Learn VLANs & Trunking on Cisco Switches in Real Life

How's it going everybody? in this video,

I'm going to show you what a trunk link

is on network switches. So a trunk link

is a connection

between two network devices,

whether they're switches or routers,

that's carrying tag traffic,

and I'll explain this. So the

only connection that I have set up

already that I'm not going to show you

is the trunk link that I have going to

the router. These two switches are going

to have two VLANs on them each. They're

going to have VLAN 10 and VLAN 20. And I

want to illustrate how these trunks are

typically used in the industry, so we're

going to go back to a scenario that I

introduced in the last lesson, Bob's

Grocery Store. So Bob's Grocery Store got

a network upgrade. They got new racks

installed, they got some newerish

network equipment, Cisco.

And they want to extend the back office

network to the upstairs as well. You know,

that Bob's Grocery Store is doing pretty

good. It's one of those double decker

grocery stores, and there's a back office

on the downstairs for people to, you know,

keep up with inventory, and there's a

back office on the upstairs for people

to keep up with in inventory and all

those other administrative tasks.

So the first floor switch is right here.

The second floor switch is

right here. So we're just going to, you

know, pretend that this switch is in

another floor

mounted to another rack

where this switch is going to be on

its own rack with its own set of

equipment. Usually in the industry, that's

how it's working. Now, we want to use the

same VLAN, VLAN 10, for the back office

network. So VLAN 10 and 20 have already

been created on both these switches. So

in the industry, if you're going to try

to extend the same VLAN across multiple

switches, no matter what floor they're on,

you need to have VLANS configured, but

the thing that I'm going to specifically

show you how to set up today is the

trunk. So what we have to do first and

this is what I recommend when you're

setting up VLANS, when you're setting up

trunking, any of that, is first, you

know, you get your plan, your diagram, you

know, as they say, proper planning

prevents poor performance.

Plan before, have your

diagram, know where you're connecting. So

the first thing we're going to do is

layer one. We're going to make our

physical connections. We've already got

one to the router. Now I want you to

help me in the comments.

If I am using gigabit 02, and

I want that to be the trunk between my

floors so that switch one and switch two

can communicate with each other, where

would I connect?

I'll show you now, but I want

you to challenge yourself so to

try to think of this on your own.

So I'm going to plug in right here,

this is gigabit 02,

and you always want your trunks to be

the fastest connection on the network. So

this isn't even that fast compared to

some of the fiber connections that exist

out there. Open up a tab, and Google

like fiber connections on switches,

you'll see like 10 gigs and more, the

speed. So we're going to connect between

the switches. You'll notice those

connections are coming up right away.

That's 'cus switches are normally

plug and play, where routers you got to

turn the ports on.

But we don't have a trunk configured

yet. So that's where I'm going to show

you

how to configure the trunks, but first,

let's connect our PCs. So I've got my

laptop over here, you can see the top of

it. I've got it over here. This is going

to be on floor two. So this is one of the

back office computers on floor two. But

we want it to be in VLAN 10. VLAN 10 is

taking up ports 1 through 12. So I'm

going to plug that in

And in real life, this might be for

the employees

workstations, could be for Voice over IP

phones, all the things in their office, right?

The same is true for floor- so

floor two, we got going. Floor one, so we

got some people down on floor one,

they're going to need their connections.

We're just using one laptop at this time

to test, but, you know, you always

want to test with at least two devices,

and then once those work, then you move

into deploying the larger groups of

hosts. So on this case, I'm going to

connect floor one,

which I've also happened to

configure VLAN 10 on, and it has ports

one through

10 in VLAN- I'm sorry, 1 through 12 on

VLAN 10 as well. So we're going to see

that come up, that should come up as well.

We see the light turning on, and it's up.

Now we're going to move over to

this.

We're going to go into floor two

switch first, and we're going to

configure the trunk. So I'll see you over there.

Okay, so now we're on our

host, we're configuring the switch, and we

want to get this switch with a trunk

link going to this switch. And in order

to do that as we did earlier, as we talked

about a few minutes ago or seconds ago,

I made a connection from

this switch on gigabit ethernet 02 to

gigabit ethernet 02 on the other switch.

So I'm going to connect a console cable

'cus I don't have SSH set up. I will show

you how to set up SSH and make it much

easier than what I'm doing now in a

future video. But for now, let me just

connect this.

I made the connection,

and now we are on the second

floor switch.

And the second floor switch

is going to be where we're going to

configure that trunk. So I'm going into

global configuration mode, and then I'm

going to go to int g02.

And I'm going to type this

command, as simple as that, switch port

mode trunk, enter. We're putting that

that port into trunking mode.

It went down and came back

up again, as we saw by the logs. And then

we're going to explicitly define which

trunks, or I'm sorry, we're going to

explicitly define which VLANs are going to

be allowed across the trunk link. When I

think of trunks, I think of them as like

toll bridges, and you're only allowed if

your VLANs tag is on the list, right? So I'm

going to do switch port trunk allow VLAN

10 comma 20. We only want those two

across. Now this could be a good form of

layer 2 segmentation at this point, where

if you believe that there's a VLAN that

doesn't need to connect to a certain

switch or get to a certain segment of

your network, you can actually exclude it

from that allow list, and traffic won't

even be trunked across the link. So I'm

going to type exit, and I'm going to do a

command, remember, as I have been

reminding y'all, configure and confirm.

