Basically Proxy ARP is the ARP that is used between one more networks. In other words, we can say that Proxy ARP provides data link dicovery between different networks.
Here, we will explain Proxy ARP with an example. For our Proxy ARP example, we will use the below topology.
Think about that, PC 1 want to ping PC 4 and it does not have PC 4’s MAC address in its ARP Cache. Here, the router has also an ARP Cache. We assume that Router’s ARP Cache has only its interfaces at the beginning.
Firstly PC 1 sends a broadcast ARP Request to learn MAC address of destination PC 4. With the other PCs in the same network, the first network side interface of the router will also receive this broadcast.
Router detects that the destination is not in this network but it knows the other network. So, router sends an ARP Reply to PC 1 with its own interface MAC address. This message means that:
“This IP Address is not in this network. But, I know how to go there. This is my MAC Address.”
Router checks its ARP Cache and it does not find any record about PC 4’s IP address and MAC Address. So, it sends a broadcast ARP Reply to the second network.
PC 4 in the second network, determines that the router that is being looked for is himself. It sends an ARP Reply, that means :