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- So let's talk a little bit
more about broadcast domains

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and how we can manipulate them
and control them on switches.

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Because after all this is
one of the big benefits

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of switches is it gives us the ability

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to control and configure
something called virtual LANs.

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So here we're going to talk
about what are virtual LANs,

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why do we need them, and how
do we configure and test them.

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Alright so in this
particular picture right here

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we have two physically distinct,

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separate local area networks.

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We have a local area network for Sales

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and a local area network for Marketing.

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They're completely separate.

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They're not connected in any way.

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Maybe we did that intentionally

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because we have security reasons.

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You know those people in
Sales, you know sometimes

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they get a little funny
and we don't want them

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sending information to
those people in Marketing,

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so we want to keep them
completely separate and distinct.

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So we look at this and
we say okay this is great

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but wouldn't it be better
if instead of having

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two separate networking
devices, two bridges,

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wouldn't it be great if we
could just have one device?

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Both departments are
connected to that one device

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but we're still able to keep
them separated from each other.

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Because right now Sales is in
their own broadcast domain.

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Right, because we know
that bridges and switches

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when they receive in a frame,
if the destination address

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of that frame is unknown,

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the switch does not
have that in its table.

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Like a broadcast, like a multicast,

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or like a unicast MAC address that

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just has never been learned,

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the switch or the bridge
will flood that frame.

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It'll send it out to all the other ports

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other than the one where it came in.

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So on the left we have a broadcast domain,

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and on the right we
have a broadcast domain.

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Wouldn't it be nice if we could
get rid of those two bridges

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and replace them with just a single device

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that still everybody could connect to

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but could maintain our
isolation and separation

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of different broadcast domains?

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And that's exactly what virtual LANs are.

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So now we have a switch
and we have configured

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our virtual LANs, and we've put the ports

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into those virtual LANs.

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And now it separates out
our broadcast domains.

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So a virtual LAN that
is the purpose of it.

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It separates broadcast domains.

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It gives you a little bit
of flexibility and control.

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Now you might be wondering,
well why would I want to

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separate out my broadcast domains?

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A variety of reasons.

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Number one.

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Every time an actual broadcast,

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an Ethernet frame with a
destination MAC address of FFFFFFFF

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or all ones in binary,
every time an Ethernet frame

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with a destination of a
broadcast hits your NIC card,

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your NIC card has to take that in,

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send it up to the CPU of your laptop,

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and your laptop has to inspect it.

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Now if it's just one
broadcast, not a big deal.

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But as the broadcast domain
gets bigger and bigger

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and bigger, if I go from having
four devices to 14 devices

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to 400 devices all in
one broadcast domain,

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you're going to see a lot of broadcasts.

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Broadcasts are used by a
lot of legitimate protocols.

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ARP uses broadcasts.

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DHCP uses broadcasts.

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There's a lot of things
that use broadcasts.

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You would be surprised at how frequently

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your laptop is sending out broadcasts

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without you even touching it,

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without you even touching the keyboard.

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So if you can imagine your CPU
is getting busier and busier

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and busier, processing
all these broadcasts

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as they're coming in.

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That's going to have an effect on you.

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Your websites are going
to seem to load slower.

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Your email's going to load slower.

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Anything that has to do with
networking on your laptop

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is going to start grinding to a halt.

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So that's one reason why
we might want to take

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a rather large network and partition it

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into different VLANs, into
different broadcast domains.

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Also for security restrictions.

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So from a layer 3 perspective,
an IP perspective,

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all the devices in one broadcast domain

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are in the same subnet.

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They're in the same IP network.

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Well when it comes to
doing security like say,

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okay I want Joe to be able to
get to this server over here,

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but I don't want Sally to be
able to get to the server.

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If everybody's on the same
subnet and same broadcast domain,

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that's possible but it's hard.

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As a matter of fact at the CCNA level,

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you don't even learn how to do that.

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Once you go into the CCNP level

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and you're starting for
your CCNP switch exam,

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then you'll learn of ways to do that.

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But it's difficult.

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It's a lot easier if I can separate people

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into different broadcast
domains, different subnets,

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there's a lot of other
ways, a lot of easier ways,

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to prevent devices from one subnet

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from talking to another subnet.

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But when we're all in the
same subnet on the same VLAN,

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that gets kind of tricky.

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So from a security
perspective, you might want to

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break up your network
into different partitions

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or different VLANs.

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So provides better security,
controls broadcast like ARP,

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and provides hierarchical subnet usage.

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Not really going to expand
on that one all that much.

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So as far as VLANs are concerned,

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and this is the way it's been for decades,

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the VLAN range is from 1 to 4094.

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So that's the VLANs you
have available to you.

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Now there are some VLANs that
are called normal-range VLANs,

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1 through 1001.

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And usually people just stick with VLANs

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in that number, in that range.

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Now it's completely up to you.

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You say okay, so I've
decided that I want Payroll,

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all of the people in Payroll
to be in one IP subnet,

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and I'll put them in a VLAN.

