1 00:00:00,090 --> 00:00:01,800 In this lesson we're going to discuss 2 00:00:01,800 --> 00:00:04,110 IPv4 address types. 3 00:00:04,110 --> 00:00:06,510 Now in IPv4, there are several different ways 4 00:00:06,510 --> 00:00:08,250 to classify our addresses, 5 00:00:08,250 --> 00:00:10,800 including by whether they're public or private addresses, 6 00:00:10,800 --> 00:00:12,960 whether they're loopback or localhost addresses, 7 00:00:12,960 --> 00:00:14,880 and whether they're an APIPA address. 8 00:00:14,880 --> 00:00:16,230 Let's take a look at each of these. 9 00:00:16,230 --> 00:00:17,820 First, we need to talk about the difference 10 00:00:17,820 --> 00:00:21,000 between a public and a private IPv4 address. 11 00:00:21,000 --> 00:00:22,590 A public IPv4 address, 12 00:00:22,590 --> 00:00:24,600 also known as a routable IP address, 13 00:00:24,600 --> 00:00:25,890 is a unique IP address 14 00:00:25,890 --> 00:00:27,870 assigned to each device on the internet 15 00:00:27,870 --> 00:00:30,240 that allows it to communicate with other devices globally 16 00:00:30,240 --> 00:00:31,233 using IPv4. 17 00:00:32,790 --> 00:00:36,450 The IPv4 system uses a 32-bit address scheme 18 00:00:36,450 --> 00:00:40,620 that allows for a total of about 4.3 billion IP addresses. 19 00:00:40,620 --> 00:00:42,270 These addresses are typically written 20 00:00:42,270 --> 00:00:44,100 in a dotted decimal notation, 21 00:00:44,100 --> 00:00:45,840 and they're divided into four octets 22 00:00:45,840 --> 00:00:48,540 that are separated by those dots or periods. 23 00:00:48,540 --> 00:00:53,540 For example, 66.51.24.12 is a public IPv4 address. 24 00:00:55,710 --> 00:00:58,140 Now, these public or routable IP addresses 25 00:00:58,140 --> 00:00:59,460 must be leased or purchased 26 00:00:59,460 --> 00:01:00,990 from your internet service provider 27 00:01:00,990 --> 00:01:03,540 because they're globally managed by ICANN, which is 28 00:01:03,540 --> 00:01:06,600 the Internet Corporation for Assigned Names and Numbers. 29 00:01:06,600 --> 00:01:09,900 So if you want a public IP address assigned to your network 30 00:01:09,900 --> 00:01:11,190 so that you can host a web server 31 00:01:11,190 --> 00:01:13,800 for your company or a Minecraft server for your kids, 32 00:01:13,800 --> 00:01:16,770 you're going to have to lease or purchase that IP address. 33 00:01:16,770 --> 00:01:18,300 Now, because ICANN is responsible 34 00:01:18,300 --> 00:01:20,790 for all of the IP addresses across the globe, 35 00:01:20,790 --> 00:01:22,470 this is a lot to deal with. 36 00:01:22,470 --> 00:01:25,080 So they created five regional internet registries, 37 00:01:25,080 --> 00:01:28,140 or RIRs to be able to assist them, 38 00:01:28,140 --> 00:01:29,940 and these are the folks who are going to be responsible 39 00:01:29,940 --> 00:01:31,830 for managing the public IP addresses 40 00:01:31,830 --> 00:01:33,930 for different regions of the world. 41 00:01:33,930 --> 00:01:35,370 If you're in North America, 42 00:01:35,370 --> 00:01:38,370 you're going to be using a A-R-I-N or ARIN. 43 00:01:38,370 --> 00:01:39,840 If you're in Latin America. 44 00:01:39,840 --> 00:01:43,380 you're going to be using L-A-C-N-I-C or LACNIC. 45 00:01:43,380 --> 00:01:44,730 If you're in Africa, 46 00:01:44,730 --> 00:01:48,030 you're going to be using A-F-N-I-C or AFNIC. 47 00:01:48,030 --> 00:01:49,950 If you're in the Asia Pacific region, 48 00:01:49,950 --> 00:01:52,173 you're going to be using A-P-N-I-C or APNIC. 