Specifications

White Paper

Cat6500(config-if)# wrr-queue random-detect max-threshold 1 40 100

This sets the WRED drop thresholds for a port with a 1p2q2t queue structure 1 to 40% for threshold 1 (Tx) and 100%

for threshold 2 (Tx).

WRED can also be disabled if required in Cisco IOS. The method used to do this is to use the “no” form of the

command. An example of disabling WRED is shown as follows:

Cat6500(config-if)# no wrr-queue random-detect queue_id

7.10 Mapping CoS to Thresholds

After thresholds have been configured, the administrator can then assign CoS values to these thresholds, so that

when the threshold has been exceeded, frames with specific CoS values can be dropped. Usually, the administrator

will assign lower priority frames to the lower thresholds, thus maintaining higher priority traffic in the queue should

congestion occur.

Figure 28. Mapping CoS to Thresholds

The above figure shows an input queue with 4 thresholds, and how CoS values have been assigned to each

threshold. The following shows how CoS values can be mapped to thresholds

Cat6500(config-if)# wrr-queue cos-map 1 1 0 1

7.11 Configure Bandwidth on Transmit Queues

When a frame is placed in an output queue, it will be transmitted using an output-scheduling algorithm. The output

scheduler process uses Weighted Round Robin (WRR - a scheduling algorithm) to transmit frames from the output

queues. Depending on the line card hardware being used, there are two; three, four or eight transmit queues per

port.