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WRED Configuration 699
■ When the length of the queue is between the minimum threshold and
maximum threshold, the WRED algorithm is used to calculate and determine
whether the packet is dropped. The specific method is that each incoming
packet is allocated with a random number, which is compared with the drop
probability of the current queue, if it is larger than the drop probability, the
packet is dropped. The longer the queue is, the higher the drop probability
is--but there is a maximum drop probability.
When WRED and WFQ is cooperated, the flow based WRED can be implemented.
During the classification, different flows have their own queues, for the flow with
small traffic, as its queue length is always smaller, the drop probability will be
smaller, too. However, as the flow with large traffic will have larger queue length,
more packets are discarded, protecting the benefit of the flow with smaller traffic.
Different from RED, the random number generated by WRED is based on the IP
priority, it considers the benefit of the high priority packets, and relatively reduce
the drop probability of the high priority packets. The 3Com router takes WRED as
its congestion avoidance policy.
WRED Configuration WRED configuration includes:
■ Enable the WRED Function of the Interface
■ Configure Weight Factors when Calculating WRED Average Queue Length
■ Set the Priority Parameters for WRED
Enable the WRED
Function of the Interface
WRED must first be enabled, and then other parameters related to WRED can be
configured.
Please perform the following configurations in the interface view.
Table 738 Enable WRED
By default, the system disables WRED so the queue avoids congestion by using the
tail-drop policy.
WRED can only operate with WFQ, and cannot be used separately or coperated
with other queue. Therefore, before the startup of WRED, WFQ must have been
applied to the interface.
Enabling WRED can be effective only in all physical interfaces, while this command
is ineffective in the logic interface.
Configure Weight
Factors when
Calculating WRED
Average Queue Length
Please perform the following configurations in the interface view.
Table 739 Configure the WRED Weighted Factor for Calculating the WRED Average
Queue Length
Operation Command
Enable the WRED function of the interface qos wred
Disable the WRED function on the
interface
undo qos wred
Operation Command