How would a network behave if one were to set the source address of an Ethernet frame to the broadcast address FF:FF:FF:FF:FF:FF?

Obviously, one would have to manually alter the relevant field in the frame to implement this as no host would/could take the broadcast address. But once this was done, what would happen?

  • In general, nothing. All of that clients traffic would be layer-2 broadcast; every machine would see it. In most cases, the switch/network would see that as a broadcast storm and shun the port.
    – Ricky
    Aug 10 '18 at 19:22
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Dec 25 '18 at 9:11

This will be declared as an invalid source mac address and packet will be dropped...

On cisco, Message is like the following

Packet received with invalid source MAC address (FF:FF:FF:FF:FF:FF)

The same for 00:00:00:00:00:00 (and maybe other such as own internal mac, broadcast mac address aso.)

  • all-ones MAC isn't an invalid source -- it's broadcast. One could say it's invalid for numerous layer-3 protocols, but not at layer-2.
    – Ricky
    Aug 10 '18 at 19:20
  • @RickyBeam, have you an example of such a protocol?
    – Golgot
    Aug 17 '18 at 13:54
  • TCP is connection oriented, so it should never been sent/received to/from a hardware broadcast address. (not that most applications would ever notice)
    – Ricky
    Aug 17 '18 at 15:46
  • Yes, but have you an example of a protocol which can be using all ones as a source MAC? Because if there is any, I'm curious how will react a layer 2 switch (Cisco 4500 clearly drop layer 2 packets from source "FF:FF:FF:FF:FF:FF" with message : invalid source MAC address")....
    – Golgot
    Aug 17 '18 at 15:58

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