Broadcast Domains
Video Activity
In this lesson, we begin by clarifying how to correctly establish a switch data link count on a physical diagram and how that differs on a logical topology diagram.
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Time
29 hours 18 minutes
Difficulty
Intermediate
Video Description
Broadcast Domain In this lesson, we begin by clarifying how to correctly establish a switch data link count on a physical diagram and how that differs on a logical topology diagram. You'll learn the definition of Transparent Bridging¸ the difference between Collision and Broadcast Domains, whether or not a switch can broadcast a router, and what its met by each port on a switch/router being its own collision domain.
Video Transcription
00:04
we have been talking about the data link clear so far.
00:07
One of the confusions that people have
00:11
with the data link clear and I will clean that up right now is let's say you have a switch.
00:18
Let's call this which one, as always,
00:21
and you have to PC is connected to the switch
00:26
PC Juan
00:28
and
00:30
PC to, and we're not gonna worry about the poor stay connected on
00:34
now. Earlier, I said that the data link lair
00:38
deals with transmission over the local data link, which means
00:42
the link between two devices to directly connected devices.
00:47
Now, people take that to mean that this link between PC one
00:54
and switch one is one data link.
00:58
No, that is incorrect. The switch itself
01:02
is one data link.
01:03
So when you draw the switch out in a diagram
01:07
that is considered a physical diagram
01:11
in a logical diagram, I would draw the same topology
01:15
as such PC one and PC to, And it is assumed that there is a switch in the middle because you really can't buy a wire at best Buy that looks like that.
01:26
So ah, switch is one data link. Everybody connected to that switch all PCs or devices that are connected to that switch are on the same data link.
01:40
So this link between Switch one and PC one No, that's not a data link. The link between PC one and PC to is the same data link,
01:52
which is why
01:53
the whole function off a switch in the process that I described earlier on how Off Switch operates is called transparent bridging.
02:01
So switch is nothing more than a bridge between PC one and PC to and from the point of view of these PCs, it is transparent. To them. It doesn't exist.
02:14
So in a logical topology you will draw out the PCs or the end devices connected to the switch, but not the switch itself.
02:23
Now, having said that, we can move on to the concept off broadcast and collision domains. So first broadcast of
02:38
what is the broadcast on me?
02:39
Well,
02:40
a broadcast domain is the area off a network
02:46
where a broadcast will spread out, too,
02:50
if sent by one device.
02:52
So let's say you have a switch with
02:54
a bunch of
02:55
PC is connected to it, and one PC sends out a broadcast frame. Remember the broadcast frame being one with all F's in the destination portion of the frame.
03:06
How far will that broadcast? Send by one PC Spread out, too.
03:12
So by default, all switches
03:15
aural Cisco switches are one broadcast domain,
03:19
so if you have a switch, it is one whole broadcast domain by default.
03:25
Routers, on the other hand, brake up broadcast. Oh means
03:30
so. A broadcast cannot transfers a router.
03:32
So let's say
03:35
you have a router,
03:37
our denoting a router
03:38
and you have a switch
03:42
attached and some PC. Let's call it P. C. One
03:47
sends out a broadcast frame.
03:51
That frame will reach the router, and the router will drop it by default.
03:55
This broadcast cannot transfer verse
04:00
go across a router,
04:02
so routers break up. Broadcast. Oh means a switch is one big broadcast domain in itself. And, of course, the hub always flood, so hub is one big broadcast don't mean to
04:15
now collision domains
04:17
commit Collision Domains are areas of the network
04:20
where if two devices transmit at the same time
04:26
and they are running half duplex Internet
04:31
and if they're running hard to put Internet and both devices transmit at the same time the frames that those devices send can collide.
04:40
So a collision domain is an area of the network where collisions can occur.
04:46
Now,
04:46
each port on a router and each port on a switch is its own collusion domain.
04:55
So once again, each port on a switch and each port on a row our is its own collision domain.
05:01
Ah, hub is one big collision domain.
05:04
So obvious. One big collision domain. One big broadcast domain.
05:09
A switch is one big broadcast. Oh mean
05:12
and each port on a switch and a router
05:15
is its own collision domain.
