again, you just need to remember that on the fourth of July, your hosts are going to go from one on the low end up to two-five-four on the high end. Okay, let's do one more example. So you've been asked to subnet the one billion dot or network into six different networks. What subnet mask are you going to use? Please pause the video and figure out the answer. Okay, before I show you the answer in the next slide, let's see how we would figure this out. The network is one 34650, so we know it's a class B network and we need to split it into six networks. So we're going to need three bits because it's two, four, eight. It's a class B. So the default subnet mask is a slash 16. We needed six networks, which was three bits. So we add three to the slash, and that will give us a slash 19. It is very easy to figure this one out. And that's showing up there with the line on our diagram as well. Some extra information that we weren't actually asked for in the question The decimal equivalent of 19 is 255-255-2240. The network addresses would be going up in blocks of 32, so one 34650, the next 115-46-5320, etc.E. And we would have 8190 hosts in each subnet because we've got 13 bits available for the host address, which to the power of 13 minus two is 8119. Okay, so that's just done for all of the different examples of subnetting. Hopefully you're confident with this now. You should be. If you've worked through all those examples, then you're going to be fine when you do the exam. When you are on the exam, there are lots of different ways that they can ask you questions, but it's all going to boil down to just a few things, which you can see here. So it could be a variation of giving a network requirement of X number of subnets and Y number of hosts per subnet. What network address and subnet mask should you be using for each subnet? The other basic question they can ask is if they give you a particular IP address and subnetmask, calculate that subnet's network address, the broadcast address,and the range of valid host IP addresses. So again, it could be any variation of those questions. They might ask it in a different way, but as long as you can answer those questions, which you can now, because we've done loads of practise examples of them, you're going to be fine for anything that they throw at you on the exam. Okay, so that's our subnetting done. We've still got a bit more to talk about IP addressing through, starting with private addressing in the next lecture.