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Which VLAN should it be?

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It's up to you.

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You could select VLAN 2 for them.

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You could select VLAN 359.

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Completely up to you.

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Completely up to you.

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It's just the main thing
to remember is that

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one IP subnet has to be in
its own unique VLAN number,

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and another IP subnet has to
be in a different VLAN number.

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You can't have two
different subnets at Layer 3

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sharing the same VLAN.

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Because if you do that,

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now they're seeing each
other's broadcasts.

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And that's exactly what
we wanted to avoid.

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Also just the reverse is true.

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I can't have a user over
here who's in one subnet,

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a user over here who's
in the exact same subnet,

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same network, but they're
in two different VLANs.

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If they're in two different VLANs,

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they're not sharing broadcasts.

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At Layer 3, they think they're
in the same broadcast domain.

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They say, oh I'm in the
same subnet as that guy.

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I can ARP for him.

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But ARP is a broadcast.

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When you send out an ARP
request for something

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that you think is in your network,

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that's making the assumption

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that that broadcast can get to that guy.

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But if in reality, he's
in a different VLAN,

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even if at Layer 3, he's
in the same subnet as you.

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But if he's in a different
broadcast domain,

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in a different VLAN, your
broadcast will not reach him.

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And I'm going to demonstrate
that here in just a moment.

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So some of the VLANs
right there in the middle,

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1002 through 1005, are reserved.

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I don't think you're ever
going to be tested on that

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they're reserved for
token ring necessarily,

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but you should remember that those ones

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there in the middle are reserved.

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You cannot use them.

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They're unusable.

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So you should probably remember

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that 1002 through 1005 are unusable.

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And then the higher
numbers 1006 through 4094

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are extended-range VLANs.

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Once again, once you get
to the CCNP switch exam,

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we learn more about those.

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And there are some caveats
and gotchas as far as

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if you want to use those,
there are certain other things

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you have to do first.

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At the CCNA level though, we
don't really get into that.

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Okay so how do I configure VLAN?

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So remember that initially
when you turn on a switch,

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review question, when you
turn on a switch are the ports

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on the switch by default
administratively down

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or administratively enabled?

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They are administratively enabled.

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Routers, their interfaces are

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administratively shut down by default.

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But by default, switch ports are up

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as soon as you plug something in.

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Now when you get a switch,

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whether it's got eight ports
or whether it's got 200 ports,

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the default behavior is
that all those interfaces

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are in VLAN 1, the default VLAN.

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You should remember that.

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VLAN 1 is already there.

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You don't have to configure it.

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It is the default VLAN and
all the interfaces are in it.

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Now if you say, oh okay well that's cool

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because that one switch is going
to be connected to Payroll.

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Nobody but Payroll is going to
be connected to that switch.

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And everybody in Payroll is
going to be in the same subnet,

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so they're going to be in
the same broadcast domain.

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No problem then.

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You don't have to create any VLANs.

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You don't have to change any VLANs.

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But if you do want to go on a switch

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and you want to create some new VLANs,

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it's a two-step process.

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Step number one is just
creating it and naming it,

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like VLAN 2, VLAN 9, just
basically telling the switch

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I'm creating a new VLAN on you.

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VLAN 200, VLAN 300, that's
literally the command.

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VLAN and the VLAN ID.

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Don't even worry about the legacy way.

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Nobody does that.

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This is the way you're going to do it.

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This is the way you're going to do it.

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Config t, go into global config mode,

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and then just type vlan and the number.

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Like vlan 5, vlan 7.

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Optionally if you want to.

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This is optional.

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You can provide it a name.

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And this kind of helps
if you're looking at

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the running config and it says VLAN 2

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and then underneath it
it says Engineering VLAN.

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And then VLAN 3, Marketing VLAN.

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Now you know, oh okay, I know
why these VLANs were created.

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You don't have to give it a name,

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but it's just kind of nice,
a descriptive characteristic.

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Now that's step number one.

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Just because I created VLAN 5,

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the switch can't read my mind.

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It doesn't have telepathy.

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It doesn't know which interfaces

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I want to put into that broadcast domain.

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So that's the second step.

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Now we have to go into
the interfaces, right.

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Interface, Fast Ethernet, whatever.

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And apply that VLAN to the interface.

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And here's how we do that.

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We type switchport mode access.

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We saw that in the last slide, right?

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In the last video?

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That's saying this interface

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is in one broadcast domain only.

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Now if all I did was type that,
it would still be in VLAN 1.

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I really wouldn't have done much.

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But then I typed switchport
access vlan whatever.

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Switchport access vlan 2

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if I want it to be in
that broadcast domain.

252
00:11:02,407 --> 00:11:04,287
Switchport access vlan 99

253
00:11:04,287 --> 00:11:07,391
if I want it to be in
that broadcast domain.

254
00:11:07,391 --> 00:11:11,558
So critical thing I want
you to take away from this,

255
00:11:12,413 --> 00:11:13,580
on switchports

256
00:11:15,591 --> 00:11:20,011
the mode dictates what
the interface is doing.