49 00:01:53,160 --> 00:01:56,340 And if you're in Europe, you're going to be using R-I-P-E, 50 00:01:56,340 --> 00:01:58,050 also known as RIPE. 51 00:01:58,050 --> 00:02:00,900 Now since my company is located here in the United States, 52 00:02:00,900 --> 00:02:02,610 when we want a public IP address, 53 00:02:02,610 --> 00:02:04,950 we will ask our internet service provider for one 54 00:02:04,950 --> 00:02:06,330 and they'll assign one to us 55 00:02:06,330 --> 00:02:08,789 and then insure us properly registered with ARIN 56 00:02:08,789 --> 00:02:10,110 because ARIN is responsible 57 00:02:10,110 --> 00:02:12,480 for all the publicly routable IP addresses 58 00:02:12,480 --> 00:02:14,700 inside the North American region. 59 00:02:14,700 --> 00:02:16,800 Now, most of the IP addresses you're going to use 60 00:02:16,800 --> 00:02:18,180 inside your own networks, 61 00:02:18,180 --> 00:02:19,320 you're not going to need one of these 62 00:02:19,320 --> 00:02:21,510 publicly routable IP addresses 63 00:02:21,510 --> 00:02:23,280 because each of these public IP addresses 64 00:02:23,280 --> 00:02:25,770 actually costs money each month for you to lease. 65 00:02:25,770 --> 00:02:28,920 And so instead, you may choose to use a private IP instead 66 00:02:28,920 --> 00:02:31,050 for your internal network devices. 67 00:02:31,050 --> 00:02:34,380 A private IPv4 address is a non-internet routable 68 00:02:34,380 --> 00:02:36,840 IP address used within a local network 69 00:02:36,840 --> 00:02:38,040 that allows for the communication 70 00:02:38,040 --> 00:02:40,050 between devices within that network 71 00:02:40,050 --> 00:02:42,780 without using a public IP address. 72 00:02:42,780 --> 00:02:45,450 Now, since these private IP addresses are not accessible 73 00:02:45,450 --> 00:02:48,810 over the internet, they can be used by anyone, at any time, 74 00:02:48,810 --> 00:02:51,900 but only within their own local area networks. 75 00:02:51,900 --> 00:02:54,390 This is why these IPs are not routable 76 00:02:54,390 --> 00:02:56,640 because there is no central authority like ICANN 77 00:02:56,640 --> 00:02:58,350 who's controlling who's using them 78 00:02:58,350 --> 00:03:00,660 and in which networks they're being used. 79 00:03:00,660 --> 00:03:02,520 In fact, if you look at the IP address 80 00:03:02,520 --> 00:03:04,230 of your computer right this minute, 81 00:03:04,230 --> 00:03:06,570 I bet that you're using an IP address that starts 82 00:03:06,570 --> 00:03:11,570 with either a 10, a 172, or 192 as its first octet. 83 00:03:11,580 --> 00:03:12,540 You don't believe me? 84 00:03:12,540 --> 00:03:14,880 Go ahead and pause the video and you can check. 85 00:03:14,880 --> 00:03:15,750 If you don't know how to check, 86 00:03:15,750 --> 00:03:17,370 I'll tell you how to do it right now. 87 00:03:17,370 --> 00:03:18,780 If you're on Windows 11, 88 00:03:18,780 --> 00:03:21,660 I want you to hold down your Windows key and press S, 89 00:03:21,660 --> 00:03:24,750 then type in CMD, and press Enter. 90 00:03:24,750 --> 00:03:29,220 Next, type in ipconfig and hit Enter. 91 00:03:29,220 --> 00:03:32,220 Now look on your screen and see your IP address. 92 00:03:32,220 --> 00:03:35,670 Does it start with a 10, a 172, or a 192? 93 00:03:35,670 --> 00:03:37,110 I bet you it does. 94 00:03:37,110 --> 00:03:38,100 Now, if you're on a Mac 95 00:03:38,100 --> 00:03:40,410 and you're watching this video over a wireless network, 96 00:03:40,410 --> 00:03:43,230 you can do this even easier to check your IP address. 