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 Beam Aug 10 at 19:22

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 Beam Aug 10 at 19:20
  • @RickyBeam, have you an example of such a protocol? – Golgot Aug 17 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 Beam Aug 17 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 at 15:58

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