Why does ARP request contain the same MAC address twice?

Question

I used Wireshark to capture frames from ARP request and reply and I've noticed that the first frame shows my MAC address as "Src" and "Sender MAC address". Why is there a need to state my MAC adress twice?

Answer 1

As long as I understand, you see your MAC address twice, once in the Data-link layer (as a source MAC) and once in the actual ARP request (as a Sender MAC Address).

The first thing you need to understand is that these are two separate protocols, so it can be the case that the same data is transferred twice. This is because in some edge cases, the MAC address of the packet can change. In this case, if the ARP did not have a MAC address inside the request, the PC that responds will not know to whom it is responding.

So, in short, let the MAC layer take care of the "navigation" and the ARP to take care of the "diplomacy", even if this might result in some duplicate information.