Defining Filters

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You create filters to identify packet flows as members of a particular class. Each filter contains selectors, which define the criteria for evaluating a packet flow. The IPQoS-enabled system uses the criteria in the selectors to extract packets from a traffic flow. The IPQoS system then associates the packets with a class. For an introduction to filters, see IPQoS Filters on page 16.

Use only as many selectors as you need to extract packets for a class. The more selectors that you define, the greater the impact on IPQoS performance.

The following table lists the most commonly used selectors. The first five selectors represent the IPQoS 5-tuple, which the IPQoS system uses to identify packets as members of a flow. For a complete list of selectors, see Figure 4, Table 4, Filter Selectors for the IPQoS Classifier.

Table 2 Common IPQoS Selectors

Name	Definition
`saddr`	Source address.
`daddr`	Destination address.
`sport`	Source port number. You can use a well-known port number, as defined in `/etc/services`, or a user-defined port number.
`dport`	Destination port number.
`protocol`	IP protocol number or protocol name that is assigned to the traffic flow type in `/etc/protocols`.
`ip_version`	Addressing style to use, either IPv4 (the default) or IPv6.
`dsfield`	Contents of the DS field, that is, the DSCP. Use this selector for extracting incoming packets that are already marked with a particular DSCP.
`priority`	Priority level that is assigned to the class. For more information, see Defining the Classes for Your QoS Policy.
`user`	Either the UNIX user ID or the user name that is used when the upper-level application is executed.
`projid`	Project ID that is used when the upper-level application is executed.
`direction`	Direction of traffic flow. Acceptable values are either `LOCAL_IN`, `LOCAL_OUT`, `FWD_IN`, or `FWD_OUT`.