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Welcome to the tutorial guide. The tutorial guide will provide a user with advise and guidance on u32 classifier. Please note that the U32 filter is the most advanced filter available in the current implementation. It is entirely based on hashing tables, which make it robust when there are many filter rules.

It is good to know what a u32 classifier is. It is a list of records, each consisting of two fields: a selector and an action. The selectors, described below, are compared with the currently processed IP packet until the first match occurs, and then the associated action is performed. The simplest type of action would be directing the packet into defined class.
A user should know that the command line of tc filter program, used to configure the filter, consists of three parts: filter specification, a selector and an action. The filter specification can be defined as:
tc filter add dev IF [ protocol PROTO ]
[ (preference|priority) PRIO ]
[ parent CBQ ]
The protocol field describes protocol that the filter will be applied to. We will only discuss case of ip protocol. The preference field (priority can be used alternatively) sets the priority of currently defined filter. Each list will be passed in the order the rules were added, then list with lower priority (higher preference number) will be processed. The parent field defines the CBQ tree top (e.g. 1:0), the filter should be attached to.

If you followed advise and guidance as provided in this tutorial guide then you would have learnt about u32 classifier.