257
00:11:20,011 --> 00:11:21,539
The main mode we've really focused on

258
00:11:21,539 --> 00:11:23,789
so far is just access mode.

259
00:11:24,870 --> 00:11:27,222
There are other modes as well.

260
00:11:27,222 --> 00:11:29,262
When we talk about trunking
in the next section,

261
00:11:29,262 --> 00:11:30,952
we're going to get into that.

262
00:11:30,952 --> 00:11:34,288
So but why I'm saying that is because,

263
00:11:34,288 --> 00:11:37,744
if you look at the
running config of a switch

264
00:11:37,744 --> 00:11:39,184
and you see on a particular interface

265
00:11:39,184 --> 00:11:42,017
it says switchport access vlan 20,

266
00:11:43,243 --> 00:11:46,801
you can't automatically
assume that that interface

267
00:11:46,801 --> 00:11:51,701
is just in VLAN 20 and it's
providing access to some device.

268
00:11:51,701 --> 00:11:55,486
You can't assume that just
from this command right here.

269
00:11:55,486 --> 00:11:57,005
This command does not tell you

270
00:11:57,005 --> 00:12:00,706
how this interface is operating right now.

271
00:12:00,706 --> 00:12:02,866
All that command says is

272
00:12:02,866 --> 00:12:06,699
if this interface ever
becomes an access port,

273
00:12:07,686 --> 00:12:11,907
if it's ever in that mode,
then while it's an access port,

274
00:12:11,907 --> 00:12:15,306
it's going to be in this VLAN right here.

275
00:12:15,306 --> 00:12:18,281
But we don't know from this
command what the mode is.

276
00:12:18,281 --> 00:12:21,448
That's where this command is critical.

277
00:12:22,342 --> 00:12:24,989
So if this interface was
in some other kind of mode,

278
00:12:24,989 --> 00:12:28,133
you might think oh okay well
if I put it in some other mode

279
00:12:28,133 --> 00:12:30,509
this right here will just
vanish from the configuration,

280
00:12:30,509 --> 00:12:31,701
right?

281
00:12:31,701 --> 00:12:32,989
Nope.

282
00:12:32,989 --> 00:12:34,157
This could be in another mode

283
00:12:34,157 --> 00:12:38,152
and you would still see
this in your running config.

284
00:12:38,152 --> 00:12:42,224
So the point I'm trying to make
to you is, step number one,

285
00:12:42,224 --> 00:12:43,490
when doing any kind of troubleshooting is

286
00:12:43,490 --> 00:12:46,657
identify what mode is my interface in.

287
00:12:47,568 --> 00:12:49,048
Because then you can
look at a running config

288
00:12:49,048 --> 00:12:52,096
and you can say oh okay well
these commands I can ignore

289
00:12:52,096 --> 00:12:54,776
because they don't apply
to the particular mode

290
00:12:54,776 --> 00:12:57,443
that I'm operating in right now.

291
00:12:59,037 --> 00:13:00,405
And some verification commands.

292
00:13:00,405 --> 00:13:02,221
Show vlan is probably the command

293
00:13:02,221 --> 00:13:04,021
you're going to use the most often.

294
00:13:04,021 --> 00:13:05,605
It shows you the VLANs that you've got

295
00:13:05,605 --> 00:13:08,341
and what interfaces are
applied to those VLANs.

296
00:13:08,341 --> 00:13:10,582
And you can also do show interface,

297
00:13:10,582 --> 00:13:13,972
like show interface Fast Ethernet 0/1,

298
00:13:13,972 --> 00:13:16,902
and then the keyword of
switchport at the end.

299
00:13:16,902 --> 00:13:18,812
Let's do some demonstrations of this.

300
00:13:18,812 --> 00:13:22,833
So for this demonstration,
I've created this topology here

301
00:13:22,833 --> 00:13:23,802
which I'm going to be using.

302
00:13:23,802 --> 00:13:26,185
So I've got switch 2.

303
00:13:26,185 --> 00:13:29,563
And in my particular lab
which is a real light,

304
00:13:29,563 --> 00:13:31,755
I'm using INE's rack
so INE's rack rentals.

305
00:13:31,755 --> 00:13:36,270
So if you ever buy some
tokens and you do some

306
00:13:36,270 --> 00:13:38,940
rack rental time on our CCNA/CCNP racks,

307
00:13:38,940 --> 00:13:40,902
that's exactly what I'm
going to be using here

308
00:13:40,902 --> 00:13:41,735
in this demonstration

309
00:13:41,735 --> 00:13:44,749
and most of our demonstrations coming up.

310
00:13:44,749 --> 00:13:46,532
So I've got a switch, but in our racks

311
00:13:46,532 --> 00:13:48,261
we don't actually have any real Hosts.

312
00:13:48,261 --> 00:13:51,332
There's no laptops or Pcs in the racks.

