System Administration Guide: IP Services

Defining Filters

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 then 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.

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 Table 37–1.

Table 33–2 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. Use either IPv4 or IPv6. IPv4 is the default.
`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 How to Define the Classes for Your QoS Policy.
`user`	Either the UNIX user ID or 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. Value is either `LOCAL_IN`, `LOCAL_OUT`, `FWD_IN`, or `FWD_OUT`.

Note –

Be judicious in your choice of selectors. 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.