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QoS – 1P3Q3T Queuing

April 20th, 2010

The Cisco 2960, 2970, 3560 and 3750 Catalyst switches support a 1p3q3t que model which provides 3 thresholds in which to drop traffic.

The first two thresholds are configurable, while the last threshold is always 100% of the queue. It is advisable to map scavenger class traffic (DSCP 8 or cs1) to queue 4 and configure the threshold to 40% of the queue. This will allow the WTD system to drop scavenger class traffic more aggressively.

The following commands map DSCP 8 to queue 4, threshold 1. Queue 4, threshold 1 is then configured to tail drop packets when 40% of the queue is utilised.

mls qos srr-queue output dscp-map queue 4 threshold 1 8
mls qos queue-set output 1 threshold 4 40 100 100 100

1p3q1t - Queuing Model

1p3q1t - Queuing Model

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