Always make sure as you go. So I'm going

to do show int trunk.

And yep, there we go, we got our

trunks. And it looks like our VLANs 10

and 20 are allowed across that trunk,

cool.

Now what I'm going to do is I'm going to

move to

this switch right here, floor one. So

I'm going to go back here, grab this

console cable, move it to the other switch.

And in real life, this might mean

I'm connecting to an access server that

already has console connections into it.

And you can Google what an access server is.

Also, if I didn't have

an access server, I would be

walking back down to that switch and

actually making that connection with my

laptop. So, you know, when we talk about SSH,

if you don't already know what it is,

you'll see why it's so important that,

you know, you set that up on switches so

that you can remotely connect to them

from wherever you're at. But

let's continue with this. Now I'm on the

first floor, you should see it change

switch dash first floor. The naming

conventions of switches, in my opinion,

you should have somewhere in

there an indicator of where they are

in your organization and building, and

where they are on the rack. 'Cus as you

can see, this network sandwich right here,

it's got a bunch of stuff, you know, a

bunch of equipment stacked. So it can

be hard to know what's what, especially

if you don't have labels on them. But if

you have a good naming convention and

labels, it can really make it easier to

find devices, especially in the heat of a

moment where all you know

what is breaking loose, and you need

to troubleshoot things quickly. So we're

going into

global config mode. I made sure to

connect to gig 02 on this switch as well.

But you're going to have to pay careful

attention to that in the real world is

what connections are going where. And

then g02, I'm going to do basically the

same commands I just did. Switchport mode

trunk and switch port trunk allow VLAN

10 comma 20.

And I'm going to exit and do show int

trunk. And we're going to see- yep, it's

trunking VLAN 10 and 20. How do I know

that this is working? One thing I haven't

shown in this video is I set up DHCP

on this router beforehand, and I trunk to

the router. In the next video, I'm

going to show you what I did on this

router, but for now, just know DHCP is on

this router, there's a trunk link from

this switch going here so that DHCP can

reach both VLANs. So if my connections

are all right and my configurations are

all right, this PC should receive an IP

address on the 19216810 network. And

that MAC, so the PC on the first

floor, should receive an IP address from

19216810 as well, because in this

particular scenario, we're testing if,

remember, two different devices on

different floors can be connected to the

same VLAN

using trunking, so we should get

those same IP. So I'm going to test this

on my Windows system by doing CMD,

opening that up. I'll make sure you can

see it, ipconfig, let's see. We don't have

one, we're getting an APIPA. Remember what

the APIPA does? APIPA is a self-assigned

IP address or automatic private IP

addressing, and it essentially tells us

our computer did not get an IP address

from DHCP so we need to troubleshoot. In

this case, I know that I just need to go

ahead and do a renew 'cus I did a

release before I started the video. So

I'm going to do renew, and we're going to

wait on that.

It should be doing the DORA process.

It's going to request the IP address

from another machine.

Let's see.

Or from the server on the network.

Sorry, my trackpad's acting crazy.

And it looks like we did receive

one, how do I know? I got a 10.3

address. So what I'm going to do is now

move on over to the MAC, and we're

going to make sure that we get a 19216810

address over on the MAC as well,

which means we got to walk down some

stairs. All right, so now I'm back

downstairs, I'm on floor one switch,

we've got the trunk configured as I

showed. And now we just want to make sure

that we're actually in VLAN 10, and I'm

going to do that by going into the

network settings on the MAC.

And we're going to go and check and

make sure. Yeah, so right there you see

using DHCP. I always like to go manual,

basically release,

renew, and just make sure it works.

So that's basically requesting

another one, and I got dot two. And we

have successfully set up

a basic trunk link between two

switches that allow us to be on two

machines to be on the same network, but

they're not on the same switch. They're

in the same VLAN, but they're not on the

same switch. And just as a recap of how

everything's connected,

I'll grab yall, come over here

and check this out.

You know, you've got what I

didn't show is the configuration of the

router, that'll be in the next video. But

just so you know, g00 is going to g01, that

this g01 on floor 2 switch is a trunk.

And then g02 is a trunk going to floor

one on g02. I actually did it on g02

as well 'cus g01 is going to the router, so

g02 trunk to g02 allowing VLANs 10 and 20.

And I've got my laptop, which you see

the light has come turned off since I

closed the laptop, but, you know, port 1

through 12 are in VLAN 10 on here.

Ports 1 through 12 are on VLAN 10 up here. So

this trunk is is essentially like a toll

bridge allowing VLANs 10 and 20. Now, if I

tried to have a VLAN 30, and I didn't

allow it across this trunk, and I had a

30 down here too, we wouldn't have

connection between those devices.

So that is trunking, just the basics of

it. I'm looking forward to seeing you in

the next video, and don't forget to keep

learning.