10. Private IP Addresses Part 1

In this lecture, you'll learn about the private address ranges. These were documented by the IETF. It's the internet engineering task force in RFC 1918. RFC stands for Request for Comments. When the IETF releases some documentation, we release it with an RFC number, meaning that other engineers can comment on it and maybe suggest improvements. But the RFC is still a finished standard as well. So the final standard as of today for private IP addressing is RFC 1918. There are a lot of other RFCs out there as well, for pretty much every technology. But if you asked me to name an RFC number, then the only one that I probably could is RFC 1918 for private addresses. Because if you're in conversation with somebody, it's quite common to call it an RFC 1918 address. Sticking with our theme of how the Internet was originally designed to work, private IP addresses were originally for hosts that should not be connected to the Internet. Because obviously, if you're an organisation and you've got a part of your network that you don't want to be connected to the Internet, you're not going to pay for public IP addresses for those hosts. That would be a waste of money to pay for IP addresses that are never going to be used. So a way that you could save money is by using private IP addresses on there instead. The other benefit you get from it is that the hosts are not going to be connected to the Internet,so it makes them more secure as well, and it locks them down so they can't talk on the Internet. So if you're thinking, "Well, why would anybody ever do that?" Maybe it's a highly secure environment. Like, maybe it's a bank. And if the bank has got a part of their network that they want to keep completely off the Internet for security reasons, they would use private IP addresses there. Another possible example is maybe you've got a high school and they've got PCs there, but the school authorities don't want the kids to be able to get on the internet again. They would use private IP addresses there. So the addresses that are private, there's a range within each of the different classes, A, B, and C. In class A, we've got 100 to ten 255-25-5255, which uses the standard class A subnet mask of eight. So we can also write it as 100eight or 100 with a subnet mask. two hundred and fifty The class B private range is one from 72160 to 1723-125-5255. That is one of 7216 00:12. So the class B range does not use the default subnet mask of 16. And the class C range of private addresses is 19216 eight to one, 9216-825-5255. So the class C range, again, it's not the default mask. It uses a slash 16, which is the normal default mask for a class B network. Okay, so those are the three ranges of private addresses. You want to have these committed to memory, so just like you're going to commit to memory the ranges for class A, class B, and class C. Also, remember what the ranges are that are used for the private addresses. This is not just for the CCNY exam, really. You're expected to know this off the top of your head when you're working in the real world as well, because you'll see that RFC 19 addresses are used a lot in the real world. I'll get to the reason for that very soon in this lecture. So let's look at an example of where we would use private addresses back in the day when we wanted to keep our hosts off of the Internet. So this is a secure environment. We've got Bank A on the left and Bank B on the right. Bank A has got a public part of their network that is used for their staff who are allowed to access the Internet. That's at one 7511 00:24. And then they've got a different part of their network which is mirror, where they have some very sensitive servers that they want to keep off the internet, and they put in their private address 10100. Bank B's public address is 190, 614, 100. And they've also got a private range which is 170, 218, 500:24. Number two is an example. You can see that here, bank A and bank B are both using 19216-8100. That's fine. They don't have any connectivity to each other at all because we're on completely separate networks. So you'll find that with private addresses, loads of organisations all over the world will be using the same private address ranges. They can't use the same public address ranges because we need to have connectivity to each other over the internet. But the private addresses don't have any kind of access to the outside of that organization. So those addresses can be reused over and over again. OK, let's revisit the IPVFour global address space problem. So, the designers of IPV Four did not realise how big the Internet was going to get. And when they first designed the IPV Four format, they assumed that 4.3 billion addresses would be more than enough for what was needed. But the problem is, we know today that four billion is nowhere near enough. Another problem is that the protocol is not efficient in the way that it allocates addresses as well.Again, because they thought that they had more than enough addresses, they didn't worry about wasting addresses. For example, the 127 address wastes an entire class A range just for loopback testing. Also, the way that large address blocks were given to organisations who were not using anywhere near as many as the actual addresses they were given. So the IPV4 address space is not big enough for how many addresses we actually need on the Internet today. So they actually ran out of addresses quite a while ago. But back in the late 80s, they realised that they were going to run out of addresses. So they started working on a solution to the problem. And in the 1990s, the solution that was developed was IPV Six. So the addresses we've been talking about up to this point and the course has been IPV Four. IPV six addresses have got a different format. Where IPV four addresses are 32 bits long,IPV six is 128 bits long. But the address space is not just four times as big as the IPV-4 is. It's actually exponentially bigger than that because we keep doubling it every time we add a bit. And the IPV Six address space is actually seven, nine times ten to the power of 28, times as many addresses as IPV Four. So there's a huge number of addresses with IPVSix, and it was developed in such a way that they should never run out of addresses again. But there's also a problem with IPV Six, just as there was a problem with IPV before. And the main issue is that there's no seamless migration path from IPV Four to IPB Six. So if you're an organization, you've already got your host deployed, you've got IPB Fouraddresses on there, and you've done all of your IPV Four addressing design, it's not easy. You can't just flick a switch and convert back to IPB Six because the address format is completely different. It's not seamlessly backwards compatible with IPB Four. So it's quite a big project to migrate from IPBFour to IPBSix if you're already an existing organization. So, because of that, network address translation was implemented as a temporary stop gap before everybody could convert to IPV 6. And the way it works is an organisation can use those RFC 1918 private IP addresses on their inside network, which are not publicly routable, so they don't work on the public Internet. But what they can do with those addresses is on the way out, they can convert them to public IP addresses on the outside. So if you're using a private IP address on the inside, whenever you communicate with anybody out on the public Internet, when the traffic gets to them, it looks like it's coming from a public IP address. So they're able to send the traffic back to you. And many hosts on the inside, so many hosts on the inside using those private IP addresses can share a few or even just a single public IP address on the outside. So let's have a look and see how this works. You see, we've got Office A on the left, and they've bought a small range of public IP addresses, which is 170, 5110, and 128, which gives them 14 addresses. And they're using the private addresses on the inside of one thing, 2116, O 24, and they've got 200 horses on the inside. Well, they're able to convert or translate those private addresses on the inside to public addresses on the outside whenever they communicate with anybody on the Internet. So if we didn't have private addresses inside, they would have required 200 public ipaddresses for those hosts on the inside. But now they're doing it with just 14. And actually, they could have done it with just one if they wanted to. So by using private addresses, and that this saves loads of addresses in the IP prefix before public address space, it also saves organisations money because we don't need to pay for those public IP addresses.

