Network infrastructure devices.
Now, for the Network plus exam, you have to be able
to identify network infrastructure devices.
This means you have to identify their icons
as well as knowing what they do,
what broadcast domains are going to break up
and what collision domains they're going to break up.
We're going to talk about all of that in this lesson.
Now, the primary devices that we use in our networks today
are routers and switches.
These devices actually evolve from bridges and hubs.
And we're going to talk about this by starting out with hubs
and working our way towards more modern things.
Now as we look at hubs, hubs are a layer one device.
They are a physical device.
They're used to connect multiple network devices
and workstations together.
You can identify them by a square icon
with an arrow pointing in both directions
when you see 'em on a chart.
These are known as multi-port repeaters.
Now, there are basically three different types of hubs.
We have passive hubs, active hubs and smart hubs.
A passive hub is simply going to repeat the signal,
but it's going to give no amplification.
Think about this, like a splitter.
If I have an eight port hub
and something comes in one port, it's going to go ahead
and pass it out to all the other ports
ports two through seven.
Now, if I have an active hub,
it's going to do exactly the same thing,
but the difference is, it's going to take the signal it got in
and it's going to boost it back up and then send it out.
Now what I mean here when I talk about boosting the signal,
is trying to overcome that 100 meter limitation
that we have with twisted pair cabling.
Because twisted pair can only go 100 meters
if you hit a passive hub, guess what?
That's still part of your 100 meters.
So if I have a 100 meter cable, a passive hub
and a 50 meter cable, it treats it like it's 150 meter cable
and your network's not going to work well.
So if you need to go long distances, you need an active hub
because it gets power, takes that signal in,
boosts it back up and restarts that 100 meter count for you.
Now, for example, my office building here
is 300 meters in length.
I can only go 100 meters with Cat5
so I might go 60 or 70 meters,
then put an active hub in there.
Then I can go another 60 or 70 meters,
put another active hub in there,
then go another 60 or 70 meters, put an active hub in there.
And every time I do it, it restarts that 100 meter limit.
Now notice I only went 60 to 70 meters
and then put the hub in there.
Why is that? Well, it's just the best practice.
If you only use 60 to 70% of that cable length,
it's going to make sure you're not coming up
towards that 100 meters, because sometimes
you just don't count things right and you might go over
and then your network's going to have problems.
So I like to keep it much further away than 100 meters.
But again, if you're using a passive hub,
all of those connections would've been added together
and it would've had about 300 meters of cable
and it wouldn't work.
Now, if I had three 60s in there,
that's going to be 180 meters of cable,
but if I put that active hub in there each time
I have 60 and 60 and 60.
And so it's not 180, it's three 60s that way.
Now the third thing we talked about is a smart hub.
And a smart hub is an active hub,
but it has enhanced features
like simple network management protocol
so that I can actively control that hub
and configure it from a distance.
It's not just a dumb device,
but it adds a little bit of intelligence this way.
Overall though, in modern networks,
you are not going to see hubs.
Almost exclusively, we're going to use switches
and I'm going to show you why in just a few minutes.
The next thing we need to talk about here though
is collision domains.
When I talk about a hub, it is a layer one device.
And like I said, it's dumb.
All it does is repeat what it's told.
And because it can be used to connect
multiple network segments together, guess what we do?
We're actually going to make a bigger collision domain
by doing that.
Let's say we want to take five or six computers
and make 'em all talk together.
Well, we need a hub to do that.
Each land segment then becomes a separate collision domain.
But, hubs don't break up collision domains
instead, they connect them.
So if I use this diagram here,
you can see that there are two four port hubs.
I have three machines on the left side
and they're talking to one hub.
I have two machines on the right side
and they're talking to their hub
and the hubs are communicating together.
This is as if all of these devices
were on one long bus cable.
They're all treated as one large collision domain.
And that becomes a big issue as we get into bigger networks
and we start putting in a 24 port hub or a 48 port hub
because all these machines start to talk at the same time
and we're going to have a lot of collisions.
So how do I fix that?
Well, that introduces the concept of a bridge.
A bridge is going to analyze
the source Mac address in the frame
and it's going to populate an internal Mac address table.
Based on that table, it's going to make forwarding decisions
based on the destination Mac in those frames,
because this is a layer two device.
In our earlier example, we had six machines on two hubs.
I can now put a bridge in between them
and break them up into two pieces.
This information will allow it to only go across
when it needs to, based on its Mac address.
