55
average queue size is average queue size = (previous average queue size x (1 – 2
–n
)) +
(current queue size x 2
–n
), where n is the exponent.
• Drop probability in percentage—The larger the value is, the greater the drop probability is.
Configuration procedure
A WRED table can be applied to multiple interfaces. For a WRED table already applied to an
interface, you can modify the values of the WRED table, but you cannot remove the WRED table.
To configure and apply a WRED table:
Step Command Remarks
1. Enter system view.
system-view
N/A
2. Create a WRED table and
enter its view.
qos wred queue table
table-name N/A
3. (Optional.) Set the WRED
exponent for average
queue size calculation.
queue
queue-id
weighting-constant
exponent
The default setting is 9.
4. (Optional.) Configure drop
parameters.
queue
queue-id [
drop-level
drop-level ]
low-limit
low-limit
high-limit
high-limit
[
discard-probability
discard-prob ]
By default, the low limit is 100,
the high limit is 1000, and the
drop probability is 10%.
5. (Optional.) Enable ECN for
a queue.
queue
queue-id
ecn
By default, ECN is not enabled
on any queue.
6. Enter interface view.
interface
interface-type
interface-number
N/A
7. Apply the WRED table to
the interface.
qos wred apply
[ table-name ]
By default, no WRED table is
applied to an interface, and tail
drop is used on an interface.
Configuration example
Network requirements
Apply a WRED table to interface GigabitEthernet 1/0/2, so that the packets are dropped as follows
when congestion occurs:
• For the interface to preferentially forward higher-priority traffic, set a lower drop probability for a
queue with a greater queue ID. Set different drop parameters for queue 0, queue 3, and queue
7.
• Drop packets according to their colors.
{ In queue 0, set the drop probability to 25%, 50%, and 75% for green, yellow, and red
packets, respectively.
{ In queue 3, set the drop probability to 5%, 10%, and 25% for green, yellow, and red packets,
respectively.
{ In queue 7, set the drop probability to 1%, 5%, and 10% for green, yellow, and red packets,
respectively.
• Enable ECN for queue 7.
Configuration procedure
# Configure a queue-based WRED table, and set different drop parameters for packets with different
drop levels in different queues.
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