Hello Rob,
You could search for that client IP on Airwave, on the TOP right hand corner in the search option, you could enter the ip in question, click the drop down and make sure to include Active, historical and all categories, it will include all the selected options, screen shot for the shown below:
The result should show the Client's that had this Ip address. Additionally you could also run a client session report and filter with the ip in-question, for the duration based on the historical retention settings on AMP for clients. As shown below:
This should also help in finding the devices that had this ip address.
Hope this helps..
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