Connecting Ethernet Scenarios

The current exam has a lot of questions and talk about different types of
scenarios.

So in this episode I want to concentrate on the different situations we can run

into when we're connecting either net in particular the many ways we can mess up
when it comes to connecting lots and lots of switches.

So let's go and get started in a few scenarios.

I'm thinking like the first one might be something that has to do with loops.

All right now I've got a pretty standard set up here what I've got is I've got a
router with a built in switch it's going out to the cloud.

Are you guys watching this video.

Don't see it but the people in my production think clouds are so terrible they're
literally giggling at me.

It's a cloud.

Trust me.

So this is going to happen after the Internet but since we're talking about loop's
scenarios I really want to concentrate over here.

So what I've got is I've got two switches that are connecting to a switch so the
switch could be in my main distribution frame.

This will be connected to my customer premises equipment whatever it might be.

But these guys are going to say maybe different floors.

It doesn't really matter.

So this setup is pretty straightforward.

All these individual connections are going out to individual computers.

Now let's just say I addles smaller switch here.

Now the switches.

Maybe I'm just using it for my own I.T. uses or something.

Now I can go ahead and connect that and the beautiful part about switches is you
can connect and pretty much any way you want with one big exception.

What I would need to avoid is creating a loop like this

what I do when I create something like this.

I create what's known as a bridging loop and without anything else to protect us
data we'll start zooming around infinitely and it will literally take down the
entire broadcast domain.

So this is something we want to avoid now.

Luckily for us many many years ago a protocol called spanning tree protocol or T.P.
was developed expressly to avoid these types of bridging loops and most switches.

It's simply a matter of just turning it on.

In fact in a lot of managed switches you can't even really turn it off easily.

And what will happen in these scenarios is that before a bridge comes along what
one of the switches usually this switch will become what's known as the root
switch.

This is all done automatically.

All we have to do is connect the switches and as long as they're all as t.p.

This takes place without any interference from us whatsoever.

So he'll call himself the root switch and we'll then watch any type of data that
goes through in any type of situation.

And what will take place is that a bridge loop is a pretty obvious thing you have a
phenomenal amount of data that's pouring through.

And what would take place.

Well let me reconnect that sort of take place is that the routes which will then
automatically without any interference from us simply turn off one of its ports.

So it's actually pretty cool the way SDP works.

And if you look at the scenario carefully even with this turned off the switches
are still properly connected and all the switches keep on working.

So SDP is the way we avoid bridging loops now.

The one problem we run into is that there is a very similar type of functionality.

It's not really looping functionality but it comes in at about this level so I want
to mention it right now.

So let's just say I've got some evil box on my network right here.

Now this evil box has a problem and the problem is is that he is doing naughty
things to my broadcast domain.

This naughty box is sending out spurious and evil information.

He is using MAC address information to create in essence denial of service

situations.

He's flooding my network with all kinds of evil stuff.

And this is usually done for denial of service or man in the middle type of
attacks.

Now also keep in mind this is a layer to attack.

This isn't something that's being happened by some guy way overseas.
This type of attack requires a physical connection to your local area network.

So it's particularly nefarious anyway and these types of situations we create

what's known as a flood.

So a flood is a bad thing that happens within our networks.

What we need are smart switches that provide a type of flood guard to prevent this
type of thing.

Now these types of controls are very very similar at least in terms of function as
spanning tree protocol because their main thing that they do is turn off ports.

So in this type of scenario if we have smart enough switches they can actually
detect incoming MAC address flooding other types of denial of service attacks and
simply turn the port off.

So while protection from bridging loops and protection from floods are in essence
two very different technologies.

The reality is they both work the same way.

They turn off ports until somebody can come in and turn it back on.

Once the system is back up and running normally Kaante It cracks me up with some of
the types of scenarios they bring up in one type of scenario.

It really wouldn't happen any more but since it's on the exam we're going to go
ahead and cover it.

Let's take a look at a situation where you're trying to take a very old switch and
plug it into a very new network here's a situation where I've got a will say this
guy on the left is a very new switch.

It's a 10 gigabit Ethernet switch.

Now the downside to this switch.

This is fairly rare but in this particular switch the only thing it can do is 10
gigabit ethernet.

That's it.

It can't do anything else.

Most switches today are auto sensing.

So if I have a gigabit Ethernet switch and I plug a 10 base t switch into it.

In most cases that high speed switch will Saluda on whenever it's talking to the
slower switch to take care of the speed differences.

But there are situations where this can come into play.

For example in this particular example I've got a very old 100 base switch and in
this particular case I mean they're all Arjay 45 connections and I just want to
plug them in.
So as we would normally do we're going to plug them in in this particular situation
we have this is just a regular switch regular port to regular port.

These are not auto sensing ports.

So we use a crossover cable in this particular scenario.

And all of a sudden it doesn't work.

