CBWFQ Operation

This topic describes class-based weighted fair queuing (CBWFQ).

CBWFQ

The WFQ algorithm is applied to classes rather than the flows themselves.

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CBWFQ extends the standard WFQ functionality to provide support for user-defined traffic classes. By using CBWFQ, network managers can define traffic classes based on several match criteria, including protocols, ACLs, and input interfaces. A FIFO queue is reserved for each class, and traffic belonging to a class is directed to the queue for that class. More than one flow, or conversation, can belong to a class.

After a class has been defined according to its match criteria, you can assign its characteristics. To characterize a class, you assign it bandwidth and maximum packet limit. The bandwidth assigned to a class is the guaranteed bandwidth given to the class during congestion.

CBWFQ assigns a weight to each configured class instead of each flow. This weight is proportional to the bandwidth that is configured for each class (weight = interface bandwidth divided by the class bandwidth). Therefore, the larger the bandwidth value of a class, the smaller its weight.

By default, the total amount of bandwidth allocated for all classes must not exceed 75 percent of the available bandwidth on the interface. The other 25 percent is used for control and routing of traffic. However, the maximum-reserved bandwidth can be configured to circumvent this limitation.

You must also specify the queue limit for the class, which is the maximum number of packets allowed to accumulate in the queue for the class. Packets belonging to a class are subject to the bandwidth and queue limits that are configured for the class.

CBWFQ vs. Flow-Based WFQ

This topic describes the benefits of CBWFQ over WFQ.

CBWFQ vs. Flow-Based WFQ

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