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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 52 Configuring QoS
Configuring QoS on the Switch
•
The low WRED threshold is the traffic level under which no traffic is dropped. The high WRED
threshold is the traffic level above which all traffic is dropped. The traffic in the queue between the
low and high WRED thresholds has an increasing chance of being dropped as the queue fills. The
default low WRED threshold is zero (all traffic has some chance of being dropped).
This example shows how to configure the low-priority transmit-queue WRED-drop thresholds:
Console> (enable)
set qos wred 1p2q2t queue 1 40:70 70:100
WRED thresholds for queue 1 set to 40:70 and 70:100 on all WRED-capable 1p2q2t ports.
Console> (enable)
Note
The threshold in the strict-priority queue is not configurable.
Allocating Bandwidth Between the Standard Transmit Queues
The switch transmits frames from one standard queue at a time using one of these dequeuing algorithms,
which use weights to allocate relative bandwidth to each queue as it is serviced in a round-robin fashion:
•
Shaped round robin (SRR)—Supported as an option on Supervisor Engine 32
1p3q8t
ports. If you
do not enable SRR, DWRR is used. SRR only allows a queue to use the specific amount of
bandwidth that the weight allocates.
•
Deficit weighted round robin (DWRR)—Supported on
1p3q1t
,
1p2q1t
,
1p3q8t
, and
1p7q8t
ports.
DWRR keeps track of any low-priority queue under-transmission and compensates in the next
round.
•
Weighted round robin (WRR)—Supported on all other ports. WRR allows a queue to use more than
the allocated bandwidth if the other queues are not using any, up to the total bandwidth of the port.
The higher the weight that is assigned to a queue, the more transmit bandwidth is allocated to it. The
ratio of the weights divides the total bandwidth of the queue. For example, for three queues on a Gigabit
Ethernet port, weights of 25:25:50 provide this division:
•
Queue 1—250 Mbps
•
Queue 2—250 Mbps
•
Queue 3—500 Mbps
Note
The actual bandwidth division depends on the granularity that the port hardware applies to
the configured weights.
To allocate the bandwidth between the standard transmit queues, perform this task in privileged mode:
The valid values for the
port_type
parameter are
2q2t
,
1p2q2t
,
1p3q1t
,
1p2q1t
,
1p3q8t
, and
1p7q8t
.
QoS maintains separate configurations for each port type. This command configures only the standard
queues; the strict-priority queue requires no configuration. The valid values for weight range from
1–255.
Task
Command
Allocate the bandwidth between the standard
transmit queues.
set qos wrr
port_type
queue1-weight
queue2-weight
[
queue3-weight
] [
srr
]
