Tutorial Class 4

In this class, I’ll be giving you the answers to the self tests in the previous class and shed more light on internetworking with some examples.

The answers to the previous self tests are as follows:

For the first question, in order for host A to ping (that is, communicate with ) host B, you need a crossover cable to connect the two switches together. I hope you remember from our Ethernet cabling class that to connect two hosts, you use a crossover cable.

For the second question, there are a variety of cables in use. For the connection between the switches,
we’d obviously use a crossover cable. We have a console connection between the router console and the computer that uses a rolled cable. Plus, the connection from the router to the switch is a straight-through cable, which is the same for the hosts to the switches.

I hope you understand those answers. If you don’t,  just go over the previous classes on Ethernet cabling and networking devices.

We’ll be understanding more about internetworking with the figure below.




 

I guess you remember this figure from our last class. Looking at the figure, how many collision domains and broadcast domains are in this internetwork?

Hopefully, you answered nine collision domains and three broadcast domains! Remember, only routers break up broadcast domains by default. And since there are three connections, that gives you three broadcast domains. But where are the nine collision domains?
The all-hub network is one collision domain; the bridge network equals three collision domains. Add in the switch network of five collision domains—one for each switch port—and you’ve got a total of nine.


The figure below which shows switched networks creating an internetwork is what is typically found today.




Okay, here LAN switches are placed at the center of the network so the routers are connecting only logical networks together. If I implemented this kind of setup, I’ve created virtual LANs (VLANs), something I’m going to tell you about in later classes. But it is really important to understand that even though you have a switched network, you still need a router to provide your inter-VLAN communication, or internetworking. Don’t forget that!
Obviously, the best network is one that’s correctly configured to meet the business requirements of the company it serves. LAN switches with routers, correctly placed in the network, are the best network design.

Now each port on the switch is a separate collision domain and each VLAN is a separate broadcast domain. But you still need a router for routing between VLANs. How many collision domains do you see here? I’m counting 10—remember that connections between the switches are considered a collision domain!



So now that you’ve gotten an introduction to internetworking and the various devices that live in an internetwork, in our next class, I will be introducing you to internetworking models. This simply talks about the  Open Systems Interconnection (OSI) reference model which was created by the International Organization for Standardization (ISO) to break the barrier of computers typically communicating only with computers from the same manufacturer.