WEBVTT 00:00:01.140 --> 00:00:07.230 Welcome to Jeremy's IT Lab. This is a free, complete course for the CCNA. If you like 00:00:07.230 --> 00:00:12.670 these videos, please subscribe to follow along with the series. Also, please like, leave 00:00:12.670 --> 00:00:15.670 a comment, and share the video to help spread this free series of videos. 00:00:15.670 --> 00:00:17.648 Thanks for your help. 00:00:18.770 --> 00:00:24.749 In this video, we will be talking about subnetting. This is a very big topic for the CCNA, but 00:00:24.749 --> 00:00:29.900 not just for the test--it’s an essential skill for a network engineer. Many people 00:00:29.900 --> 00:00:35.591 have trouble understanding subnetting, but let me assure you, it is not difficult. Subnetting 00:00:35.591 --> 00:00:41.809 is very simple if you take it step by step. So, I’m going to split subnetting into two, 00:00:41.809 --> 00:00:46.879 or maybe even three, videos so we can take our time to really understand subnetting without 00:00:46.879 --> 00:00:52.610 getting lost. Now, because subnetting is such an important topic, and many people have trouble 00:00:52.610 --> 00:00:58.260 with it, there are already plenty of subnetting videos on YouTube. Of course, feel free to 00:00:58.260 --> 00:01:02.920 check out those videos too--there are some different tricks and techniques people teach 00:01:02.920 --> 00:01:08.210 that can speed up the subnetting process. I, however, will simply outline the basic 00:01:08.210 --> 00:01:14.310 steps involved in subnetting. I will avoid overcomplicating the topic. My end 00:01:14.310 --> 00:01:20.430 goal for these videos is that you understand and can do subnetting. So, let’s get started. 00:01:20.430 --> 00:01:28.020 So, what will we cover in this video? Just a couple of things. First is CIDR, pronounced 00:01:28.020 --> 00:01:35.420 “CIDR,” which stands for Classless Inter-Domain Routing. What exactly is that? Well, remember 00:01:35.420 --> 00:01:42.610 I introduced the IPv4 address classes, such as Class A, B, and C? Well, CIDR throws all 00:01:42.610 --> 00:01:48.750 that away and lets us be more flexible with our IPv4 networks. Then, of course, we’ll 00:01:48.750 --> 00:01:54.369 cover the process of subnetting, taking it step by step so you don’t get lost. 00:01:54.369 --> 00:02:00.009 Now, before I get into CIDR, let’s review these IPv4 address classes so we can then 00:02:00.009 --> 00:02:06.909 understand the need for classless IPv4 addressing. There are five classes of IPv4 addresses: 00:02:06.909 --> 00:02:14.800 A, B, C, D, and E. Class A addresses have a first octet beginning with zero, and the rest 00:02:14.800 --> 00:02:20.480 of the bits can either be zero or one. This leads to a decimal range for the first octet of 00:02:20.480 --> 00:02:29.250 0 to 127. Remember, an IPv4 address is 32 bits, so there are 4 octets--4 groups of 8 00:02:29.250 --> 00:02:42.180 bits--in an IPv4 address. This makes the Class A address range from 0.0.0.0 through 127.255.255.255. 00:02:42.180 --> 00:02:46.960 Now, remember, there are some special and reserved addresses in these ranges that can’t be 00:02:46.960 --> 00:02:52.060 used for normal IP addresses on a device, but for this video, we’ll just include all 00:02:52.060 --> 00:02:59.510 of them in Class A. Class B addresses have a first octet beginning with 10, and the 00:02:59.510 --> 00:03:06.560 other 6 bits can be either 0 or 1. This gives a range for the first octet of 128 through 00:03:06.560 --> 00:03:18.750 191. The address range for Class B is 128.0.0.0 through 191.255.255.255. Class C addresses 00:03:18.750 --> 00:03:25.019 have the first three bits set to 110, and the others can be either zero or one. If you write 00:03:25.019 --> 00:03:33.530 that range in decimal, it is 192 through 223. The address range is therefore 192.0.0.0 00:03:33.530 --> 00:03:42.750 through 223.255.255.255. Class D addresses begin with 1110 in binary, which gives 00:03:42.750 --> 00:03:49.709 a range of 224 through 239 for the first octet of the address. This means that the address range 00:03:49.709 --> 00:04:02.000 for Class D is 224.0.0.0 through 239.255.255.255. Finally, Class E addresses begin with 1111 00:04:02.000 --> 00:04:11.470 in binary, so the first octet range is 240 through 255, and therefore the address range is 240.0.0.0 00:04:11.470 --> 00:04:14.090 through 255.255.255.255. 