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In WRED algorithm, an upper limit and a lower limit are set for each queue, and the packets in a queue
are processed as follows.
z When the current queue length is smaller than the lower limit, no packet is dropped;
z When the queue length exceeds the upper limit, all the newly received packets are dropped;
z When the queue length is between the lower limit and the upper limit, the newly received packets
are dropped at random. The longer the queue, the more likely the newly received packets may be
dropped. However, a maximum drop probability exists.
In WRED, random numbers are generated to determine the packets to be dropped. As the dropping
policy is determined by IP precedence, packets with lower precedence are more likely to be dropped.
WRED prevents global TCP session synchronization. It enables other TCP sessions to be free of a TCP
session slowed down because of its packets being dropped. In this way, TCP sessions can operate in
different rates in any case and the link bandwidth can be fully utilized.
Traffic mirroring
Traffic mirroring identifies traffic using ACLs and duplicates the matched packets to the destination
mirroring port or CPU depending on your configuration. For information about port mirroring, refer to the
Mirroring module of this manual.
QoS Configuration
Complete the following tasks to configure QoS:
Task Remarks
Configuring Priority Trust Mode
Optional
Configuring the Mapping between 802.1p
Priority and Local Precedence
Optional
Setting the Priority of Protocol Packets
Optional
Marking Packet Priority Optional
Configuring Traffic Policing Optional
Configuring Line Rate Optional
Configuring VLAN Mapping
Optional
Configuring Queue Scheduling
Optional
Configuring WRED Optional
Configuring Traffic Mirroring Optional
Configuring Priority Trust Mode
Refer to section Priority Trust Mode for introduction to priority trust mode.
Configuration prerequisites
z The priority trust mode to be adopted has been determined.
z The port where priority trust mode is to be configured has been determined.
z The port priority value has been determined.