# QoS Filter

A [Quality Of Service](/glossary/q/qos) Filter is used by [classful QDiscs](/glossary/q/qdisc) to determine which [QoS Class](/glossary/q/qos_class) a [packet](/glossary/p/packet) should belong to.

The filter contains a number of parameters/conditions that the packet needs to match in order to be enqueued in the appropriate class.