I'm learning about Ethernet frames and networks and Wireshark has been very useful.

I have a doubt regarding broadcasting and ARP request, since we don't know the Target MAC address, in the ARP's header it is set to FFFF.FFFF.FFFF in order to request said information.

When I'm using Wireshark I notice how some ARP headers have the Target MAC Address set to 0000.0000.0000 ; the Ethernet header's hw Address, however, is always set to all 1's.

My question here is, which MAC address must be all 1's? The ethernet's or the arp's? Or is a ARP's MAC address set to 0's also a valid flag for broadcasting?

Thank you.

  • Are you referring to ARP requests or ARP replies?
    – Zac67
    Jan 27, 2022 at 17:50
  • 1
    RFC 826, An Ethernet Address Resolution Protocol explains how that works. It is a relatively small RFC that is easy to understand. It was designed to work with multiple hardware address sizes.
    – Ron Maupin
    Jan 27, 2022 at 17:51


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