# Switching Logic and Concepts

Video Activity
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Time
23 hours 18 minutes
Difficulty
Beginner
CEU/CPE
23
Video Transcription
00:01
Hello and welcome back to Ice and the one interconnecting Cisco networking devices. Part one. This is Episode 2 to 2. Switching logic and concepts. I'm Trenton, Karen. I'll be restructured for this course in the last video would win over the Lesson 2.2 overview and did a few pre assessment questions
00:17
this episode of recovering the layer to switch fording logic.
00:22
All right, so learning objectives for this we're gonna go over the 40 logics. We're gonna look at how the switches determine where to send the frames and just do a few quick examples.
00:33
So quick pre assessment here before begin.
00:36
Where do you think a switch or what do you think of switch uses to determine where to send a frame? Hopefully remember this from the pre assessment. Give you just a second.
00:47
All right, remember, uses that destination back address.
00:52
All right, so switches remember, they are primarily layer two devices. Sometimes later. Three will go over that later. But for now, think of them as Larry two devices. The primary role is to Ford Frames to the correct destination Mac address, right? You want to go from point A to point B and What it does is uses that Ethan a header. The Layer two header,
01:11
which has the destination Mac address.
01:12
Okay,
01:14
so in case you don't know, I'll draw out. Kind off.
01:19
What? My devices are here.
01:22
All right, so here
01:26
are my routers.
01:30
I have a couple access points.
01:34
Maybe that's a look. That was up. I haven't played with him yet.
01:37
I have my essay are addictive security appliance.
01:42
This is actually my raspberry pi d n a server
01:47
used from a main rotor. And this bunch here is my switches
01:55
these up to is actually some p o. He switches
01:59
get curious the power over Ethan, so they'll power up those access points and
02:04
things like that.
02:07
It's a little bit to switch for 40 logic. So when when it comes in and wants to decide if it wants that Ford or not afford by not fording is actually gonna be filtering that Mac
02:19
filtering that frame
02:21
that's based on the destination Mac address. So it afford. It looked at the Mac address table determines if it has entries. If it doesn't have an entry, what it's gonna do is just flood that frame out so it sends out all ports except for the one that it came in on. Right?
02:37
So if it doesn't have an entering the Mac table, floods out all ports except for the one that came in.
02:44
If it goes seven entry, it'll go out. That interface that's in the Mac address table,
02:47
if by filtering which would be not afford, would mean that
02:53
the frame comes in on fast Ethernet 0 24
03:00
and it looks in the Mac address today. One says, Okay for this Mac, I need to go out fast. Ethernet 0 24 So it'll just discard that frame
03:08
because it knows that it already came in on that interface.
03:13
So that's what happens if you know, for some reason that the switch that afford it from, or maybe if you have a hab over on that side that is connected to
03:22
that, you know that Hubble broadcast out off frames
03:25
and the switch will say Okay, well, this device should have gotten it already. So
03:30
then another way that we switches will use ah, spanning tree protocol, and that's to avoid loops. So we'll go over that little bit. The next episode.
03:39
We'll see it a little later.
03:45
All rights affording unit cast for him. So, you know, cast remember is a 1 to 1
03:50
frame. So point a to point B. That's it.
03:54
So what happens here is after the switches place the computer into the Mac address table like officer right there.
04:00
Um,
04:01
and then a packet comes in destined for an R P. C. The switch is gonna consult that Mac table or Mac addressed it will see where that destination Mac is. And like I said, if it doesn't know where to send it,
04:12
it's gonna flood that frame out. All pours except for the one that it came in on.
04:16
What if it does have that entry in the Mac address date? What's on Lee gonna send out that one interface and on Lee, that one interface.
04:25
So here we'll go over a quick example Here, I'm gonna go over a few examples,
04:30
so let's say we have
04:34
We want to go from here to here. We're gonna send these to it
04:39
04:41
So you see that these are already in the Mac address table here,
04:46
so it just goes out,
04:47
you know, it comes in F A 01 says Okay, I have an entry for a B B B. I'm gonna send it out F a zero to
04:56
Right.
04:59
So let's say he,
05:00
uh let's say computer one here at a A wants to send it over to the far right computer over here to D d d.
05:10
The
05:11
frame is gonna come in. He's gonna look at the table and say, OK, we need to go out F 80 23 here.
05:18
I'm gonna go out here. He's going to see the frame destined for Dee Dee Dee
05:24
and say, OK, where do I need to go? I need to go to F A 01
05:28
Send it out here
05:30
and let's say we go from D D d. He says, Okay, I need to send something to the bottom computer. Don't on CCC.
05:38
So it's gonna happen as he sends it down here. It says, Okay, got f a 0 23
05:44
We're here,
05:45
and what this one is actually going to do is it's gonna fill in this
05:49
anchor filling this Mac table entry
05:54
with this
05:55
entry because it doesn't have one for DDD yet,
05:59
so it actually will know where to send it.
06:02
It was like. Okay, cool. We have in our entry,
06:06
so that one will get replied. There.
06:10
Now, let's say this computer CCC wants to send a frame to computer. Eh, Eh?
06:16
What's gonna happen is gonna come into here.
06:20
He's not gonna know where to send it, because, Okay, we have no entry over here for a A.
06:26
So he's just gonna say, OK, go every port,
06:30
he's got every port here,
06:33
and he's just gonna say Okay,
06:35
well, I went for a come back over here.
06:39
Go this way. He's gonna come over here. We're going for a And now we have two friend to the exact same frames
06:46
coming in or a
06:48
what? If you have computers that don't know, we're gonna go here, then here, here, in back over here. Just gonna create a huge loops. So that's where spanning tree actually comes in. And again, we're gonna go that in the next episode, I'll show you why we use banditry and how that's useful. What? It actually does a little bit.
07:08
All right, so quick. Post assessment here.
07:11
What happens if a friend comes into a switch and the destination Mac is not in the camp table?
07:16
So what happens to it? Think about it. We just went over there for a second.
07:26
All right? It's gonna flood out. All the interface is, except for the one that came in on
07:33
are in the next episode. We're gonna look at the learning Mac addresses and what it doesn't flooding the frames.
07:40
And as always, if you guys have questions, wanna say How are you going to shoot me? A message? Otherwise, thank you for watching this episode. And I look forward to teaching. Interested? Thank you.
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