This lecture, you will learn the network routine care, let me actually increase the size a little
bit.
Just look.
So.
Eternity requires that all nodes to be directly connected to the same local network.
This requirement is a major limitation for a truly global network because it's not practical to physically
connect to every node, to every other node.
So rather than require that all launched were directly connected, the source and this nation addresses
a little data to be routed over different networks until the data reaches the desired destination.
Not as shown in this figure here.
So.
This in this category created one, this shows the Ethernet networks, each with separate IP network
address range.
So as you can see here, the operating system networks stack not here UM encapsulates the application
and transport layer of data, and it pulls an IP packet with the source address from one hundred ninety
two point one point one point one hundred one and the destination address here.
As you can see here, um, 100 actual, not 100 is the 200, because this is the ISO, the different
range two hundred point 200 zero one fifty.
So then the networks stack needs to send an Ethernet frame.
But because the destination IP address doesn't exist on any Ethernet network that the node is connected
to, the network stack consults its operating system operating system routing table actually, so it
will look routing table.
So in this example, the routing table contains an entry uh, for IP address two hundred, uh, zero
point one point fifteen.
So the entry indicates to the router to an IP address one hundred and one hundred ninety two point one
point one point one to this knows how to get to that this nation address.
So actually.
In this case, in our case, these RUATORIA, the North, where to go with this?
And then, um.
And so this stage is completed and the new stage comes.
This is the third stage.
So then the operating system uses ERP as in previous lecture, we will write something here.
What are your premiums here?
Is this resolution protocol?
Uh, actually, this is the entropy is under this resolution protocol.
So.
And the operating system uses other resolution protocol to look up to the router's Mac address at one
hundred ninety two point one points one point one and the original IP packet is encapsulated within
the internet frame.
That Mac address here.
So now and then Ruth receives the eternal frame and unpacks the IP packet here when the router checks
to this initial IP address is determined that the IP packet is not designed for the router but for a
different node on another connected network.
In this case, the router looks up the Mac address of this device two hundred zero point one point fifteen.
Um, and.
Encapsulates the original IP packet into the new Ethernet frame and sent it onto the network, too.
This is the network two and this is a network run network.
One here and network two.
Here.
So unless later this nation or receives the estimates frame and unpacks the IP packet and process its
contents processes its contents that the recruiting process might be repeated multiple times.
Uh, for example, if the router was not directly connected to the network containing the node of two
hundred zero point one point fifteen, it would consult its own routing table and determine the next
router.
It could send the IP packet to the.
Clearly, it will be impractical for every node on the network to know how to get every other node on
the internet.
If there is an explicit, uh, routing entry for this nation, the operating system provides a default
routing table entry called the default gateway, which contains the IP address of a router that can
forward IP packets within this nation.