Key Guidelines for Implementation 573Key Guidelines forImplementationConsider the following guidelines when you configure QoS on yourLayer 3 switching module.Procedural Guidelines Configure classifiers and controls in the following order:1 Define a classifier, or choose a predefined classifier. Identify a particulartype of traffic that you want to regulate and define a classifier for thistraffic via the Administration Console. The rules for defining classifiers aredifferent for flow versus nonflow classifiers.2 Create controls to apply to your classifiers. A control enables theMultilayer Switching Module to direct the traffic to one of the availabletransmit queues or drop the traffic. When you define a control, you can:a Assign a rate limit to the incoming classified traffic (optionally, on aper-port basis).b If you specify a rate limit, define what should be done with thenonconforming excess (that is, traffic that exceeds the rate-limitparameters).c Apply an IEEE 802.1p priority tag value to forwarded traffic.General Guidelines n You must define a classifier before you can assign a control to it.n A classifier does not affect traffic scheduling until you configure acontrol for that classifier.n Traffic that is not classified and controlled is treated with a transmitpriority of best (best effort) using the default classifier (499) and thedefault control (1). All such packets are conforming packets.n You cannot remove or modify the default classifier (499).n You cannot remove the default control (1), but you can modify it.n When you specify a TCP or UDP source and destination port range fora flow classifier, limit the range as much as possible (for example, to asingle TCP or UDP port or to a small range of ports). If the classifierapplies to a wide range of TCP or UDP ports, you increase the amountof classified traffic on the Multilayer Switching Module and consumevaluable QoS resources (cache entries).n If you have defined a control and you want to remove or modify theassociated classifier, you must remove the control before you canremove or modify the classifier.
