Original subtitles

So in summary when the device wants to communicate

with another device in the same subnet.

It will send a broadcast onto the local segment to find

the MAC address of the device using the target IP address.

So in this case A sends the frame to the hub.

The hub because it's a multi port repeater will send the frame

out of all ports except the port on which it arrive.

So both the router and host C received the frame.

Network Interface Card will only accept unicast traffic destined 10

to the Mac address or they�ll accept broadcast traffic 11

as well as accepting multicast traffic 12

for multicast addresses that they've subscribed to. 13

The router has a MAC address of G on interface F0/0 14

so the router will receive the broadcast 15

and forward the ARP request to high layer protocols. 16

The router will be able to see at layer 3 that this is an ARP request 17

for IP address 10.1.1.2 but the router in this example is configured 18

with IP addresses 10.1.1.100 and 10.1.2.100 so the router will drop 19

the frame because the ARP request is not for one of one its IP addresses. 20

Routers do not forward broadcast, so this broadcast is not forwarded 21

out of interface F0/1. 22

So the broadcast received by the router is dropped. 23

The network interface card on PC C will received the broadcast 24

and see that this is an ARP request forwards IP address. 25

So it will then reply with an ARP reply 26

as we�ve seen in the Wireshark capture. 27

PC C will update its ARP cash to show that IP address 10.1.1.1 is 28

associated with MAC address A and it will then send the frame to the hub 29

The hub will forward the frame out of all ports 30

because it�s a multiport repeater. 31

The router in this example will receive a frame from the hub 32

but because the destination MAC address is A 33

and it�s not the MAC address of the router 34

which is G the router will drop the frame. 35

A will also receive a copy of the frame 36

when A receives the frame it will accept it 37

because the destination address is A and its MAC address is A. 38

it will then update its ARP cache with and ARP entries 39

stating that IP address 10.1.1.2 is associated with MAC address C. 40

so the ARP reply allows A to update its ARP cache. 41

At this point no user traffic has been transmitted 42

what�s happen here is that the devices have simply worked out 43

which MAC addresses are associated with which IP addresses. 44

So A now knows that MAC address C is associated with IP address 10.1.1.2