I have been informed by certain networking professionals that ARP replies can and sometimes actually are broadcast packets instead of unicast. If and when would you use a broadcast ARP reply?
ARP – Can ARP Replies Be Broadcast?
arpbroadcastethernetprotocol-theory
Best Answer
According to the RFC826 (An Ethernet Address Resolution Protocol) the sender has to:
But as you pointed out why an host would use the broadcast address in an ARP reply? Maybe because this could seem clever: using the L2 broadcast address all the hosts in the LAN would immediately know a new (IP,MAC) pair saving time. Actually this method is not desired by the RFC (even if they refer to periodic broadcasting):
It also depends on the host's OS to add in the ARP table a tuple learned by a broadcasted message.
EDIT: As stated in the comments the RFC 5227 updates the RFC 826 and it says