11. Private IP Addresses Part 2

Let's talk about how things are actually done most commonly today. Then, back in the early two thousand, a lot of industry experts predicted that everybody would be using IPB Six within a few years because of a shortage of IPB Four Addresses. But it hasn't actually worked out that way. And in today's networks, most enterprises are using RFC 1918 IPV Four Addresses with Nat. So if you go and you work for a company, chances are you're going to see something very similar to the previous slide where you're using private IP addresses for all of your inside hosts and you're translating them to the public IP address on the outside when they go out to the Internet. The reasons for this are stated in RFC 1918. Actually, it actually has the security benefit of hiding your inside hosts by default because those private IP addresses are not routable on the Internet. If you send traffic to a private IP address and it gets out to the Internet, the Internetrouter is just going to drop that traffic. So you have your private IP addresses, you can route between your hosts on the inside network, and you can route between your hosts over your own wide area network. But you cannot send traffic to a private IP address on the Internet because all the different companies using those private IP addresses on the Internet would not know which one to send it to. Therefore, internal use within the organization. Another reason that there's been a slower than expected uptake of IPB Six is that the IPB Six Address Format is completely different. We've actually got a section that focuses on IPBSix later, and you're going to see that it's completely alien to the IPB four format. And all of the network engineers that are around today are very, very comfortable with IP. They're used to working with it day in and day out, but a lot of them are not comfortable with working with IPVSix because their organisation isn't using it yet. So if you go and speak to one of these engineers, They're probably not thrilled with the idea because it's completely new to them, but they're already familiar with IPVFour and can provide you with an answer. Well, we're already using private addresses and that's not causing any issues. Everything's working just fine. So I put all the time, effort,and money into converting IPV Six. So that's why it's been slower for everybody on the Internet to move over to IPV six than was originally expected. But IPV6 is still found in a lot of places, mostly in service provider networks. The majority of service provider networks will support both IPV Four and IPV Six. You'll also see it being used for mobile services,like on your mobile phone, because there are lots of mobile phones and it's relatively new technology. So IPV Six was already out, and there was already a shortage of IPB Four addresses. So for mobile services, we're mostly on IPV Six. Where you'll also see it is in countries which had a later adoption of the internet, such as India and China. Okay, one last thing: spare Public IPV four addresses were exhausted in 2011. So IPV Six is still the future path. So you see that most companies today are using the RFC 1918 addresses and that butit will slowly move over to IPV Six. Other than that, you still need to understand subnetting. So don't think, oh, well, if we don't have that IPV-4 address-based problem, why did I have to spend all that time in Reception learning about subnetting? You're still going to do subnetting even when you're using private IP addresses on the inside because you still need to do your logical addressing and you also need to be able to understand and troubleshoot IP. So, everything that you have learned in this section is very applicable to the real world. And also, of course, for passing your CCNE exam, because we have the entire private IP address space to work with. It's common to see today's real world enterprises using 24subnets for their end hosts, a 30 for a point-to-point link, and a slash 32 for the loopbacks. Remember, we'll talk about loopbacks more later. They're not complicated anyway. It's just a management address on the router or the switch. Complex vSLM. Remember when we did the vSLM lesson and I said, "Work out what the subnet mask sizes will be for the different departments in New York and Boston and see where the network addresses will begin?" That would be a complex VLSM where we've got one subnet and we're dividing it up into smaller subnets with different sized subnet masks. And it's quite complicated when you do that too, because you have to think, okay, well, where does the actual network portion of the address begin and end? What's the broadcast address, et cetera? If you're using a slash 24, it's super obvious. You just look at it and you know that up to the end of the third octet is the network address and the fourth octet is the host address. So it's very simple to use a class when we're using private addresses on the inside. We don't have a problem with a lack of IP addresses. We can use the entire private address space. So it's very common to use a slash just because it's the easiest thing to do. And easy is good because it makes fewer mistakes and it makes troubleshooting easier. Where you will see VLSM being used is if an organisation is actually using public IP addresses on the inside,which does sometimes still happen, and they need to maximise the use of their public IP addresses. We don't want to waste any because we're paying for them. Then you might see more complex VLSM being used in that kind of scenario. Okay, this is the last thing to tell you here about using contiguous addresses. So when you are using private addresses on the inside,like you see here, you're still going to want to do route summarization for the same reasons that we spoke about when we did the Cider lecture earlier, which is that you're going to compartmentalise the different parts of your network from one part of your network to another part of your network. You're only going to send a summary rather than every single route. So the example here, we've got Region A on the left and it's using 100 OS 24, 100, 124, etc. Up to 100 x 5524. Region B within the same organisation on the right is using 1011 and so on. We connect the two routers between Region A and Region B,and from Region A we can advertise ten 00:16, and from Region B to Region A we advertise ten 100:16. So, rather than advertising all 255 or 56 routes in both directions, we only advertise one route. So it takes up less memory on the routers because we've got fewer routes that are known to the routers. And also, if there's a problem, the impact stays local to that particular region. So, to be able to do this, you need to be careful with the way that you plan your network addressing. And you need to make sure that you allocate them in contiguous blocks like you see here. A mistake would be to do it like you see here. So here on the left I've got 100,then 100 two, and then ten one, three, and on the right I've got ten, etc. So I'm mixing up my ten OHS and my ten ones. So because of this, I can't advertise from left to right because some of the OHS are already on the right. If you made a mistake in your network address planning, as has happened here, you must advertise all routes everywhere. That's going to end up taking a lot more resources from your routers, and it's going to make the network a lot less stable and harder to troubleshoot. So be careful when you're doing your network addressing and carefully planned out at the start. Make sure that your addressing is done in contiguous blocks so that you can do your summarisation. Okay, that's it. That is done on the IP addressing and the subnetting. I just have one more lecture to tell you where you can find additional resources.