97 00:03:43,230 --> 00:03:45,330 Simply go ahead and press down the Option Key 98 00:03:45,330 --> 00:03:48,000 on your keyboard and then click on that wifi icon 99 00:03:48,000 --> 00:03:50,340 in the top right corner of your menu bar. 100 00:03:50,340 --> 00:03:52,230 Look down under your wireless network name 101 00:03:52,230 --> 00:03:54,540 and you're going to see your IP address, again, 102 00:03:54,540 --> 00:03:59,040 I bet you your starts with a 10, a 172, or a 192. 103 00:03:59,040 --> 00:04:01,440 Now, am I a magician that I can guess your IP address 104 00:04:01,440 --> 00:04:02,820 magically over the internet? 105 00:04:02,820 --> 00:04:04,260 Well, not really. 106 00:04:04,260 --> 00:04:05,640 You see, those three values 107 00:04:05,640 --> 00:04:08,610 are part of what we call the private IP ranges. 108 00:04:08,610 --> 00:04:10,620 This includes something like 10 dot something, 109 00:04:10,620 --> 00:04:12,030 dot something, dot something. 110 00:04:12,030 --> 00:04:15,390 or 172.16 dot something, dot something 111 00:04:15,390 --> 00:04:19,260 or 192.168.1 dot something. 112 00:04:19,260 --> 00:04:21,060 If you're using a private IP 113 00:04:21,060 --> 00:04:24,150 and I said they are not routable or usable on the internet, 114 00:04:24,150 --> 00:04:25,950 how are you actually connecting to my servers 115 00:04:25,950 --> 00:04:27,240 to watch this video right now 116 00:04:27,240 --> 00:04:29,190 because you have a private IP? 117 00:04:29,190 --> 00:04:30,300 Now, that's a great question 118 00:04:30,300 --> 00:04:32,190 and I'm really glad that you asked it. 119 00:04:32,190 --> 00:04:34,080 Now, the way this works is by using something 120 00:04:34,080 --> 00:04:36,480 known as network address translation. 121 00:04:36,480 --> 00:04:39,150 Network address translation, or NAT, 122 00:04:39,150 --> 00:04:40,680 is a method used in networking 123 00:04:40,680 --> 00:04:42,930 that allows a single device, like a router, 124 00:04:42,930 --> 00:04:44,820 to act as an agent between the internet, 125 00:04:44,820 --> 00:04:46,140 or the public network, 126 00:04:46,140 --> 00:04:48,000 and a local or private network 127 00:04:48,000 --> 00:04:50,160 to remap your private IP addresses 128 00:04:50,160 --> 00:04:52,050 into a single public IP address 129 00:04:52,050 --> 00:04:54,030 and then back again to facilitate 130 00:04:54,030 --> 00:04:56,340 the communication between those two devices 131 00:04:56,340 --> 00:04:59,460 and to conserve the global IP address space. 132 00:04:59,460 --> 00:05:01,860 Essentially, whenever your computer wants to access 133 00:05:01,860 --> 00:05:03,780 a resource on the internet, like our website 134 00:05:03,780 --> 00:05:05,310 at diontraining.com, 135 00:05:05,310 --> 00:05:07,470 your computer's going to reach out to your network's router 136 00:05:07,470 --> 00:05:09,900 using its internal private IP address. 137 00:05:09,900 --> 00:05:12,870 This router will then conduct a network address translation 138 00:05:12,870 --> 00:05:16,170 to change your private IP address into a public IP address 139 00:05:16,170 --> 00:05:19,530 on the other side of the router and an associated port. 140 00:05:19,530 --> 00:05:21,450 Then it will make the request to the web server 141 00:05:21,450 --> 00:05:22,710 on your behalf, 142 00:05:22,710 --> 00:05:24,810 when the data comes back from that web server, 143 00:05:24,810 --> 00:05:26,220 your router's going to receive it 144 00:05:26,220 --> 00:05:29,190 and translate it from that public IP address and port 145 00:05:29,190 --> 00:05:31,230 back into your local private IP address 146 00:05:31,230 --> 00:05:33,780 and forward that traffic back to your system. 