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:
Source address
Destination address
Source port
Destination port
In IPQoS, these fields are referred to as the 5-tuple.
The IPQoS classifier module, ipgpc, 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.
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 about how to define classes, see Defining the Classes for Your QoS Policy.
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 whether 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:
Source address and destination addresses
Source port and destination port
Protocol numbers
User IDs
Project IDs
Differentiated Services Codepoint (DSCP)
Interface index
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 about creating filters, see How to Define Filters in the QoS Policy.