Now coming to the second benefit of VLANs, the ARP broadcast message is received by only hosts which
are present in the same subnet that is Vlan as the source host C So in this example let us assume that
host C is the originator of ARP broadcast message.
So when host C issues are broadcast message, the ARP broadcast message enters into L2 switch from Port
P8.
Now since Port P8 is operating in Vlan ten, therefore our broadcast message gets tagged with Vlan ten.
Now the L2 switch forwards or floods.
The ARP broadcast message, which is tagged with Vlan ten only on the ports which are operating in Vlan
ten.
So as a result the L2 switch floods the ARP broadcast message only on port number P6.
Right?
So eventually this behavior and shows that ARP broadcast message is received only by host machines,
which is present in the same Vlan as the ARP broadcast request generator.
So you can see that in this topology, the ARP broadcast message is received only by Machine D, which
is operating in Vlan ten.
Right and the ARP broadcast message request generator that is machine C is also operating in Vlan ten.
So if you remember in normal Vlan unaware switches switch is used to flood a broadcast message on all
the outgoing ports, but in Vlan aware switches, switches, floods, the ARP broadcast message on all
the ports which are operating in the same Vlan.
Right.
So here C shall always issue the ARP broadcast message for host machine present in Vlan ten only that
is machine C will always issue a broadcast message to resolve the Mac address for the IP address, which
belongs to its own subnet.
Now, if this is the case, then why would you bother the host machines which are present outside the
Vlan ten?
So in this case, the host machines A, B, E, and F would never going to receive our broadcast request
message or any other message that is generated by machine C or machine D.
So you can see that using the concept of VLANs, we are able to achieve even more granular solution
to thrashing.
Note that the machine issues the broadcast message to know the Mac address for the machine which belongs
to its local subnet.
So note that machine C will never going to issue our broadcast message to know the Mac address for IP
address which do not belong to its own local subnet.
So Machine C would never try to attempt to know the Mac address of machine.
A machine.
E machine b machine F or in general any other machine which is present outside the Vlan ten.
So this is the reason that our broadcast message should be limited to the subnet or to the Vlan in which
the broadcast message request generator is present.
So in this case, it is useless to leak the broadcast message outside the Vlan ten because the broadcast
message generator that is machine C is present in Vlan ten.