1 1 00:00:00,629 --> 00:00:02,200 Routing fundamentals. 2 2 00:00:02,200 --> 00:00:04,380 All right, we have covered a lot of information 3 3 00:00:04,380 --> 00:00:05,700 up to this point in the course, 4 4 00:00:05,700 --> 00:00:09,190 but we still haven't left our local area network yet. 5 5 00:00:09,190 --> 00:00:10,690 Once we're ready to leave our network, 6 6 00:00:10,690 --> 00:00:12,600 this is where routers are really going to start 7 7 00:00:12,600 --> 00:00:14,090 coming into play. 8 8 00:00:14,090 --> 00:00:15,330 When we start talking about connecting 9 9 00:00:15,330 --> 00:00:16,880 to subnets within our network 10 10 00:00:16,880 --> 00:00:19,410 or connecting our internal network and an external network, 11 11 00:00:19,410 --> 00:00:20,920 we have to use a router. 12 12 00:00:20,920 --> 00:00:22,700 So in this section of the course, 13 13 00:00:22,700 --> 00:00:25,470 we're going to be talking all about routing fundamentals. 14 14 00:00:25,470 --> 00:00:26,830 The first thing you must understand 15 15 00:00:26,830 --> 00:00:30,110 is the function of a router, which is to route traffic. 16 16 00:00:30,110 --> 00:00:31,440 Now, I know that sounds kind of silly, 17 17 00:00:31,440 --> 00:00:33,210 but essentially that's what it's going to do. 18 18 00:00:33,210 --> 00:00:35,750 It's going to forward the traffic in one direction or another 19 19 00:00:35,750 --> 00:00:37,780 between different subnets or between an internal 20 20 00:00:37,780 --> 00:00:39,830 and external network or between two different 21 21 00:00:39,830 --> 00:00:41,260 external networks. 22 22 00:00:41,260 --> 00:00:43,390 Each subnet or external network is going to be 23 23 00:00:43,390 --> 00:00:45,680 its own broadcast domain because routers 24 24 00:00:45,680 --> 00:00:47,970 are used to separate broadcast domains. 25 25 00:00:47,970 --> 00:00:50,140 Unlike switches, which are layer two devices, 26 26 00:00:50,140 --> 00:00:52,680 and therefore can only maintain one broadcast domain 27 27 00:00:52,680 --> 00:00:54,690 for everything that's connected to the switch, 28 28 00:00:54,690 --> 00:00:56,690 the routers are going to be layer three devices. 29 29 00:00:56,690 --> 00:00:58,680 And they're used to separate and break apart 30 30 00:00:58,680 --> 00:01:01,360 those broadcast domains into smaller portions to provide 31 31 00:01:01,360 --> 00:01:04,300 additional efficiency and security to your networks. 32 32 00:01:04,300 --> 00:01:06,190 Now, before we go too far in this lesson, 33 33 00:01:06,190 --> 00:01:08,100 it's important to note that there's a difference 34 34 00:01:08,100 --> 00:01:10,460 between the real world and the exam. 35 35 00:01:10,460 --> 00:01:11,460 In the real world, 36 36 00:01:11,460 --> 00:01:14,300 you may often find yourself using a layer three switch, 37 37 00:01:14,300 --> 00:01:16,510 also known as a multi-layer switch. 38 38 00:01:16,510 --> 00:01:19,650 When you do this, it can perform routing functions for you. 39 39 00:01:19,650 --> 00:01:21,520 Many small office home office networks 40 40 00:01:21,520 --> 00:01:23,280 or small and medium sized businesses 41 41 00:01:23,280 --> 00:01:25,430 will often opt to use a layer three switch 42 42 00:01:25,430 --> 00:01:27,360 because it can handle both functions. 43 43 00:01:27,360 --> 00:01:28,840 It can handle layer two forwarding 44 44 00:01:28,840 --> 00:01:30,140 when it's acting like a switch 45 45 00:01:30,140 --> 00:01:32,980 and layer three routing when it acts as a router. 46 46 00:01:32,980 --> 00:01:34,610 For the exam though, remember, 47 47 00:01:34,610 --> 00:01:36,610 if you're using a multi-layer switch, 48 48 00:01:36,610 --> 00:01:38,550 it is functioning as a router. 