1 00:00:07,140 --> 00:00:09,940 - Okay, next on the list, let's talk about subnet masks. 2 00:00:10,950 --> 00:00:13,620 The subnet mask is something you're gonna use 3 00:00:13,620 --> 00:00:15,930 in conjunction with an IP address. 4 00:00:15,930 --> 00:00:19,860 and we'll use IPv4 addresses for our example. 5 00:00:19,860 --> 00:00:24,210 So let's say we have an IP address at 192.168.1.100, 6 00:00:32,190 --> 00:00:33,540 just as an example. 7 00:00:33,540 --> 00:00:37,470 That's our IPv4 32 bit IP address. 8 00:00:37,470 --> 00:00:42,470 The subnet mask, and I'll just label that as SM, for this 9 00:00:42,780 --> 00:00:47,780 will normally be 255.255.255.0. 10 00:00:53,160 --> 00:00:56,760 And this tells us two things, 11 00:00:56,760 --> 00:00:59,850 the network portion of our IP address 12 00:00:59,850 --> 00:01:02,790 and the host portion of our IP address. 13 00:01:02,790 --> 00:01:05,770 So if we take a look at the triple 255 14 00:01:08,040 --> 00:01:13,040 and we line that up, we'll see that that equals 192.168.1. 15 00:01:13,500 --> 00:01:15,603 It corresponds to that, I should say. 16 00:01:17,040 --> 00:01:22,040 Every 255 together creates the network portion 17 00:01:22,050 --> 00:01:23,100 of the address. 18 00:01:23,100 --> 00:01:27,360 So the network that the computer is on is 192.168.1. 19 00:01:27,360 --> 00:01:30,930 Then you have that last octet, that zero. 20 00:01:30,930 --> 00:01:34,350 If you see a zero, then that deals with the host portion. 21 00:01:34,350 --> 00:01:37,953 And in this case, the host portion is gonna be 100. 22 00:01:41,760 --> 00:01:45,000 Other classes of IP networks 23 00:01:45,000 --> 00:01:47,400 will use different subnet masks. 24 00:01:47,400 --> 00:01:49,980 This is a class C address. 25 00:01:49,980 --> 00:01:51,930 In a class B network, 26 00:01:51,930 --> 00:01:55,820 such as say 172.16.1.1, just for example, 27 00:01:59,970 --> 00:02:04,360 you might have a subnet mask that is 255.255.0.0. 28 00:02:09,750 --> 00:02:14,750 So once again, the 255s indicate the network portion. 29 00:02:18,240 --> 00:02:22,320 So 172.16 is the network that you're on. 30 00:02:22,320 --> 00:02:25,830 And then 0.0 is the host portion. 31 00:02:25,830 --> 00:02:30,830 So .1.1 is gonna be the post portion of the IP address. 32 00:02:32,100 --> 00:02:34,890 And so that's a class B example. 33 00:02:34,890 --> 00:02:37,560 Rounding it out, the biggest networks, 34 00:02:37,560 --> 00:02:40,590 enterprise networks, government networks, they use class A. 35 00:02:40,590 --> 00:02:44,797 An example of that might be 10.0.0.1. 36 00:02:48,030 --> 00:02:51,600 And the typical subnet mask for a class A address 37 00:02:51,600 --> 00:02:56,527 or a class A network would be 255.0.0.0. 38 00:02:58,020 --> 00:03:00,390 And you can see the pattern here. 39 00:03:00,390 --> 00:03:04,800 So in a class A network the 10 is the network number. 40 00:03:04,800 --> 00:03:07,920 And you can see that is indicated by the 255. 41 00:03:07,920 --> 00:03:12,920 The zeros indicate the host number, 0.0.1. 42 00:03:12,960 --> 00:03:15,900 You can have lots and lots of IP addresses, 43 00:03:15,900 --> 00:03:20,900 16 million in the class A 10 network. 44 00:03:21,090 --> 00:03:26,090 So again, this is class A, this is class B, 45 00:03:26,220 --> 00:03:28,263 and this is class C. 46 00:03:29,940 --> 00:03:34,830 This is all in what's known as classful IP addressing, 47 00:03:34,830 --> 00:03:35,970 which you may or may not use. 48 00:03:35,970 --> 00:03:39,270 You might use CIDR or another type of concept, 49 00:03:39,270 --> 00:03:40,890 which we'll cover later. 50 00:03:40,890 --> 00:03:42,060 So keep that in mind. 51 00:03:42,060 --> 00:03:45,960 You might have classless, but in this case 52 00:03:45,960 --> 00:03:49,890 we're talking about classful IP addressing, classful. 53 00:03:49,890 --> 00:03:53,310 So we have our class A, class B, and class C. 54 00:03:53,310 --> 00:03:54,570 And it's that subnet mask 55 00:03:54,570 --> 00:03:56,880 that defines what portion of the IP address 56 00:03:56,880 --> 00:04:00,663 is the network portion and what portion is the host portion. 57 00:04:02,040 --> 00:04:03,690 And that's it for the sub lesson.