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 VLS 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 newer is uh

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 the second floor switch is

right here so we're just going to you

know pretend that this switch is in

another in another

floor round mounted to another rack

where this switch is 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 banss when you're setting up

trun drunking 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 is

layer one we're going to make our

physical connections we've already got

one to the router now I I want you to

help me in the

comments if I am using gigabit Z 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 I I want

you to challenge yourself so to uh 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 uh 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 cuz 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 computerss on floor Tu 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 Voiceover IP

phones uh all the things in their office

right the same is true for floor uh 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 where 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 um I'm going to

connect floor

one which I've also happened to

configure VLAN 10 on and it has ports

one through

10 uh 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

um 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've got 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 uh as we talked

about a few minutes ago or seconds

ago I moved I 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

cuz 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 these this

command as simple as that switch Port

mode trunk enter we're putting that uh

that pour into trunking

mode It came 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 VLS 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 VLS 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 vlm 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 in

trunk and yep we 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 um also um I would if I didn't have

an access server I would would be

walking back down to that switch and

actually making that connection with my

laptop so you know when we talk about SS

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 where you're wherever you're at but

let's continue with this now I'm on the

first floor you should see it chain

switch Das first floor the naming

conventions of switches in my opinion

you should you should have somewhere in

there an indicator of where they are and

in in your organization and building and

where they are on the rack cuz as you

can see this network sandwich right here

it's got a bunch of stuff you know a

bunch of equipment uh 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 of a

moment where all you know all you know

what is breaking loose and um 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 in

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 uh in this video is I set up DHCP

on this router beforehand and I trunk to

the router in 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 both vs so if my connections

are all right and my configurations are

all right this PC should receive an IP

address on the 1921 16810 Network and

that Mac so the the PC on the first

floor should receive an IP address from

1 19 2 168 10 as well because in this

particular scenario we're testing if

remember two two different uh devices on

different floors can be connected to the

same

VLAN uh 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 ip config let's see we don't have

one we're getting an aipa remember what

the apipa does aipa 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 re uh renew cuz 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 track pad'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 move on over to the mac and we're

going to make sure that we get a 1 19

21681 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 uh 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 Vin 10 and I'm

going to do that by going into the

network work 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 trun 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 Vin but they're not on the

same switch and just as a recap of how

these everything's

connected I'll grab yall come over here

and check this

out you 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 g0 is going to G 1 that

this g01 on floor 2 switch is a trunk

and then g02 is a trunk going to floor

one on uh g02 I actually did it on g02

as well CU g01 is going to the router so

g02 trunk to g02 allowing VL 10 and

20 and I've got my laptop which you see

the light has come turned off since I I

closed the laptop but you know it Port 1

through 12 had are in VLAN 10 on here

ports 1 through 12 on VLAN 10 up here so

this trunk is is essentially like a toll

bridge allowing VLS 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

connction C between those 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