Configuring Weighted Random Early Detection; Restrictions - Cisco ASR 9000 Series Configuration Manual

How to Configure Modular QoS Congestion Avoidance on Cisco IOS XR Software

Configuring Weighted Random Early Detection

WRED drops packets selectively based on IP precedence. Edge routers assign IP precedences to packets
as they enter the network. WRED uses these precedences to determine how it treats different types of
traffic.
When a packet arrives, the following actions occur:
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Restrictions

You cannot configure WRED in a class that has been set for priority queueing (PQ).
You cannot use the random-detect command in a class configured with the priority command.
When configuring the random-detect dscp command, you must configure one of the following
commands: shape average, bandwidth, and bandwidth remaining.
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Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
QC-70
D r a f t — C i s c o C o n f i d e n t i a l
The average queue size is calculated.
If the average is less than the minimum queue threshold, the arriving packet is queued.
If the average is between the minimum queue threshold for that type of traffic and maximum
threshold for the interface, the packet is either dropped or queued, depending on the packet drop
probability for that type of traffic.
If the average queue size is greater than the maximum threshold, the packet is dropped.
configure
policy-map policy-name
class class-name
random-detect dscp dscp-value min-threshold [units] max-threshold [units]
bandwidth {bandwidth [units] | percent percentage-value}
bandwidth remaining percent percentage-value
shape average {percent | value [units]}
exit
interface type instance
service-policy {input | output} policy-map
end
or
commit
Configuring Modular QoS Congestion Avoidance on Cisco ASR 9000 Series Routers
OL-17239-01