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Discovering computer networks: hands on in the Open Networking Lab
Discovering computer networks: hands on in the Open Networking Lab

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3.3 Switching

In this part you will look at switching. Switches operate at the Network Access layer of the TCP/IP model. You will see how switches use MAC addresses to deliver data frames within a local area network.

Watch the video below, which is about 3 minutes long.

Switching

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Now you can have a go with another simulated network.

Activity 3 Try it out

5 minutes

  • 1. Open this network [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] that has a switch and 2 PCs.

  • 2. Find the MAC addresses of the PCs.

    Click Reveal answer if you would like a hint.

  • Click on PC1, open a command prompt (by clicking on Open console), type ipconfig /all, and look for the physical address.

Watch the video below, which is about 5 minutes long.

More on switching

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Activity 4 Think about

5 minutes

In the example you have just watched, the switch only has four ports but switches can have 48 ports or more. Can you think why it might not be a good idea to have too many devices connected by just switches?

Answer

All devices connected by a switch will be in the same broadcast domain which means every time a host or server sends a broadcast, all devices will receive and have to process that broadcast. If broadcast domains are too large, network response times can become slow. You’ll see later that using routers as well as switches enables broadcast domains to be broken up, as they do not forward broadcasts by default.

Watch the video below, which is about 4 minutes long.

MAC address tables

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Activity 5 Try it out

15 minutes

  • 2. Add another PC and make a note of the port number it is connected to.

    Click Reveal answer if you would like a hint.

  • Drag and drop a PC onto the workspace or click on Add device and follow the instructions, selecting PC under ‘Device type’. Click on Connect devices and follow the instructions to connect the new PC to the switch, selecting the next available FastEthernet port on the switch. Make a note of the port number you select.

  • 3. Configure the new PC with a suitable IP address and subnet mask.

    Click Reveal answer if you would like a hint.

  • To configure with a suitable IP address and subnet mask (which you will need to identify from the IP address of the network and those already in use), click on the new PC, then Edit device and then the Interfaces tab. Input the IP address and subnet mask and click Submit.

  • 4. Find the MAC address of the new PC.

    Click Reveal answer if you would like a hint.

  • Open a command prompt, type ipconfig /all and find the physical address. Make a note of the MAC address of the PC.

  • 5. Log on to the switch and identify the new PC in the MAC address table.

    Click Reveal answer if you would like a hint.

  • Send a broadcast ping from one of the PCs (you will need to identify the broadcast address from the IP address of the network). Select the switch, open a command prompt and type enable. Then type show mac-address-table. Find the new PC using the MAC address and port you identified earlier.