313
00:13:51,332 --> 00:13:53,836
So I'm actually using Routers.

314
00:13:53,836 --> 00:13:57,034
This is actually Router
1, Router 2, and Router 3.

315
00:13:57,034 --> 00:13:59,306
But I'm going to pretend
that they're Hosts.

316
00:13:59,306 --> 00:14:02,250
I've just given them IP addresses,

317
00:14:02,250 --> 00:14:04,762
and we're just going to be
using them to initiate pings.

318
00:14:04,762 --> 00:14:06,770
So they're not going to be
doing any fancy routing stuff.

319
00:14:06,770 --> 00:14:08,819
Let's just pretend that they're Hosts.

320
00:14:08,819 --> 00:14:11,210
And I changed their
names, their Host names,

321
00:14:11,210 --> 00:14:15,967
to Host 1, Host 2, Host 3 just
for demonstration purposes.

322
00:14:15,967 --> 00:14:17,583
Okay.

323
00:14:17,583 --> 00:14:21,655
So let's go on to Switch 2 to begin with.

324
00:14:21,655 --> 00:14:24,514
And what I recommend that you
might want to do is right now

325
00:14:24,514 --> 00:14:25,438
if you haven't already done this,

326
00:14:25,438 --> 00:14:28,390
take a screenshot of this image.

327
00:14:28,390 --> 00:14:30,198
That way when I log into the devices,

328
00:14:30,198 --> 00:14:32,839
you can be looking at the screenshot

329
00:14:32,839 --> 00:14:35,415
while I'm showing you the command line

330
00:14:35,415 --> 00:14:38,359
and you won't get confused
as to which device I'm in

331
00:14:38,359 --> 00:14:40,990
and port numbers and
all that kind of stuff.

332
00:14:40,990 --> 00:14:42,686
Okay so hopefully you had enough time

333
00:14:42,686 --> 00:14:46,987
or you've paused the video and
you've taken that screenshot.

334
00:14:46,987 --> 00:14:48,820
So let's go over here.

335
00:14:50,477 --> 00:14:54,126
So first of all, I'm going to
go ahead and I am in Switch 2.

336
00:14:54,126 --> 00:14:55,659
Remember user exec mode.

337
00:14:55,659 --> 00:14:56,922
You can't really do anything from here,

338
00:14:56,922 --> 00:14:59,005
so I want to type enable.

339
00:15:00,074 --> 00:15:00,938
So the first thing I want to see is

340
00:15:00,938 --> 00:15:03,186
what VLANs are in this switch.

341
00:15:03,186 --> 00:15:04,770
Honestly I don't know if this switch

342
00:15:04,770 --> 00:15:06,809
has just the default VLANs.

343
00:15:06,809 --> 00:15:08,309
There might be some other VLANs in here

344
00:15:08,309 --> 00:15:10,535
from some previous labs that I did.

345
00:15:10,535 --> 00:15:14,365
So I'm just going to type show vlan.

346
00:15:14,365 --> 00:15:16,645
Okay it just has the default VLAN.

347
00:15:16,645 --> 00:15:18,478
So we see here VLAN 1.

348
00:15:20,464 --> 00:15:22,776
There has been no name configured

349
00:15:22,776 --> 00:15:25,704
so the name is just default.

350
00:15:25,704 --> 00:15:27,201
And it's active.

351
00:15:27,201 --> 00:15:29,600
And you can see these are all the ports

352
00:15:29,600 --> 00:15:31,433
that are in that VLAN.

353
00:15:32,680 --> 00:15:36,747
Now if a port, if you know
there's a port on the switch

354
00:15:36,747 --> 00:15:38,507
but it does not show up here,

355
00:15:38,507 --> 00:15:40,894
but you know that port is actually up

356
00:15:40,894 --> 00:15:42,320
and connected to something,

357
00:15:42,320 --> 00:15:44,392
if it's not anywhere in this output,

358
00:15:44,392 --> 00:15:48,650
that means that port
is not an access port.

359
00:15:48,650 --> 00:15:52,283
Only ports that are in
the switchport mode access

360
00:15:52,283 --> 00:15:54,946
will show up here as access ports

361
00:15:54,946 --> 00:15:57,490
in the various VLANs that you've got.

362
00:15:57,490 --> 00:15:59,756
If it's not here then that
means it's in some other mode,

363
00:15:59,756 --> 00:16:02,346
probably what we call trunking mode

364
00:16:02,346 --> 00:16:04,706
that we'll talk about in another video.

365
00:16:04,706 --> 00:16:08,044
So right now we have this
and so if we look at that,

366
00:16:08,044 --> 00:16:09,747
that means all three of these interfaces

367
00:16:09,747 --> 00:16:11,555
are in the same VLAN.

368
00:16:11,555 --> 00:16:14,388
Let me go ahead and bring them up.

369
00:16:18,103 --> 00:16:19,551
By the way, this command
I'm doing right here,

370
00:16:19,551 --> 00:16:22,967
this is a useful command on
switches, interface range.

