Servers Networks: 12: A Simple Network

Abgabe einreichen

Fällig: Donnerstag, 30. April 2026, 23:59

Learning Target

Simulate a basic local area network
Ping devices and inspect network traffic
Understand how switches use IP and MAC addresses

Instructions

In this assignment, we will be simulating a small local area network (LAN).

Part 1: Build the network

Step 1: Open FILIUS

Open FILIUS and make sure you are in design mode. This is the mode used to build or change the network.

Step 2: Add the devices

Drag these into the workspace:

- 3 computers or notebooks
- 1 switch

The specific placement doesn't matter. However, the connections between them do.
Here are three examples of how it could look:

Step 3: Configure each computer

Click on each computer and set its:

- Name
  - A hostname should only contain letters(A-Z), numbers(0-9) or dashes(-)
  - The instructions will refer to them as PC-A, PC-B, and PC-C
  - You can use more unique names if you wish
- IP address
  - Use unique IP addresses that share the same numbers for the first 3 octets
    - We will use 192.168.0.x for this lab since it is commonly used on home networks.
  - Each device must have a different value for the last octet
  - Do not use 0, 1 or 255 for computers on a network:
    - 0 and 255 are reserved
    - 1 is usually assigned to the network gateway

Where does the word octet come from?
In binary, each number of an IP address or mask can range from 0 to 255. Every one of these values can be expressed using an 8-bit binary number.
0 = 00000000, 255 = 11111111
Since each value can be expressed using exactly 8 binary digits, they are often referred to as "octets".

- Subnet Mask
  - Since all of the IP addresses use the same first 3 octets, we will use this subnet mask:
    - 255.255.255.0
    - This means that the first 3 octets of an IP address will determine the network and only the last octet will determine the specific device on our network.

Step 4: Connect the network

Use the connection tool to connect each computer with a cable to the switch.

Part 2: Start the simulation

Step 1: Switch to simulation mode

Click the green arrow to enter simulation mode. This mode is used to test the network and run software on the devices.

A network operates near the speed of light (electron speed). You may find it easier to follow the network's operation by slowing it down quite a bit.

Step 2: Install the command line

Click on PC-A and install the Command Line application using the Software Installation utility.

Note: If you can't do this, then your network simulation is not running.

If the bottom or side panels are hidden, you can show them at any time by using the buttons at the edge of the designer :

Part 3: Test the network

Step 1: Send a ping from PC-A to PC-B

The ping command will:

- send four "ping" requests
- wait for the four "pong" replies
- summarize the success rate similar to this

On PC-A, open the command line and ping another computer by name and then by IP address:

Notice that one of these worked and the other did not. There is currently no service installed to translate hostname --> IP address.

A hostname is meaningless to the switch. It will only forward traffic using a MAC address.
When communicating within a local network, a device needs to find out the MAC address of the device it wants to talk to.
It can does this using an Address Resolution Protocol (ARP) broadcast.

The machine with the desired IP address will respond with its MAC address.
Then, the frame can be sent through the switch to the destination using the correct MAC address.

Analogy:

Sally needs to give a message to someone named Scott Beyer in a crowded room.

She shouts, “Who here is Scott Beyer?”

Scott answers, “I am!”

Now Sally knows exactly who Scott is and where he is, so she can deliver the note to him.
But, this only works if they are in the same room.

Connection:
Sally’s shout is like an ARP broadcast. Scott’s reply is like the ARP response. Once the sender learns the correct identity, the message can be delivered to the right destination. But this only works if they are on the same local network (more technically, they must be on the same subnet or broadcast domain).

Step 2: Watch the network traffic

View the exchanged data for PC-A. Right-click on the device and choose Show data exchange:

A window will open showing each network transmission event.

Look closely at the first set of messages:

- The first two lines are used to figure out the physical address of the other computer using ARP (Address Resolution Protocol).
- The later lines are the echo request (ping) and echo reply (pong) messages using ICMP (Internet Control Message Protocol).

Step 3: Click on the traffic lines

Click different lines in the data exchange window and inspect the information shown. Here's an example for an ARP broadcast:

Part 4: Observe switch learning

Step 1: Ping PC-C

From PC-A, send a ping to PC-C.

From PC-A, send another ping to PC-B.

Step 2: Identify and think about what has changed

Answer these questions:

1. What happened before the actual ping messages started?
2. Why do you think the switch did not know where to send data at first?
3. What does the switch seem to learn after the first request?
4. Why is it useful for a switch to remember devices on the network?

Step 3: Identify and think about what has changed

Answer these questions:

1. What is the job of a switch in a LAN?
2. What is the difference between an IP address and a MAC address?
3. Why are there extra messages before the first ping reply?
4. How does a switch forward messages more efficiently?
5. Why do you think this process is only used within our local area network?

Feel free to use external resources to help you solidify your answer, but use your own words.