So guys resuming from the previous lecture, let us now quickly go through the steps which are required
in order to take a frame from Gateway L3 router.
To the final destination host machine.
Be right.
So in step number ten, the frame that is received by the router was tagged with Vlan 12.
Right?
Because the frame was received by l3 router on a trunk line and we know that on the trunk line only
Vlan tagged packets travel.
So the frame that was received by L3 router from source host machine A was tagged with Vlan 12.
Now in step 11, the L3 router checks the destination IP address is specified in the IP header of the
packet.
And L3 router thus finds out that the frame belongs to Svi 11.
Network ID.
So you can see that the network ID of Svi 11 is 14 .1.1.0 slash 24 and the destination IP address that
is 14 .1.1.1 is a member of network ID of Svi 11 subnet.
So in the next step, router finds out the Vlan which has a binding with Svi 11.
Right.
So in this case it will be Vlan 11.
Right?
Now we know in this topology that the router interfaces which are operating in Vlan 11 is P-8.
That is this interface which is also which is also named as IFR, right.
So now in the next step, router can prepare the frame in which the source Mac address will be the Mac
address of the outgoing interface, which is Mr..
The destination Mac address will be the Mac address of destination host machine B that is M, The source
IP address and destination IP address will remain unchanged.
Now one thing to note here is that that if router do not know the destination mac address of destination
machine B, then the router would have launched the ARP broadcast request message to know the Mac address
corresponding to IP address.
14 .1.1.4 on all the interfaces operating in Vlan 11.
But here we have assumed that L3 router has already have an entry for Mac address corresponding to IP
address.
14 .1.1.1.
So using its ARP cache, the L3 router can actually prepare this frame.
Right.
Now, the next thing that L3 router does is to retag this frame from Vlan 12 to Vlan 11.
Why Vlan 11?
Because in step number 12 router, find out that the destination subnet is actually Vlan 11.
So as a result, in step number 16, Router sends out the frame on interface eight.
That is this interface.
Now you can see that host B eventually receives the untagged frame.
So you can see that when L3 router places the frame on the wire, then that frame was tagged with Vlan
11, and when this frame enters the L2 switch, the L2 switch will make use of its Mac address table
in order to further forward this frame.
So using Mac address table, the L2 switch will forward the frame out of access port P6 and eventually
the frame reaches the host machine B and this frame will be untagged.
So you can see that it required us 17 steps in order to take a frame which was generated by a host machine,
a to destination host machine B provided that host machine A and host machine B are operating in different
VLANs.
So this is how inter Vlan routing works.
So you can see that the entire process of Inter Milan routing can be logically divided into two parts.
First part involves that taking a frame from source host machine A to the Gateway L3 router.
And the second part involves taking a frame from Gateway L3 router to the destination host machine B.
So that was all about inter Vlan routing.