The reason why we see OP traffic rather than ICMP traffic is on Ethernet before two devices can communicate.
They need to use OP to discover one another's MAC addresses so before ICMP traffic can even be sent
rather to acting as PC two needs to send an OP to discover Router Four's Mac address, but it never
discovers it because the traffic never reaches router four, so it never receives an OP reply and therefore
cannot send ICMP traffic.
So in switch to.
Interface.
Range gigabit.
Zero two.
Two three.
Switch port.
Trunk encapsulation port one key switch port mode trunk switch port.
No.
Negotiate at the moment.
Interface gigabit zero two.
On switch to is shut down.
I'll just do the same here.
To prove the point, we are forcing the traffic basically to go via the hub so that we can do a Wireshark
capture and see traffic on the network.
So now let's start another Wireshark capture.
Ken wrote a to paying writer for now.
Notice the ping succeeds.
If we look at our traffic.
We can see the OP.
I'll stop this Wireshark capture for the moment.
There's the broadcast asking for Mac address associated with IP address ten.
One, two, four.
As you can see, it's a broadcast sent from router two.
It's an ADA two, two, one, q frame.
So in the eight two, two, two, one Q portion, once again we can see that the VLAN is two.
There is the OP request looking for the MAC address associated with IP address ten 124.
He has the reply.
What you'll also notice is the VLAN ID is two, so it's coming back as a tagged frame from ten one to
4 to 10 1 to 2.
So there's the OP reply.
It's not a broadcast because it knows the MAC address of router two already, so it goes directly to
the MAC address of router two.
And then if we scroll down a bit further, we can see the ICMP echo messages.
So here's an echo from ten one to 2 to 10 1 to 4.
Once again, notice the VLAN ID is two.
Here's the reply from ten 1 to 4.
So it's an echo reply to ten.
One, two, two.
VLAN id is two.
So those frames are being tagged between the two devices.
Let's stop that capture and started again in genius three.
Now what about traffic from rather one, two, rather three.
That's using vlan one which is the untagged VLAN.
So rather one pinging router three ping succeeds.
Router two pinging.
Router four ping succeeds.
I'll just filter for ICMP.
So there's the ICMP message from router one to router three.
Notice it's a standard ethernet frame.
The ISA type is IP version four.
There is no ED one q tagging on the echo or the echo reply.
It's standard ethernet frames because that's the native VLAN.
Scrolling down, however, he has router two, pinging router four and notice once again there is the
tag.
So let's put router one and router three into VLAN ten and see how that affects the tagging of traffic.
So on switch one.
VLAN ten interface gigabit zero zero.
Switch port access vlan ten.
Do something similar on switch to VLAN ten.
Interface gigabit zero zero switch port access.
VLAN ten.
So now when router one.
Ping's router three.
What happens now?
It might take a while because spanning tree needs to converge.
So back on switch one show spanning tree.
For VLAN.
Ten ports are now forwarding.
So let's do the ping again.
Notice the ping now succeeds and in our Wireshark capture.
If we scroll right down.
What we should see now is the.
VLAN number as an example is VLAN ten.
So ID is ten can see the hexadecimal.
There's the decimal.
So at layer two in the Ethernet frame, notice the type is a 2 to 1 Q in edit 2 to 1.
Q The type is IP version four indicating that IP version four is used at layer three.
There's the ping, here's the reply.
But notice once again the VLAN number is VLAN ten.
If I changed this VLAN to VLAN 11 as an example.
With the ping succeed.
So vlan 11 rather interface gigabit zero zero switch port access.
VLAN 11.
I made the mistake of putting interface vlan 11.
I should have said simply VLAN 11 to create the VLAN, but in this case the switch did create the VLAN
for me.
You need to be careful with that because some switches won't do that for you.
But you can see VLAN 11 has been created.
Gigabit zero zero is in VLAN 11.
So this is in VLAN 11, the support is in VLAN ten can router one, ping router three and you can see
at the moment it can't.
In our Wireshark capture rather wan still has a cached mac address for router three, so it's sending
ICMP traffic, but notice it's tagged with VLAN 11 and no reply is received back because the traffic
never gets to router three.
The support is in VLAN ten, the support is in VLAN 11, so the traffic never reaches this port.
We can see that once again by doing a capture.
Helping rather three from rather one.
And what you'll notice in the output here is there is no OP and no ICMP traffic received on this port
at all.
Even though we're out of one is pinging rather three.
On the captur between the switches we can see the ICMP traffic with VLAN 11, but the switch when it
receives traffic on VLAN 11 is not going to forward it out of this port or this port.
So essentially goes nowhere.
It's going to be dropped by the switch because there are no access ports in VLAN 11.
So the traffic never hits rather three but on switch two.
If we created VLAN 11 and then went onto the port and put it into VLAN 11, what we would see now is
that the pings do succeed.
Now once again, it may take a while for spending tree to converge.
You can see the pings arriving.
Notice, 913 is the sequence number.
Pings are arriving at switch to.
But we may need to just wait a while for spending tree to converge.
And there you go.
Just converged so we can see the ping from router one to router three using VLAN 11 and there's a reply
on VLAN 11.
So physically this topology looks.
As follows Just ignore the hub for the moment.
So pretend that the hub is not there.
Physically.
We've got two PCs connected to switch one and two pieces connected to switch two, but logically rather
one acting as PC one and router three acting as PC three are connected to each other and two and four
are connected to each other.
They are totally separated from each other and won't be able to ping each other unless we enable interval
and routing on one of the switches and configure default gateways on the PCs to talk to each other via
their default gateway.