Cisco IE 4000, Software Configuration Manual

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Configuring QoS
QoS Treatment for Performance-Monitoring Protocols
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You cannot configure priority queuing for the class-default of an output policy map.
For more information, see Configuring Output Policy Maps with Class-Based Priority Queuing, page 633 .
This example shows how to configure the class out-class1 as a strict priority queue so that all packets in that class are
sent before any other class of traffic. Other traffic queues are configured so that out-class-2 gets 50 percent of the
remaining bandwidth and out-class3 gets 20 percent of the remaining bandwidth. The class class-default receives the
remaining 30 percent with no guarantees.
Switch(config)# policy-map policy1
Switch(config-pmap)# class out-class1
Switch(config-pmap-c)# priority
Switch(config-pmap-c)# exit
Switch(config-pmap)# class out-class2
Switch(config-pmap-c)# bandwidth remaining percent 50
Switch(config-pmap-c)# exit
Switch(config-pmap)# class out-class3
Switch(config-pmap-c)# bandwidth remaining percent 20
Switch(config-pmap-c)# exit
Switch(config-pmap)# exit
Switch(config)# interface gigabitethernet 0/1
Switch(config-if)# service-policy output policy1
Switch(config-if)# exit
This example shows how to use the priority with police commands to configure out-class1 as the priority queue, with
traffic going to the queue limited to 20000000 bps so that the priority queue will never use more than that. Traffic above
that rate is dropped. The other traffic queues are configured to use 50 and 20 percent of the bandwidth that is left, as in
the previous example.
Switch(config)# policy-map policy1
Switch(config-pmap)#
class out-class1
Switch(config-pmap-c)# priority
Switch(config-pmap-c)# police 200000000
Switch(config-pmap-c)#
exit
Switch(config-pmap)# class out-class2
Switch(config-pmap-c)# bandwidth percent 50
Switch(config-pmap-c)#
exit
Switch(config-pmap)# class out-class3
Switch(config-pmap-c)# bandwidth percent 20
Switch(config-pmap-c)#
exit
Switch(config-pmap)# exit
Switch(config)#
interface gigabitethernet 0/1
Switch(config-if)# service-policy output policy1
Switch(config-if)# exit
Congestion Avoidance and Queuing
Congestion avoidance uses algorithms such as tail drop to control the number of packets entering the queuing and
scheduling stage to avoid congestion and network bottlenecks. The switch uses weighted tail drop (WTD) to manage the
queue sizes and provide a drop precedence for traffic classifications. You set the queue size limits depending on the
markings of the packets in the queue. Each packet that travels through the switch can be assigned to a specific queue
and threshold. For example, specific DSCP or CoS values can be mapped to a specific egress queue and threshold.
WTD is implemented on traffic queues to manage the queue size and to provide drop precedences for different traffic
classifications. As a frame enters a particular queue, WTD uses the packet classification to subject it to different
thresholds. If the total destination queue size is greater than the threshold of any reclassified traffic, the next frame of
that traffic is dropped.