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If a request is being sent via unicast or broadcast, would that show in the destination or source address?

asked 2020-03-06 20:43:13 +0000

I'm very new to Wireshark and am having some issues trying to determine if a certain request packet is being sent via unicast or broadcast. I can see the source MAC address and the destination MAC address but I'm just not entirely sure which address I should be looking into to find out. Any information would be greatly appreciated! :) I've tried looking on Google but can't find much regarding this. I would assume that I should be looking at the source address being the request is coming from that address but I'm not entirely sure. Thanks!!

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answered 2020-03-06 20:56:49 +0000

Guy Harris gravatar image

"Sent" is the key word here; the destination MAC address is the MAC address to which a packet is being sent, so that's the address to check. The source MAC address just says who's sending it; they can send broadcast or unicast packets, so the source address can't tell you whether it's broadcast or unicast.

By the way, there's another possibility - multicast - so:

  • if the destination MAC address is ff:ff:ff:ff:ff:ff, it's broadcast;
  • otherwise, if the "IG bit" is set, meaning it's a group address, it's multicast;
  • otherwise, it's unicast.

The IG bit is the low-order bit of the first byte, so if, for example, it's 0x80, it's unicast, as that bit is clear, but if it's 0x81, it's multicast, as that bit is set.

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Chuckc gravatar imageChuckc ( 2020-03-06 21:03:03 +0000 )edit

Thanks that really helped me out! I appreciate it!

ohh_bnertt12312 gravatar imageohh_bnertt12312 ( 2020-03-06 21:13:10 +0000 )edit

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Asked: 2020-03-06 20:43:13 +0000

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Last updated: Mar 06