So welcome back, guys.
In this module we will going to learn Valence that is virtual local area network.
So let us discuss the agenda of this module.
In this module we will going to discuss what are lands and what are the drawbacks of lands.
The next we will discuss that how virtual local area networks addresses the lands drawbacks.
Then we will discuss how VLANs are deployed using L2 switches.
And finally we will discuss that how L2 routing is done using virtual local area networks.
So going forward, let us start with the discussion of what exactly local area networks are.
So we already have learned that what subnet is.
So let us do some revision.
So you can see in this topology we have an L three router on the left hand side of an L three router.
We have internet connectivity, whereas on the right hand side of an L three router we have a subnet.
So remember every physical interface of an L three router actually hosts a subnet.
So in this case, the physical interface IFR of L three router hosts a subnet whose network ID is 12
.1.1.0 slash 24.
And in this subnet there are three host machines which are present.
The machines are D, E and F.
So you can see that the IP addresses which are configured for these machines are such that all of these
IP addresses falls or is the member of this subnet.
So hosts D and F are in the same subnet because they are assigned an IP address which are in the same
subnet.
Right.
And they are connected to the same physical wire.
So whenever these two conditions are satisfied for a set of machines, then those set of machines are
set to be present in the same local area network.
So hosts D, E and F forms traditional local area network.
Why they form traditional local area network?
Because they satisfy these two conditions.
Right.
So LAN is an outdated technology.
Today VLANs has taken over.
LAN enforces the mobility constraint.
Note the word LAN enforces the mobility constraints on hosts and machines for to become a member of
a subnet.
And this is the biggest drawback of local area network.
So we will going to elaborately study that.
Why this is a drawback of local area network and how this drawback is resolved or addressed by a virtual
local area networks.
So we will study in detail that how LAN enforces the mobility constraint on hosts or machines which
are present in that particular local area network.
Now here, mobility constraint means a constraint on a machine to change its physical position from
one part of the network to another part of the network.
So we will study the land drawbacks in detail in the coming slides.
So next, let us discuss that.
When should multiple hosts be placed in the same subnet?
That is what will be the scenario when a network administrator would decide to place a given set of
machines in the same subnet?
Right.
So what do you think?
Why would you choose?
So it is why Why would you choose to place two or more hosts in the same subnet?
So there are multiple reasons for that.
So let us go through those reasons.
We will choose to place multiple machines or hosts in the same subnet when they perform the same logical
operations.
For example, all students of computer science branches can be placed in subnet one, whereas all students
of electronics branch can be placed in a subnet two.
So here it is not very difficult to actually understand that all computer science students could be
placed in one subnet because they are likely to access the subnet or the network in the same way they
will most probably would like to visit the same website, will download the same kind of material.
And et cetera.
ET cetera.
Right.
So all the entities or machines which are likely to perform same logical operations could be placed
in the same subnet.
Second reason could be that that the machines or host which are likely to access the same network resources
could be placed in the same subnet.
For example, allow access to all hosts which are present in subnet one two website.
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So anyways, going forward, the point number three says that all the machines or hosts, which require
the same quality of service from the network, could be placed in the same subnet.
So example of this would be that that allow all hosts in subnet one a download speed of 50 Mbps whereas
allow only download speed of ten Mbps for all the hosts present in subnet two.
The administrator would like to do such a configuration and all the machines which the administrator
would like to receive a download speed of 50 Mbps.
The administrator would like those machines to be present in subnet one.
Right.
And the final criteria on the basis of which you would like to separate out the machines in different
subnet is the fast and secure communication.
That is the example of this, would be that all the hosts which are present in subnet one can securely
communicate with each other because no traffic from outside subnet one or any traffic from inside subnet
one ever leaks.
Right, so all the machines which are present in the same subnet can communicate with each other and
none of the packets generated by any of the machines present in that particular subnet can ever leave
the subnet or none of the traffic from outside the subnet can ever enter into that particular subnet.
So this type of isolation provides a secure communication between the machines which are present in
the same subnet, and that entire subnet is a kind of isolated from the rest of the world.
So you can see that there are for good reasons because of which you would like to group the physical
machines and host together to be deployed and placed in one subnet.