WEBVTT

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 Welcome to this video on a review of
 InterVLAN routing for our CCNA 200

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-301 bootcamp. So InterVLAN routing
 is talking about a situation where

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 we have hosts in one VLAN needing to
 send their packets to hosts or A

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-host in a different VLAN.

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 Normally with this layer 2 switching
 that couldn't happen.

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 So we need something that can route the
 packets between those two subnets.

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 Now there are three
 ways to do that.

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 We could use a router on a stick model
 where the switch itself is just

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 a layer 2 switch.

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 The switch has no knowledge of routing
 and he's just forwarding his packets

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 to a router that's doing
 all that work.

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 We could actually enable the switch itself
 for routing with switched virtual

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 interfaces or we could convert some
 of the switching ports to layer 3

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 routed ports. If we do the router on
 a stick model the router will have

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 subinterfaces which is a single point
 of failure and probably not something

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 you want to do. So let's
 look right here.

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 So router on a stick
 simply means this.

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 I have my switch right here.

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 I have my router right here and I have
 a single interface connected to

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 that router. Now that single interface
 is configured as a VLAN trunk.

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 So on the switches side
 it's pretty easy.

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 All you have to do is switch port trunk
 encapsulation dot 1Q and then

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 we do switch port mode trunk.

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 That's all we have to do.

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 A little bit more work here on the
 router side which we'll talk about

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 in just a second but the whole point
 behind this is on the switches side.

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 We have a bunch of
 different VLANs.

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 This might here might be VLAN 2.

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 We might have some other hosts here
 in VLAN 3 and some other hosts here

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 in VLAN 4. And if the switch is not
 going to the routing force and the

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 router will we need all this traffic
 to be able to go up this trunk.

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 So it can be routed back and
 forth between by the switch.

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 I mean by the router,
 not the switch.

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 So in order to do this what we're going
 to do is we're going to go on

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 to this router's physical interface
 and we're going to break it up into

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 sub interfaces. So the physical interface
 might be fast ethernet 0 slash

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 0. All we have to do there
 is no shut and that's it.

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 And then we create these logical
 sub interfaces one per VLAN.

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 So we would say fast ethernet
 0 slash 0 dot.

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 And then we could put any number after
 the dot we want but typically we

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 put the number of the
 VLAN after the dot.

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 So why don't we start
 with 0 slash 0 dot 2.

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 Fast ethernet 0 slash 0 dot 3 and
 fast ethernet 0 slash 0 dot 4.

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 Then we have to tell
 each sub interface.

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 Hey, I need you to do 802
 dot 1 queue tagging.

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 So you can recognize incoming tags
 and you can apply outgoing tags.

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 So we use the encapsulation.

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 Dot 1 queue and then we put
 the VLAN number in there.

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 Capsulation dot 1 queue 3.

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 Capsulation dot 1 queue 4.

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 And then lastly, we put our
 IP addresses on here.

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 We put the IP address.

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 It's appropriate for VLAN 2.

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 Whatever subnet that
 is an IP address.

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 It's appropriate for VLAN
 3 and IP address.

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 It's appropriate for VLAN 4.

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 And that's what we see
 here on this slide.

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 Create our sub interfaces and then on each
 sub interface we do the encapsulation

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 dot 1 queue command
 and an IP address.

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 And then the router will be able to
 route between those sub interfaces

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 because they have created
 connected routes.

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 And a router can route back and forth
 between connected routes all day

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 long. We don't need any routing
 protocol or anything to do that.

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 Now, like I said in the previous slide,
 the downside to this is that router

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 is a single point of failure.

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 If it fails, those hosts will not
 have any default gateway anymore.

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 Or maybe the router itself
 might not fail.

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 Maybe somebody yanks out that cable, that
 trunking cable between the router

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 and the switch. So for that reason,
 it might be better just to have the

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 switch itself do the
 routing for us.