12. Where to Get More Subnetting Practice

We finished everything related to IP addressing and subnetting. And if you're like me and have not very good attitudes, you're probably going to be glad to hear that. Don't worry, everything else that we're going to cover is not match base and you're not going to have to add anything up in your head. Everything else that you're going to get tested is about the different features that are available, what they do, how to configure them, and how to troubleshoot them. But if you are not sure about subnet and you want some more practise with that, then there are some good resources that I've put on the screen for you here. So let's have a look at these. The first is subnet inquiries.com. So I'll click on the link here. And what this is, it's a website that has questions, the same type of questions that you could see on the CCNA exam. And every time you refresh it, it will come up with a new question. For example, what's the first valid host in the subnet that the node 192-168-2527 belongs to? Another one which is similar is www.subnetting.org. It's the same kind of thing every time. It will give you a new question. Again, same type of question, and it's really a variation of everything that we covered earlier in this course. So you should be confident that you can answer any of these questions now. So check the question. When you figure it out, you can click "Reveal answer," which tells you the answer and then you can go on to the next question. So this is really good for practising subnetting. And again, if you're like me, you're not going to just learn this in one goal and then have it down. You're probably going to want to practise it a little bit. Don't spend hours on end practising subnetting. That's no fun for anybody. But to get ready for the exam, you could just come in here and spend five or ten minutes a day just working through a few problems. And if you do that for days or even weeks before the exam, you'll be fine when you get those subnetting questions. Another thing to tell you is that in the real world, people don't do subnets in their heads. Typically, if it wasn't obvious already, what we do is use a subnet calculator. So what you can do is go to Google and in Google search, just search for "subnet calculator" and you'll see there is a heap of results that you will get. I'll just click on the top one here to show you an example. So what this is useful for is if you are doing something in the real world and you need to figure something out. Also, if you're doing exam practise and you want to check that you got the answer right, you can just come in here,plug in the numbers, and it will give you the answer. Okay, that's it. Subnet and done. Let's move on to some other features now.

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