Layer 2 Switch Operations

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Section three, layer two switch operation. Alright, welcome back everyone. Now we're going to go ahead and get into layer two, switch operations, which is kind of funny name that they're given it but okay. Ah we understand how things how switches learn. Okay, so we do understand that. All right, but we need to again go back to the basics and assured me in our network we use the following csma CD.

I shouldn't have to explain this to you. I'll just do this real quick. We know that CAC csma CD, works on Ethernet period, whether you have a home or switch bridge, whatever I first call for sir, the first person that gets to the wire gets to send their frame out. All right, if a collision occurs, meaning by whatever, look to two frames on the wall at the same time, then you actually get this collision. Everybody backs off. Everybody waits a certain period of time.

And then you get to transmit again. That's the estimate city collision. Oh, wow, carrier sense multiple access collision detection. Okay. And here it is one of the problems with this, obviously, a lot of collision occurs. But when you're using switches and we VLAN them out, you don't have that issue.

We're in a shared collision domain, you have half duplex, you don't have the full bandwidth coming out of each port at all times. Okay. And then obviously, needless to say bandwidth is reduced because of that. So if you think you're getting 100 megabits per second and thousand megabits per second, you're not, the more things you plug in in a shared collision environment. Okay, you're going to go ahead and diminish. The bandwidth.

Alright, now layer two switching decisions about forwarding are based on destination MAC addresses, we know, we know that switches at layer two, okay. They learn source addresses. Now within that frame, obviously there's the destination MAC address as well. But worse as you either know switch provides isolation between connected hosts in several ways. First of all the collision domain scope is limited, meaning everybody's in their own collision domain. Full Duplex obviously is now available to you.

Okay, because it's a private collision domain. So you have the full duplex you can send and receive at the same time, errors and frames are not propagated. Why? Because it's using that method that I said earlier, is using the store and forward meaning it will take in the entire frame. store it, and then making sure it's okay. And then it forwards it out to whatever port.

Now you can limit its broadcast and other types of filtering or forwarding become possible become possible due to this. Okay. But again, one thing I need you to focus on because even in the CCNA and CCNP, there's actually conditions are about 40 are based on destination MAC addresses. Yes. Where is it going? We'll look at the destination MAC address, because that's what they want you to look at.

Where's this coming from? Where's it going to? You gotta look at the destination MAC address for that particular asset. Okay, now layer two switches basically a multi port transparent bridge. Yes, each port is his own land segment. Of course, it could be.

It has its own collision domain. villain does verbiage confuse you? Because when I see this as a line segment, what am I gonna mean line segment That's the only way you're gonna have 24 VLANs and 124 port switch. No, it just means its own its own collision domain. That's it. It will use a store and forward frame technology.

Remember there's code through and there's another one which I still don't remember okay? But this is all old stuff, okay. But now using sort of four which is good all that means is that it just waits for the whole frame to get in the switch and then send it out. Okay, switches will not forward any frame unless it knows the destination MAC address. If it does not know the destination MAC address, what do you think? If it doesn't know words, you know going to, alright, that is going to flood all the ports except the one it's learned the source MAC from in order to find that destination.

This is called unicast unicast flooding. We know this. There's not new information to us. We know that layer two switches do this. They don't know. They're not aware what port this destination MAC addresses.

They send out a flood on Yeah, Hey, who's the owner of this? And then they'll come back with a reply. So always switches color MAC addresses statically or dynamically and of course, you know about sticky you know about taking straggling means you statically go in there and you type pay this MAC address is going on this port, not feasible, not feasible. All switches, learn dynamically MAC addresses, they do this, but they're volatile, they'll switch every time. So using the sticky command which you have, which I've shown in the CCNA. Okay, using the sticky command, you can go ahead and say, Hey, this MAC address or this port will allow us you know, As soon as I switch port security features what it is.

So as far as security, Mac sticky, meaning it's going to learn it dynamically, but now, it's going to be there permanently stuck on that port. Right, which is a security feature. So if anybody takes it out, cuz you know about the violation and all that, but you switches learning dynamically, by default, the learning MAC addresses dynamically, I want to host is attached to that particular switch. It literally had first has to go through the switch. So the switch can say, Okay, here's that source address. Where's that destination MAC address, where what port Am I going to map it to?

But if you use thinking, one of the good things about that is that hey, because you do it based on the range of ports you do within the ports, you put in that sticky come in, it's going to learn dynamically, but they're going to make it permanent is going to show up as a statically assigned MAC address. And that's all for security. purposes, that's all. Alright, ah decisions are made simultaneously by independent portions of switching hardware. So yes, layer two forwarding table, obviously, security ACLs and then QoS. And really this comes into play when we're doing especially voice voice.

Here's what a new table that you never heard of before. You heard of the cam, which is the MAC address table. But now you had the T cam table lookups that have occurred the frame in this place into the appropriate egress queue on the appropriate outbound switchboard. All that is all that is, is okay. I've learned this MAC address through this Ingress, because they came into the switch word I put this destination MAC address so I know where the egress or the outside the exit is. That's it.

That's all it's saying. I learned through this incoming port, whereas the outgoing port, so I don't know how to put it as using these two Particular tables to do so to do so. Okay. And we'll get into more information about t cam tables and all that. So don't worry. Okay.

Oh, we got a blank screen. All right. So that's basically it. But again, we know we know already how switches actually learn. We know this, okay? And they learn source MAC addresses, and they all know their destination MAC address, they'll go out and float out of every other port.

Okay, until he gets a reply except the port it's in. Alright, so that's it. Those who aren't gone to the next one. See you there.

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