Connecting three PCs using hub

Submitted on Mon, 04/22/2024 - 22:47

Earlier, we connected two PCs directly in point to point connection. Now, to connect three PCs we will need an additional device. In this case, we will use a hub and see how it works.

To see its working, we will use Packet Tracer’s simulation feature.

Step 1. Create a network as shown below:

To select hub, select Network Devices, hub then PT-hub.

Assign the following IP addresses to the three PCs.

Since, in a /30 network, only two devices can be connected, to connect three devices we use the /29 network which can connect 6 devices.

Subnet mask for /29 prefix length is

Step 2. Switch to simulation from Realtime.

Step 3. Click on Show All/None to remove all the visible events.

Step 4. Click on Edit Filters and select ICMP and ARP.

Step 5. Select a simple PDU and click on two PCs to send the PDU. (pc0 to pc1)

Here, we can see that two PDUs are created. One for ICMP and ARP. Since, ICMP requires MAC addresses of the destination interface, ARP PDU is created to find the destination’s MAC address.

Now, we can click on the forward button to see the PDUs in action.

  1. ARP PDU arrives at the hub from PC0.

  1. The ARP PDU is flooded to the rest of the PCs connected to the hub. PC2 drops the PDU as the ARP PDU is trying to find out the MAC address of PC1.

  1. PC1 sends back the ARP PDU with details of its MAC address. The ARP PDU arrives at the hub.

  1. The hub again floods the ARP PDU to the rest of the devices. PC2 has to drop the packet again.

  1. Now, the MAC address of PC1 is known to PC0. Hence, ICMP PDU now arrives at the hub.

  1. The hub again floods the ICMP PDU. PC2 has to drop the packet as the ICMP PDU is not destined to that PC.

  1. PC1 replies with the ICMP PDU. The ICMP PDU arrives at the hub.

  1. Hub again floods the ICMP PDU.

Hence, we can see that the hub has a major issue with flooding. Due to this, a lot of unnecessary broadcast traffic is created in the network. This causes performance issues.