1 00:00:05,120 --> 00:00:06,580 You need to know how to read 2 00:00:06,580 --> 00:00:10,300 MAC addresses and what they mean and to help us do that. 3 00:00:10,310 --> 00:00:13,680 Let's make this practical and use Packet Tracer. 4 00:00:13,790 --> 00:00:19,420 So please open packet tracer and follow me and make sure that you see something similar. 5 00:00:19,460 --> 00:00:23,870 The numbers that you get may be different but we'll manually configure MAC addresses in Packet Tracer 6 00:00:24,130 --> 00:00:25,770 because it's easy to do that. 7 00:00:25,820 --> 00:00:31,520 So make sure that you can view the MAC addresses and then gonna show you how to work with hexadecimal 8 00:00:31,730 --> 00:00:37,970 and how to convert numbers from binary to hex, hexadecimal to decimal and so forth. 9 00:00:38,000 --> 00:00:45,620 So the first thing is let's get a switch and I'll get a 3560 switch and drag that into the topology. 10 00:00:45,620 --> 00:00:47,690 I'll go to end devices. 11 00:00:47,690 --> 00:00:54,860 Grab a PC, grab a laptop, add that to the topology go to network connections and get a straight-through 12 00:00:54,860 --> 00:01:01,970 cable and connect the PCs Ethernet interface to the switch on gigabit 001. 13 00:01:02,060 --> 00:01:07,460 You don't have to use exactly the same interfaces it's really up to you but what I've done here is connect 14 00:01:07,490 --> 00:01:10,830 the PC to the switch to make it easier to follow. 15 00:01:10,850 --> 00:01:17,510 I'll go to preferences and I'll show the port labels in my diagram, so fast 16 00:01:17,510 --> 00:01:22,570 Ethernet0 in the PC he is connected to gigabit 101 on the switch. 17 00:01:22,580 --> 00:01:31,100 I'll connect to the second gig interface to the laptop on fastethernet0 so we've got our devices 18 00:01:31,100 --> 00:01:32,360 in our topology. 19 00:01:32,420 --> 00:01:37,730 The switch needs a power supply so grab a power supply and add that to the switch. 20 00:01:37,880 --> 00:01:40,580 And as you can see the switch is now booting up. 21 00:01:40,580 --> 00:01:47,500 But now let's view the MAC addresses on the devices it's on PC 1 go to fast ethernet0 22 00:01:47,510 --> 00:01:50,830 this is the MAC address of the PC by default. 23 00:01:50,870 --> 00:01:59,180 I'm gonna give it an IP address of 10 1 1 1 with a subnet mask of slash 24 or 2 5 5 2 5 5 2 5 5 0 24 00:01:59,210 --> 00:02:04,540 If you don't understand that yet don't worry too much we'll talk a lot about subnetting, in later videos 25 00:02:05,150 --> 00:02:08,490 but for the moment, I've configured the PC with those details. 26 00:02:08,570 --> 00:02:09,590 I'll go to desktop. 27 00:02:09,590 --> 00:02:14,930 Command prompt and if we type IP config like you would on a Windows computer. 28 00:02:14,930 --> 00:02:19,820 Notice there's the IP address of the PC, IP config slash all. 29 00:02:20,000 --> 00:02:25,030 There is the MAC address of the PC not easy to read. 30 00:02:25,040 --> 00:02:29,750 We'll change that in a moment, but for the moment I want to show you that the switch will learn those 31 00:02:29,750 --> 00:02:36,350 MAC addresses so hence it's important for you to learn hexadecimal on the laptop go to config fast 32 00:02:36,380 --> 00:02:37,620 ethernet0 33 00:02:37,700 --> 00:02:45,020 I'll configure this laptop with an IP address of 10.1.1.1 and a subnet mask of that 34 00:02:45,230 --> 00:02:47,630 255 255 255 0 35 00:02:47,630 --> 00:02:55,880 There's the MAC address of this PC, so if I go to command prompt on the laptop and type IP config slash 36 00:02:55,910 --> 00:03:01,660 all there's the IP address there's the MAC address back on the P.C.. 37 00:03:01,700 --> 00:03:10,520 PC1, PC starts with 0 0 0 4 laptop starts with triple 0 6, the first half of this address is the 38 00:03:10,550 --> 00:03:12,080 vendor code. 39 00:03:12,200 --> 00:03:18,980 Second half is a unique identifier for the MAC address, but notice please when I type a command such 40 00:03:18,980 --> 00:03:20,910 as ARP dash a. 41 00:03:20,990 --> 00:03:22,880 It says there are no arp entries. 