CCNA Course Episode 2: How Routers Work and Connect Networks

this is episode 2 of my free ccna course and a huge shout out to boson software the official sponsor of

the ccna course they are the reason this can be made available for free so i highly encourage

you to go check them out they have the absolute best ccna ccnp labs and practice exams

this is a router but what is it routers connect us to the internet they also connect this to other networks

in this video we're going to see why we need them and what they do in our networks

and why i have so many of them holy junk sauce and of course we're going to be lobbying

we're going to watch how a frame and then a packet will go across a network access a web server and then give us

information back this is how the internet works you're going to learn that today let's

get started [Music] oh by the way i'm giving away some bozon

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link below to enter the contest hurry up it's going away soon johnny wants some coffee and we're gonna

help him get it check this out in our last video we talked about this guy right here

a switch he's got multiple ports you connect your computers to him and they can talk and that's exactly

what's happening here johnny mark denny and lisa are all on the same network and the switch allows them to

talk to each other and in our last video we explored how the switch actually helps them talk

what goes on inside this thing and it's it's pretty cool but you see now johnny this is

this is johnny in real life he's a he's a raspberry pi johnny doesn't want to just talk to lisa mark and denny

johnny wants coffee the coffee is actually way over here on a completely different network and

johnny's over here not good right how does johnny get coffee and when i say johnny wants coffee of course he wants

to go out to networkchuck.coffee and order some coffee but this server where this website lives

networkchuck.coffee is on a different network here the switch can't help him he needs help from somebody else

he needs a router this guy right here oh this guy this is a cisco 2911 router one of my favorites oh it's beautiful

now routers come in all shapes and sizes this is just one type of cisco router this is a ubiquiti router looks very

different and then typically your home routers look nothing like what i just showed you a router is the perfect

solution for this because a router's job is to connect networks let's put one on there this is

actually a virtual version of a 2911 router look just like the one i showed you how neat

so we'll put the router in between and notice on a cisco router there's no ports on the front they're all in the

back so let me turn that slicker around now plug johnny's switch in to the router

and then i'll plug the copy network into the router as well let's do that in virtual world bam bam

and once more now before we keep going i want to ask you a question do we actually need this

router i mean why can't we just do this let's take away our connections

move this router out of the way and then let's just connect our switches directly to each other

that should work right no no well here's why i mean we could connect these two

switches and make them one giant switch and that's essentially what would happen but the reason these guys over here and

then my coffee server over here on different networks isn't because they're connected to two

different switches that's not it it's because of these guys right here their ip addresses we will go more in

depth on this later because there's a lot more to it but just know that when we talk about a network

we're normally referring to ip addresses and a group of ip addresses so notice i have two groups of ip

addresses here 10.1.1.0 through 10.1.1.255. with my configuration as long as you

have an ip address in that range you're on the same network now this right here 23.27.38.0 through 232738255

that's a completely separate network but you know what don't take my word for it let's actually try this let's see if

it'll work let's go back to packet tracer now as a quick 30 second refresher on how a

switch works we'll have johnny try to ping mark over here and then we'll have him try to ping my

copy server over here and see what happens so i'll click on johnny wake him up come on johnny let me get this stuff

out of the way we'll go to his desktop we'll go to his command prompt and let's bring up a simulation real

quick so we'll click on the simulation button at the bottom right so we can watch this stuff happen in

bullet time and i'm going to show you something that i did not show you on the last video

and that's how johnny will learn mark's mac address now why is it so important for johnny to learn

mark's mac address well if you recall from our last video the switch the only language he speaks is layer two

that's all he knows mac addresses this layer two address right here now when johnny pings mark

he's gonna be pinging his ip address so his message when he gets it ready we'll be pinging

10.1.1.2 if johnny were writing a letter that's what he would put as the address but if that's all johnny had when he

sent this message to the switch the switch would be like why is this envelope blank i can't even

see ip addresses who is this going to that's what would happen so johnny must know the mac address of mark

in order for the switch to know how to get it to anywhere but how this is what happens so from johnny i'm

going to ping mark's ip address 10.1.1.2 and boom let's watch what happens all right johnny's got some envelopes he's

ready to send them out these are frames right now notice we have a new message we're dealing with

it's called arp or addressed resolution protocol essentially it's a way that johnny can find out

what mac address is tied to 10.1.1.2 because he has to know that to be able to send it to mark let's open that up

and see what's inside let's click on that and again we're dealing with layer 2 mac

addresses but also notice down here we have some information about this arp packet like for example the source ip is

johnny's source ip 10.1.1.3 and then the destination ip right here 10.1.1.2 that's the missing mac address

