Device Location: BIA, Slot and Subdevice

The location of a device in a Point System stack is usually described by two values, the serial number of the cabinet in which it is installed (called a Burned In Address or BIA) and the slot in that cabinet.

The slots in which media converters, management modules and the like are installed and the ports on stand-alone switches are numbered starting with 1 (There is never a slot ‘0’). Manageable power supplies occuply slots 125 through 128.

Wide devices that take up multiple slots are plugged in to the connector for the leftmost slot, and their location is identified by that single slot.

In certain products, there is a third device identification value known as a Subdevice index. Subdevices exist when the count of some hardware resource in a single device varies between configurations of a product, or any other time an additional dimension is required by a table.

For example, the CBFTF100 Ethernet Switch is shipped in several different configurations that have varying numbers of ports. Each port has a different subdevice index. Rather than have dozens of MIB variables for ports that don’t always exist, we have a variable number of ports which are distinguished by the subdevice index. So, if we had a three-port CBFTF100 installed in slot 7 of a cabinet whose BIA is 2345, we would use the following OIDs to check the link status of the three ports:


Note that you must supply the Subdevice Index for all columns for MIB tables containing subdevices, even though some columns don’t have anything to do with subdevices. These columns contain information that is global to the entire device. In these cases, a subdevice index of 1 is specified. For example, the OID one would use to Get the serial number of the device in the previous example (which is not specific to any port of the switch) would be:


One can tell at a glance whether or not a device has subdevices by looking for a SubdeviceIndex column. If the column exists, the device has subdevices, and every column whose MIB Variable name ends in “Tbl” contains subdevice specific information. Other columns (like SerialNumber) contain device-global data, and the placeholder value ‘1’ should be used for subdevice, as above.