42 00:03:22,940 --> 00:03:26,960 arp is used to find the MAC address of another device in the network 43 00:03:26,960 --> 00:03:32,360 It's basically a broadcast sent out into the network saying who has this IP address and then that device 44 00:03:32,360 --> 00:03:34,280 will reply back with its MAC address. 45 00:03:35,060 --> 00:03:36,810 So back on the laptop, 46 00:03:36,980 --> 00:03:44,810 If I type arp dash A, notice it says no arp entries are found arp is used to discover the MAC address of 47 00:03:44,870 --> 00:03:51,320 another device in ethernet devices have MAC addresses allocated to them by vendors 48 00:03:51,410 --> 00:03:55,910 If I want to talk to your device I need to know what your MAC address is to be able to send the traffic 49 00:03:55,940 --> 00:03:57,370 onto the ethernet network. 50 00:03:57,830 --> 00:04:03,500 So if the laptop pings the PC, it's basically going to send a broadcast into the network saying who 51 00:04:03,500 --> 00:04:07,260 has this IP address and then that PC will reply back. 52 00:04:07,340 --> 00:04:16,010 Notice now when we type arp-a, we see that this IP address is using this MAC address and that's correct. 53 00:04:16,010 --> 00:04:24,470 Per the information on PC1, back on the PC IP config slash all shows us that the PC has this 54 00:04:24,470 --> 00:04:31,730 IP address and this MAC address, the laptop has learnt the MAC address of the PC and in the same way 55 00:04:32,000 --> 00:04:35,950 the PC has learnt the MAC address of the laptop. 56 00:04:36,470 --> 00:04:40,850 So that's an example where hexadecimal values are used but it's not only there. 57 00:04:40,850 --> 00:04:45,810 If I have a look at the switch, I'm gonna bypass the initial configuration on the switch. 58 00:04:45,850 --> 00:04:50,930 Now don't worry too much if you don't know the commands on Cisco switches in a lot of detail yet you'll 59 00:04:50,930 --> 00:04:52,660 learn as we go along. 60 00:04:52,760 --> 00:04:59,480 Enable takes us to privilege mode and here I can type show MAC address table to see the MAC address table 61 00:04:59,600 --> 00:05:04,770 on the switch, the switch has learned where the devices are the whole idea with a switch is when it 62 00:05:04,770 --> 00:05:09,280 receives traffic at one port it needs to switch that traffic out of another port needs to know where 63 00:05:09,280 --> 00:05:14,890 the devices are so that it can efficiently send the traffic to only the correct ports. 64 00:05:14,890 --> 00:05:20,280 So in other words if traffic arrives on this interface going to the laptop we only want to send it out 65 00:05:20,280 --> 00:05:21,640 of this interface. 66 00:05:21,690 --> 00:05:25,800 Now the switch doesn't have other interfaces connected at the moment but if we did we wouldn't want 67 00:05:25,800 --> 00:05:30,960 to send that traffic out of all interfaces we would want to limit it to this one interface. 68 00:05:30,960 --> 00:05:34,620 So the switch learns where devices are in the network. 