he's trying to find out mark's mac address and then of course because this is a layer 2 frame we're talking about

mac addresses so the source mac address that the switch will use is johnny's mac address but then look at the destination

what the junk is that ffffffff this is what's called a broadcast address it's the layer 2 switch equivalent of someone

going who belongs to 10.1.1.2 when he sends it to that mac address

it's going to go out to everybody watch what happens we'll click next it goes to the switch let's open up that

packet and take a look or frame i'm sorry see it happens now look at this this is so cool so

over here the switch receives it and then it's about to send it out and notice

it's going to go out all these ports on layer one which remember layer one's the physical it's these

ah i just unplug something out oh that sound it's all the physical stuff so let's click next

and boom art message is going everywhere and what will happen is lisa will go oh i'm not 10.1.1.2 and neither

am i says denny but mark yeah mark is 10.1.1.2 so he says hey that's me i'm your guy i'm over here

johnny so we'll step forward in time mark is the only one who responds saying yes that is me so he'll send and then

the switch sends that to johnny so johnny now knows mark's mac address so we can send him a ping if i open that

frame up that's sent to the switch we see the source is johnny's mac address and the destination is

mark's mac address and if we click continue it'll go to mark mark will respond bam johnny gets it if

we check our terminal real quick our command prompt it's happening if you click real time it will just

continue so that's what happens when someone's on the same network johnny knows

that mark is on the same ip network but what happens when johnny tries to get to the network

coffee company let's see let's have him ping it so we'll open up johnny once more here

go to his command prompt and we'll ping the ip address of my copy server so ping 23.227.38.65

let's go to our simulation so we can watch this in real time and let's hit enter boom okay so far so

good we have an arp frame that johnny's getting ready to find out where my coffee server lives maybe his mac

address let's open it up and see click on that message and huh do you notice anything weird here you

know what pause the video right now and see if you notice anything that might be strange

unpause okay here we go so just like before johnny's sending a frame to a broadcast address to say hey

who's got this ip address but he's not asking about the ip address of my coffee server

no no look here this is a source ip this is his ip address but he's trying to discover the ip

address or the mac address rather of 10.1.1.1 why because when he tried to find out

mark's mac address this right here was 10.1.1.2 that was the destination why is this

different because johnny knows johnny knows the coffee server is not on his network

so he's not even gonna try to connect to that coffee server on layer two he's not gonna try to

discover his mac address he gives up immediately watch what happens let's step forward in time so johnny sends

this arp message saying anyone out there are you 10.1.1.1 and the switch will send this

out and as we step forward in time stepping forward stepping forward stepping

forward no one responds johnny keeps sending out arp request does anybody have 10.1.1.1

does anybody have it and no one responds who is 10.1.1.1 and why is johnny trying to talk to him

let's find out it comes down to how we configure johnny let's open up johnny real quick

go to his config and the answer is right here there it is 10.1.1.1 is his gateway gateway is

another word in the networking world we use for router as i said before johnny knows

that people in his network are 10.1.1.0 through 10.1.1

johnny knows that if anyone has an ip address in that range they're in his network

they're in his neighborhood he can just walk over and talk to him find out where they are like yeah i know bill he just

lives two doors down i can walk over there and talk to him but if johnny tries to reach an ip

address outside that range he knows it's not in his network and he's gonna need some help he needs help

connecting to a different network and that's where a router comes in so let's throw the router back in there and

have some fun this is gonna be so cool watch this now before we move on it's important for you to know that i did

pre-configure this router not a crazy amount of configuration but i did add some configuration to make this work

for the most part switches work out of the box no problem a router's a bit more complicated because it has to know how

to route between networks he's a router he has the map of how to get to things i'll

show you what i mean check this out we're going to have johnny here once again try to peeing

networkchuck.coffee let's open up his command prompt so i'll go to his command prompt we'll go back to our

simulation we're in simulation mode bullet time mode and let's watch some crazy router magic

happen so we're gonna ping the coffee server and go now same story as before johnny knows that this is not

on his network he knows that bob lives in another state and he can't just walk over there he's like i gotta use my

gateway i gotta find my router and his router will be connected to his network watch what happens a step forward in

time the art message is sent out to the broadcast and keep in mind the same reason that

johnny's sending an art packet for the router is the same reason he had to send one

for mark he doesn't know the mac address for 10.1.1.1 and he must know the mac address so the

switch will know how to get his stuff to the router the switch sends it out to everyone and lisa

denney mark this server right here which i can talk about here in a moment they're all like yeah that's not me but

then the router's like that's me i'm 10.1.1.1 and he sends a reply back saying yep that