If instead, it just wants to talk
to another PC that's on the hub it's sharing,
it never even has to go to that bridge
and those three machines on the left
will never hear the communication.
This adds security and efficiency to our network
and it breaks up that collision domain into two parts.
If I take a hub and I take a bridge
and I marry them together, guess what I get?
I get a switch.
A switch is a layer two device, just like a bridge.
It's used to connect multiple network segments together,
just like a hub.
Essentially, I want you to think of a switch
as a multi-port bridge.
It's going to have every single port
act as if it was a hub, with a bridge on every port.
This way it breaks up the collision domain
into a single collision domain for each and every port.
It's going to learn the Mac addresses
of the things that are touching that port
and it's going to make forwarding decisions
based on those Mac addresses, just like a bridge would.
It's going to analyze the source Mac address
and that's going to decide where to send the information
based on its internal table, just like a bridge would.
So when I have a switch, each port on there
is going to represent an individual collision domain,
but everything on that switch
is all part of the same broadcast domain.
Now, let's talk about how this works in the real world
when we're dealing with a switch.
Now, let's say I'm sitting here at PC1
and I want to take remote control of the server
by using SSH or Secure Shell, how can I do that?
If I'm sitting here on PC1
and I have a Mac address, let's say, of 12 Bs, I want to talk
to the server who has a Mac address of all 12 Cs.
I'm going to refer to PC1s Mac address as BB
and server's Mac address as CC for simplicity's sake
as I go through and talk in this lesson.
Now notice I have the switch tables at the bottom
and right now they are empty.
They don't even know who's connected to them.
But when PC1 talks the first time, its Mac address of BB
says to switch one, hey, I want to talk to server CC.
So it sends out a thing called an ARP packet.
That ARP packet is going to go to switch one
and check its table.
If the table sees it and says,
well, I don't know how to get to CC,
so I'm going to push out that ARP packet to every other port
that I have on my switch and see if I can find it for you.
Now, before the switch starts pushing that information out
to try to find CC, it does know one thing for certain,
it knows where BB is, because it just talked to it.
So since BB came up on port 0/1,
it wants to put that in its table.
And then it's going to push out
the ARP packet to everyone else.
So PC2 then says, hey, I'm not CC,
so I'm going to ignore you.
PC5 goes, I'm not CC and it ignores the switch as well.
Switch two goes, hmm, I don't know who CC is,
but even though it's not in my Mac address table,
I'll forward that out to all the other people on my switch
and see if I can find it.
That's the idea here. That's what we do with a broadcast.
So it sends it out to its broadcast domain,
which has PC3, PC4 and server
and the ARP packet goes out.
And it goes, hey, I also learned
that switch one knows where BB is,
so I'm going to put that in my port table
So if people ask me for BB, I know who to talk to.
And as the ARP goes out,
it goes out to all of the servers and all of the PCs.
The server goes, oh, hey, I'm CC
so it responds with an ARP packet back to switch two
and says, hey, CC, that's me
you should send me all that traffic.
So what is switch two going to do?
It's going to populate its table with CC being on port two
and it forwards that back to the requester on switch one.
When switch one gets it, it populates its table
and pushes it back to requester at PC1.
At this point, everyone in the network
got queried to say, who is CC?
And that was a lot of traffic
to figure out who the server was.
That worked pretty much just like a hub,
but at this point, everybody now knows
where CC is and BB is.
And so now that we know that
when PC1 sends out the SSH packet and says,
I want to talk, guess what happens?
It goes to switch one.
And instead of bugging everybody,
switch one only sends it out port 0/2
because it knows that is where CC was.
That gets to switch two and when switch two gets it,
it's going to send it out its port 0/2
because it knows that's where server was.
So now we have a two-way connection that's been established
between the PC and the server through those two switches.
And all of the other PCs out there, PC2, PC3,
PC4, and PC5, they don't hear any of this
and they operate on their own
without dealing with that SSH traffic.
So we have just minimized the amount of bandwidth
that's been eaten up by five or six times
because we removed all that extraneous information,
all the extraneous equipment from this equation.
This is why switches improve our network performance
and our security so much.
And at this point, switch one and two are only sending out
the traffic between PC1 and server across one line.
So PC2, PC3, PC4, PC5, never hear it.
And if PC2 and PC3 wanted to start talking,
they could at the same time
because these switches also support full duplex.
And so I can have a communication
between the server and PC1
and another separate communication between PC2 and PC3
and it's not going to disturb each other.
This is where our efficiency comes in
when we deal with switching.
