System Administration Guide: IP Services

Classifier (ipgpc) Overview

In the Diffserv model, the classifier selects packets from a network traffic flow. A traffic flow consists of a group of packets with identical information in the following IP header fields:

In IPQoS, these fields are referred to as the 5-tuple.

The IPQoS classifier module is named ipgpc. The ipgpc classifier arranges traffic flows into classes that are based on characteristics you configure in the IPQoS configuration file.

For detailed information about ipgpc, refer to Classifier Module.

IPQoS Classes

A class is a group of network flows that share similar characteristics. For example, an ISP might define classes to represent the different service levels that are offered to customers. An ASP might define SLAs that give different levels of service to various applications. For an ASP's QoS policy, a class might include outgoing FTP traffic that is bound for a particular destination IP address. Outgoing traffic from a company's external web site might also be defined as a class.

Grouping traffic into classes is a major part of planning your QoS policy. When you create classes by using the ipqosconf utility, you are actually configuring the ipgpc classifier.

For information on how to define classes, see How to Define the Classes for Your QoS Policy.

IPQoS Filters

Filters are sets of rules that contain parameters called selectors. Each filter must point to a class. IPQoS matches packets against the selectors of each filter to determine if the packet belongs to the filter's class. You can filter on a packet by using a variety of selectors, for example, the IPQoS 5-tuple and other common parameters:

For example, a simple filter might include the destination port with the value of 80. The ipgpc classifier then selects all packets that are bound for destination port 80 (HTTP) and handles the packets as directed in the QoS policy.

For information on creating filters, see How to Define Filters in the QoS Policy.