So far as I know, Address Resolution Protocol (ARP), translates the IP address of a computer on a local network to an equivalent layer 2 address (MAC address), such as sending a packet from machine A to B using level-2 switch.
It is therefore necessary that all involved parties are on the same LAN, isn't it?
Must an ARP broadcast query packet contain the target node's MAC address?
Perhaps only the IP address will suffice?
The entire point of an ARP broadcast is to resolve the MAC address of a particular computer owning an IP address.
Wireshark translates the packet like this: Who has 192.168.x.254? Tell 192.168.x.23.
When broadcast, all machines check their IP configuration for the listed IP and reply to the source machine if their own IP matches.
Without a target IP, there isn't much sense to the protocol. Note that the MAC is FF:FF:FF:FF:FF:FF meaning "broadcast to everyone" and all computers can read the packet sent. Otherwise, the packet goes to a specific MAC if in the packet, or is silently ignored if there's no MAC.
Q: It is therefore necessary that all involved parties are on the same LAN, isn't it?
A: Yes.
Q: Must an ARP broadcast query packet contain the target node's MAC address?
A: An ARP query is a query for the destination MAC address. If the querying host already knows the destination MAC address then it doesn't have to query for it via ARP.