00:04:14.090 --> 00:04:21.970 However, only the Class A, B, and C addresses can be assigned to a device as an IP address, 00:04:21.970 --> 00:04:28.680 as Classes D and E have special purposes, as I mentioned in the IPv4 addressing videos. Class 00:04:28.680 --> 00:04:34.550 A addresses have an 8-bit prefix length, meaning the first octet identifies the network and 00:04:34.550 --> 00:04:40.200 the other three octets are used for individual hosts within the network. Class B addresses 00:04:40.200 --> 00:04:45.530 have a 16-bit prefix length, so the first two octets identify the network, and the last 00:04:45.530 --> 00:04:51.610 two octets identify individual hosts within that network. Class C addresses have a prefix 00:04:51.610 --> 00:04:57.600 length of 24, so the first three octets are used to identify the network, and only the 00:04:57.600 --> 00:05:03.340 last octet is used to identify individual hosts within that network. 00:05:03.340 --> 00:05:08.280 The different prefix lengths give different characteristics to these classes. As you can 00:05:08.280 --> 00:05:14.130 see, there are few Class A networks available--only 128, actually less than that because 00:05:14.130 --> 00:05:21.280 some are reserved, like the 127.0.0.0 range, which you may remember is used for loopback 00:05:21.280 --> 00:05:26.870 addresses. Because only the first octet of a Class A address is used for the network ID, 00:05:26.870 --> 00:05:32.040 there are three whole octets available for addresses within each Class A network, 00:05:32.040 --> 00:05:40.410 so there are 16,777,216 addresses in each Class A network. That is 00:05:40.410 --> 00:05:48.220 2 to the power of 24, because there are three octets (3 times 8 = 24 bits). Class B 00:05:48.220 --> 00:05:55.270 addresses are different. There are more Class B networks--16,384--but fewer addresses per 00:05:55.270 --> 00:06:03.250 network, 65,536, which is still many addresses, of course. Finally, there are very 00:06:03.250 --> 00:06:12.850 many Class C networks--2,097,152 networks--but only 256 addresses per network. 00:06:12.850 --> 00:06:19.850 So, how does a company get their own network address range to use? Well, IP addresses are assigned to 00:06:19.850 --> 00:06:26.250 companies or organizations by a nonprofit American corporation called the IANA, the 00:06:26.250 --> 00:06:32.850 Internet Assigned Numbers Authority. The IANA assigns IPv4 addresses and networks to companies 00:06:32.850 --> 00:06:39.160 based on their size. For example, a very large company might receive a Class A or Class B 00:06:39.160 --> 00:06:44.370 network. Remember, there are lots of available addresses to use for hosts in each Class A 00:06:44.370 --> 00:06:49.910 and Class B network. While a small company might receive a Class C network, because there 00:06:49.910 --> 00:06:56.810 are fewer addresses in each Class C network--only 256. However, this system led to many 00:06:56.810 --> 00:07:02.881 wasted IP addresses, so multiple methods of improving this system have been created. Let 00:07:02.881 --> 00:07:08.680 me give you an example of how this strict system of addresses can waste IP addresses. 00:07:08.680 --> 00:07:15.820 So, here are two routers. As you can see, R1 has three networks connected to it here. 00:07:15.820 --> 00:07:20.910 Remember that routers are used to connect different networks, so each of these links is a separate 00:07:20.910 --> 00:07:28.280 Layer 3 network, different IP networks. R2 also has three networks connected here. Perhaps 00:07:28.280 --> 00:07:33.300 each of these networks will have a few switches, with many end hosts such as PCs and servers 00:07:33.300 --> 00:07:39.650 connected to these switches. However, there is one more network here. That’s this network 00:07:39.650 --> 00:07:45.290 connecting these two routers. This is known as a point-to-point network, meaning 