So guys, to start with, we will start with building the topology that you can see on the screen.
Now, this is a very simple topology in which you have an L2 switch S5 and you have two host machine
S1 and S2, right?
The loopback IP address of the host machine S1 is 122 .1.1.1 and loopback IP address of the host machine
S2 is 122.1 .1.2 and L2 switches devices do not have any IP address configuration because they work
on purely on layer two layer and you can see that the interface H1 Ethernet zero of host machine H1
is connected to interface S5 Ethernet zero.
Right?
So every interface in the topology has a definite name.
The interface which belongs to the host machines are configured with an IP address.
So in this case, you can see that one Ethernet zero is configured with an IP address.
Ten .0.1.1 slash 24.
Right.
And you can see that the host machine, S1 and S2 are present in the same subnet.
How you determine whether they are present on the same subnet because they are configured with the because
they have a local interface which is configured with an IP address such that both of these interfaces
belongs to the same subnet.
Right.
Also the interfaces which is on the switch side, that is S5 Ethernet zero and S5 Ethernet one are the
interfaces of the L2 switch and therefore we need to put those interfaces into some Vlan.
So for demonstration purpose we have chosen a Vlan id ten.
Right.
So the interfaces of the L2 switch needs to be put inside a Vlan and therefore both of these interfaces
of an L2 switch has been configured with a Vlan ten in access mode.
So this is our description of this topology.
We will write a Python program in order to build up this network topology.
And I will show you how host machine H1 can ping H2 and vice versa.
And once we achieve this milestone, then we will going to do add on on this topology to add more complexity,
right?
So in the next phase, what we will going to do is that we will going to add two more host machines
to this topology, but this time these two host machines would be present in a different subnet that
is Vlan 20, right?
So needless to say that the topology on the right hand side is exactly the mirror image of the topology
on the left hand side, right.
So whatever steps you would follow in order to build the topology on the left hand side, exact same
similar steps is required in order to build the topology on the right hand side of this L2 switch.
But now, given that the host machines on the left hand side are present in Vlan ten and the host machines
on the right hand side are present in Vlan 20, they cannot do any data exchange or communication without
having an L3 routing in place.
Right.
Communication between host machines present in a different subnet is achieved by L3 routing.
So therefore, in order to establish the communication between host machines present in Vlan 20 and
the host machines present in Vlan 20, we were going to add an L3 router to this topology.
Right.
So I will show you the building up of this network topology in an incremental manner step by step.
So in the next lecture video we will start with building up of this very simple network topology using
Python.