When a host sends an ARP request packet out, what is the destination address of the frame?

When a MAC address is unknown for the destination IP address or the default gateway, the ARP request is sent in the form of a broadcast. If the destination MAC address was the router's MAC address, the router would be the only device to receive the ARP request frame. The host's MAC address is what we need to process the framing of data; therefore, it is the reason for the ARP request to all listening nodes. In IPv4, ARP uses broadcasts to forward the ARP request to all listening network devices. Multicast is used in IPv6 for node discovery, but it does not use ARP.