00:07:45.290 --> 00:07:51.591 that it’s a network connecting two points, in this case, R1 and R2. For example, this 00:07:51.591 --> 00:07:57.570 might be a connection between offices in different cities, let’s say San Francisco and New York. 00:07:58.540 --> 00:08:04.900 So, because this is a point-to-point network, we don’t need a large address block, so 00:08:04.900 --> 00:08:14.020 let’s use a Class C network, 203.0.113.4. Because this is a Class C network, there are 00:08:14.020 --> 00:08:22.620 256 addresses in the network, minus one for the network address (203.0.113.0), minus one 00:08:22.620 --> 00:08:30.740 for the broadcast address (203.0.113.255), minus one for R1’s address, which I’ll 00:08:30.740 --> 00:08:40.300 assign as 203.0.113.1, and minus one for R2’s address, which I’ll assign as 203.0.113.2. 00:08:40.300 --> 00:08:45.326 That’s a total of four addresses used and 252 addresses wasted. 00:08:45.326 --> 00:08:48.730 Clearly, this is not an ideal system. 00:08:50.840 --> 00:08:56.980 Before introducing CIDR, here’s another quick example of address waste. A company, 00:08:56.980 --> 00:09:05.310 Company X, needs IP addressing for 5,000 end hosts. This is a problem, why? A Class C network 00:09:05.310 --> 00:09:11.140 does not provide enough addresses, so a Class B network must be assigned. Because a Class 00:09:11.140 --> 00:09:18.020 B network allows for about 65,000 addresses, this results in about 60,000 addresses being wasted. 00:09:19.610 --> 00:09:23.970 When the Internet was first created, the creators did not predict that the Internet would become 00:09:23.970 --> 00:09:30.150 as large as it is today. This resulted in wasted address space, like the examples I showed 00:09:30.150 --> 00:09:35.890 you, and there are many more examples that I could show you. The total IPv4 address space 00:09:35.890 --> 00:09:40.970 includes over 4 billion addresses, and that seemed like a huge number of addresses when 00:09:40.970 --> 00:09:52.060 IPv4 was created, but now address space exhaustion is a big problem. There's not enough addresses. One way to solve, or remedy, this problem is 00:09:52.060 --> 00:10:00.190 CIDR. The IETF (Internet Engineering Task Force) introduced CIDR in 1993 to replace 00:10:00.190 --> 00:10:02.110 the classful addressing system. 00:10:03.760 --> 00:10:10.311 With CIDR, the requirements of Class A addresses to use an 8-bit network mask, Class 00:10:10.311 --> 00:10:18.190 B to use 16, and Class C to use 24 were removed. This allowed larger networks 00:10:18.190 --> 00:10:24.270 to be split into smaller networks, allowing greater efficiency. These smaller networks 00:10:24.270 --> 00:10:29.340 are called subnetworks, or subnets. Let’s look at an example of splitting a 00:10:29.340 --> 00:10:33.990 larger network into a smaller network so you can see how it works. 00:10:33.990 --> 00:10:40.780 Here’s the same point-to-point network we looked at before. Previously, it was assigned 00:10:40.780 --> 00:10:48.640 the 203.0.113.0/24 network space, but that resulted in lots of wasted addresses. Let’s 00:10:48.640 --> 00:10:55.830 write this out in binary. Here’s the binary, with the dotted decimal underneath. Now, the 00:10:55.830 --> 00:11:04.680 prefix length is 24, so here’s the network mask, also known as the subnet mask: 255.255.255.0. 00:11:04.680 --> 00:11:11.210 Remember, all 1s in the subnet mask indicate that the same bit in the address 00:11:11.210 --> 00:11:16.850 is the network portion. In this case, I’ve made the network portion blue, and the host portion 00:11:16.850 --> 00:11:26.381 is red. Well, how many host bits are there? 8, because it’s one octet. So, how many potential hosts, or how 00:11:26.381 --> 00:11:33.520 many usable addresses, are there? Well, the formula is this: 2 to the power of 8 minus 00:11:33.520 --> 00:11:41.830 2 equals 254 usable addresses. What is the 8? Well, it’s the number of host bits, which is 00:11:41.830 --> 00:11:48.840 8 in this case. And why minus 2? Those are the network address and the broadcast address. 00:11:48.840 --> 00:11:53.760 We can’t assign them to a device, so we have to remove them from the number of usable addresses. 