Cisco Catalyst 3560X-24P Command Reference Manual page 411

Chapter 2 Catalyst 3750-X and 3560-X Switch Cisco IOS Commands
Usage Guidelines Use the mls qos queue-set output qset-id buffers global configuration command to allocate a fixed
number of buffers to the four queues in a queue-set.
The drop-threshold percentages can exceed 100 percent and can be up to the maximum (if the maximum
threshold exceeds 100 percent).
While buffer ranges allow individual queues in the queue-set to use more of the common pool when
available, the maximum number of packets for each queue is still internally limited to 400 percent, or 4
times the allocated number of buffers. One packet can use one 1 or more buffers.
The egress queue default settings are suitable for most situations. You should change them only when
Note
you have a thorough understanding of the egress queues and if these settings do not meet your QoS
solution.
The switch uses a buffer allocation scheme to reserve a minimum amount of buffers for each egress
queue, to prevent any queue or port from consuming all the buffers and depriving other queues, and to
decide whether to grant buffer space to a requesting queue. The switch decides whether the target queue
has not consumed more buffers than its reserved amount (under-limit), whether it has consumed all of
its maximum buffers (over-limit), and whether the common pool is empty (no free buffers) or not empty
(free buffers). If the queue is not over-limit, the switch can allocate buffer space from the reserved pool
or from the common pool (if it is not empty). If there are no free buffers in the common pool or if the
queue is over-limit, the switch drops the frame.
Examples This example shows how to map a port to queue-set 2. It configures the drop thresholds for queue 2 to
40 and 60 percent of the allocated memory, guarantees (reserves) 100 percent of the allocated memory,
and configures 200 percent as the maximum memory this queue can have before packets are dropped:
Switch(config)# mls qos queue-set output 2 threshold 2 40 60 100 200
Switch(config)# interface gigabitethernet2/0/1
Switch(config-if)# queue-set 2
You can verify your settings by entering the show mls qos interface [interface-id] buffers or the show
mls qos queue-set privileged EXEC command.
Related Commands Command
mls qos queue-set output buffers
queue-set
show mls qos interface
show mls qos queue-set
OL-21522-02
Description
Allocates buffers to a queue-set.
Maps a port to a queue-set.
buffers Displays QoS information.
Displays egress queue settings for the queue-set.
Catalyst 3750-X and 3560-X Switch Command Reference
mls qos queue-set output threshold
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