Brocade BigIron RX Series Configuration Guide - Manual (Page 575)

BigIron RX Series Configuration Guide 497
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Configuring packet drop priority using WRED
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To set the wq parameter for queues with a queue type of 1 to 25%, use the following command.
BigIron RX(config)#qos queue-type 1 wred averaging-weight 25%
This gives the current queue size a weight of 25% over the statistical average queue size.
Syntax: [no] qos queue-type <queue-type> wred averaging-weight <avg-weight-value>
The <queue-type> variable is the number of the forwarding queue type that you want to configure
the averaging-weight (Wq) parameter for. There are eight forwarding queue types on device
Routers. They are numbered 0 to 3.
The <avg-weight-value> variable is the weight-ratio between instantaneous and average queue
sizes. It can be one of the 13 values expressed as 1 to 13 described in
Table 103 . The default
value is 9 which maps to a Wq value of.19%.
Configuring the drop precedence parameters
The DSCP/TOS bits in packets are used to prioritize packet delivery for specified queue types.
These values are from 0 to 3. Packets with a DSCP/TOS value of 0 are least likely to be dropped
and packets with a DSCP/TOS of 3 are most likely to be dropped.
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/TOS value. The following sections describe how to set the following drop
precedence parameters for each of the four DSCP/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”
• Packets that do not have the DSCP/TOS value set are assigned a drop precedence equal to the
DSCP/TOS level of 0.
Setting the maximum drop probability
To set the maximum drop probability when the queue size reaches the Max-average-q-size value to
20% use the following command.
BigIron RX(config)#qos queue-type 1 wred drop-precedence 0 drop-probability-max
20%
6 1.56%
7 0.78%
8 0.4%
9 0.2%
10 0.09%
11 0.05%
12 0.02%
13 0.01%
TABLE 103 Possible Wq values (Continued)
Averaging weight
setting Wq value as a percentage