147 00:05:33,780 --> 00:05:35,250 Now, there's a lot more to understand 148 00:05:35,250 --> 00:05:38,220 with network address translation, also known as NAT, 149 00:05:38,220 --> 00:05:40,350 but we're going to save that for a separate lesson 150 00:05:40,350 --> 00:05:42,180 to fully cover everything you need to know 151 00:05:42,180 --> 00:05:44,190 about network address translation. 152 00:05:44,190 --> 00:05:46,050 But for now, I just want you to realize 153 00:05:46,050 --> 00:05:50,010 that it converts or translates a private IP into a public IP 154 00:05:50,010 --> 00:05:52,770 and then back again on behalf of your system. 155 00:05:52,770 --> 00:05:53,970 Now for the exam 156 00:05:53,970 --> 00:05:56,250 and your real life role as a network technician, 157 00:05:56,250 --> 00:05:57,960 it's going to be really important to memorize 158 00:05:57,960 --> 00:06:00,480 the ranges for the private IP addresses. 159 00:06:00,480 --> 00:06:03,180 These ranges are defined in the request for comments 160 00:06:03,180 --> 00:06:05,010 1918. 161 00:06:05,010 --> 00:06:07,200 Now a request for comments, or RFC, 162 00:06:07,200 --> 00:06:08,700 is a formal publication 163 00:06:08,700 --> 00:06:12,660 from the Internet Engineering Task Force known as the IETF. 164 00:06:12,660 --> 00:06:15,000 These RFCs are authored by individuals 165 00:06:15,000 --> 00:06:16,590 or groups of computer scientists 166 00:06:16,590 --> 00:06:18,840 who want to document new technologies or standards 167 00:06:18,840 --> 00:06:20,160 that they're proposing. 168 00:06:20,160 --> 00:06:22,740 In the case of RFC 1918, 169 00:06:22,740 --> 00:06:24,750 it was used to document how organizations 170 00:06:24,750 --> 00:06:27,720 could conduct address allocation for private intranet, 171 00:06:27,720 --> 00:06:29,460 which we now call intranets 172 00:06:29,460 --> 00:06:32,700 by using private or non-routable IP addresses. 173 00:06:32,700 --> 00:06:36,660 In RFC 1918, there are specific ranges of private IPs 174 00:06:36,660 --> 00:06:40,650 described for class A, class B, and class C networks. 175 00:06:40,650 --> 00:06:42,720 If you're working with a class A address, 176 00:06:42,720 --> 00:06:45,270 anything that starts with a 10 in the first octet 177 00:06:45,270 --> 00:06:47,730 is going to be considered a private IP. 178 00:06:47,730 --> 00:06:52,050 This includes the entire range of IPs from 10.0.0.0 179 00:06:52,050 --> 00:06:56,010 all the way up to 10.255.255.255, 180 00:06:56,010 --> 00:06:59,670 for a total of 16.7 million IP addresses, 181 00:06:59,670 --> 00:07:01,560 that are private and available for use 182 00:07:01,560 --> 00:07:04,380 at any time you want inside of your networks. 183 00:07:04,380 --> 00:07:06,270 If you're working with a class B address, 184 00:07:06,270 --> 00:07:07,440 anytime you see something that starts 185 00:07:07,440 --> 00:07:10,860 with a 172.16, dot something, dot something, 186 00:07:10,860 --> 00:07:13,620 going all the way up to 172.31, 187 00:07:13,620 --> 00:07:15,150 dot something, dot something, 188 00:07:15,150 --> 00:07:18,270 this is considered to be in the private IP range as well. 189 00:07:18,270 --> 00:07:21,420 Now this includes just over 1 million IP addresses 190 00:07:21,420 --> 00:07:25,410 or 16 times 256 times 256. 