00:11:53.760 --> 00:12:01.560 So, we have 254 usable addresses, but we only need two--one for R1 and one for R2. 00:12:01.560 --> 00:12:09.200 However, CIDR allows us to use different prefix lengths, so it doesn’t have to be 24. 00:12:09.200 --> 00:12:13.860 Let’s get some practice calculating the number of hosts within different prefix lengths. 00:12:13.860 --> 00:12:34.210 203.0.113.0/25, 203.0.113.0/26, 203.0.113.0/27, /28, /29, /30, /31, and finally /32. I’ve 00:12:34.210 --> 00:12:39.730 put /31 and /32 in red because they’re a little bit special, as you’ll see when you 00:12:39.730 --> 00:12:46.120 try to calculate it. So, pause the video here and try to calculate how many usable addresses 00:12:46.120 --> 00:12:53.850 are on each network. Okay, let’s check out the answers. 00:12:53.850 --> 00:13:01.720 So, here is 203.0.113.0/25, but this time with a /25 mask. Notice that the network portion 00:13:01.720 --> 00:13:06.570 of the address has extended into the first bit of the last octet, and the mask 00:13:06.570 --> 00:13:15.910 in dotted decimal is now written as 255.255.255.128. I changed the color of the extra bit to purple, 00:13:15.910 --> 00:13:21.140 but it is part of the network portion, which is the blue part. If you don’t remember how to convert 00:13:21.140 --> 00:13:27.130 from binary to dotted decimal, make sure you review that; it’s very important for subnetting. 00:13:27.130 --> 00:13:31.520 Now, there are 7 bits in the host portion of the address, so the number of usable addresses 00:13:31.520 --> 00:13:40.280 is 2 to the power of 7 minus 2, which equals 126. Once again, we only need two addresses-- 00:13:40.280 --> 00:13:47.290 one for R1 and one for R2--so we will be wasting 124 addresses. That’s better than wasting 00:13:47.290 --> 00:13:53.890 252 addresses with a /24 prefix length, but it’s still wasteful. 00:13:53.890 --> 00:14:02.160 How about a /26 prefix length? Notice that it’s now written as 255.255.255.192 in dotted 00:14:02.160 --> 00:14:08.351 decimal, because two bits of the last octet are now part of the network portion. Since 00:14:08.351 --> 00:14:14.940 there are six host bits, there are now 62 usable addresses in this network. If we were to use 00:14:14.940 --> 00:14:23.640 a /26 network mask for the 203.0.113.0 network, we would be wasting 60 addresses. Getting 00:14:23.640 --> 00:14:27.730 better, but we can make this network even smaller. 00:14:27.730 --> 00:14:33.690 Now that you get the idea, let’s speed it up. For a /27 prefix length, the mask is written 00:14:33.690 --> 00:14:42.660 as 255.255.255.224 in dotted decimal. There are now five host bits, so that means there are 00:14:42.660 --> 00:14:50.390 30 usable addresses. As you can see, the address space is getting smaller and smaller as we extend the network mask. 00:14:50.650 --> 00:15:00.921 For a /28 prefix length, the mask is written as 255.255.255.240 in dotted decimal. There 00:15:00.921 --> 00:15:08.180 are now only four host bits, so that means there are 14 usable addresses. After assigning addresses 00:15:08.180 --> 00:15:14.500 to R1 and R2, this would mean only 12 wasted addresses, but we can make this address space 00:15:14.500 --> 00:15:19.680 even smaller to make our addressing even more efficient. 00:15:19.680 --> 00:15:28.330 If we use a /29 prefix length, the mask is written as 255.255.255.248 in dotted decimal. 00:15:28.330 --> 00:15:34.920 Now we have only three host bits, so that means there are just six usable addresses. Again, 00:15:34.920 --> 00:15:41.510 after we give R1 and R2 addresses, there would be only four wasted addresses. 00:15:41.510 --> 00:15:50.140 If we use a /30 prefix length, the mask is written as 255.255.255.252 in dotted decimal. 00:15:50.140 --> 00:15:56.921 There are now only two host bits, so that means two usable addresses. So, this is perfect. There 00:15:56.921 --> 00:16:03.060 are four total addresses: the network address, the broadcast address, R1’s address, and 00:16:03.060 --> 00:16:07.899 R2’s address. That means zero wasted addresses. 