49 49 00:01:38,550 --> 00:01:40,390 And so we're going to treat it as a router, 50 50 00:01:40,390 --> 00:01:42,060 or a layer three device. 51 51 00:01:42,060 --> 00:01:43,710 Now in this entire section, 52 52 00:01:43,710 --> 00:01:46,280 we're going to be referring to these devices as a router, 53 53 00:01:46,280 --> 00:01:49,840 even if I'm using a multi-layer switch in the real world. 54 54 00:01:49,840 --> 00:01:52,820 Now for the exam, if they say switch, 55 55 00:01:52,820 --> 00:01:55,230 they're talking about a standard layer two switch. 56 56 00:01:55,230 --> 00:01:57,820 If they say multi-layer switch or router, 57 57 00:01:57,820 --> 00:02:00,720 they're referring to layer three functionality of a device 58 58 00:02:00,720 --> 00:02:04,360 that we call a router during this course and the exam. 59 59 00:02:04,360 --> 00:02:08,010 So how does the basic router perform this work? 60 60 00:02:08,010 --> 00:02:10,020 Well, let's consider this diagram here. 61 61 00:02:10,020 --> 00:02:12,110 I have two networks, one on the left side 62 62 00:02:12,110 --> 00:02:13,920 and one on the right side of the screen. 63 63 00:02:13,920 --> 00:02:16,790 As you can see, PC one is connected to our left network, 64 64 00:02:16,790 --> 00:02:19,230 and PC two is connected to our right network. 65 65 00:02:19,230 --> 00:02:21,330 Now, to connect these two networks together, 66 66 00:02:21,330 --> 00:02:23,670 we have two routers and a serial connection 67 67 00:02:23,670 --> 00:02:25,930 or wide area network connection between them. 68 68 00:02:25,930 --> 00:02:28,810 For now, we're not going to focus too much on that connection 69 69 00:02:28,810 --> 00:02:29,810 because we're going to cover that 70 70 00:02:29,810 --> 00:02:31,290 in a different section of the course 71 71 00:02:31,290 --> 00:02:33,810 when we talk about all the different WAN technologies. 72 72 00:02:33,810 --> 00:02:36,340 Right now just realize that there's connection between them, 73 73 00:02:36,340 --> 00:02:37,920 and it's a long-distance one. 74 74 00:02:37,920 --> 00:02:40,260 This could be a fiber connection, a serial connection, 75 75 00:02:40,260 --> 00:02:43,180 a satellite connection, a VPN or any other kind of link. 76 76 00:02:43,180 --> 00:02:44,740 It really doesn't matter right now. 77 77 00:02:44,740 --> 00:02:47,180 As long as you understand that there is connectivity between 78 78 00:02:47,180 --> 00:02:49,410 these two routers and they can communicate to each other 79 79 00:02:49,410 --> 00:02:52,230 over that WAN connection, that's all we need to know. 80 80 00:02:52,230 --> 00:02:54,190 Now if I'm sitting at PC one and 81 81 00:02:54,190 --> 00:02:56,030 I want to send a message to PC two, 82 82 00:02:56,030 --> 00:02:58,810 I can't just send it through ARP like I did with a switch. 83 83 00:02:58,810 --> 00:03:00,150 If you remember back in switching, 84 84 00:03:00,150 --> 00:03:02,840 we talked about how PC one would send an ARP packet 85 85 00:03:02,840 --> 00:03:03,673 to the switch. 86 86 00:03:03,673 --> 00:03:05,150 And if it didn't know where to deliver it, 87 87 00:03:05,150 --> 00:03:07,310 it would send out every single switch port 88 88 00:03:07,310 --> 00:03:08,800 based on that MAC address. 89 89 00:03:08,800 --> 00:03:12,030 Well, PC one can and will still do that. 90 90 00:03:12,030 --> 00:03:14,610 But what's going to happen here is that our ARP request is 91 91 00:03:14,610 --> 00:03:16,700 going to go up to the switch and the switch is going to 92 92 00:03:16,700 --> 00:03:19,240 realize that it doesn't know the MAC address associated with 93 93 00:03:19,240 --> 00:03:20,150 that request. 