WEBVTT 00:00.730 --> 00:02.350 Network routing. 00:03.040 --> 00:09.460 Ethernet requires the all nodes to be directly connected to the same local network. 00:10.340 --> 00:17.480 This requirement is a major limitation for a truly global network because it's not practical to physically 00:17.480 --> 00:21.080 connect every node to every other node. 00:21.410 --> 00:25.790 Rather than require that all nodes to be directly connected. 00:27.510 --> 00:34.770 The source and destination addresses allow the data to be routed over different networks until the data 00:34.770 --> 00:39.710 reaches to the desired destination node as shown here. 00:43.940 --> 00:52.130 In this diagram, you are seeing two Ethernet networks, each with separate IP address ranges. 00:54.260 --> 01:02.480 Here in this lecture, I will explain how the IP uses this model to send the data from the node at one 01:02.480 --> 01:03.140 network. 01:03.140 --> 01:04.220 Number one. 01:05.060 --> 01:05.480 Who? 01:05.480 --> 01:06.710 Network number two. 01:08.700 --> 01:11.640 The operating system network Stack node. 01:12.510 --> 01:13.080 Here. 01:15.930 --> 01:24.000 Encapsulates the application and transport layer data, and it builds an IP packet with a source address 01:24.000 --> 01:28.650 of 192 point. 01:30.080 --> 01:35.240 168 .0. 101. 01:36.240 --> 01:38.520 And the destination address of. 01:39.900 --> 01:44.430 20 .0. 1.45. 01:45.050 --> 01:51.980 Then, as a step to the network, stack needs to send an Ethernet frame. 01:52.720 --> 01:59.320 But because the destination IP address is not exist on any Ethernet network that the node is connected 01:59.320 --> 02:06.010 to The network Stack consults an operating system routing table. 02:08.440 --> 02:15.580 In this example, the routing table contains an entry for the IP address. 02:16.460 --> 02:21.890 20.0 .1. 50 or 45. 02:23.190 --> 02:27.300 The entry indicates that a router on the IP address 02:27.330 --> 02:33.060 192.168 02:33.060 --> 02:36.930 .0. 101. 02:38.050 --> 02:41.770 Knows how to get that destination address. 02:42.960 --> 02:52.290 And then the operating system uses ARP address resolution protocol to look up the Router's Mac address 02:52.290 --> 02:54.480 at this 100. 02:55.590 --> 02:59.910 92.168 .0. 101. 03:00.710 --> 03:08.030 And the original IP packet is encapsulated within the Ethernet frame with the MAC address. 03:09.540 --> 03:14.910 The router receives the internet frame and unpacks. 03:18.750 --> 03:20.310 The IP packet. 03:20.870 --> 03:28.070 When the router checks the destination IP address, it determines that the IP packet is not designed 03:28.070 --> 03:35.450 for the router or destined for the router, but for a different node on another connected network. 03:36.170 --> 03:47.990 The router looks up the MAC address of this IP address 20 .0. 1.45 encapsulates the original IP packet 03:47.990 --> 03:54.110 into new Ethernet frame and sends it onto network number two. 03:55.400 --> 04:03.230 The destination node receives the Ethernet frame, unpacks the IP packet and process its contents. 04:03.230 --> 04:06.650 And this routing process might be repeated multiple times. 04:06.650 --> 04:13.970 For example, if the router was not directly connected to the network containing the node of 20 .0. 04:13.970 --> 04:19.730 1.45, it will consult its own routing table and determine the next router. 04:19.730 --> 04:24.020 It could send the IP packet, though clearly it wouldn't. 04:24.320 --> 04:30.950 It would be impractical for every node on the network to know how to get to every other node on the 04:30.950 --> 04:31.490 internet. 04:31.490 --> 04:37.130 If there is no explicit routing entry for the destination, the operating system provides a default 04:37.130 --> 04:43.790 routing table entry, and this is called the default Gateway, which contains the IP address of a router 04:43.790 --> 04:48.200 that can forward IP packets to their destinations.