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This document answers a question on the significance of the egress threshold values in the Cisco Catalyst 3750 Series Switches.
In this configuration example,
Switch(config)#mls qos queue-set output 1 threshold 1
3200 3200 100 3200
3200 is the threshold percentage for WTD (Weighted Tail Drop). This number decides how many buffers to utilize from the common pool before the packets are tail dropped. Through this configuration, we tell the switch that thresholds 1, 2, and 3 on egress queue 1 in queue-set 1 are equal and they are free to utilize the common pool up to the configured value (3200). In this example, the drop threshold is 3200 and the maximum threshold and reserved threshold are set to 100%.
The total available common pool for egress buffers varies from one platform to the other. They are more limited in 2960-S: 2MB for the whole system (downlink ports + uplink ports), while 3750-X has 2MB for each set of 24 downlink ports and 2MB for uplinks.
100 is the reserved percent of the buffers for that queue. For example, lets say you have preconfigured 'mls qos queue-set output 1 buffers 15 45 20 20'. Then, 'mls qos queue-set output 1 threshold 1 3200 3200 100 3200' means that queue 1 has 100% of 15% of the total buffers available as reserved.