Apart from the three user-defined classes, there are three reserved classes. The reserved classes are not configurable by the user, however.
The three reserved classes are:
The IFC class classifies all traffic originating from or destined for the APIC. It is a strict priority class (whereby minimum and maximum bandwidth is guaranteed).
The control class is also a strict priority class and prioritizes control traffic, such as protocol packets, and all SUP traffic (supervisor engine).
The SPAN class is a best-effort class, utilizing deficit weighted round robin (DWRR). DWRR serves to equal out the amount of bandwidth used; an example would be that if on one "turn" the queue uses 25% of the bandwidth, bursting ...