05:19
Now, collisions can only happen when you're running half duplex Internet
05:24
Before I draw the diagram
05:27
for broadcasting collision domains, I have to explain what eternity ISS
05:31
Eternity is a layer to protocol that runs at 10 megabits per second
05:38
half duplex.
05:39
So the speed is 10 megabits per second, and it runs at half Duplex, which something called C. S. M. A. C D.
05:46
Which stands for carrier sense multiple access with collision detection.
05:50
So first, let me take care off the duplex part. If it
05:55
Internet runs at half duplex,
05:58
have duplex means that bi directional communication is possible, but only in one direction at a time, and as an example, you can think of a walkie talkie
06:08
with the walkie talkie. Only one person can be talking at a time. Both people can't talk at the same time.
06:15
Full duplex in opposition means bidirectional communication is possible. You can transmit both ways and simultaneously, which is at the same time, and you can think of that as a phone conversation.
06:28
And then you have simplex, which is only unit directional communication but
06:31
not part of the CNN.
06:34
The C S M S C D. Part or carrier sense multiple access with collision detection part
06:41
when you're running half duplex eternity and two devices transmit at the same time. When it's not allowed,
06:46
the frames can collide.
06:48
And when this collision happened, see, SMS CD is constantly listening in on the while.
06:55
And when C. S. M S E. D, which is built into half duplex Ethernet,
06:59
here's a collision. It sends out a jamming signal to all the devices,
07:02
and it asks all the devices to stop transmitting for a randomized time period. So let's say if they have four devices and one of them gets told, do
07:13
stopped transmitting for 10 milliseconds and another one gets told to stop transmitting for 50 and 1/3 1
07:19
for 12 and 1/4 1 400 milliseconds When they try to retransmit, the chances are lesson that they will re transmit at the same time. And hence the collision avoidance comes in. Hence the name
07:32
carrier sense multiple access carrier sense. I'm listening to the wire. Multiple access. More than two people can be on the media or on a switch at the same time
07:44
with collision detection now have said that each port on a switch is its own collision toe.
07:50
So
07:53
is that true? Now it is No, because
07:57
ports on a switch
07:59
by default running full duplex mode.
08:01
So in full duplex Internet bi directional communication can happen at the same time. You don't need C S M a. C D two devices can't transmit at the same time. And collisions won't happen,
08:13
however, since each port on a switch is its own collision domain.
08:18
If you do
08:20
well, if a company does not have the money to spend and they do something like this, they put ah huh on one of the switch ports. And then they put a bunch of PCs
08:31
on this hub
08:33
hubs by default or half to place.
08:35
Then you're gonna have bunch of collisions when these PC strategy transmit through the hull,
08:41
so each port is its own collision domain.
08:43
However, if you connect a hug to one of the port, of course the device is connected to the hub
08:48
will have collisions.
08:50
Now
08:52
I have seen,
08:52
well,
08:54
such a diagram or such a question being asked on the CCN exam, so I'm going to go through it real quick.
09:03
So let's say we have four PCs attached to the switch and then you have a router,
09:09
and then you have, ah, hub on this end and you have to PCs attached to this hub.
09:16
We'll make them PC for
09:18
and P C. Five.
09:20
Now the question would be how many broadcasts and collision domains are in this apology
09:28
or this network diagram Topology being synonymous with network diagram?
09:33
Well,
09:35
since I said, each port on a switch is its own collision domain, and each port on a router H Ethernet port on a router is its own collision domain. We have one collision domain here, one
09:46
then the four ports that are connected to the PCs 2345 And then this side, since it as a hub is one big collision domain.
09:56
So we have six
10:00
collision domains. How about broadcast? Oh, means, well, let's say PC to sends a broadcast out.
10:05
How far will that broadcast Spread
10:09
PC 13 and four will get that broadcast, and the router will get hit with that broadcast. But the router will not allow it to transfers.
10:18
So you have one collision broadcast domain on this side. You're one broadcast domain on
10:24
my left hand side of the router
10:26
and then one broadcast domain on the right hand side of the road.
10:31
So
10:31
in this topology, you have
10:35
two
10:39
broadcast
10:43
domains
10:43
by default. Remember, I keep saying by default, and that's for a reason.
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