00:16:07.899 --> 00:16:19.150 Before moving on to look at the /31 and /32 prefix lengths, let me clarify a little bit. So, instead of 203.0.113.0/24, 00:16:19.150 --> 00:16:30.170 we will use 203.0.113.0, which is a subnet of that larger Class C network. 203.0.113.0 00:16:30.170 --> 00:16:38.089 includes the address range of 203.0.113.0 through 203.0.113.3. Let me show you that 00:16:38.089 --> 00:16:50.420 in binary. Here is 203.0.113.0 in binary, the host portion all zeroes. Here is 203.0.113.1, 00:16:50.420 --> 00:17:00.380 203.0.113.2, and 203.0.113.3. These are the four addresses in the network, with these two being 00:17:00.380 --> 00:17:07.351 the two usable addresses, which are assigned to R1 and R2. So, we took up four addresses with 00:17:07.351 --> 00:17:14.880 this subnet. What about the other addresses in the 203.0.113.0/24 range? The remaining 00:17:14.880 --> 00:17:24.709 addresses in the address block, which are 203.0.113.4 through 203.0.113.255, are now available 00:17:24.709 --> 00:17:33.559 to be used in other subnets. That’s the magic of subnetting. Instead of using 203.0.113.0/24 00:17:33.559 --> 00:17:42.480 and wasting 252 addresses, we can use /30 and waste no addresses. Or, perhaps there is another 00:17:42.480 --> 00:17:47.340 way to make this even more efficient. Let’s look into it. 00:17:47.340 --> 00:17:57.010 If we use a /31 prefix length, the mask is written as 255.255.255.254 in dotted decimal. 00:17:57.010 --> 00:18:06.100 There is now only one host bit, so that means zero usable addresses. Two to the power of one is two, 00:18:06.100 --> 00:18:12.030 minus two for the network and broadcast addresses, means zero addresses that we can assign to devices. 00:18:12.030 --> 00:18:20.350 So, you used to not be able to use /31 network prefixes because of this. However, for a point-to-point 00:18:20.350 --> 00:18:26.070 connection like this, it actually is possible to use a /31 mask. Let's check it out. 00:18:27.460 --> 00:18:41.179 So, here’s the 203.0.113.0/31 network. R1 is 203.0.113.0, and R2 is 203.0.113.1. The 00:18:41.179 --> 00:18:50.740 203.0.113.0/31 network consists of addresses from 203.0.113.0 through 203.0.113.1, which 00:18:50.740 --> 00:18:58.580 is actually only two addresses. Here they are in binary. There’s 203.0.113.0, and 00:18:58.580 --> 00:19:05.559 there’s 203.0.113.1. Normally, this would be a problem because it leaves no usable 00:19:05.559 --> 00:19:10.240 addresses after subtracting the network and broadcast addresses, but for point-to-point 00:19:10.240 --> 00:19:15.530 networks like this, a dedicated connection like this between two routers, there is actually 00:19:15.530 --> 00:19:20.900 no need for a network address or a broadcast address. So, we can break the rules in this 00:19:20.900 --> 00:19:27.290 case and assign the only two addresses in this network to our routers. Note that if 00:19:27.290 --> 00:19:32.020 you try this configuration on a Cisco router, you’ll get a warning like this, reminding 00:19:32.020 --> 00:19:37.490 you to make sure that this is a point-to-point link, but it is a totally valid configuration. 00:19:37.490 --> 00:19:49.560 So, once again, the remaining addresses in the 203.0.113.0/24 address block, which are 203.0.113.2 through 203.0.113.255, 00:19:49.560 --> 00:19:54.730 are now available to be used in other networks. But this time, we've 00:19:54.730 --> 00:20:02.110 saved even more addresses, using only two addresses instead of four for this point-to-point connection. 00:20:02.110 --> 00:20:08.130 People still do use 30 for point-to-point connections at times, but 31 masks are totally 00:20:08.130 --> 00:20:12.380 valid and more efficient than 30, so I recommend this method. 