Brocade Multi-Service IronWare QoS and Traffic Management Configuration Guide (Supporting R05.6.00) - Manual (Page 136)

122 Multi-Service IronWare QoS and Traffic Management Configuration Guide
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Configuring packet drop priority using WRED
4
The avg-weight-value variable is the weight-ratio between instantaneous and average queue sizes.
It is described as the Wq parameter in
“Weighted Random Early Discard (WRED)” on page 118. It
can be one of the 13 values expressed as 1 to 13 described in Table 30 . The default value is 9
which maps to a Wq value of .19%.
Configuring the maximum instantaneous queue size
You can set the maximum size to which a queue is allowed to grow. Packets that cause the queue
to grow beyond this setting are unconditionally dropped. To set the maximum instantaneous queue
size for queues with a queue type of 1 to 32000 KBytes, use the following command.
Brocade(config)#qos queue-type 1 max-queue-size 32
Syntax: [no] qos queue-type queue-number max-queue-size max-queue
The queue-type variable is the number of the forwarding queue type that you want to configure the
instantaneous-queue-size parameter for. There are eight forwarding queue types on Brocade
devices. They are numbered 0 to 7.
The max-queue variable is the maximum size to which a queue is allowed to grow. It is defined in
Kbytes. The default values are shown in
Table 31 .
Configuring the drop precedence parameters
The DSCP or TOS bits in packets are used to prioritize packet delivery for specified queue types.
These values are from 0 to 4. Packets with a DSCP or TOS value of 0 are least likely to be dropped
and packets with a DSCP or TOS of 3 are most likely to be dropped.
NOTE
In addition to bits in the DSCP, the DP option can use other fields (in the PCP header or the EXP bit
header) to control WRED in the priority queues.
In addition, the maximum drop probability, the minimum and maximum average queue size, and
the maximum packet size can be configured to apply selectively to packets with a specified queue
type and DSCP or TOS value. The following sections describe how to set the following drop
precedence parameters for each of the four DSCP or TOS values for each of the four queue types:
• “Setting the maximum drop probability”
• “Setting the minimum and maximum average queue size”
• “Setting the maximum packet size”
NOTE
Packets that do not have the DSCP or TOS value set are assigned a drop precedence equal to the
DSCP or TOS level of 0.
Setting the maximum drop probability
To set the maximum drop probability for queue type 1 and drop precedence 0 when the queue size
reaches the Max-average-q-size value to 20% use the following command.
Brocade(config)#qos queue-type 1 wred drop-precedence 0 drop-probability-max 20%
Syntax: [no] qos queue-type queue-type wred drop-precedence drop-precedence-value
drop-probability-max p-max