69 00:05:34,770 --> 00:05:42,650 If we change the MAC address of the PC so going back to the PCs config, we will click on fastethernet 70 00:05:42,720 --> 00:05:43,480 0 71 00:05:43,590 --> 00:05:51,480 I could as an example set the MAC address to 0 0 C 0 and then just make it a number like that a whole 72 00:05:51,480 --> 00:05:58,440 bunch of ones notice a MAC address consists of six hexadecimal values this is hex which is the vendor 73 00:05:58,440 --> 00:06:06,240 code and then six hexadecimal values which is the unique identifier for the MAC address a hex value 74 00:06:06,450 --> 00:06:09,810 is 4 binary bits and I'll explain that in more detail in a moment. 75 00:06:09,810 --> 00:06:11,070 This is a 48 76 00:06:11,160 --> 00:06:20,100 bit number, we've got twelve hexadecimal values and a MAC address twelve times 4, 48 bits, each number has 77 00:06:20,100 --> 00:06:22,020 a hexadecimal number. 78 00:06:22,110 --> 00:06:28,090 What I'll do now is change the MAC address of the laptop so go to config fast ethernet0 79 00:06:28,320 --> 00:06:34,800 Let's make that 0 0 C 0 2 2 2 2 and a bunch of twos. 80 00:06:34,850 --> 00:06:43,050 So I've changed the MAC address of the laptop as well if I type IP config that's the IP address to slash 81 00:06:43,110 --> 00:06:43,830 all. 82 00:06:44,010 --> 00:06:50,490 Make this bigger that shows us the MAC address of the P.C. has changed or the laptop in this case has 83 00:06:50,490 --> 00:06:51,380 changed. 84 00:06:51,570 --> 00:06:59,970 So now arp-a, the arp cache has timed out or has been flushed in this example there are no arp entries. 85 00:06:59,970 --> 00:07:07,590 If the laptop pings the PC and type arp-a now you can see that the Mac address of value has been 86 00:07:07,590 --> 00:07:08,450 updated. 87 00:07:08,670 --> 00:07:17,610 So the laptop has learnt the new MAC address associated with the PC and in the same way the PC has 88 00:07:17,610 --> 00:07:26,490 learnt that was the previous entry but PC has learnt the new MAC address of the laptop and the switch 89 00:07:26,760 --> 00:07:29,390 will have learnt the new MAC addresses. 90 00:07:29,520 --> 00:07:35,580 Now it still has the old MAC addresses in its MAC address table they will time out after a period of 91 00:07:35,580 --> 00:07:42,150 time but for the moment it's got both the old MAC addresses and the new MAC addresses in its MAC address 92 00:07:42,150 --> 00:07:48,660 table, a switch learns where the MAC addresses of devices are in the network and then basically switches 93 00:07:48,660 --> 00:07:53,330 the traffic from one MAC address to another depending on who's talking to who. 94 00:07:53,340 --> 00:07:58,710 So as you can see here MAC addresses are used in a lot of places you need to know how to read MAC addresses 95 00:07:58,740 --> 00:08:00,150 you need to know what that means. 96 00:08:00,240 --> 00:08:03,750 If I tell you that that's a 48 bit number, you need to know that. 97 00:08:03,810 --> 00:08:05,400 Why, why is it 48? 98 00:08:05,400 --> 00:08:10,470 So let's talk about the theory and I'll show you how to do conversions from one numbering system to 99 00:08:10,470 --> 00:08:11,180 another. 100 00:08:11,190 --> 00:08:15,520 Don't forget that IP version 6 also uses hexadecimal. 101 00:08:15,600 --> 00:08:19,140 So if I type IP config slash all on the 102 00:08:19,180 --> 00:08:27,220 PC notice link-local IP version 6 address, DHCP client identifier. 103 00:08:27,240 --> 00:08:29,690 These are all hexadecimal numbers. 104 00:08:29,760 --> 00:08:36,030 We've got a Bluetooth hexadecimal number, hexadecimal is used in multiple places you need to know how 105 00:08:36,030 --> 00:08:37,570 to work with hexadecimal. 106 00:08:37,650 --> 00:08:41,520 So now let's talk about the theory of hexadecimal and how to do conversions.