So guys, going forward.
So similarly, as in traditional routing, in inter Vlan routing, also we need to do these two things.
That is configuring a default route on the host machines.
And if the host machine do not know the Mac address of the default gateway, then the host machine needs
to perform ARP Resolution for Default Gateway IP Address.
So let us see how the host machine present in a Vlan can perform these two steps.
So coming to the default route, that is what default route you should configure on the host machine
present in a Vlan.
So you can see in this diagram that we have a host machine A and the host machine B which are present
in Vlan 12 and Vlan 11 respectively.
Now you can see that the default route that is configured on the host machine A is this entry.
That is if the host machine A wants to send a data to any host machine which is present in a remote
subnet, then the next hop IP address is 13 .1.1.1 and local outgoing interface is.
Similarly, the default routing entry for the host machine B would be this one.
Now the question arises that why the gateway IP address of host Machine A is different from the gateway
IP address of the host machine B.
So going forward.
So to support interval and routing, every host machine in the network is configured with the default
route.
So we have already learned that the host machine A and the host machine B are configured with the default
route.
So the default route of a host machine must be equal to the IP address of Svi interface, which is bind
to Vlan on which the host machine is present.
Right.
So going with this scheme default route for the host machine A will be 13 .1.1.1.
That is this one.
Why?
Because host machine A is present in Vlan 12 and will end 12 has a binding with Svi 12 and Svi 12 is
configured with an IP address.
13 .1.1.1.
Right.
So we have applied this rule here and following this rule, the default gateway IP address for the host
machine A will be 13 .1.1.1.
Similarly, the default gateway IP address for the host machine B will be 14 .1.1.1 because B is present
in Vlan 11 and Vlan 11 has a binding with Svi 11 so you can see that Vlan 11 has a binding with Svi.
11.
Right.
So the default route is installed in A's routing table in this format.
So we already know the semantics of a default route and we have already covered the details of default
route in one of our previous module in this course.
So whenever the host needs to send a frame to a destination machine which is outside its own subnet,
that is the destination machine is present in a remote subnet, then the host machine uses a default
route in order to send a frame to the gateway router.
So you can see that this concept is nothing new.
So you can see that for the host machine present in a Vlan, we still need to configure the default
gateway IP address for the host machines so that host machine would know where to forward the packet
in case the destination machine belongs to a remote subnet.
Now going forward, our resolution for default routes.
So whenever the host machine needs to send a data to another host machine present in a remote subnet,
the host machine needs to send a frame to the default gateway IP address, which is 13 .1.1.1.
Right.
And in order to send this frame, it should also know the Mac address which maps to this IP address.
13 .1.1.1.
So the question is that whose Mac address l3 router would return if it receives a broadcast message
for ARP resolution of IP address equal to IP address of C interface.
Right.
So here the machine A will issue the ARP broadcast request message to know the Mac address for IP address.
13 .1.1.1 and this 13 .1.1.1 is the IP address of one of the local interface of l3 router.
So which local interface?
The Svi 12, which is logical interface.
Since L3 Rooter is the owner of this IP address.
Therefore, L3 router has the responsibility to reply back with ARP reply.
So for example host machine a issues the ARP broadcast message to know the Mac address for default gateway
IP Address 13 .1.1.1 and you can see that 13 .1.1 is the IP address which is configured on 12 logical
interface.
Right?
So 12 is a logical interface.
Then the question arises that whose mac address should l3 router must return in ARP reply.
Right, because Mac addresses is a property of physical interfaces only physical interface that is actual
real physical hardware have Mac addresses.
Logical interfaces do not have any Mac addresses assigned to them.
So if L3 router has to reply with the Mac address corresponding to IP address 13 .1.1.1 then whose Mac
address should.
L3 router must reply.
Obviously, SBI or SBI 11 will not going to have any Mac addresses configured on them because they are
logical interfaces and they are really not real physical piece of hardware.
So the simple answer to this question is that that L3 router will reply with the Mac address of physical
interface on which our broadcast message is received.
Right.
So in this case the L3 router will going to reply back with the Mac address is equal to master, which
is the Mac address that is configured on physical interface IFR.
Thus L-3 Router returns Mac address is equal to master.
In reply for IP address is equal to svis IP addresses.
That is IP address configured on any Svi interface configured on a router which is 14 .1.1. 1 or 13
.1.1.1.
So the conclusion is that that if the host machine a issues the ARP broadcast request message to know
the Mac address for IP address 13 .1.1.1 the L3 router will return back.
The Mac address is equal to m r in ARP reply.
Similarly, if host machine B issues an r broadcast request message to know the Mac address for IP address.
14 .1.1.1 the L3 router will return.
The Mac address is equal to m r in ARP reply.
Therefore, the ARP resolution for Gateway IP address for host machine A and host machine B will get
them.
The next hop Mac address is equal to M r.
So you can see here that like in case of traditional routing here, also the host machine needs to know
the Gateway router Mac address in order to send a frame to a destination host machine which is present
in a remote subnet.
So here we have learned nothing new, just the same traditional L3 routing concepts.