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Network routing.

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Ethernet requires the all nodes to be directly connected to the same local network.

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This requirement is a major limitation for a truly global network because it's not practical to physically

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connect every node to every other node.

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Rather than require that all nodes to be directly connected.

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The source and destination addresses allow the data to be routed over different networks until the data

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reaches to the desired destination node as shown here.

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In this diagram, you are seeing two Ethernet networks, each with separate IP address ranges.

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Here in this lecture, I will explain how the IP uses this model to send the data from the node at one

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network.

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Number one.

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Who?

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Network number two.

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The operating system network Stack node.

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Here.

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Encapsulates the application and transport layer data, and it builds an IP packet with a source address

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of 192 point.

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168 .0. 101.

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And the destination address of.

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20 .0. 1.45.

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Then, as a step to the network, stack needs to send an Ethernet frame.

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But because the destination IP address is not exist on any Ethernet network that the node is connected

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to The network Stack consults an operating system routing table.

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In this example, the routing table contains an entry for the IP address.

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20.0 .1. 50 or 45.

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The entry indicates that a router on the IP address

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192.168

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.0. 101.

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Knows how to get that destination address.

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And then the operating system uses ARP address resolution protocol to look up the Router's Mac address

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at this 100.

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92.168 .0. 101.

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And the original IP packet is encapsulated within the Ethernet frame with the MAC address.

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The router receives the internet frame and unpacks.

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The IP packet.

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When the router checks the destination IP address, it determines that the IP packet is not designed

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for the router or destined for the router, but for a different node on another connected network.

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The router looks up the MAC address of this IP address 20 .0. 1.45 encapsulates the original IP packet

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into new Ethernet frame and sends it onto network number two.

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The destination node receives the Ethernet frame, unpacks the IP packet and process its contents.

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And this routing process might be repeated multiple times.

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For example, if the router was not directly connected to the network containing the node of 20 .0.

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1.45, it will consult its own routing table and determine the next router.

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It could send the IP packet, though clearly it wouldn't.

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It would be impractical for every node on the network to know how to get to every other node on the

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internet.

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If there is no explicit routing entry for the destination, the operating system provides a default

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routing table entry, and this is called the default Gateway, which contains the IP address of a router

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that can forward IP packets to their destinations.