is me the switch tells johnny hey this guy lives here that's his address walk on over so johnny does if we open

up that frame that just arrived at the switch we can see the source is indeed johnny

and the destination is the router and then we'll step forward in time it arrives at the router and

then we have something blinking and flashing let me let me zoom in on that this is so cool what's happening right

here let's open up the freaking out guy right now isn't that working fun oh my gosh okay

here's what's happening now what are the router receive right here well if you just look at layer one and layer two we

know that he received this frame on his gigabit zero zero interface as this little message says right here but

because we have layer three involved we know that to be called a packet remember that's what routers do man they

are all about layer three they are layer three devices they can handle the ip addresses

that's the language they speak so this is what the router received notice it's from

the mac address that belongs to johnny right here and it's to his interface but then look

what he's sending out and notice what's missing layer two now according to his layer

three map he knows that two two three.227.38.65 is that way but that's layer three he

doesn't know where he lives at layer two and because he's about to send this frame to the switch he doesn't know how

to tell the switch how to get to him and that's important and that's the reason we have this freak out message like i i

don't i don't know what his layer two address is so how does the router find out

well how did johnny find out an art message he says hey where is 23 blah blah and he

broadcast that out watch right next to the freakout message we have the art message right here

from the router to the broadcast and we're looking for anyone that has this ip address

anybody got this anybody out there and let's step forward in time and watch this happen

so he sends the art message to the switch the switch broadcast it out and because the server is the only one that

is on the network he receives it the server's like hey that's my name that's me i'm over

here so he sends the response to the switch the switch is like yeah i know where

this guy is hey router i found him i know that everyone knows where everyone is johnny's ready to send his message so

if you open up johnny's message over here i want you to pick up on this in the

layer 3 header johnny has his ip address as the source the coffee server as the destination but

on the layer 2 level we have his mac address as the source and then the destination is the mac

address of the router so layer 3 right here is directions for the router saying hey router this is

where i want my message to go and then layer 2 right here is directions for the switch saying hey

switch this is where i want my frame to go it's going to go to the router and the router will take care of the rest

let's watch it happen step forward in time the switch receives it if we open that message up we can see it's only

layer 2 because the switch can only see layer 2. it's going straight to the router so we

send it to the router this is so cool isn't it it's amazing let's open up that router's

message and look at that this is the message he received so layer two it's from mark's mac address

to his mac address layer three it's from mark's ip address to networkchuck.coffee's ip address and

now for the outbound message because he learned where the coffee server's mac address is

he can send it out so here's the layer three and then for the switch he's got the directions right here

from his mac address to the coffee server's mac address which ended in one ac7 if you look at that yet

it matches up right there let's watch it happen boom the switch sends it out and the

coffee server got it and then the coffee server replies and sends it back the router

sends it through the switch gets it and then johnny gets it isn't that amazing and this happens millions of

times every day across networks across the world isn't that just crazy now i want to show

you one more thing it's kind of a sneak preview to what we're going to be talking about later but obviously

johnny he wants to order some coffee from networkchuck.coffee but you can't order coffee

by just pinging the web server you have to visit the website and we can do that let's have johnny do that right now so

i'm going to reset everything and we'll get this thing ready this is going to be amazing

don't let this overwhelm you we will go over the details of how this works later on but i just want to i just want

to show you because it's so neat i i can't help myself so we're still in simulation mode let's open up johnny

real quick and instead of going to the command prompt we can go to his web browser so

i'll click on web browser right there and the website is network chuck dot coffee now the main difference here

is that we're not using an ip address at least to start with it's this friendly name that we know we normally

use like facebook.com youtube.com but how does that work we know the switch loves mac addresses

and that's what he talks that's the language he talks layer two the router loves layer three ip

addresses who deals with names like this well the short answer is no one johnny must know the ip address

or rather johnny's computer must know the ip address so when he types this networkcheck.coffee url in there's got

to be some way that his computer can find out what the real ip address is which we just pinged

moments earlier that's called dns and that's what our dns server here is for let's watch it happen

i'll click go and boom oh whoops i forgot to configure the dns server if i go to config

under his uh default gateway we have dns server which stands for domain name service

and i'll put in the ip address of our dns server up there 10.1.1.50 this guy right here so let's go back to

our our web browser and try it again go and here we go all over again we have another art packet because johnny

needs to get the information on networkchuck.coffee he needs to learn the ip address and he knows that this

server the dns server knows the information that's 10.1.1.50 and that's his first job so he has to go

through the process again of learning the mac address of the dns server let's walk through that now

