1316 Configuring Class-of-Service
• Weighted Random Early Detection (WRED)—Drops packets queued for
transmission selectively based their drop precedence level. For each of four
drop precedence levels on each WRED-enabled interface queue, you can
configure the following parameters:
– Minimum Threshold: A percentage of the total queue size below
which no packets of the selected drop precedence level are dropped.
– Maximum Threshold: A percentage of the total queue size above
which all packets of the selected drop precedence level are dropped.
– Drop Probability: When the queue depth is between the minimum
and maximum thresholds, this value provides a scaling factor for
increasing the number of packets of the selected drop precedence level
that are dropped as the queue depth increases. The drop probability
supports configuration in the range of 0 to 10%, and the discrete
values 25%, 50%, and 75%. Values not listed are truncated to the next
lower value in hardware.
CoS Queue Usage
CoS queue 7 is reserved by the system and is not assignable. It is generally
recommended that the administrator utilize CoS queues 0 to 3, as CoS
queues 4-6 may be used by the system for other types of system traffic, for
example, routing protocol PDU handling.
Default CoS Values
Table 41-1 shows the global default values for CoS.
Table 41-1. CoS Global Defaults
Parameter Default Value
Trust Mode 802.1p
802.1p CoS value to queue mapping 802.1p CoS Queue
0, 3 1
1, 2 0
4, 5 2
6, 7 3
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