1 00:00:00,430 --> 00:00:07,840 So once again, the format of an IP address in this case, IP version four is a 32 bit binary number. 2 00:00:08,020 --> 00:00:15,030 It's divided into four parts or four octets, which are eight bits or one byte in size. 3 00:00:15,040 --> 00:00:22,270 So an IP address could be written as follows in binary in dotted decimal notation, or it could be written 4 00:00:22,270 --> 00:00:25,810 as follows in dotted decimal notation. 5 00:00:26,290 --> 00:00:34,960 So just to summarize, it's a four byte number or 32 bit number, typically written in dotted decimal 6 00:00:34,960 --> 00:00:39,980 notation, but be aware that it's actually a binary address of 32 bits. 7 00:00:40,000 --> 00:00:46,720 Please refer to the binary videos if you're not sure about the formatting or conversion of binary to 8 00:00:46,720 --> 00:00:48,220 decimal and back again. 9 00:00:48,220 --> 00:00:51,970 An octet is eight binary bits or one byte. 10 00:00:52,120 --> 00:00:58,600 One byte equates to eight binary bits, so an IP version for address consists of four octets such as 11 00:00:58,600 --> 00:01:04,180 x x x x, where x is an octet or eight bits or one byte. 12 00:01:04,360 --> 00:01:10,360 Now using our street analogy, again, it's possible to have the same house number on different streets. 13 00:01:10,360 --> 00:01:14,980 So a house one could be on Oxford Street as well as Cambridge Street. 14 00:01:15,010 --> 00:01:21,370 House number one should just not appear twice on the same street, but number one is permitted on different 15 00:01:21,370 --> 00:01:23,230 streets in the same way. 16 00:01:23,230 --> 00:01:31,720 Here, it's possible to have number one on network 10.1, 1.0 slash 24, as well as number one on network 17 00:01:31,720 --> 00:01:34,450 12 .1.1.0 slash 24. 18 00:01:34,480 --> 00:01:37,840 The same number can appear on different networks. 19 00:01:38,200 --> 00:01:42,100 I'll explain the slash 24 in a moment when we discuss network mosques. 20 00:01:42,100 --> 00:01:47,770 But in this example, we have network 10.1, .1.0 and 12.1 and 1.0. 21 00:01:47,770 --> 00:01:54,460 And it's possible to have multiple devices with the host portion of the IP address set to one. 22 00:01:54,670 --> 00:02:02,410 The same host portion can appear twice as in in this example or many times in a network or the internet, 23 00:02:02,410 --> 00:02:05,890 as long as the network portion is different. 24 00:02:07,190 --> 00:02:12,590 Now, one thing you'll learn about networking is that things are constantly changing. 25 00:02:12,770 --> 00:02:20,270 Address classes or class ful networks were used in the internet from 1981 until the introduction of 26 00:02:20,270 --> 00:02:27,470 classless inter domain routing in 1993, which is commonly known as CIDR or C IDR. 27 00:02:27,500 --> 00:02:34,910 Now, prior to 1993, address classes were used to divide the IP version for address space into five 28 00:02:34,910 --> 00:02:36,140 address classes. 29 00:02:36,470 --> 00:02:43,610 The three that we're going to concentrate on here are class A, B and C, which are used for unicast 30 00:02:43,610 --> 00:02:44,510 traffic. 31 00:02:44,690 --> 00:02:51,950 Class D is used for multicast and class E is reserved for future or experimental purposes. 32 00:02:52,340 --> 00:02:56,450 Address classes have been superseded in IP version six. 33 00:02:56,450 --> 00:03:03,260 IP Version six does not use address classes, and an IP version for address classes have been replaced 34 00:03:03,260 --> 00:03:04,280 with CIDR. 35 00:03:04,370 --> 00:03:10,940 So the different classes of addresses A, B and C were used to accommodate different sizes of networks, 36 00:03:10,940 --> 00:03:13,910 which aided in the classification of those networks. 37 00:03:13,910 --> 00:03:20,510 So as an example, a class full, a address supports about 16 million IP addresses. 38 00:03:20,690 --> 00:03:28,880 So once again, we had Class A, B and C, these have been replaced or superseded by CIDR or C, IDR 39 00:03:28,880 --> 00:03:36,320 and address classes such as A, B and C were determined and then allocated by the honor or Internet 40 00:03:36,320 --> 00:03:38,030 assigned numbers authority. 41 00:03:38,330 --> 00:03:42,680 This format is not used entirely in its original format today. 42 00:03:42,710 --> 00:03:47,120 Here's an entry on Wikipedia showing the list of Class A addresses. 43 00:03:47,210 --> 00:03:51,920 So each class A address has approximately 16 million IP addresses. 44 00:03:51,920 --> 00:03:55,850 And if we scroll down the list, we can see various examples. 45 00:03:55,850 --> 00:04:06,800 AT&T have 12, Xerox 13, HP 15 Dec 16, so 15 and 16 are now owned by HP. 46 00:04:06,830 --> 00:04:12,560 Apple have 17, MIT 18 for 19 and so forth and so on. 47 00:04:12,860 --> 00:04:24,800 So notice as an example, Apple Own 17 0.0.08 Apple have 16 odd million public IP addresses that are 48 00:04:24,800 --> 00:04:26,570 part of the class a address. 49 00:04:26,780 --> 00:04:35,540 So in the original IP address format, a class address consists of eight network bits and 24 host bits. 50 00:04:35,630 --> 00:04:39,980 Hence it's written a/8 denoting eight network bits. 51 00:04:40,520 --> 00:04:46,700 Now this was fine when the internet was small, but it quickly became a limiting factor and thus multiple 52 00:04:46,700 --> 00:04:50,840 addresses were introduced with different size and network portions. 53 00:04:51,110 --> 00:04:56,120 Hence we have Class A, class B and class C addresses. 54 00:04:56,450 --> 00:05:04,460 Please note once again that class full addresses were replaced in 1993 with classless into domain routing 55 00:05:04,490 --> 00:05:07,100 or c IDR, also called CIDR. 56 00:05:07,430 --> 00:05:13,160 However, you may still come across commands that use the class full address format. 57 00:05:13,160 --> 00:05:18,050 An example of that is the network command within routing protocols. 58 00:05:18,380 --> 00:05:25,670 So as an example, if you use the network command on a rip routing process, the command is written 59 00:05:25,670 --> 00:05:27,920 in a class full format. 60 00:05:28,490 --> 00:05:33,590 It's also worth knowing a bit of the history and understanding why we have problems with a lack of IP 61 00:05:33,590 --> 00:05:34,670 addressing today. 62 00:05:34,970 --> 00:05:37,640 Hence it's worth your learning about Crossville addresses. 63 00:05:37,640 --> 00:05:44,060 For completeness, the breaking up of addresses was originally used to try and save or conserve IP addresses 64 00:05:44,060 --> 00:05:50,270 but did not work in its original format and thus was expanded and changed by CIDR. 65 00:05:50,690 --> 00:05:56,480 I'll explain CIDR in a moment, but let's first look at the various address classes in more detail.