1 00:00:01,400 --> 00:00:08,060 This lecture, you will learn the network routine care, let me actually increase the size a little 2 00:00:08,060 --> 00:00:08,330 bit. 3 00:00:10,310 --> 00:00:10,990 Just look. 4 00:00:14,650 --> 00:00:15,010 So. 5 00:00:17,170 --> 00:00:22,690 Eternity requires that all nodes to be directly connected to the same local network. 6 00:00:23,080 --> 00:00:30,220 This requirement is a major limitation for a truly global network because it's not practical to physically 7 00:00:30,220 --> 00:00:32,680 connect to every node, to every other node. 8 00:00:33,190 --> 00:00:39,340 So rather than require that all launched were directly connected, the source and this nation addresses 9 00:00:39,370 --> 00:00:44,890 a little data to be routed over different networks until the data reaches the desired destination. 10 00:00:44,890 --> 00:00:47,910 Not as shown in this figure here. 11 00:00:48,740 --> 00:00:49,120 So. 12 00:00:50,630 --> 00:00:57,380 This in this category created one, this shows the Ethernet networks, each with separate IP network 13 00:00:57,380 --> 00:00:58,310 address range. 14 00:00:58,820 --> 00:01:08,330 So as you can see here, the operating system networks stack not here UM encapsulates the application 15 00:01:08,480 --> 00:01:16,190 and transport layer of data, and it pulls an IP packet with the source address from one hundred ninety 16 00:01:16,190 --> 00:01:21,830 two point one point one point one hundred one and the destination address here. 17 00:01:21,830 --> 00:01:29,840 As you can see here, um, 100 actual, not 100 is the 200, because this is the ISO, the different 18 00:01:29,840 --> 00:01:34,670 range two hundred point 200 zero one fifty. 19 00:01:35,520 --> 00:01:40,670 So then the networks stack needs to send an Ethernet frame. 20 00:01:40,670 --> 00:01:46,790 But because the destination IP address doesn't exist on any Ethernet network that the node is connected 21 00:01:46,790 --> 00:01:54,410 to, the network stack consults its operating system operating system routing table actually, so it 22 00:01:54,410 --> 00:01:55,790 will look routing table. 23 00:01:56,270 --> 00:02:04,100 So in this example, the routing table contains an entry uh, for IP address two hundred, uh, zero 24 00:02:04,100 --> 00:02:05,980 point one point fifteen. 25 00:02:06,410 --> 00:02:16,550 So the entry indicates to the router to an IP address one hundred and one hundred ninety two point one 26 00:02:16,550 --> 00:02:23,660 point one point one to this knows how to get to that this nation address. 27 00:02:25,020 --> 00:02:26,520 So actually. 28 00:02:31,300 --> 00:02:40,420 In this case, in our case, these RUATORIA, the North, where to go with this? 29 00:02:42,230 --> 00:02:44,340 And then, um. 30 00:02:46,200 --> 00:02:50,490 And so this stage is completed and the new stage comes. 31 00:02:50,650 --> 00:02:51,690 This is the third stage. 32 00:02:51,780 --> 00:02:58,500 So then the operating system uses ERP as in previous lecture, we will write something here. 33 00:02:58,710 --> 00:03:00,210 What are your premiums here? 34 00:03:00,330 --> 00:03:02,610 Is this resolution protocol? 35 00:03:03,640 --> 00:03:08,400 Uh, actually, this is the entropy is under this resolution protocol. 36 00:03:09,540 --> 00:03:09,960 So. 37 00:03:12,470 --> 00:03:23,240 And the operating system uses other resolution protocol to look up to the router's Mac address at one 38 00:03:23,810 --> 00:03:30,140 hundred ninety two point one points one point one and the original IP packet is encapsulated within 39 00:03:30,140 --> 00:03:31,280 the internet frame. 40 00:03:31,990 --> 00:03:33,940 That Mac address here. 41 00:03:35,470 --> 00:03:44,860 So now and then Ruth receives the eternal frame and unpacks the IP packet here when the router checks 42 00:03:44,860 --> 00:03:51,760 to this initial IP address is determined that the IP packet is not designed for the router but for a 43 00:03:51,760 --> 00:03:54,310 different node on another connected network. 44 00:03:54,460 --> 00:04:03,280 In this case, the router looks up the Mac address of this device two hundred zero point one point fifteen. 45 00:04:04,000 --> 00:04:05,290 Um, and. 46 00:04:06,770 --> 00:04:14,120 Encapsulates the original IP packet into the new Ethernet frame and sent it onto the network, too. 47 00:04:14,150 --> 00:04:18,020 This is the network two and this is a network run network. 48 00:04:18,950 --> 00:04:22,610 One here and network two. 49 00:04:23,540 --> 00:04:23,870 Here. 50 00:04:25,370 --> 00:04:33,110 So unless later this nation or receives the estimates frame and unpacks the IP packet and process its 51 00:04:33,110 --> 00:04:39,410 contents processes its contents that the recruiting process might be repeated multiple times. 52 00:04:40,460 --> 00:04:46,130 Uh, for example, if the router was not directly connected to the network containing the node of two 53 00:04:46,130 --> 00:04:52,220 hundred zero point one point fifteen, it would consult its own routing table and determine the next 54 00:04:52,220 --> 00:04:52,670 router. 55 00:04:52,820 --> 00:04:55,730 It could send the IP packet to the. 56 00:04:55,730 --> 00:05:02,390 Clearly, it will be impractical for every node on the network to know how to get every other node on 57 00:05:02,390 --> 00:05:02,960 the internet. 58 00:05:03,260 --> 00:05:09,890 If there is an explicit, uh, routing entry for this nation, the operating system provides a default 59 00:05:09,890 --> 00:05:16,370 routing table entry called the default gateway, which contains the IP address of a router that can 60 00:05:16,370 --> 00:05:18,710 forward IP packets within this nation.