Okay, so let's see if we can practically answer these questions.
To do that I'm gonna use simulation mode in packet tracer and I'm gonna change the filters to
only show ARP and ICMP messages.
I don't wanna see all the other traffic types in the network. So let's see what happens when PC 1 pings
PC 4. PC 1 has an IP address of 10 111, PC 4 has an IP address of 10 114 so we're going
to send ICMP traffic
in other words ping traffic
from PC 1 to PC 4 and then we're going to observe what happens. Now in this example
I'll only send two packets.
In other words two pings, notice what happens in the network there's ICMP traffic but there is also an
ARP frame that's generated.
PC 1 needs to learn the MAC address of PC 4
so it sends out an ARP which is a broadcast requesting the target MAC address of PC 4. So in answer
to our first question, what type of packet is sent
initially? The answer is a ARP packet which is a broadcast packet.
We've proven that by running simulation mode in Packet Tracer.
Now this is a broadcast and in this network, the devices are connected to a hub so the traffic should
be flooded to all devices in the network except the device that sent the packet.
So who receives the packet?
PC 2 does,
PC 3 does and so does PC 4, PC 2 and PC 3 will drop the packets because the ARP packet is not for
their IP address, PC 2 as an example is configured with IP address 10 112 so PC 2 is gonna drop the
packet.
The ARP request is for IP address 10 114 so both PC 2 and PC 3
drop the packet but PC 4 will accept the packet and what it should do now is send back an ARP reply.
So if we look at this packet notice the inbound packet to the hub is an ARP reply packet with the MAC
address of PC 4 this is PC 4s IP address
this is its MAC address.
We can verify that by using the IP config command and I should say IP config slash all notice the MAC
address which is the source MAC address of the frame and that's the source MAC address we see over here.
So the next question is, who receives the return traffic?
So if I click capture forward notice PC 1, PC 3 and PC 2 receive the return traffic so it PC
1, PC 2 and PC 3.
PC 2 and PC 3 will drop the ARP reply because it's not destined to them when we look at that packet
we can see that the destination MAC address is PC1 and we can confirm that by looking at the config
of PC1 notice the MAC address is this, so PC2 and PC 3 will drop the ARP
reply. We're then asked when ping traffic is sent from PC 1 to PC 4 who receives the traffic.
Now it's a hub so the traffic will be flooded.
So here's the ICMP message we can see that it's an Ethernet 2 frame using IP 4 at layer 3 and
we can see it's an ICMP packet and when we click capture forward notice
PC 2, PC 3 and PC 4 receive the traffic but again PC 2 and PC 3 will drop the packet because
it's not destined to them when we look at the inbound PDU or protocol data unit on PC 4 we can
see that the destination IP address is PC 4 and the destination MAC address is
PC 4 we can verify that once again by using the IP config slash all command and we can see the MAC
address of
PC 4. So that's going to continue now
When the
PC 4 replies to PC 1
the traffic is flooded and this is the problem with the hub even though the conversation is between
PC 1 and PC 4 everyone in the network receives the traffic.