What you're looking at here is a speed problem.

This is a rare thing today and with so many switches auto sensing and auto speeding
this is a rare scenario.

However for the exam this is something you want to watch out for.

This can be a very tricky problem to diagnose because most of the time when you
have a speed mismatch either.

Absolutely nothing is going to happen.

You won't even have a link like that would be a interesting one.

But the only other real way to tell is that the speed lights on these two different
ports will show up as different speeds in that particular case.

There's nothing you can do but you probably want to junk this old guy and get
something a little bit more modern.

OK.

Here's a situation where I have four switches now in this particular case.

Two of these switches are regular 100 based T switches.

No problem there.

These two switches up here are also 100 based T.

But there's a little bit of a trick in this case.

If you look very very carefully you'll see each one of these has a dedicated one
gigabit port now dedicated high speed ports while they are becoming less common
today.

You'll still see them on a lot of different types of switches.

The trick is being able to wire these properly what you don't want to do in these
scenarios is end up with speed differences that you don't want to take advantage of
even if this one gig can go down to 100.

If you're spending the money for a high speed port you might as well be using it.

So in a situation like this what I would probably be doing is I would be connecting

to 1 gig ports on each of these switches and treating that is like a little mini
backbone.

And once I have that backbone then I can go ahead and make interconnections between
switches something like this.
Personally though if I had a setup like this what I would be doing is I'd get rid
of these I'd put in for the switches with the 1 gig and then have another a fifth
switch act as my backbone.

That's a one gigabit switch and plug all the one gigabit ports into that one
backbone switch.

Not because it wouldn't work but because we want to take advantage of the speed
that we have.

We don't want to be wasteful of a good gigabit port.

One thing I love about modern switches is the concept of auto sensing is pretty
much built into just about all switches today.

If you connect two switches together the days of worried about uplink ports and
crossover cables has pretty much faded.

However this is a common question that Theo likes to ask.

So lets go over a scenario where uplink ports and crossover cables might be the
solution to a scenario.

We've got a situation here where I've got four computers that are connected on a
network.

These two computers connected to this which are able to communicate just fine.

These two computers connected on this which are also able to communicate just fine.

However they can't talk across the switches to each other.

So these guys can't talk to these guys and these guys can't talk to these guys.

First of all when you're running into network scenarios not just on comp exams but
in the real world.

Take advantage of big clues like this.

Where would the problem be if these guys can talk to each other but not to these
guys.

You should be automatically thinking about the interconnection between those.

So not to digress too much but a lot of times on these come exams thinking about
where the weak spot can be where the fault can be is often the big first step to
getting that answer right.

Anyway taking a look at this in this particular case I'm going to tell you that
this is just a regular straight through cable that we've plugged in in this
particular situation.

These switches don't like that.

If you take a look.

These are kind of older school switches that have uplink ports on it.
And these types of situations you're going to have to make some choices if you run
into a switch that still has an uplink port.

You can take a straight through cable go to any regular port to an uplink port.

That's one way to do it.

Secondly you could go the uplink port to a regular port here using a straight
through cable.

I'm going to use an uplink port if it's there for me but if you don't want to use
the uplink port then just use a crossover cable.

In that case take from one regular port to another regular port with a crossover
cable and those two switches will start to talk.

And yes because somebody always asked this question Mike could I take a crossover
cable and run from uplink port to uplink port.

You can but if I ever see it I will tease you mercilessly.

The great thing about modern ethernet switches is that everything today is full
duplex.

When you are working with these switches whenever you have an individual computer
you just plug it in and it will auto negotiate the best possible speed it can get
and pretty much all the best speeds today will go full duplex.

However there is one situation left where you might run into what we called duplex
problems and to show you that we don't even need a switch.

Here's a simple situation where I've got two computers this actually happened to me
not that long ago I was on a flight and I wanted to talk to my buddy's computer who
was sitting right next to me and he's like well how can we network these things at
36000 feet.

And I said not a problem.

And I pulled out a piece of cable but it wasn't just a regular piece of cable it
was a crossover cable.

What I did is I connected the two computers together.

No switch no nothing directly together with a crossover cable.

Knowing that it would work but it didn't work.

The problem I ran into and this happens a lot these days with you know Windows 10
and such is that these guys will try to negotiate the best possible speed which is
always going to be full duplex.

And here is one situation where we're actually going to intentionally change the
duplex from full to a half duplex in this one scenario.

You need to go into device manager find your network card click on its properties
and scroll through.

And instead of just letting it go to auto negotiate put it on half duplex by

putting on half duplex.
Each computer will automatically show up in the other computers network
neighborhood.

Pretty neat feature.

Spanning Tree Protocol (STP)

Proper switch configuration will avoid bridging loops

Match switch speeds to network speeds to avoid a slowdown due to speed mismatch

Most current switches autodetect, eliminating crossover and uplink cable

requirements