371
00:16:22,967 --> 00:16:25,581
This way you can group a
bunch of interfaces together.

372
00:16:25,581 --> 00:16:29,158
And now the configuration
command I apply is going to apply

373
00:16:29,158 --> 00:16:31,262
across all of them at the same time.

374
00:16:31,262 --> 00:16:32,760
So I don't have to get into each interface

375
00:16:32,760 --> 00:16:34,782
one at a time at a time.

376
00:16:34,782 --> 00:16:37,792
So I'll just do no shutdown.

377
00:16:37,792 --> 00:16:40,702
I disabled them
purposefully before this lab

378
00:16:40,702 --> 00:16:42,369
just to demonstrate.

379
00:16:43,280 --> 00:16:46,280
Okay so I'm going to go into Host 1.

380
00:16:49,431 --> 00:16:51,608
And we can see that
Host 1 in his ARP table

381
00:16:51,608 --> 00:16:54,360
all he knows about is himself.

382
00:16:54,360 --> 00:16:58,707
Now because they are all
three in the same subnet.

383
00:16:58,707 --> 00:17:01,087
You can see they're all
three in the 1.2.3 network.

384
00:17:01,087 --> 00:17:03,337
And I'll put a circle here.

385
00:17:05,079 --> 00:17:09,246
They're all three in the
same VLAN which is VLAN 1.

386
00:17:12,992 --> 00:17:16,069
They should be able to
exchange broadcasts.

387
00:17:16,069 --> 00:17:18,236
So if on PC 1 I ping PC 2,

388
00:17:20,286 --> 00:17:21,333
the first thing it's going to do,

389
00:17:21,333 --> 00:17:22,980
it's going to send out an ARP request.

390
00:17:22,980 --> 00:17:25,124
So my first ping will probably fail.

391
00:17:25,124 --> 00:17:28,039
That ARP request will be a broadcast.

392
00:17:28,039 --> 00:17:32,206
So when it's broadcast,
PC 2 and PC 3 will see it.

393
00:17:33,258 --> 00:17:36,603
And then PC 2 will respond
back to that with an ARP reply.

394
00:17:36,603 --> 00:17:38,611
And then the ping should go through.

395
00:17:38,611 --> 00:17:40,955
So if PC 1 can actually ping PC 2,

396
00:17:40,955 --> 00:17:42,707
that will prove the broadcast works.

397
00:17:42,707 --> 00:17:44,499
And actually because this is a Router,

398
00:17:44,499 --> 00:17:46,499
I have the ability to turn on a debug

399
00:17:46,499 --> 00:17:48,659
to actually watch the ARP go out.

400
00:17:48,659 --> 00:17:50,766
And I'm going to do that.

401
00:17:50,766 --> 00:17:51,849
So debug arp.

402
00:17:55,026 --> 00:17:57,359
So here we go, ping 1.2.3.2.

403
00:18:00,948 --> 00:18:04,281
Alright undebug all turns off the debug.

404
00:18:05,841 --> 00:18:08,274
So we can see here, as
soon as I did the ping,

405
00:18:08,274 --> 00:18:10,524
we see IP ARP sent request.

406
00:18:13,054 --> 00:18:14,654
So he sent an ARP request.

407
00:18:14,654 --> 00:18:16,118
He says this is me.

408
00:18:16,118 --> 00:18:17,934
This is my MAC.

409
00:18:17,934 --> 00:18:20,550
And I'm looking for 1.2.3.2.

410
00:18:20,550 --> 00:18:23,110
I don't know his MAC.

411
00:18:23,110 --> 00:18:25,846
And because they are in
the same broadcast domain,

412
00:18:25,846 --> 00:18:27,750
we received an ARP response.

413
00:18:27,750 --> 00:18:29,083
Received, reply.

414
00:18:30,978 --> 00:18:33,259
And now we can see here the MAC address.

415
00:18:33,259 --> 00:18:37,005
And then the pings were
successful after that.

416
00:18:37,005 --> 00:18:40,140
Now I'm also going to do the same thing.

417
00:18:40,140 --> 00:18:43,003
I'm going to ping 1.2.3.3.

418
00:18:43,003 --> 00:18:44,179
He's ARPing for him right now.

419
00:18:44,179 --> 00:18:45,843
I turned off the debug.

420
00:18:45,843 --> 00:18:47,787
And now when I do show arp,

421
00:18:47,787 --> 00:18:51,158
we can see he's learned about
everything in his ARP table.

422
00:18:51,158 --> 00:18:53,870
So all three of these guys
know about each other.

423
00:18:53,870 --> 00:18:56,787
Now look what happens if I do this.

424
00:18:58,227 --> 00:19:01,977
I'm going to leave these
two ports in VLAN 1,

425
00:19:03,963 --> 00:19:07,436
but I'm going to take this port right here

426
00:19:07,436 --> 00:19:11,519
and I'm going to create
a new VLAN called VLAN 2.

