Part 05 - Layer 2 Data Link Part II Switches

Video Activity

In this section we revisit hubs and examine their limitations in the context of layers one through three. This discussion will set things up for the higher-level functions that occur at layer 3. Hubs are layer 1 devices that are pretty much obsolete these days with the widespread availability of inexpensive layer 2 switches. The primary limitation ...

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Time
12 hours 41 minutes
Difficulty
Advanced
CEU/CPE
13
Video Description

In this section we revisit hubs and examine their limitations in the context of layers one through three. This discussion will set things up for the higher-level functions that occur at layer 3. Hubs are layer 1 devices that are pretty much obsolete these days with the widespread availability of inexpensive layer 2 switches. The primary limitation of hubs is that they send data out of all ports. This results in multiple collision domains on a single device, which is highly inefficient, not to mention very insecure. Layer 2 switches have the ability to direct traffic based upon layer 2 MAC addresses. This provides immediate relief in terms of data collisions by providing a single collision domain and isolation at the port level. However, broadcast isolation is not possible with layer 2 switches and network congestion is still present. Routers are the solution to this issue and we'll have a look at them in the next section covering Layer 3 of the OSI reference model.

Video Transcription
00:04
Okay. Now, the second part of the data link layer, because really, we talk about media access control. We talked about the LLC layer, you know, kind of the the softer side, the software side off battling. But let's talk about hardware little bit. Now. I didn't spend a ton of time
00:21
in layer one talking about a hub because hubs air really obsolete.
00:25
The reason hubs are obsolete is, um
00:29
it will for a couple of reasons. First of all,
00:32
ah, hub is a layer one device that sends all data out all ports, all the con. So think about Mia's an attacker, any pork that I plug into on a hub. I have access to all the data, every system that's plugged into that home and in older environments, we would go Hup two hup two hub.
00:51
So I might have access to
00:53
dozens of computers. Dad is perhaps data, perhaps even more so from a security perspective, that was a very bad thing. But also from a traffic perspective. Ah, Hub. Sending all that out, all ports, all the time. Every system plugged into a hub was competing with each other for time on the cable.
01:11
If you'll remember. We talked about
01:14
Carrier Sense multiple access with collision detection. So what that meant was
01:19
carrier sense the network hardwood since the cable, since the media and determined cannot transmit now. But when you have ah, hub environment, especially Hup two hup two hup. So many systems are competing with each other for time on the cable that you're just gonna have collision after collision after collision.
01:38
Remember, The other thing that I said is the best thing I have ever did.
01:42
Ah huh, did cheat.
01:45
That's why we said, Well, I want a hub here because it was cheap. Well, with the f it of Netgear and Lexus switches that were cheap. And, you know, you could get a switch today for 35 40 bucks. The price of a hum. Now we don't really need hubs because I have switches that are cheap that do a lot more than hubs, too.
02:02
So the reason hubs are obsolete is there security nightmare
02:06
and they're no longer the cheapest fame in town. Okay, I could get a lot more functionality for the same calls from a switch. So what is that functionality? What is it that a switch gives me that I didn't get with a hub.
02:17
Well, two big things. First of all, I get traffic addressing based on Mac addresses, so that's very big. That's very, very significant. That's very important,
02:27
because a switch sort of acts like a police officer at an intersection, directing, directing traffic out the appropriate port. Remember Hub all data out all ports all the time, But that switching says Instead says traffic for computers. Ego out Port one. Traffic for computer Q. Go out Port 13.
02:46
So that's very helpful for directing traffic. But a big impact that a switch gives us is the reduction in collisions in every port on a switch is its own collision to May.
02:58
Okay, so
03:00
what we do today, You know, at one point time we plug our hubs into switches to reduce collision domains. But now we plug. Our systems are PC is directly and reports on the Swiss the switches. So each PC has its own port on the switch,
03:14
each port on the switches, its own collision domain. So we've all but eliminated collision traffic simply by using switches and again because the switches air so cheap today. Ah, we get the cheap benefit of Ah huh. But we get collision domain isolation,
03:31
and we also get Mac addresses. So that's really, really important.
03:36
Now the one piece that we do not get is we do not get broadcast isolation.
03:42
A. So broadcasts. A lot of applications are very broadcast driven,
03:47
right? Um, and a lot of service is air broadcasts driven. Earlier, we talked about art and we talked about art being addressed. Resolution protocol. It's a way for a system to find the Mac address of another system.
04:02
Well, you know, I like as people
04:05
our broadcast good or bad.
04:09
And the answer is yes, they were good or bad or more accurately, they're good and bad.
04:14
Um, broadcast clog up the network. You know, if if I you know, if you look at this illustration here, if this top computer has an application that's broadcast based,
04:25
maybe ah, these two guys are in the sales to Maine, Let's say,
04:29
and there's a sales application that's very broadcast intensive.
04:33
Everybody on this network is going to get that broadcasts and they don't clog things up. But we can't
04:40
right now with the current environment, totally get rid of broadcast because address resolution protocol idiot, she feed lots of service is do rely on broadcast so we're not looking to totally eliminate them, at least not yet. That's one of the things that I p Version six is going to do.
04:57
They're gonna replace Broadcast remains our broadcast with what are called any casts with your little more efficient. But
05:02
that's beyond where we're going right now. So bottom line is a switch does not isolate broadcast traffic.
05:10
Ah, switch isolates collision domains and uses Mac addresses.
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