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In the previous video, we have created 2 topology
like this. Here we have room 1 and here we have room 2.

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In the room 1, we have 2 vlan, which is
vlan 10 for accounting and vlan 20 for marketing.

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In the room 2, we also have same vlan, which is
vlan 10 for accounting and vlan 20 for marketing.

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Until now, we know that between different
vlan can not communicate yet.

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So PC in vlan 10 can not communicate with
PC in vlan 20. But communication inside

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vlan should be ok. Let’s say here PC 1
should be able to communicate with PC 2.

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Now the question is, how
if two PC in the same vlan,

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but in the different room. Can
they communicate each others?

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For example, here we want to communicate from
vlan 10 in the room 1 with vlan 10 in the room 2.

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Now let’s try to connecting switch 1 and switch 2.
Okay now here room 1 is connected to room 2.

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Now let’s try to ping from vlan 10 in
room number 1 to vlan 10 in room number 2.

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Okay here we can see that the result is
failed. Let’s try again,

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okay still failed.

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Why this is failed? This is because the
interface that connecting between switch

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is not in the vlan 10. Let’s verify
it, enable, and then show vlan brief.

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Oh I am sorry, here we can see that
fa0/5 and fa0/6 is in the vlan 10,

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this is because our configuration in the
previous video. Now let’s set this two

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interface to the vlan 1 again. Remember that
by default, all interface is in the vlan 1.

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Conf t, interface range fa0/5-6, switchport access
vlan 1. Now let’s verify it, do show vlan brief.

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Okay here we can see that fa0/5-6 is
in the default vlan, which is vlan 1.

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Now let’s see in the switch 2.

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Enable, show vlan brief. Here we
can see that fa0/5 is in the vlan 1.

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This is why vlan 10 in the room 1 and vlan 10
in the room 2 can not communicate each others.

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Because interface that connecting
this two switch is in the vlan 1,

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so vlan 10 can not passing this interface.
Because this interface only allow vlan 1 to pass.

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Here also same with vlan 20, vlan 20 in the room 1

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also can not communicate
with vlan 20 in the room 2.

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So the question is, how we can communicate between
vlan 10 in the room 1 to vlan 10 in room 2?

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Here we can assign interface fa0/5
in both of switch to vlan 10.

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So here let’s go to interface fa0/5, switchport
mode access, and then switchport access vlan 10.

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Now let’s verify it, do show vlan brief. Okay
here we can see that fa0/5 now is in the vlan 10.

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Next let’s configure in the switch
2. Conf t, go to interface fa0/5.

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Switchport mode access, and
then switchport access vlan 10.

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Let’s verify it, do show vlan brief. Okay here
we can see that now fa0/5 is in the vlan 10.

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Now, vlan 10 in the room 1 should be able to
communicate with vlan 10 in room 2. Let’s try it.

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Okay here is still failed, let’s try again.

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and here we can see that now is successful.

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This is because interface between switch is in
the vlan 10. So vlan 10 can pass this interface.

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But the question is, how about vlan 20?

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Let’s try it.

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Okay here the result is failed. Why? Because interface between switch now Is in the vlan 10.

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Absolutely vlan 20 can not pass this interface.

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We can assign the interface
between switch to vlan 20,

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but vlan 10 will not able to
communicate between rooms.

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So the solution for this problem is we can

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use trunk. We will configure the interface
that connecting this two switch become trunk.

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If we configure the interface to trunk,

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so the interface can pass any packet from
any vlan. So vlan 10 can pass the interface,

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vlan 20 can pass the interface, and
all of vlan can pass the interface.

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Let’s try it. Open switch 1, interface fa0/5, and
then switchport mode trunk. Okay this is how we

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can configure trunk in cisco switch. Easy right?
Now let’s move to switch 2,

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interface fa0/5, switchport mode trunk.
And now Let’s verify,

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to verify the trunk, we can use
command do show interface trunk

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Here we can see that we have
trunk interface, which is fa0/5.

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Now let’s try to ping from vlan
10 room 1 to vlan 10 room 2.

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Okay here we can see that the result is success.
Let’s try for vlan 20. Okay here also success.

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So now, same vlan between room can
communicate each others.

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Because we already configure trunk between switch.
Okay I think enough for this video.

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I hope you understand the function of trunk.

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Thankyou for watching and see you on the next video.