427
00:19:12,791 --> 00:19:16,866
And I'm going to put this
interface in that port.

428
00:19:16,866 --> 00:19:20,283
So that's step number one, let's do that.

429
00:19:23,159 --> 00:19:24,958
So the first step is to create the VLAN.

430
00:19:24,958 --> 00:19:28,086
So I have to go into global
configuration mode to do that.

431
00:19:28,086 --> 00:19:30,003
And I just type vlan 2.

432
00:19:31,231 --> 00:19:33,326
And I could give it a name if I want.

433
00:19:33,326 --> 00:19:35,993
Name let's just say Engineering.

434
00:19:37,553 --> 00:19:38,511
Okay.

435
00:19:38,511 --> 00:19:40,943
And now I haven't done, I
haven't applied the VLAN

436
00:19:40,943 --> 00:19:42,343
to an interface yet.

437
00:19:42,343 --> 00:19:45,182
So now when I do the show vlan command,

438
00:19:45,182 --> 00:19:48,924
you can see there it is with the name.

439
00:19:48,924 --> 00:19:52,563
But there are no interfaces
associated with it yet.

440
00:19:52,563 --> 00:19:54,027
So now what I need to
do is I need to go to

441
00:19:54,027 --> 00:19:56,450
interface Fast Ethernet 0/3

442
00:19:56,450 --> 00:19:59,367
and apply VLAN 2 to that interface.

443
00:20:02,986 --> 00:20:04,290
And that is the switchport.

444
00:20:04,290 --> 00:20:08,066
We want to do switchport mode access

445
00:20:08,066 --> 00:20:10,899
and then switchport access vlan 2.

446
00:20:12,962 --> 00:20:15,866
That's the command that
moves it from VLAN 1,

447
00:20:15,866 --> 00:20:19,283
which is what it was in, now into VLAN 2.

448
00:20:20,323 --> 00:20:23,706
And now if I do the show vlan command,

449
00:20:23,706 --> 00:20:26,956
now we see that interface is in VLAN 2.

450
00:20:28,022 --> 00:20:28,855
Okay.

451
00:20:30,198 --> 00:20:33,115
Now here's an interesting question.

452
00:20:34,188 --> 00:20:36,188
If we go over to Host 1,

453
00:20:38,293 --> 00:20:39,126
show arp,

454
00:20:40,741 --> 00:20:42,131
okay?

455
00:20:42,131 --> 00:20:46,298
He thinks that 1.2.3.3 is
this MAC address right here.

456
00:20:48,261 --> 00:20:52,453
I can't memorize that, so
I'm just going to remember

457
00:20:52,453 --> 00:20:55,036
the last four characters, 6dd8.

458
00:20:56,438 --> 00:20:57,271
6dd8.

459
00:20:59,619 --> 00:21:00,452
So this is

460
00:21:02,776 --> 00:21:03,609
6dd8.

461
00:21:04,729 --> 00:21:06,305
That's him.

462
00:21:06,305 --> 00:21:07,722
And Router 1 says

463
00:21:10,732 --> 00:21:12,149
in his ARP table,

464
00:21:13,836 --> 00:21:15,836
1.2.3.3 equals MAC 6dd8.

465
00:21:22,393 --> 00:21:26,106
Make this a little bit bigger here.

466
00:21:26,106 --> 00:21:30,023
Okay, but this MAC address,
back when Router 1,

467
00:21:31,268 --> 00:21:34,268
Host 1 ARPed, the ARP was successful

468
00:21:35,107 --> 00:21:39,443
back when PC 3 was in the same
VLAN, when he was in VLAN 1.

469
00:21:39,443 --> 00:21:42,943
And 6dd8 was originally learned in VLAN 1.

470
00:21:44,028 --> 00:21:46,493
Is it still in VLAN 1?

471
00:21:46,493 --> 00:21:50,550
Well let's take a look
at the MAC address table.

472
00:21:50,550 --> 00:21:52,467
Show mac address-table.

473
00:21:54,420 --> 00:21:58,704
And we're looking for an
address ending with 6dd8.

474
00:21:58,704 --> 00:22:01,704
Look at this, 6dd8 is now in VLAN 2.

475
00:22:05,089 --> 00:22:05,922
In VLAN 2.

476
00:22:09,363 --> 00:22:13,292
So what's going to happen if PC 1 pings,

477
00:22:13,292 --> 00:22:15,186
because he already has
an ARP entry, right?

478
00:22:15,186 --> 00:22:16,826
He already thinks hey I
don't have to ARP anymore.

479
00:22:16,826 --> 00:22:18,610
I know the guy's MAC address.

480
00:22:18,610 --> 00:22:21,643
Let's think about what's
going to happen here.

481
00:22:21,643 --> 00:22:24,370
So it's going to come in this way.

482
00:22:24,370 --> 00:22:28,914
And I'm going to draw it over
here because I have more room.

483
00:22:28,914 --> 00:22:31,664
So the IP source will be 1.2.3.1.