191 00:07:25,410 --> 00:07:27,720 Now, these class B private IP ranges 192 00:07:27,720 --> 00:07:29,820 are actually the hardest ones for you to memorize, 193 00:07:29,820 --> 00:07:30,900 and for this reason, 194 00:07:30,900 --> 00:07:33,660 the exam writers love to ask you questions about them, 195 00:07:33,660 --> 00:07:35,340 so keep those in mind. 196 00:07:35,340 --> 00:07:37,650 Now, if you're looking at class C addresses, 197 00:07:37,650 --> 00:07:40,440 anything that starts with a 192.168 dot something, 198 00:07:40,440 --> 00:07:43,950 dot something, is going to be a private IP. 199 00:07:43,950 --> 00:07:48,390 This includes the entire range of 192.168.0.0, 200 00:07:48,390 --> 00:07:52,620 all the way up to 192.168.255.255, 201 00:07:52,620 --> 00:07:57,620 which gives us 65,536 private IP addresses for us to use. 202 00:07:57,750 --> 00:07:59,910 Now, I want you to commit these ranges to memory, 203 00:07:59,910 --> 00:08:01,500 write them down in your notes. 204 00:08:01,500 --> 00:08:03,510 Remember, class A is pretty easy. 205 00:08:03,510 --> 00:08:05,100 Anything with a 10 in the front 206 00:08:05,100 --> 00:08:08,310 is going to be a private IP in the class A range. 207 00:08:08,310 --> 00:08:10,200 Class C is also pretty easy. 208 00:08:10,200 --> 00:08:12,930 Anything that starts with 192.168 209 00:08:12,930 --> 00:08:15,510 is going to be a private class C address. 210 00:08:15,510 --> 00:08:18,510 But class B, that's where most of my students struggle 211 00:08:18,510 --> 00:08:20,190 because it's a little bit odd. 212 00:08:20,190 --> 00:08:21,630 It contains anything that starts 213 00:08:21,630 --> 00:08:24,570 with 172.16 dot something, dot something, 214 00:08:24,570 --> 00:08:27,990 all the way up to 172.31 dot something, dot something, 215 00:08:27,990 --> 00:08:30,600 which is essentially 16 class B ranges, 216 00:08:30,600 --> 00:08:31,890 all sitting next to each other, 217 00:08:31,890 --> 00:08:33,690 but they kind of start out in this weird place 218 00:08:33,690 --> 00:08:38,400 in the middle of the 172 range by doing 172.16 219 00:08:38,400 --> 00:08:41,100 up to 172.31. 220 00:08:41,100 --> 00:08:43,799 So on test day, CompTIA may try to trick you 221 00:08:43,799 --> 00:08:47,280 and say, which of these addresses is not a private IP? 222 00:08:47,280 --> 00:08:48,207 And then they'll give you something like 223 00:08:48,207 --> 00:08:51,570 172.12 dot something, dot something. 224 00:08:51,570 --> 00:08:53,580 Now this IP looks like a private IP 225 00:08:53,580 --> 00:08:55,260 because it starts with 172, 226 00:08:55,260 --> 00:09:00,227 but it isn't because it's not between 172.16 and 172.31. 227 00:09:01,380 --> 00:09:03,300 So it's actually a public IP 228 00:09:03,300 --> 00:09:05,250 because it's outside of that range. 229 00:09:05,250 --> 00:09:07,290 So be really careful when you're seeing an address 230 00:09:07,290 --> 00:09:08,940 that starts with 172 231 00:09:08,940 --> 00:09:11,970 because it has to be within 172.16 232 00:09:11,970 --> 00:09:13,767 dot something, dot something up to 233 00:09:13,767 --> 00:09:16,770 172.31 dot something, dot something. 234 00:09:16,770 --> 00:09:19,380 to be a private class B IP. 235 00:09:19,380 --> 00:09:21,690 any of the other 172 dot something, dot something, 236 00:09:21,690 --> 00:09:22,860 dot something addresses 237 00:09:22,860 --> 00:09:24,990 will be considered a public IP, 238 00:09:24,990 --> 00:09:27,240 so don't get that wrong on the exam. 239 00:09:27,240 --> 00:09:29,610 Next, we need to take a look at some special types 240 00:09:29,610 --> 00:09:31,980 of IP addresses known as the loopback 241 00:09:31,980 --> 00:09:33,840 or localhost addresses. 