00:20:14.130 --> 00:20:23.030 But, we still haven't looked at the 32 mask. A 32 mask is written as 255.255.255.255 in 00:20:23.030 --> 00:20:29.620 dotted decimal, making the entire address the network portion. There are no host bits. 00:20:29.620 --> 00:20:35.280 If you calculate this using our formula, you will get one usable address. Clearly, the 00:20:35.280 --> 00:20:41.510 formula doesn't work in this case. You won't be able to use a 32 mask in this case, and 00:20:41.510 --> 00:20:47.461 you will probably never use a 32 mask to configure an actual interface. However, there 00:20:47.461 --> 00:20:53.180 are some uses for a 32 mask. For example, when you want to create a static route not 00:20:53.180 --> 00:21:00.410 to a network, but to just one specific host, you can use a 32 mask to specify that exact host. 00:21:00.410 --> 00:21:05.710 Anyway, I'll talk about that later in the course. Just know that 32 masks are 00:21:05.710 --> 00:21:10.090 used at some points, but you don't have to worry about them for now. 00:21:10.090 --> 00:21:15.550 Here's a simple chart showing the dotted decimal subnet masks and their equivalent 00:21:15.550 --> 00:21:21.170 in CIDR notation. That's right, the way of writing a prefix with a slash followed 00:21:21.170 --> 00:21:29.780 by the prefix length, like 25, 26, etc., is called CIDR notation because it was introduced 00:21:29.780 --> 00:21:36.880 with the CIDR system. Previously, only the dotted decimal method was used. Note that 00:21:36.880 --> 00:21:41.630 I've shown you only how to subnet a class C network so far, but we will look at 00:21:41.630 --> 00:21:49.790 class B and class A networks as well, with prefix lengths like 17, 11, 9, etc. 00:21:49.790 --> 00:21:55.500 I spent a lot of time on just that one example, but I hope you can see the use of 00:21:55.500 --> 00:21:59.891 subnetting--dividing a larger network into smaller networks called subnets. 00:21:59.891 --> 00:22:07.130 Instead of using the whole 203.0.113.0/24 network for the point-to-point connection, we can 00:22:07.130 --> 00:22:14.070 use a 30 subnet and use only four addresses, or even better, use a 31 subnet and use only 00:22:14.070 --> 00:22:20.290 two addresses. I'll give one more example of subnetting before finishing up this video. 00:22:20.290 --> 00:22:23.870 In the next video, I'll give you some practice problems and walk you through them so you 00:22:23.870 --> 00:22:26.710 can get some hands-on practice with subnetting. 00:22:26.710 --> 00:22:33.620 So, here's a scenario: There are four networks connected to R1, with many hosts connected 00:22:33.620 --> 00:22:40.760 to each switch. There are 45 hosts per network. R1 needs an IP address in each network, so 00:22:40.760 --> 00:22:49.710 its address is included in that 45-host number. You have received the 192.168.0.14 network, 00:22:49.710 --> 00:22:54.080 and you must divide the network into four subnets that can accommodate the number of 00:22:54.080 --> 00:23:01.950 hosts required. First off, are there enough addresses in the 192.168.0.14 network in 00:23:01.950 --> 00:23:09.010 the first place? We need 45 hosts per network, including R1, but also remember that each 00:23:09.010 --> 00:23:15.800 network has a network and broadcast address, so that's plus two. So, we need 47 addresses per subnet. 00:23:15.800 --> 00:23:24.240 47 times 4 equals 188, so there's no problem in terms of the number of hosts. 00:23:24.240 --> 00:23:32.560 192.168.0.0/24 is a class C network, so there are 256 addresses. Therefore, we will be able to assign 00:23:32.560 --> 00:23:36.460 four subnets to accommodate all hosts, no problem. 00:23:36.460 --> 00:23:43.160 Okay, let's see how we can calculate the subnets we need to make. We need four equal-sized subnets 00:23:43.160 --> 00:23:50.450 with enough room for at least 45 hosts. Here, I've written out 192.168.0.10 00:23:50.450 --> 00:24:00.480 with a 30 mask, 255.255.255.252. I skipped 32 and 31 since these aren't point-to-point links. 00:24:00.480 --> 00:24:08.190 We can't use 31 and definitely can't use 32. Since there are two host bits, 00:24:08.190 --> 00:24:14.290 the formula to determine the number of usable addresses is 00:24:14.290 --> 00:24:20.970 2^2 - 2. 2^2 is 2 times 2, which is 4, so that means there are two usable addresses 00:24:20.970 --> 00:24:28.220 in a 30 network. Clearly, not enough room to accommodate the 45 hosts we have. 00:24:28.220 --> 00:24:36.330 How about if we use a 29 mask to make these subnets? Can we fit the 45 hosts we need? There are three host bits, 00:24:36.330 --> 00:24:43.710 so the formula is 2^3 - 2. 