In the Diffserv model, the classifier is responsible for organizing selected traffic flows into groups on which to apply different service levels. The classifiers that are defined in RFC 2475 were originally designed for boundary routers. In contrast, the IPQoS classifier ipgpc is designed to handle traffic flows on hosts that are internal to the local network. Therefore, a network with both IPQoS systems and a Diffserv router can provide a greater degree of differentiated services. For a technical description, refer to the ipgpc (7ipp) man page.
The ipgpc classifier does the following:
Selects traffic flows that meet the criteria specified in the IPQoS configuration file on the IPQoS-enabled system
The QoS policy defines various criteria that must be present in packet headers. These criteria are called selectors. The ipgpc classifier compares these selectors against the headers of packets that are received by the IPQoS system. ipgpc then selects all matching packets.
Separates the packet flows into classes, network traffic with the same characteristics, as defined in the IPQoS configuration file
Examines the value in the packet's differentiated service (DS) field for the presence of a differentiated services codepoint (DSCP)
The presence of the DSCP indicates whether the incoming traffic has been marked by the sender with a forwarding behavior.
Determines what further action is specified in the IPQoS configuration file for packets of a particular class
Passes the packets to the next IPQoS module specified in the IPQoS configuration file, or returns the packets to the network stream
For an overview of the classifier, refer to Classifier (ipgpc) Overview. For information on invoking the classifier in the IPQoS configuration file, refer to IPQoS Configuration File.
The ipgpc classifier supports a variety of selectors that you can use in the filter clause of the IPQoS configuration file. When you define a filter, always use the minimum number of selectors that are needed to successfully retrieve traffic of a particular class. The number of filters you define can impact IPQoS performance.
The folowing table lists the selectors that are available for ipgpc.
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