242 00:09:33,840 --> 00:09:36,630 Now, the loopback address, also known as the localhost, 243 00:09:36,630 --> 00:09:38,070 is a specialized IP address 244 00:09:38,070 --> 00:09:42,450 that is always assigned as 127.0.0.1. 245 00:09:42,450 --> 00:09:45,450 Now all the way back in 1986 when this was created, 246 00:09:45,450 --> 00:09:47,370 the developers weren't really worried about wasting 247 00:09:47,370 --> 00:09:51,600 IP addresses because there were 4.3 billion IPv4 addresses. 248 00:09:51,600 --> 00:09:53,430 So they simply went ahead and dedicated 249 00:09:53,430 --> 00:09:58,430 the entire 127.0.0.0/8 range, or 16.7 million IPs 250 00:10:00,330 --> 00:10:02,790 to be used as the internet host loopback address, 251 00:10:02,790 --> 00:10:05,040 also known as our localhost. 252 00:10:05,040 --> 00:10:06,630 Now, the loopback address is used 253 00:10:06,630 --> 00:10:08,160 so that any higher level protocol 254 00:10:08,160 --> 00:10:10,410 can send data back to the host itself 255 00:10:10,410 --> 00:10:12,750 without going out to a switch or router. 256 00:10:12,750 --> 00:10:15,360 Essentially, this creates a loopback to the host, 257 00:10:15,360 --> 00:10:16,770 and it's often used for troubleshooting 258 00:10:16,770 --> 00:10:18,570 and testing your network protocol software 259 00:10:18,570 --> 00:10:20,160 on a given system. 260 00:10:20,160 --> 00:10:22,320 Now, because of the way the standard was defined, 261 00:10:22,320 --> 00:10:25,380 anything that starts with a 127 in the first octet 262 00:10:25,380 --> 00:10:27,660 is going to be treated as a loopback address. 263 00:10:27,660 --> 00:10:29,610 But almost always you're going to see this written 264 00:10:29,610 --> 00:10:33,690 as 127.0.0.1 for this purpose. 265 00:10:33,690 --> 00:10:36,990 That means the other 16.7 million IPs 266 00:10:36,990 --> 00:10:39,300 inside the 127 dot something, dot something, 267 00:10:39,300 --> 00:10:40,320 dot something range, 268 00:10:40,320 --> 00:10:42,387 are really simply wasted as part of this loopback 269 00:10:42,387 --> 00:10:44,640 or localhost range. 270 00:10:44,640 --> 00:10:46,860 Now you've heard me call the loopback IP address 271 00:10:46,860 --> 00:10:50,280 of 127.0.0.1, the localhost, 272 00:10:50,280 --> 00:10:52,020 and almost every computer in the world, 273 00:10:52,020 --> 00:10:55,410 if you type in the word localhost inside of your computer, 274 00:10:55,410 --> 00:10:57,240 your local DNS settings are going to resolve 275 00:10:57,240 --> 00:11:00,450 that back to 127.0.0.1. 276 00:11:00,450 --> 00:11:02,400 If you want to go into your command line right now 277 00:11:02,400 --> 00:11:07,020 and type in ping localhost, or ping 127.0.0.1, 278 00:11:07,020 --> 00:11:09,000 you're going to get the exact same results 279 00:11:09,000 --> 00:11:11,340 because localhost is the human readable name 280 00:11:11,340 --> 00:11:15,720 for the IP address of 127.0.0.1. 281 00:11:15,720 --> 00:11:17,790 Now, there's another special IP address range 282 00:11:17,790 --> 00:11:21,120 you need to be aware of, and this is called APIPA. 283 00:11:21,120 --> 00:11:24,060 Now APIPA, spelled A-P-I-P-A, 284 00:11:24,060 --> 00:11:26,460 is the automatic private IP addresses, 285 00:11:26,460 --> 00:11:29,070 and these APIPA addresses are dynamically assigned 286 00:11:29,070 --> 00:11:30,360 by your operating system 287 00:11:30,360 --> 00:11:33,150 whenever the network's DHCP server is unavailable 288 00:11:33,150 --> 00:11:35,730 and an IP address was not already statically assigned 289 00:11:35,730 --> 00:11:40,730 to your system, the APIPA range is 169.254.0.0 290 00:11:41,370 --> 00:11:46,370 and it goes all the way up to 169.254.255.255, 291 00:11:46,410 --> 00:11:50,610 which consists of 65,536 possible APIPA addresses 292 00:11:50,610 --> 00:11:52,050 that you can use. 293 00:11:52,050 --> 00:11:54,300 Now, basically anytime you see an IP address 294 00:11:54,300 --> 00:11:58,170 reported as 169.254, dot something, dot something. 