484
00:22:35,659 --> 00:22:38,576
The IP destination will be 1.2.3.3.

485
00:22:40,694 --> 00:22:44,027
The MAC source will be whatever PC 1 is.

486
00:22:46,439 --> 00:22:50,606
And the MAC destination is
going to be xxxx.xxxx.6dd8.

487
00:22:54,681 --> 00:22:56,858
Now when that comes into this port,

488
00:22:56,858 --> 00:22:58,891
what's that switch going to do?

489
00:22:58,891 --> 00:23:01,217
You might think oh well no problem.

490
00:23:01,217 --> 00:23:03,658
I means he's going to look at
his MAC at his table, right

491
00:23:03,658 --> 00:23:06,273
and he's going to find 6dd8.

492
00:23:06,273 --> 00:23:09,233
And he's going to find it's
associated to port 0/3.

493
00:23:09,233 --> 00:23:10,731
I mean after all that's what
we see right here, right?

494
00:23:10,731 --> 00:23:11,715
There it is.

495
00:23:11,715 --> 00:23:13,045
Here's the problem.

496
00:23:13,045 --> 00:23:14,193
Look at this.

497
00:23:14,193 --> 00:23:15,945
The MAC address table does not just

498
00:23:15,945 --> 00:23:19,168
store the MAC address and a port.

499
00:23:19,168 --> 00:23:22,418
It also stores what VLAN it belongs to.

500
00:23:23,703 --> 00:23:26,256
So this is going to be a problem for us,

501
00:23:26,256 --> 00:23:30,435
because when this frame
comes in, going to 6dd8,

502
00:23:30,435 --> 00:23:32,179
the switch is going to say oh

503
00:23:32,179 --> 00:23:35,187
it came in on a port that's in VLAN 1.

504
00:23:35,187 --> 00:23:39,354
In my MAC address table I
need to find 6dd8 in VLAN 1.

505
00:23:40,498 --> 00:23:42,538
And he's not going to find it

506
00:23:42,538 --> 00:23:46,348
because it's not in
VLAN 1, it's in VLAN 2.

507
00:23:46,348 --> 00:23:48,767
And so guess what, our
ping is going to fail.

508
00:23:48,767 --> 00:23:50,200
The switch is not going to say oh okay,

509
00:23:50,200 --> 00:23:51,942
well I'm going to just
allow this frame to jump

510
00:23:51,942 --> 00:23:55,061
from one broadcast domain
to another broadcast domain.

511
00:23:55,061 --> 00:23:56,436
The switch is not going to do that.

512
00:23:56,436 --> 00:23:58,769
Remember this a virtual LAN.

513
00:23:59,798 --> 00:24:03,069
In a real LAN, in a real LAN,
when you put an Ethernet frame

514
00:24:03,069 --> 00:24:05,590
on the wire, the destination MAC address

515
00:24:05,590 --> 00:24:09,462
for that frame has to be
somebody on your wire.

516
00:24:09,462 --> 00:24:11,335
That is the rules of Ethernet.

517
00:24:11,335 --> 00:24:12,710
When you put an Ethernet
frame on the wire,

518
00:24:12,710 --> 00:24:15,662
it's destined for somebody on your wire.

519
00:24:15,662 --> 00:24:16,694
Now if you're trying to get your packet,

520
00:24:16,694 --> 00:24:18,702
if you're trying to get
your data to somebody

521
00:24:18,702 --> 00:24:21,590
on another wire, the
destination MAC address

522
00:24:21,590 --> 00:24:24,558
has to be a Router that's on your wire.

523
00:24:24,558 --> 00:24:27,598
So you can get that frame to
the Router who's on your wire

524
00:24:27,598 --> 00:24:30,205
and then he can route
it to another subnet.

525
00:24:30,205 --> 00:24:32,138
But this is not going to work here

526
00:24:32,138 --> 00:24:34,242
because this would be breaking
the rules of Ethernet.

527
00:24:34,242 --> 00:24:37,170
If this ping actually
worked, that would mean that

528
00:24:37,170 --> 00:24:40,170
PC 1 was putting an
Ethernet frame on his wire

529
00:24:40,170 --> 00:24:42,115
with a destination MAC
address of something

530
00:24:42,115 --> 00:24:44,346
that was not on his wire.

531
00:24:44,346 --> 00:24:48,720
And it somehow magically hopped
from one wire to the other,

532
00:24:48,720 --> 00:24:51,095
from one LAN to the other.

533
00:24:51,095 --> 00:24:52,775
But the whole reason
we create virtual LANs

534
00:24:52,775 --> 00:24:54,442
is to separate them.

535
00:24:55,495 --> 00:24:58,828
So PC 1 should not be able to ping PC 3.

536
00:25:00,149 --> 00:25:01,728
Now this is all in theory here.

537
00:25:01,728 --> 00:25:03,973
Because they're on two
separate broadcast domains,

538
00:25:03,973 --> 00:25:05,829
even though he has the MAC address.