94 94 00:03:20,150 --> 00:03:23,050 So it's going to forward it out as default gateway. 95 95 00:03:23,050 --> 00:03:25,200 The default gateway is the router. 96 96 00:03:25,200 --> 00:03:28,030 Now that router is then going to respond to the ARP request 97 97 00:03:28,030 --> 00:03:30,150 on behalf of the destination device. 98 98 00:03:30,150 --> 00:03:31,060 At this point, 99 99 00:03:31,060 --> 00:03:33,740 we're now going to have to leave MAC addresses behind 100 100 00:03:33,740 --> 00:03:36,920 because MAC addresses only work internally in our network. 101 101 00:03:36,920 --> 00:03:38,120 Once we get to the router, 102 102 00:03:38,120 --> 00:03:39,990 we're going to switch to using IP addresses 103 103 00:03:39,990 --> 00:03:42,570 or logical addressing at layer three. 104 104 00:03:42,570 --> 00:03:44,630 This is where we begin to make our layer two 105 105 00:03:44,630 --> 00:03:46,210 to layer three transitions. 106 106 00:03:46,210 --> 00:03:47,060 At this point, 107 107 00:03:47,060 --> 00:03:48,850 PC one has determined the MAC address 108 108 00:03:48,850 --> 00:03:50,020 for where the router is 109 109 00:03:50,020 --> 00:03:52,650 because it needs to send the packet to get out of this local 110 110 00:03:52,650 --> 00:03:56,010 area network and leave to go find this device. 111 111 00:03:56,010 --> 00:03:57,930 The left router in this case wants to send 112 112 00:03:57,930 --> 00:03:59,440 the information to PC two, 113 113 00:03:59,440 --> 00:04:02,300 because that's what PC one told it to do, to do that, 114 114 00:04:02,300 --> 00:04:04,440 it's going to pass the information over to router two, 115 115 00:04:04,440 --> 00:04:06,740 and then router one is going to get the data frame, 116 116 00:04:06,740 --> 00:04:09,170 which is layer two from PC one. 117 117 00:04:09,170 --> 00:04:11,540 The writer will repackage it up as a packet, 118 118 00:04:11,540 --> 00:04:14,640 which is layer three, and then add an IP header to it. 119 119 00:04:14,640 --> 00:04:17,360 This allows router one to then push the data over its 120 120 00:04:17,360 --> 00:04:19,710 default connection as an IP packet. 121 121 00:04:19,710 --> 00:04:22,030 And the data will then be sent across the serial connection 122 122 00:04:22,030 --> 00:04:23,600 to get to router two. 123 123 00:04:23,600 --> 00:04:24,433 All right, 124 124 00:04:24,433 --> 00:04:25,900 once that packet gets to router two, 125 125 00:04:25,900 --> 00:04:26,733 router two is going to 126 126 00:04:26,733 --> 00:04:29,590 strip off the IP header and bring it back down to layer two 127 127 00:04:29,590 --> 00:04:32,860 data frames by adding a MAC address for PC two. 128 128 00:04:32,860 --> 00:04:35,750 This way it's going to correlate PC two's MAC address with the 129 129 00:04:35,750 --> 00:04:37,370 destination IP of the packet, 130 130 00:04:37,370 --> 00:04:40,760 because router two knows who PC two is, it's on its network. 131 131 00:04:40,760 --> 00:04:43,820 Now, since router two knows the MAC address for PC two, 132 132 00:04:43,820 --> 00:04:46,550 it can call to PC two directly over layer two 133 133 00:04:46,550 --> 00:04:48,870 and send that data frame through the switch. 134 134 00:04:48,870 --> 00:04:50,890 The switch is going to take that information and push it 135 135 00:04:50,890 --> 00:04:53,300 from router two down to PC two 136 136 00:04:53,300 --> 00:04:55,650 just as if the two of them were computers sitting on the 137 137 00:04:55,650 --> 00:04:58,010 same switch, trying to communicate locally. 