295 00:11:58,170 --> 00:11:59,670 This means your device was unable 296 00:11:59,670 --> 00:12:02,610 to complete the DHCP request and assignment process, 297 00:12:02,610 --> 00:12:03,960 and because that device isn't getting 298 00:12:03,960 --> 00:12:06,870 a normal private IP from our network using DHCP, 299 00:12:06,870 --> 00:12:08,520 it's going to simply choose one at random 300 00:12:08,520 --> 00:12:10,710 from the APIPA range instead. 301 00:12:10,710 --> 00:12:12,720 Now, when your workstation first boots up, 302 00:12:12,720 --> 00:12:14,850 it's going to attempt to get a dynamic IP address 303 00:12:14,850 --> 00:12:16,950 using the DHCP protocol. 304 00:12:16,950 --> 00:12:21,150 It goes through a four step process known as DORA, D-O-R-A. 305 00:12:21,150 --> 00:12:24,960 This stands for Discover, Offer, Request, and Acknowledge. 306 00:12:24,960 --> 00:12:25,860 Now if something goes wrong 307 00:12:25,860 --> 00:12:28,080 with this DHCP negotiation process, 308 00:12:28,080 --> 00:12:30,060 the system won't be able to get an IP address 309 00:12:30,060 --> 00:12:31,620 from the DHCP server. 310 00:12:31,620 --> 00:12:34,140 Now, if this happened, your computer would just crash 311 00:12:34,140 --> 00:12:36,540 because it would keep trying over and over and over again 312 00:12:36,540 --> 00:12:37,950 and nothing would happen. 313 00:12:37,950 --> 00:12:40,470 So what the brilliant engineers of the Internet Task Force 314 00:12:40,470 --> 00:12:42,810 did was create this special range of IPs 315 00:12:42,810 --> 00:12:45,600 called APIPA to overcome this challenge. 316 00:12:45,600 --> 00:12:47,790 Basically, it says if you have a workstation 317 00:12:47,790 --> 00:12:50,730 that can't get a DHCP assignment for a dynamic IP address, 318 00:12:50,730 --> 00:12:52,290 within a certain amount of time, 319 00:12:52,290 --> 00:12:55,380 that workstation will just give up and pick its own address 320 00:12:55,380 --> 00:12:59,430 from this special APIPA range of 169.254 dot something, 321 00:12:59,430 --> 00:13:00,480 dot something. 322 00:13:00,480 --> 00:13:02,160 So if you ever find a computer 323 00:13:02,160 --> 00:13:03,720 that cannot connect to the internet, 324 00:13:03,720 --> 00:13:06,330 the first thing you should check is its IP address. 325 00:13:06,330 --> 00:13:09,210 You can do this using ipconfig on Windows Systems, 326 00:13:09,210 --> 00:13:13,140 ifconfig on Mac Systems or ip on Linux Systems. 327 00:13:13,140 --> 00:13:16,530 If you see an IP address that starts with 169.254, 328 00:13:16,530 --> 00:13:17,940 dot something, dot something, 329 00:13:17,940 --> 00:13:20,190 then you know it's a DHCP problem 330 00:13:20,190 --> 00:13:22,140 and you need to check the DHCP server 331 00:13:22,140 --> 00:13:23,430 to make sure it's working properly 332 00:13:23,430 --> 00:13:25,380 and handing out private IP addresses 333 00:13:25,380 --> 00:13:28,680 from the class A, class B, or class C range. 