HP MSR2000/3000/4000 Router Series ACL and QoS Configuration Guide

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probability. When the average queue size exceeds the upper threshold, subsequent packets are
dropped.
• Drop precedence—A parameter used for packet drop. The value 0 corresponds to green packets,
the value 1 corresponds to yellow packets, and the value 2 corresponds to red packets. Red packets
are dropped preferentially.
• Exponent for average queue size calculation—The greater the exponent, the less sensitive the
average queue size is to real-time queue size changes. The formula for calculating the average
queue size: average queue size = ( previous average queue size x (1 – 2
–n
) ) + (current queue size
x 2
–n
), where n is the exponent.
• Denominator for drop probability calculation—The greater the denominator, the smaller the
calculated drop probability.
Configuring WRED on an interface
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enter interface view.
interface interface-type
interface-number
N/A
3. Enable WRED.
qos wred [ dscp | ip-precedence ]
enable
By default, tail drop is
adopted.
4. (Optional.) Set the WRED
exponent for average queue
size calculation.
qos wred weighting-constant exponent
The default setting is 9.
5. (Optional.) Set the
drop-related parameters for a
precedence value.
qos wred { ip-precedence
ip-precedence | dscp dscp-value }
low-limit low-limit high-limit high-limit
discard-probability discard-prob
By default, low-limit is 10,
high-limit is 30, and
discard-prob is 10.
Repeat this command to
configure more precedence
values.
Configuration example
Network requirements
• Enable IP precedence-based WRED on interface Ethernet 1/1.
• Set the following parameters for packets with IP precedence 3: lower threshold 20, upper threshold
40, and drop probability denominator 15.
• Set the exponent for average queue size calculation to 6.
Configuration procedure
# Enter system view.
<Sysname> system-view
# Enter interface view.
[Sysname] interface ethernet 1/1
# Enable IP precedence-based WRED.