2^3 is 2 times 2 times 00:24:43.710 --> 00:24:51.910 2, which is 8. Therefore, there are six usable addresses, not enough for 45 hosts. 00:24:51.910 --> 00:25:00.250 How about if we use 28? There are four host bits, so the formula is 2^4 - 2. 00:25:00.250 --> 00:25:07.710 2^4 is 2 times 2 times 2 times 2, which is 16. So, that means there are 00:25:07.710 --> 00:25:13.410 14 usable addresses--once again, not enough for 45 hosts. 00:25:13.410 --> 00:25:23.400 How about 27? There are five host bits, so the formula is 2^5 - 2. And 2^5 00:25:23.400 --> 00:25:30.169 is 2 times 2 times 2 times 2 times 2, which equals 32. So that means 00:25:30.169 --> 00:25:35.370 30 usable addresses. Again, not enough for 45 hosts. 00:25:35.370 --> 00:25:43.740 How about a 26 subnet mask? There are now six host bits, so the formula is 2^6 - 2. 00:25:43.740 --> 00:25:51.480 2^6 is 2 times 2 times 2 times 2 times 2 times 2, which equals 64. 00:25:51.480 --> 00:25:59.120 That means there are 62 usable addresses. So, it looks like we've found our number. 27 00:25:59.120 --> 00:26:04.960 doesn't provide enough address space, but 26 provides more than we need, so we have to 00:26:04.960 --> 00:26:10.940 go with 26. Unfortunately, you can't always make subnets have exactly the number of addresses 00:26:10.940 --> 00:26:16.570 you want. There might be some unused address space. That's actually fine, since it's good 00:26:16.570 --> 00:26:20.500 to have some room for growth anyway. 00:26:20.500 --> 00:26:26.571 So, I think this video has gone on long enough. Instead of finishing this task in this video, I'll make 00:26:26.571 --> 00:26:36.660 it this week's quiz. The first subnet, subnet one, is 192.168.0.16. What are the remaining 00:26:36.660 --> 00:26:42.660 subnets? To help you out, here's a hint: Find the broadcast address of subnet one. 00:26:42.660 --> 00:26:50.120 The next address after that is the network address of subnet two. And then just repeat the process for subnets 00:26:50.120 --> 00:26:56.780 three and four. Post your answers in the comment section, and I'll also go over the answer in the next video. 00:26:57.970 --> 00:27:05.300 So, what did we cover in this video? We covered CIDR (Classless Inter-Domain Routing), which 00:27:05.300 --> 00:27:10.680 removes the rules of class A, B, and C networks and lets us be more flexible with network 00:27:10.680 --> 00:27:17.030 addressing, according to the size of the network. We also covered the process of subnetting, 00:27:17.030 --> 00:27:22.040 but mostly just the basics. Hopefully, you understand the purpose of subnetting and 00:27:22.040 --> 00:27:27.120 know a little bit about how to do it. I will clarify and expand upon many things in the 00:27:27.120 --> 00:27:33.960 next video, but also feel free to ask any questions you have in the comments section. 00:27:33.960 --> 00:27:38.760 For today's video, there won't be a practice lab; that will be after I've finished explaining everything about 00:27:38.760 --> 00:27:43.760 subnetting. There will be flashcards, however, to help you review some of the things learned 00:27:43.760 --> 00:27:48.120 in this video. You can download them from the link in the description. 00:27:48.120 --> 00:27:53.280 I've also recently enabled the membership feature for my channel. If you want to leave 00:27:53.289 --> 00:27:59.070 a monthly tip to support me, this is another great way to do so. Click "Join" here under 00:27:59.070 --> 00:28:00.650 the video to check it out. 00:28:01.710 --> 00:28:08.230 For those who become a JCNP (Jeremy Certified Network Professional) level supporter, I'll 00:28:08.230 --> 00:28:14.700 give you a shoutout at the end of my videos. So, first of all, thank you so much to Vance Simmons. I just 00:28:14.700 --> 00:28:19.080 enabled the membership feature and haven't said anything about it yet, and he became my first 00:28:19.080 --> 00:28:24.670 JCNP level supporter. Thank you so much for supporting the channel. I hope the videos are helping 00:28:24.670 --> 00:28:30.107 you out. 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