138 138 00:04:58,010 --> 00:05:00,620 When PC two wants to send a response to PC one, 139 139 00:05:00,620 --> 00:05:02,640 this process is going to be reversed. 140 140 00:05:02,640 --> 00:05:05,250 And that way the communication can continue back and forth 141 141 00:05:05,250 --> 00:05:07,820 between PC one, its switch, router one, 142 142 00:05:07,820 --> 00:05:11,420 the WAN connection, router two, its switch, and PC two. 143 143 00:05:11,420 --> 00:05:12,790 Alright, so a quick summary 144 144 00:05:12,790 --> 00:05:15,070 of what we just saw in terms of data flow. 145 145 00:05:15,070 --> 00:05:17,600 We started out with layer two pieces of information called a 146 146 00:05:17,600 --> 00:05:19,780 data frame coming from PC one. 147 147 00:05:19,780 --> 00:05:20,970 When it got to router one, 148 148 00:05:20,970 --> 00:05:23,330 it got packaged up as a layer three packet 149 149 00:05:23,330 --> 00:05:25,010 to cross the wide area network. 150 150 00:05:25,010 --> 00:05:26,350 When it got to router two, 151 151 00:05:26,350 --> 00:05:28,360 it stripped it back down to layer two, 152 152 00:05:28,360 --> 00:05:29,800 to make it a data frame again, 153 153 00:05:29,800 --> 00:05:32,410 using MAC addresses to deliver it to PC two 154 154 00:05:32,410 --> 00:05:33,820 on its local network. 155 155 00:05:33,820 --> 00:05:36,120 Essentially, this is how routing works. 156 156 00:05:36,120 --> 00:05:38,060 Now at this point, it's pretty simple, 157 157 00:05:38,060 --> 00:05:40,590 but it's going to get a lot more complicated as we start to 158 158 00:05:40,590 --> 00:05:43,050 move packets across not just a direct way in link 159 159 00:05:43,050 --> 00:05:43,940 like this one, 160 160 00:05:43,940 --> 00:05:46,360 but over the world's largest wide area network, 161 161 00:05:46,360 --> 00:05:47,530 the internet. 162 162 00:05:47,530 --> 00:05:49,070 Now in this section of the course, 163 163 00:05:49,070 --> 00:05:51,050 we're going to talk about all the different protocols 164 164 00:05:51,050 --> 00:05:52,190 that are used in routing, 165 165 00:05:52,190 --> 00:05:54,150 including static and dynamic routing 166 166 00:05:54,150 --> 00:05:57,080 and address translation and multicast routing. 167 167 00:05:57,080 --> 00:05:59,410 We're going to spend some time in three different domains in 168 168 00:05:59,410 --> 00:06:01,790 this section of the course, including domain one, 169 169 00:06:01,790 --> 00:06:03,870 networking fundamentals, domain two, 170 170 00:06:03,870 --> 00:06:06,150 network implementations and domain five, 171 171 00:06:06,150 --> 00:06:07,530 network troubleshooting. 172 172 00:06:07,530 --> 00:06:08,760 Within these domains, 173 173 00:06:08,760 --> 00:06:13,440 we're going to focus on objectives 1.4, 2.2 and 5.5. 174 174 00:06:13,440 --> 00:06:16,210 Objective 1.4 states that given a scenario, 175 175 00:06:16,210 --> 00:06:18,140 configure a subnet and use appropriate 176 176 00:06:18,140 --> 00:06:19,830 IP addressing schemes, 177 177 00:06:19,830 --> 00:06:22,750 objective 2.2 states that you must be able to compare and 178 178 00:06:22,750 --> 00:06:25,050 contrast running technologies and bandwidth management 179 179 00:06:25,050 --> 00:06:28,720 concepts, and objective 5.5 states that given a scenario, 180 180 00:06:28,720 --> 00:06:31,310 you must troubleshoot general networking issues. 181 181 00:06:31,310 --> 00:06:34,300 So let's get started talking all about routing our packets 182 182 00:06:34,300 --> 00:06:35,800 in this section of the course.