Keys and MAC addresses
Devices are indexed two primary ways in Kismet:
- Keys - A key is unique for each device. The key is derived from the MAC address, but contains additional information about the PHY type. - This allows multiple devices to have the same MAC under different PHY types; this can be particularly important when using non-traditional PHY types like those derived from SDR captures, when the devices do not have an actual MAC address. 
- MAC addresses - The MAC address is a (theoretically) unique identifier given to each device at manufacture time. It is used to identify the device uniquely on a network. - Typically, the the IEEE assigns each manufacturer a block of addresses with a common header (the OUI) and the manufacturer is responsible for creating unique identifiers within that block. - For datasources without a defined MAC address, Kismet will attempt to synthesize a MAC address from the unique data available. 
MAC address masking
On queries and filters affecting MAC addresses, Kismet supports complete addresses or partial addresses with masking.
A masked address resembles the syntax typically used for IP network masking: [MAC]/[MASK].
For instance, to match only the OUI, a masked MAC of:
"aa:bb:cc:00:00:00/ff:ff:ff:00:00:00"
This would match any MAC address where the OUI, or first three bytes, are “aa:bb:cc”. A similar feature to match on the first four bytes would be:
"aa:bb:cc:dd:00:00/ff:ff:ff:ff:00:00"