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 And in most modern network designs
 today, that's what you'll actually

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 see. That the switch itself, the access
 layer switch is actually doing

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 the routing and serving
 as the default gateway.

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 So you can do that
 in one of two ways.

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 So we could use SBIs.

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 So we could just simply say, okay, well,
 I've got VLAN 2, so I'll create

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 an interface. Well, actually just
 take a look at the next slide.

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 Right here, I'll create
 an interface VLAN 2.

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 And then I'll put an IP address on
 it that's in the same subnet as all

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 my hosts in VLAN 2.

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 And then I've got some hosts here in
 VLAN 3, so I'll create an interface

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 VLAN 3, put an IP
 address on there.

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 Now, the switches, most switches don't
 have routing enabled by default.

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 So you can create switch virtual interfaces,
 that's what we call these

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 interface VLANs right here.

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 You can create these all day long, but
 they won't be able to route packets

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 back and forth between them.

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 That's why on most switches, we also
 have to enable IP routing globally

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 to enable it to do that.

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 That turns on routing
 functionality.

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 And then, of course, we'd have to
 get our DHCP server involved.

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 Our DHCP server would have to know
 that when a DHCP discover comes in

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 from somebody in VLAN 2, the DHCP server
 should say, oh, your default

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 gateway is 2.2.2.2.

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 And for you guys over there in VLAN
 3, your default gateway is 3.3.3.3.

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 Or, of course, we could make it even
 easier and configure this exact same

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 switch as our DHCP server.

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 One other alternative you could do is
 we could have layer 3 routed ports.

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 So an example of this is done on
 the distribution layer switches.

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 Let me give you an
 example of that.

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 Let's say we have a
 switch right here.

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 Switch 1. And he's got
 something like this.

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 So this is going to be VLAN 1.

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 Actually, let's make it
 even simpler like this.

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 Let's say we've got three
 access layer switches.

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 Switch 1, switch 2, and switch 3.

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 Each access layer switch is
 only serving a single VLAN.

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 So maybe this guy here
 is serving VLAN 1.

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 This access layer switch.

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 He's only doing VLAN 2.

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 And this other guy.

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 He's doing VLAN 3.

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 Okay. And they're all connected
 up to a distribution switch.

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 Who's going to do the routing back
 and forth between these VLANs?

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 Well, we could on this distribution
 switch, we could say, hey, I'm going

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 to make this an access
 port in VLAN 1.

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 And then in that switch, I'm going
 to create interface VLAN 1 and put

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 an IP address on it like we
 just saw in the last slide.

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 And then we can say, hey, I'm going
 to make this an access port in VLAN

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 2 and create a switch virtual
 interface for that.

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 You could do that.

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 Or we could just say, hey, I'm going
 to go this interface right here and

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 do these two commands.

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 No switch port. And now that it's now
 I've just converted into what's

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 called a routed interface.

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 And now I can actually put
 an IP address on it.

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 And that IP address.

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 So 1.1.1.99. That can serve as the
 default gateway for all the people

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 in VLAN 1. And I could do
 the same thing over here.

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 I could say no switch port on that and
 give him an IP address that will

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 be serving as the default gateway
 for all the people in that VLAN.

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 So that's what we mean
 by routed interfaces.

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 Interfaces where we disabled
 their switch port capability.

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 They're no longer in a VLAN.

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 And they're just like an interface
 and a router where you can stick an

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 IP address on. Now remember, even if
 we do that on the switch, we're still

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 globally going to want to type IP routing
 to enable to route between our

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 connected interfaces.

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 Here's an example of that.

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 Just like it drew on the whiteboard
 just a moment ago.

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 I don't think there's really anything
 to add to this picture.

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 And we can do show
 IP route connected.

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 To verify that routing is actually enabled,
 whether it be on our router

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 or on our switch.

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 So that concludes this video
 on inter VLAN routing.

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 I hope you found it helpful.