334 00:13:28,680 --> 00:13:30,150 Now, that's as deep as we need to go 335 00:13:30,150 --> 00:13:31,980 into DHCP for right now, 336 00:13:31,980 --> 00:13:35,010 but we will come back to DHCP later on in its own lesson 337 00:13:35,010 --> 00:13:36,930 to dive much deeper into how it works 338 00:13:36,930 --> 00:13:39,150 and the kind of information it can provide your computer 339 00:13:39,150 --> 00:13:42,270 in addition to that dynamically assigned IP address. 340 00:13:42,270 --> 00:13:44,400 All right, I know that was a ton of information 341 00:13:44,400 --> 00:13:46,710 in this video and if I went too fast for you, 342 00:13:46,710 --> 00:13:48,300 I do recommend that you go ahead 343 00:13:48,300 --> 00:13:50,670 and watch this video a second time. 344 00:13:50,670 --> 00:13:52,590 There is so much important information in here 345 00:13:52,590 --> 00:13:55,140 that you need to know as a good network technician 346 00:13:55,140 --> 00:13:56,580 and for the exam. 347 00:13:56,580 --> 00:13:58,650 So remember, when you're trying to understand 348 00:13:58,650 --> 00:14:00,360 IPv4 address types, 349 00:14:00,360 --> 00:14:02,670 it's really important that you recognize the distinctions 350 00:14:02,670 --> 00:14:05,520 between public and private IPv4 addresses, 351 00:14:05,520 --> 00:14:07,153 as well as the special ranges like loopback, 352 00:14:07,153 --> 00:14:09,690 localhost, and APIPA addresses. 353 00:14:09,690 --> 00:14:11,640 Now, public IPv4 addresses 354 00:14:11,640 --> 00:14:14,310 are unique global identifiers that are needed for devices 355 00:14:14,310 --> 00:14:15,930 to communicate over the internet. 356 00:14:15,930 --> 00:14:18,390 And these public IP addresses are managed by ICANN 357 00:14:18,390 --> 00:14:20,130 and its regional bodies. 358 00:14:20,130 --> 00:14:21,930 Private IP addresses on the other hand, 359 00:14:21,930 --> 00:14:23,850 are only used within our local networks 360 00:14:23,850 --> 00:14:25,800 and they allow for internal communication 361 00:14:25,800 --> 00:14:28,080 without being directly exposed to the internet. 362 00:14:28,080 --> 00:14:29,460 This helps us save money 363 00:14:29,460 --> 00:14:30,720 and it also helps us to preserve 364 00:14:30,720 --> 00:14:33,150 the limited public IP version four address space 365 00:14:33,150 --> 00:14:34,950 that is available today. 366 00:14:34,950 --> 00:14:36,630 The loopback or localhost address 367 00:14:36,630 --> 00:14:37,980 is used for internal testing 368 00:14:37,980 --> 00:14:40,050 of your device's network protocols. 369 00:14:40,050 --> 00:14:43,080 The loopback or localhost address is usually just going to use 370 00:14:43,080 --> 00:14:46,680 127.0.0.1 as its IP address, 371 00:14:46,680 --> 00:14:49,320 but the entire 127 dot something, dot something, 372 00:14:49,320 --> 00:14:52,339 dot something range is actually reserved for loopback 373 00:14:52,339 --> 00:14:53,670 and localhost use. 374 00:14:53,670 --> 00:14:56,220 The automatic private IP address, or APIPA, 375 00:14:56,220 --> 00:14:58,290 is a fallback for network configurations 376 00:14:58,290 --> 00:14:59,940 whenever DHCP fails, 377 00:14:59,940 --> 00:15:01,980 but they are considered to be private IPs 378 00:15:01,980 --> 00:15:04,140 and not routable over the internet. 379 00:15:04,140 --> 00:15:06,780 If you see a device has been assigned an APIPA address, 380 00:15:06,780 --> 00:15:08,910 you should check its network connectivity first, 381 00:15:08,910 --> 00:15:10,320 and if that's working properly, 382 00:15:10,320 --> 00:15:12,660 you then need to go on to check the DHCP server 383 00:15:12,660 --> 00:15:14,613 to make sure it's reachable and online.