In a previous Nugget, we took a look at some predictions
regarding network traffic and what the Mac Address
Tables would look like on some switches.
In this Nugget, you and I get to verify, or at least
see if our predictions were correct.
Here in the top we have Switch 1, and in the bottom,
we have Switch 2.
And these are Cisco switches.
And to make it a little bit easier and more direct,
I've created a few aliases.
So if we do the command, Show Alias and press Enter,
I've created an alias called clean.
So what that basically means is, if we type in the word clean,
it's automatically going to execute the command Clear, Mac
Address Table Dynamic, which will remove any previously
learned dynamic Mac addresses from the Mac Address Table.
Also I created a little alias called SMT,
for Show Mac Address Table.
And on the switch, if I type that alias name,
it'll issue the command Show, space, Max, space,
Address-Table on the Cisco switch.
And it will help us focus on the prediction of our Mac address
tables, rather than having to type that out
in full each time.
So starting on Switch 1, we'll go ahead and issue the command
Clean, which is Clear Mac Address-Table, space Dynamic,
and we'll do the same thing on Switch 2.
Then we'll do an SMT just for grins on each one,
for Show Mac Address Table.
So we're starting off with a clean slate.
Next, let's go over to PC-1, clear it's ARP cache,
and then do a ping from PC-1 over to PC-2.
So here on PC-1, we'll do a Clear ARP.
Now on these virtual machines that I'm running,
that's the command to clear the ARP cache.
So the command to clear an ARP cache on a local computer
is going to vary based on the device you're
using, whether it be Windows, or Linux, or some other platform.
So if we do a Show ARP, the ARP cache of the ARP table
is empty on this device.
And let's go ahead and do our ping.
So we're going to ping over to PC-2 at 10.100.0.2,
press Enter.
That looks fantabulous.
Let's go take a look at our Mac Address Tables on both Switch 1
and Switch 2 and see if our predictions were correct.
So here on switch one and switch two,
we'll hit the up arrow key to do the Show Mac Address Table
command.
And let's verify.
So we have two entries for VLAN 100.
One is PC-1, one is PC-2.
They are both dynamically learned.
And PC-1 was learned on GIG0/1.
And PC-2 was learned on GIG0/2.
And that's exactly the prediction that we had,
based on looking at both the ARP request and reply, as well
as the ping request and reply.
And now on switch two, we have one dynamically learned Mac
address, that is PC-1's Mac address, right there.
It was learned on switch two on its GIG1/0,
which the trunk interface.
And because it came in with an 802.1q tag,
saying this broadcast is ARP request was associated with
VLAN 100, switch two knows that that Mac address is associated
with VLAN 100.
And it can be reached off that GIG1/0 port.
So my friend, here's what's next.
I would like us to take each of these scenarios independently.
So we'll call them A, B, and C. And with each one of them,
imagine having clean MAC Address Tables with nothing in them.
And also the PCs with no initial ARP cache entries at all.
And then based on the traffic from PC-1 to PC-4,
predict what the Mac Address Tables
will be on Switch 1 and 2.
And then starting again, we clean up caches and clean
tables, do that same scenario for situation B.
And then once again for situation C.
And then what we'll do together in a separate Nugget
is we'll walk through the logic of those three
additional scenarios, as well as the implementation
and verification that our predictions were correct.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.