stepping forward in time sends an art message the switch will broadcast that to everyone

the dns server responds because that's his ip address and he's like here's my mac address that's me

the switch sends that to johnny and johnny's like yes so now johnny can send his dns query to

find out where networkchuck.coffee is what's the ip address so he'll get that message ready so we

sends it out it goes to the dns server we'll take a quick little peek inside that real quick and we'll open that up

and a lot of stuff going on there that's the other layers we'll talk about don't worry about that but essentially

the server's like yeah i know where that is here you go johnny here's the information so he sends it to the switch

the switch sends it to johnny johnny learns where this is let's open it up real quick i'll show

you let's open that up and we'll go to the inbound pdu details again don't worry about that

just yet we'll scroll down all the way to the bottom we can see that the information

the dns answer is right here the name networkcheck.coffee and then here's the

response the ip address of our server so we'll step forward in time

johnny will send his http get request we'll cover more on that later to the router to the switch now what you

might be noticing is that we didn't go through the whole process of learning the mac address of the router and the

router learned the mac address of the the coffee server no no it remembered it puts that in its cache

and it stores it so we don't have to do it all over again now i will eventually forget that information so it can

relearn it but again more on that later so let's step forward in time it goes to the

server the server gets it responds back and you know what i'm going to switch to real

time let's open up our web page and there it is you need to drink coffee right now

and there's our website as you can tell it's been expertly designed and by the way that's real if you want to buy my

coffee network coffee it's delicious that's what i'm drinking right now

it's real now i've got this lab and a link below if you didn't follow along with me throughout this go and open it

now and try it for yourself it's really cool to walk through all this and just see it happen like this is

how the internet works this is what what happens when you get on your computer and you go to

youtube.com this process happens this right here is your home router

you're johnny now the real internet isn't this simple right the the real internet is a is

going to be like this router connected to another router connected to another

router connected to another router and then eventually getting to my coffee website as we covered in the first video

but the process is still the same the router is connecting these two separate networks i remember

when i say network i'm referring to the ip addresses layer 3. these guys over here have a different

group of ip addresses than these guys over here your home network will be a different group of ip addresses from

the rest of the world and that's why you need a router to connect to the internet and inside of this router's brain if you

pop him open he has a map to other networks and to the internet like you know let's take a look

let's have you enter another cisco cli command right now let's pop it open let's do this

i'm going to click on the router we'll jump on over to his cli tab we'll hit enter and then type in enable

to see his map his map of ip addresses and where to reach different networks we'll do

show ip route this is a command that network engineers use all the time you're already doing

networking right now let's hit enter and boom i'm going to expand this out a little bit here

and this might look a little overwhelming but here's all it's saying the group of ip addresses that johnny

belongs to is right here 10.1.1.0 24. that's just a shorthand way referring to

10.1.1.0 through 255. and in the router's map he knows that it's actually directly

connected to his interface gigabit ethernet one or i'm sorry zero zero and the same goes

for my coffee network over here there's the network and again it's a shorthand way of saying 23.227.38.03255. and

that's actually directly connected to gigabit 01. so when johnny said hey i want some coffee i want to order it

right now and he sent his packet to the router saying here it is i want to go to this

guy the router's like oh well let me check my map oh there it is there's the network it's

actually connected to my gigabit zero one interface i'm gonna send it out that interface

that's how the router knew now this is very simplistic routing routing gets crazy like if you were to look at a

router on the internet you know let me show you real quick this is actually one of the routers on the

internet check this out i'll enter the command show bgp which is a routing protocol

we'll learn more about those later ipv4 unicast and let's see what we got and all of

these are routes to different networks on the internet like i can keep going i mean look at this this is insane

this is this router's map this router is probably huge very expensive router but this is an example of a how

big the internet is and b what a router can do why it's so powerful all right we'll never reach the

end of this i'm just going to stop and that was episode two now i changed it from days to episodes

makes more sense for me if you have any comments or questions let me know below i would love to hear your feedback on

this if you need help don't be shy ask some questions below either myself or some

others will join in and help you out or hey join my discord we've got so many professionals in there who are willing

to help out with really any questions you have and if you want to help me do more of this

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below by joining you help us create more free content there's also some amazing content on the site

for myself david and and others coming very soon not to mention if you're a this is it army member you're gonna have

your names at the end of this video so look at it and if you haven't already try some networks coffee

the official copy of the ccna i'm gonna claim it that's what's happening right now

and of course a huge thank you to boson software for sponsoring this free ccna course they're the reason this can

be made free so go check them out and enter my contest below alright that's all i've got episode two

done i'll see you in episode three [Music]