To set up communication between switch one and switch to this port needs to be configured as a trunk
port.
I'm also going to configure these ports as trunk ports so that we can capture traffic and see the encapsulated
frames between the switches, starting with switch one.
The first thing I'm going to do is make everything static.
So switch port mode access on gigabit zero zero and then switch port.
No.
Negotiate to disable DTP.
Do something similar on gigabit is zero one switch port mode access switch port.
No.
Negotiate.
Do show.
Run.
So this port zero zero is configured as an access port in VLAN one.
DTP is disabled.
Gigabit.
Zero one is configured as an access port and VLAN two http is disabled.
So we now need to configure ports two and three as trunk ports and disabled http.
So interface gigabit is zero to switch port mode trunk.
And it's going to fail, as you can see there, because we have to tap switch port trunk encapsulation
and in this example we'll use dot one Q and then switch port mode trunk to make it a trunk port.
A trunk port allows multiple VLANs to traverse that port switch port.
No, negotiate.
Let's do something similar.
On Porch three set the encapsulation to dot one Q set the mode to trunk.
Disable DTP and then I'll not shut those two ports.
So show.
Interface.
Gigabit a zero to switch port.
This command shows us that gigabit zero two is enabled as a Layer two interface.
It's been administratively configured as a trunk and it's operating as a trunk.
The encapsulation used is dot one Q.
That's how it was configured and that's how it's operating.
DTP has been disabled.
The native VLAN or untagged VLAN on this link is VLAN one.
All VLANs are allowed across the trunk.
Now, we can also use the command show interface trunk that shows us a nice summary of information.
So Port two and Port three have been manually configured for trunking using editor one.
Q They are currently trunking.
The native VLAN is VLAN one.
VLANs 1 to 4094 are permitted on those ports.
The VLANs allowed and active in the management domain of islands.
1 to 2 VLANs in the spanning tree forwarding state on gigabit zero two is one and two and on three is
two.
So we've configured switch one with these ports being access ports.
Currently this PC is in VLAN two.
And this PC is in VLAN one.
Now can router one, ping router two and router three and can router two ping any of those routers so
it can write a one turn off debugging here.
Ping ten 113.
Yes, it can.
Can it ping ten 114.
Yes, it can.
This port allows vlan one to traverse it using the untagged vlan.
So the frame goes across this link as an untagged frame goes across this link as an untagged frame and
then goes across these two links as untagged.
Switch two hasn't been configured for VLANs.
It's using a default config, so show vlan brief on the switch.
Shows that only VLAN one exists on switch two.
So let's put PC four into VLAN two and let's see if PC four and PC two can ping each other.
Turn off debugging on router two acting as our PC show IP interface brief.
This PC has an IP address of 10.1 to 2.2, so I'll give this one an IP address of 10.1 to 2.4.
It's currently configured with this IP address.
So let's change that.
10.1 or 2.4.
Paying 10.1 or 2.2.
What you'll notice is the pings fail.
Rather to and rather for cannot ping each other.
And the question is why?
Why can they not ping one another?
Well, the first problem is we haven't configured VLAN two on the switch switch two and we haven't put
this port into VLAN two.
So on switch two, I'm going to set it to STP mode transparent so that we have to manually configure
everything.
I'm going to create VLAN two, but notice please, even though you create the VLAN, no ports are put
into that VLAN by default.
So show interface gigabit is zero one switch port.
That's the interface here.
Shows me that that port is in VLAN one.
So what I need to do is go onto that port switchboard mode access.
To ensure that it's an access port that is the default switch port access VLAN to switch port no negotiate
to turn off all auto negotiations so that we have to manually configure everything and then explain
how it works.
So show interface gigabit zero one switch port.
The support.
Gigabit zero is enabled which using static access administrative mode and is operating as a static access
port.
It's in VLAN two at the moment, so all PC to be able to ping PC for let's do the ping again.
Ping fails from.
Four out of four, two out of two.
And it also fails in the reverse direction.
These two are not able to ping each other.
Let's disable this port and force the traffic to go through the hub and then do a Wireshark capture
to see what's going on.