Okay.
So let's do a test.
What happens if we move one of these ports into a different VLAN?
Now earlier when I was doing this test, I had some problems in three.
So what I'm going to do is I'm going to shut gigabit zero two down and gigabit to zero three.
So the only interfaces that are now up are zero zero and zero one.
In this topology, just to start with a simple network.
To make a point.
So those interfaces are up, up.
The other interfaces are down.
What I'll also do actually is just shut down any other interfaces to make sure that things converge
quicker.
So shut down.
That range.
And this range of interfaces.
Show IP interface.
Brief.
Also shut down.
Gigabit 3/023.
So show IP interface brief.
All interfaces are shut down except for those two interfaces.
So gigabit zero zero gigabit zero one.
Is rather one able to ping rather to.
Yes, it is.
But if we put this interface gigabit is zero one into VLAN two, what will happen with the pings.
So switch port access vlan two.
Now before I press enter, notice the ping succeeds.
I'll repeat this 100 times.
And then hit enter on the switchboard access VLAN command.
Notice the pings are starting to time out.
So as soon as I moved the port from one VLAN to another, the devices are not able to communicate with
each other.
So spanning tree shows that gigabit zero one is still in the learning phase of spanning tree.
So we'll wait for a while for spanning tree to converge and then do the test again.
But what I'd like you to see is these two devices were in the same subnet and in the same VLAN and they
were able to ping each other.
As soon as we moved one port to a different VLAN they were no longer able to ping each other.
Spanning trees forwarding on VLAN two on port gigabit to zero one.
It's also forwarding on gigabit zero zero.
On VLAN one.
So if we use the show spending tree summary command, we can see that VLAN one is forwarding, VLAN
two is forwarding.
There are no blocking ports.
Yet rather one is not able to ping rather two and rather two is not able to ping rather one.
Because they are in separate vlans is rather too aware that it's in a separate VLAN.
The answer is no because no tagging information or no VLAN information is going to be sent on this port.
It's an access port, so we just have standard Ethernet frames.
There is no VLAN port information transmitted on any of the frames going out of that port.
Now to prove this, let's add some IP addresses onto switch one.
So interface VLAN one IP address ten one one.
Let's make it two, five, four.
And then interface.
VLAN two IP address ten 12254 with a mosque.
Now I need to know.
Shut both of those.
So go back onto vlan one and no, shut it.
So these are layers three switched virtual interfaces on the switch.
We are basically creating a layer three IP address on the switch for the relevant VLAN.
So as an example, the switch can ping rather one.
On VLAN one.
It lost the first ping because of ARP but switch one can ping right of one it can't ping router two
because router two needs to be configured with the right IP address for VLAN two.
But before I do that, notice when I do a CAPTCHA under that port.
Traffic from the switch to the rudder is untagged.
It's a standard Ethernet frame.
IP traffic.
There is no tagging at all.
And as a last test, what I'll do is configure right a two so interface f0/0 IP address ten .1.2.2.
So I've moved it from one subnet to another.
Paying 2 to 2.
The switch can ping rather to on this port.
Is the traffic tagged?
So do the ping a gain full time for ICMP traffic.
Notice there is no tagging information at all.
It's just standard Ethernet.
So what is the summary of this test?
The PCs in the topology are unaware of VLAN traffic.
These are access ports or untagged ports.
In other words, a two, two, two, one.
Q Tagging is not used on these ports.
Can write a one ping router of.
So can it ping ten.
One, two, two.
At the moment it won't be able to because the routers don't have default routes configured.
So I'm going to turn off IP routing on these routers to turn them into PCs or dumb devices and type
IP default gateway.
And in this case, the default gateway of router two will be this IP address on router one.
No IP routing.
That's a command that turns an expensive router into a dumb device.
IP Default Gateway ten .1.12254.
So rather one has a default gateway configured.
Can it ping its default gateway?
Yes, it can.
Can it ping rather to.
At the moment it can.
And the reason why is that on the switches.
IP routing.
Is configured by default.
However, if I typed no IP routing, which is true on a lot of switches, the pings will not succeed
because the switch is not doing into VLAN routing to enable into VLAN routing on a layer three switch
such as this or a physical switch, you need the IP routing command to route between the VLANs.
So to prove this on rather to I'll do a debug IP ICMP so we can see if ICMP traffic is getting to the
router.
Do the ping again.
And notice there are the echo replies.
We can do something similar on router one.
And there are the echo replies.
Debug IP packet will give us low level information.
I'll repeat this only once.
So we'll send one ping which succeeded over there.
And what you can see is the packet was rooted out of the router and sent to the destination is an IP
packet.
So in other words, these end devices connected to a switch are unaware that the switch is using VLANs.
The configuration of the switches as follows show run interface gigabit zero zero.
That port is using default config, which is which means that it's an access port in VLAN one gigabit
zero two is an access port in VLAN two.
IP writing is enabled and we've configured layer three IP addresses on the two VLANs to allow the switch
to rot between the two VLANs configured, which in turn allows router one and router two to communicate
with each other.
Now if router one and router three are put into the same VLAN and router two and router four put into
the same VLAN, that kind of information needs to be communicated from one switch to another using a
2 to 1 key.
So this port needs to be configured as a trunk port.
So let's prove that and then configure it.