Now, the next thing we have to deal with is a router,
because when we deal with switches,
we're dealing with layer two devices
we're dealing with Mac addresses.
That's not going to help us if we go across to the internet.
And so if we want to connect to dissimilar networks
like an internal network and an external network,
IE, your LAN and the internet,
then we need to make routing decisions.
To make these forwarding decisions
also known as routing decisions
this is going to be based on logical network information
such as IPv4 or IPv6 and switches aren't aware of that.
Switches only know about layer two and Mac addresses.
Routers are all about layer three and IP addresses.
Routers are much more feature rich
and they support a broader range of interface types as well.
And so you might have a router that has a serial port on it.
It might have a copper RJ45 port on it.
It might have an ST fiber connector on it.
You might have a GBIC or an SPF or a QSPF on it.
These all have multiple connectors where we can use a router
to connect different networks
and even different types across them.
Switches on the other hand tend to be all one.
They're either all fiber or all copper,
depending on which one you buy.
Now, routers have one distinct advantage over a switch
and this is that they can actually separate out
broadcast domains.
Now going back to our earlier example,
I had three PCs on the left and two on the right,
they're talking to those two switches.
Now, if the router wasn't there,
this would be just one big broadcast domain
with five collision domains in it.
Now, because I put a router in there,
I actually have two separate broadcast domains
and that's going to help me reduce
the traffic and reduce the noise.
Now, this is going to lead
to a lot of efficiency in our networks.
We're not going to get into how routers work
at this particular point in time
we will dig into that later in a separate lesson
because there is a lot to cover there.
Now, another thing you may come across
is what's known as a layer three switch.
And this tends to confuse a lot of students
because when we talk about switches being layer two
and routers being layer three,
it's a lot cleaner and easier.
But over time, they decide to make these things
and make these things called layer three switches,
which really muddy the waters.
Now, just like we took hubs and bridges
and we combined them to make a switch,
well, somebody got the idea
of taking a switch and a router and combining them
and they call that a layer three switch.
Layer three switches are layer three devices
that are used to connect multiple networks together
and they can perform routing functions.
Now, they can do routing decisions just like a router
and they can connect network segments just like a switch.
Because they act like a router,
each of their ports is going to act
as its own broadcast domain and its own collision domain.
This is a really efficient way
of doing things on an internal network
because you can use these layer three switches
and do things quickly.
Now, if you have a very large network, though,
I would not recommend
using layer three switches as your router
because they're not as efficient at routing
as a dedicated router would be.
If you're in a small office or a home office environment
and you have 20 or 30 machines, you can replace a router
and a switch with a single layer three switch,
and that will work well and save you some money
because they are cheaper than having two devices
'cause you only need one.
But if you're going to be in a very large network,
I do prefer having a dedicated router
because they are much faster
for large scale routing operations.
Now the last thing I want to talk about here on the screen
is I have a nice little summary chart for you
that's going to show you the five type of devices
that we just talked about.
We talked about hubs and bridges,
switches, multi-layer switches,
also known as layer three switches and routers.
It'll show you all the possible
collision domains that they have
and the possible broadcast domains that they have.
Remember, hubs are just like one shared cable,
one collision, one broadcast,
whereas a bridge adds a collision domain
for each port on that bridge,
and it still has one broadcast.
A switch is just like a bridge
and so it has one purport and one broadcast domain.
Routers and multi-layer switches operate the same way
so you have one port that is a collision domain
and one port is also a broadcast domain.
Now you can see the layer of operations
here on the right side.
Hubs are operating at layer one,
bridges and switches operate at layer two
multi-layer switches, also known as layer three switches
and routers operate at layer three.
Now, one last thing I want to talk about
with multi-layer switches or layer three switches
and it's for the exam.
For the exam, I want you to remember
that anytime they mention a switch,
they are talking almost exclusively
about a layer two switch.
Whenever you hear the word switch on the exam,
always be thinking layer two devices
that are focused on Mac addresses.
If you hear routers, those are layer three devices
and they're focused on IP addresses.
Now, the only exception to this rule
is if the test specifically states in the question
the phrase multi-layer switch or layer three switch.
If they use those terms of multi-layer switch
or layer three switch, then you can treat it like a router.
Otherwise, always treat a switch
as a layer two device for the exam.
This trips up a lot of my students who are used to dealing
with switches in routers in the real world,
because most switches you're going to buy nowadays
in a small office, home office environment
are going to be layer three or multilayer switches.
But for the exam, a switch is a layer two device.