Networking/Computing Tips/Tricks

Great question, and one I get all the time.

As most of you know, the manufacturer of a networking device that uses MAC addressing can be identified by the OUI - Organizationally Unique Identifier.  OUI's are obtained from the IEEE.  You can find a complete list here.  The OUI is essentially the first 24 bits of the MAC address field (it is actually 22 bits - detail details).

The problem with the question is that Apple for example may have dozens or hundreds of OUI's.  

Luckily, Wireshark can perform number name resolution for MAC addresses.  We see this in the packet dissection:

Screen Shot 2017 06 21 at 12.42.15 PM

If we right click on the source MAC address field and select Apply as a filter, we get the following syntax:

Screen Shot 2017 06 21 at 12.45.03 PM

So the first 3 bytes (3c:07:54) must be an Apple OUI.  

If we modify the filter to this, trying to get all systems that have the OUI:

Screen Shot 2017 06 21 at 12.47.00 PM

We have several problems.  First, any Ethernet MAC above this range will be included, but more importantly we have not considered all the other Apple OUI's.

Another coice would be to use "Apple":

Screen Shot 2017 06 21 at 12.49.50 PM

But we can see that Wireshark's display filter mechanism does not accept that syntax.

The solution is to use a "hidden" protocol field that the Wireshark Expert actually has for MAC addresses.   It is called the 'eth.addr_resolved' field.  Further, instead of using the '>=' operator we need to use the 'contains' operator, thus if the MAC address of any packet is resolved from the large number of OUI's to be 'Apple' we have found all the Apple based traffic.  Here it is:

Screen Shot 2017 06 21 at 12.54.20 PM

There is your answer.  Hope that helps.

If you are interested in exploring other Wireshark Expert hidden fields, on a MAC click Wireshark> Preferences> Protocols, and on a Windows machine click Edit> Preferences> Protocols and then select the 'Display hidden protocol items':

Screen Shot 2017 06 21 at 12.56.36 PM

This does not need to be on for the filter above to work.  But one can imagine using these hidden fields to expand contents of your Profiles and filters.



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