WEBVTT 00:01.400 --> 00:08.060 This lecture, you will learn the network routine care, let me actually increase the size a little 00:08.060 --> 00:08.330 bit. 00:10.310 --> 00:10.990 Just look. 00:14.650 --> 00:15.010 So. 00:17.170 --> 00:22.690 Eternity requires that all nodes to be directly connected to the same local network. 00:23.080 --> 00:30.220 This requirement is a major limitation for a truly global network because it's not practical to physically 00:30.220 --> 00:32.680 connect to every node, to every other node. 00:33.190 --> 00:39.340 So rather than require that all launched were directly connected, the source and this nation addresses 00:39.370 --> 00:44.890 a little data to be routed over different networks until the data reaches the desired destination. 00:44.890 --> 00:47.910 Not as shown in this figure here. 00:48.740 --> 00:49.120 So. 00:50.630 --> 00:57.380 This in this category created one, this shows the Ethernet networks, each with separate IP network 00:57.380 --> 00:58.310 address range. 00:58.820 --> 01:08.330 So as you can see here, the operating system networks stack not here UM encapsulates the application 01:08.480 --> 01:16.190 and transport layer of data, and it pulls an IP packet with the source address from one hundred ninety 01:16.190 --> 01:21.830 two point one point one point one hundred one and the destination address here. 01:21.830 --> 01:29.840 As you can see here, um, 100 actual, not 100 is the 200, because this is the ISO, the different 01:29.840 --> 01:34.670 range two hundred point 200 zero one fifty. 01:35.520 --> 01:40.670 So then the networks stack needs to send an Ethernet frame. 01:40.670 --> 01:46.790 But because the destination IP address doesn't exist on any Ethernet network that the node is connected 01:46.790 --> 01:54.410 to, the network stack consults its operating system operating system routing table actually, so it 01:54.410 --> 01:55.790 will look routing table. 01:56.270 --> 02:04.100 So in this example, the routing table contains an entry uh, for IP address two hundred, uh, zero 02:04.100 --> 02:05.980 point one point fifteen. 02:06.410 --> 02:16.550 So the entry indicates to the router to an IP address one hundred and one hundred ninety two point one 02:16.550 --> 02:23.660 point one point one to this knows how to get to that this nation address. 02:25.020 --> 02:26.520 So actually. 02:31.300 --> 02:40.420 In this case, in our case, these RUATORIA, the North, where to go with this? 02:42.230 --> 02:44.340 And then, um. 02:46.200 --> 02:50.490 And so this stage is completed and the new stage comes. 02:50.650 --> 02:51.690 This is the third stage. 02:51.780 --> 02:58.500 So then the operating system uses ERP as in previous lecture, we will write something here. 02:58.710 --> 03:00.210 What are your premiums here? 03:00.330 --> 03:02.610 Is this resolution protocol? 03:03.640 --> 03:08.400 Uh, actually, this is the entropy is under this resolution protocol. 03:09.540 --> 03:09.960 So. 03:12.470 --> 03:23.240 And the operating system uses other resolution protocol to look up to the router's Mac address at one 03:23.810 --> 03:30.140 hundred ninety two point one points one point one and the original IP packet is encapsulated within 03:30.140 --> 03:31.280 the internet frame. 03:31.990 --> 03:33.940 That Mac address here. 03:35.470 --> 03:44.860 So now and then Ruth receives the eternal frame and unpacks the IP packet here when the router checks 03:44.860 --> 03:51.760 to this initial IP address is determined that the IP packet is not designed for the router but for a 03:51.760 --> 03:54.310 different node on another connected network. 03:54.460 --> 04:03.280 In this case, the router looks up the Mac address of this device two hundred zero point one point fifteen. 04:04.000 --> 04:05.290 Um, and. 04:06.770 --> 04:14.120 Encapsulates the original IP packet into the new Ethernet frame and sent it onto the network, too. 04:14.150 --> 04:18.020 This is the network two and this is a network run network. 04:18.950 --> 04:22.610 One here and network two. 04:23.540 --> 04:23.870 Here. 04:25.370 --> 04:33.110 So unless later this nation or receives the estimates frame and unpacks the IP packet and process its 04:33.110 --> 04:39.410 contents processes its contents that the recruiting process might be repeated multiple times. 04:40.460 --> 04:46.130 Uh, for example, if the router was not directly connected to the network containing the node of two 04:46.130 --> 04:52.220 hundred zero point one point fifteen, it would consult its own routing table and determine the next 04:52.220 --> 04:52.670 router. 04:52.820 --> 04:55.730 It could send the IP packet to the. 04:55.730 --> 05:02.390 Clearly, it will be impractical for every node on the network to know how to get every other node on 05:02.390 --> 05:02.960 the internet. 05:03.260 --> 05:09.890 If there is an explicit, uh, routing entry for this nation, the operating system provides a default 05:09.890 --> 05:16.370 routing table entry called the default gateway, which contains the IP address of a router that can 05:16.370 --> 05:18.710 forward IP packets within this nation.