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In a previous Nugget, we took
a look at some predictions

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regarding network traffic
and what the Mac Address

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Tables would look
like on some switches.

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In this Nugget, you and I
get to verify, or at least

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see if our predictions
were correct.

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Here in the top we have
Switch 1, and in the bottom,

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we have Switch 2.

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And these are Cisco switches.

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And to make it a little
bit easier and more direct,

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I've created a few aliases.

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So if we do the command,
Show Alias and press Enter,

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I've created an
alias called clean.

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So what that basically means is,
if we type in the word clean,

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it's automatically going to
execute the command Clear, Mac

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Address Table Dynamic, which
will remove any previously

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learned dynamic Mac addresses
from the Mac Address Table.

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Also I created a little
alias called SMT,

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for Show Mac Address Table.

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And on the switch, if
I type that alias name,

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it'll issue the command
Show, space, Max, space,

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Address-Table on
the Cisco switch.

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And it will help us focus on the
prediction of our Mac address

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tables, rather than
having to type that out

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in full each time.

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So starting on Switch 1, we'll
go ahead and issue the command

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Clean, which is Clear Mac
Address-Table, space Dynamic,

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and we'll do the same
thing on Switch 2.

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Then we'll do an SMT just
for grins on each one,

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for Show Mac Address Table.

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So we're starting off
with a clean slate.

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Next, let's go over to
PC-1, clear it's ARP cache,

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and then do a ping
from PC-1 over to PC-2.

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So here on PC-1,
we'll do a Clear ARP.

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Now on these virtual
machines that I'm running,

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that's the command to
clear the ARP cache.

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So the command to clear an
ARP cache on a local computer

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is going to vary based
on the device you're

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using, whether it be Windows, or
Linux, or some other platform.

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So if we do a Show ARP, the
ARP cache of the ARP table

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is empty on this device.

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And let's go ahead
and do our ping.

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So we're going to ping
over to PC-2 at 10.100.0.2,

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press Enter.

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That looks fantabulous.

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Let's go take a look at our Mac
Address Tables on both Switch 1

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and Switch 2 and see if our
predictions were correct.

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So here on switch
one and switch two,

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we'll hit the up arrow key to
do the Show Mac Address Table

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command.

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And let's verify.

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So we have two
entries for VLAN 100.

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One is PC-1, one is PC-2.

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They are both
dynamically learned.

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And PC-1 was learned on GIG0/1.

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And PC-2 was learned on GIG0/2.

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And that's exactly the
prediction that we had,

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based on looking at both the
ARP request and reply, as well

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as the ping request and reply.

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And now on switch two, we have
one dynamically learned Mac

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address, that is PC-1's
Mac address, right there.

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It was learned on switch
two on its GIG1/0,

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which the trunk interface.

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And because it came
in with an 802.1q tag,

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saying this broadcast is ARP
request was associated with

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VLAN 100, switch two knows that
that Mac address is associated

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with VLAN 100.

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And it can be reached
off that GIG1/0 port.

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So my friend,
here's what's next.

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I would like us to take each of
these scenarios independently.

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So we'll call them A, B, and
C. And with each one of them,

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imagine having clean MAC Address
Tables with nothing in them.

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And also the PCs with no initial
ARP cache entries at all.

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And then based on the
traffic from PC-1 to PC-4,

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predict what the
Mac Address Tables

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will be on Switch 1 and 2.

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And then starting again, we
clean up caches and clean

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tables, do that same
scenario for situation B.

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And then once again
for situation C.

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And then what we'll do
together in a separate Nugget

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is we'll walk through
the logic of those three

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additional scenarios, as
well as the implementation

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and verification that our
predictions were correct.

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Until then, I hope this has
been informative for you,

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and I'd like to thank
you for viewing.

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