539
00:25:05,829 --> 00:25:07,746
Let's see what happens.

540
00:25:11,136 --> 00:25:12,499
Show arp.

541
00:25:12,499 --> 00:25:13,332
Okay.

542
00:25:13,332 --> 00:25:14,415
Ping 1.2.3.3.

543
00:25:17,288 --> 00:25:18,267
Ah, there we go.

544
00:25:18,267 --> 00:25:20,517
See, I'm just getting dots.

545
00:25:21,609 --> 00:25:25,776
So the ping is not working
even though he has a MAC entry.

546
00:25:27,283 --> 00:25:28,155
It's not working because they're on

547
00:25:28,155 --> 00:25:30,475
different broadcast domains.

548
00:25:30,475 --> 00:25:31,308
Now watch this.

549
00:25:31,308 --> 00:25:33,611
I'm going to clear out his ARP table.

550
00:25:33,611 --> 00:25:34,444
Clear arp.

551
00:25:35,835 --> 00:25:38,002
So now when I do show arp.

552
00:25:39,710 --> 00:25:42,210
Clear arp, let's say, 1.2.3.3.

553
00:25:47,339 --> 00:25:48,172
Okay.

554
00:25:48,172 --> 00:25:49,755
So 1.2.3.3 is gone.

555
00:25:51,766 --> 00:25:53,404
Debug arp.

556
00:25:53,404 --> 00:25:55,321
Now let's ping 1.2.3.3.

557
00:25:57,611 --> 00:25:59,203
Sending a request.

558
00:25:59,203 --> 00:26:00,755
Sending a request.

559
00:26:00,755 --> 00:26:01,763
Sending a request.

560
00:26:01,763 --> 00:26:06,678
He's not getting any responses
because these are broadcasts.

561
00:26:06,678 --> 00:26:07,998
So he sent all these requests

562
00:26:07,998 --> 00:26:10,214
but he didn't get any ARP reply.

563
00:26:10,214 --> 00:26:12,926
Even though this guy's in
the same subnet as him,

564
00:26:12,926 --> 00:26:15,375
he was in a different virtual LAN.

565
00:26:15,375 --> 00:26:17,527
And broadcasts from this virtual LAN,

566
00:26:17,527 --> 00:26:22,065
ARP requests were not allowed
to go into this virtual LAN.

567
00:26:22,065 --> 00:26:26,232
Even when PC 1 knew what
the MAC address of PC 3 was,

568
00:26:27,600 --> 00:26:29,120
it still couldn't get over here

569
00:26:29,120 --> 00:26:31,168
because the rules of Ethernet say,

570
00:26:31,168 --> 00:26:33,336
when you put an Ethernet
frame on the wire,

571
00:26:33,336 --> 00:26:35,001
it has to be destined for somebody

572
00:26:35,001 --> 00:26:38,456
in your broadcast domain, in your LAN.

573
00:26:38,456 --> 00:26:40,856
In this case, they're not in the same LAN.

574
00:26:40,856 --> 00:26:44,233
They're in separate virtual LANs.

575
00:26:44,233 --> 00:26:45,361
One other thing I want to show you is

576
00:26:45,361 --> 00:26:49,477
the output of that other
command that we saw.

577
00:26:49,477 --> 00:26:51,158
So we already looked at show vlan,

578
00:26:51,158 --> 00:26:52,749
and you're going to use that command a lot

579
00:26:52,749 --> 00:26:55,189
in your networking career.

580
00:26:55,189 --> 00:26:59,047
You can also do show
interface, Fast Ethernet

581
00:26:59,047 --> 00:27:02,332
and then whatever it is, and
the keyword of switchport.

582
00:27:02,332 --> 00:27:05,366
This is a very useful command.

583
00:27:05,366 --> 00:27:08,810
Number one it shows you,
what is my operational mode?

584
00:27:08,810 --> 00:27:10,747
Static access.

585
00:27:10,747 --> 00:27:14,914
So administrative mode means,
what am I configured to do?

586
00:27:15,903 --> 00:27:20,001
Operational mode means,
what I am actually doing?

587
00:27:20,001 --> 00:27:22,462
Sometimes what you're
configured to do doesn't work

588
00:27:22,462 --> 00:27:25,486
because it relies on things
that aren't turned on

589
00:27:25,486 --> 00:27:26,718
or aren't working properly.

590
00:27:26,718 --> 00:27:29,104
And so your operational
mode will be different.

591
00:27:29,104 --> 00:27:30,854
But right now we're the same.

592
00:27:30,854 --> 00:27:32,055
But look down here.

593
00:27:32,055 --> 00:27:35,222
Access Mode VLAN, VLAN 2, Engineering.

594
00:27:36,307 --> 00:27:40,414
So that says, if this is
operationally an access port,

595
00:27:40,414 --> 00:27:44,581
which it is, if that's true,
then this will be in VLAN 2.

596
00:27:45,972 --> 00:27:49,805
And that concludes this
video on virtual LANs.