8 hours 19 minutes
with our next section network connectivity devices. We're going to talk about devices that help us join systems together. So that way we can communicate.
I'm going to start out with hubs. I'm going to start out the way things used to be because I really do think it helps us understand the benefit of the devices that we're using today
up at the top, where you see Layer one that refers back to the OSI model,
the first device we're going to talk about as a hub. When I came into computer back in the nineties, hubs were very, very popular. They were a good, quick, easy way to connect a bunch of computers, and that was it. That was the benefit, that they were cheap and easy, and they would provide connectivity. As a matter of fact, When I came in, the hubs weren't even powered. They were just metal racks that you plugged into to provide a conduit for the signal.
Obviously, the hub doesn't have any sort of intelligence. It doesn't direct traffic or segment. The network hub simply sends all the data out. All the ports all the time of computer A has data to send to computer be that traffic goes out all the ports, so it's available to Computer C and D and J and K and any other devices that might be plugged into the network.
If you can think about that, if I had a sniffer plugged into a hub, that would just be a bonus, because I would have access to everything on the network. That's one of the many reasons we don't use hubs today because from a security perspective, that could be very dangerous. One thing I'll mention is that when the data goes out, all parts to all hosts
the network card examines the data frame, and what it's looking for is Destination Mac address that is its own.
So when be looks at data, it looks at the Mac address and says, Oh, that's for me and pulls it off the network or that isn't for me and leaves it alone
all a sniffer does examine all packets the same way all frames the same way. But it's interfaces in a mode called promiscuous mode, which means sniffer doesn't care who the Mac addresses for, and it doesn't care about destination Address.
The sniffer simply pulls all traffic off the network, regardless of the destination.
Promiscuous mode sounds like it should be a lot more fun than that, but all it means is the network card is going to pull traffic regardless of the destination.
With the security issues of hubs and all data out all the ports all the time, there is no sort of directing traffic or help for collisions. So in a hub environment, we have a lot of collisions. We have all data going out of all the ports to everybody, and we have what's referred to as one big collision domain. A switch is going to fix that problem for us because one of the first things it does is isolate traffic into collision domains.
Each port on a switch is its own collision domain. If we go back to the Hub, every host in this illustration is part of the same collision domain, which means they're all competing for time on the cable.
When we replaced those hubs and switches, Each host has its own collision domain, which basically means computer edge, just competing with itself for time on the cable. So we have all but eliminated collisions and our Ethernet network just by bringing switches in.
Another thing that a switch does that helps us out. A lot is direct traffic. A switch learns the network over time and learns which host is at which part, using Mac addresses. If you remember Rost model discussion, we set switches for Layer two devices.
Mac address scene is later, too, so the switch uses a Mac address, sends out the data and learns that the data has picked up on Port three by computer beat.
It takes Bees Mac address and loads it into a table called the Cam Table.
Ultimately, it keeps track of Mac addresses and their match for sort of like a police officer at a busy intersection, directing traffic out of the appropriate port when the power is out.
If you think about that going back to our discussion about having a sniffer plugged in, if we plug, it's never into port to no traffic is going to be directed to port to, because nobody is sending traffic to the sniffer.
One of the ways that we mitigate against sniffing the network is to use switches.
However, sometimes a network admin wants to sniff their own network,
and they want to see what type of traffic is going around, what's being sent with passwords in plain text or how much broadcast traffic there is.
In that case, I plug a sniffer into the switch and can enable the administrative mode called port S P A N.
What port S P. A N allows all traffic to be mirrored out that particular report, so I can expect it.
So we've got our switches
down at the bottom. I have a little asterisk that I mentioned bridges.
Bridges were predecessors switches. Bridges are also layered to devices, and they were used to connect to things like token ring network to an Ethernet network. But they still provided the use of isolation and collision domains. They're kind of the precursor to what we have today and what we know today switches
when we had a nice little environment with switches. One problem we didn't solve with broadcast Tropic. Here's a network let's say, have the sales people. The salespeople are over here to the left, their computer, J and K.
The sales people have an application that generates a lot of broadcast. If we go back to the previous slide. Any system that has a broadcasting in this environment, that broadcast goes to the entire network. That's what a broadcast does goes out to everybody on the entire network and our illustration here. I only have two computers that need that broadcast from the sales application, but it's going to everybody. Too much traffic.
The more broadcast that people don't need, the more the network gets bogged down so router can be brought in to isolate broadcast traffic. Maybe I want the sales network submitted from the rest of the network to control broadcast traffic in the middle. I have a group of computers from the human resources group, and they have very sensitive data. So I want to segment that network so I can apply. Some security
may be in force upset, maybe be very strict on who accesses those network systems. So I create a segment for them and they're on their own sub net,
then with VoIP. Quality of service is really important for boy.
By that I mean being able to prioritize traffic so that the VoIP network, it's all the bandwidth that it needs.
That would be another reason to submit a network quality of service. Basically, what I've needed to do is segment my network out based on either broadcast traffic security needs quality of service or maybe just based on logical connectivity,
it makes sense to group a certain group of computers in the same network, just based on access and location.
A router can do those services for me, and a router is a layer three device.
So not only can it segment the network into different sub nets, but the different subnets can communicate.
Even though this illustration looks and works great. The problem is that writers are expensive. I don't necessarily mean when you look at your receipt is going to be that much higher than a switch. But with the switch, you're going to get lots of ports. When you purchase a router, you're going to get one port, one land port.
The routers are primarily used today to get off your local area network, so you get a single alien port.
What we've got to find a way to do is that we have to have in this picture, but make it cheaper. That's what's coming up next.
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