How to Define Filters in the QoS Policy

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 and associate them with a class. (For an introduction to filters, see Filters.)

Before you can perform the next steps, you should have completed the procedure How to Define the Classes for Your QoS Policy.

1. Create at least one filter for each class in the QoS organizational table that you created in How to Define the Classes for Your QoS Policy.

   Consider creating separate filters for incoming and outgoing traffic for each class, where applicable. For example, add an ftp-in filter and an ftp-out filter to the QoS policy of an IPQoS-enabled FTP server. Then you can define an appropriate direction selector in addition to the basic selectors.

2. Define at least one selector for each filter in a class.

   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 6–1.

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   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 you define, the greater the impact on IPQoS performance.

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   Table 2–4 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 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 V4 or V6. V4 is the default.
   dsfield	Contents of the DS field, that is, the DS codepoint. 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 Prioritizing the Classes.
   user	Either the UNIX userID 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.

Use the template that was introduced in Table 2–2 to fill in filters for the classes you defined.

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