Cisco Catalyst 2000 Configuration Handbook page 253

232 Cisco LAN Switching Configuration Handbook
Tip All port types assign frames with CoS 5 to their strict-priority queues (except 1q4t,
which has none). The 1p1q0t ports have no thresholds; all frames with CoS values other
than 5 are assigned to the standard queue and dropped when the queue is 100 percent
full.
a. (Optional) Tune the ingress queue ratio:
Caution When using this command, all ports cycle through a link-down and link-up
process. In a production network, this causes a network outage while the ports are down
and while they progress through the spanning-tree states again.
b. (Optional) Set the congestion-avoidance thresholds.
(interface) rcv-queue queue-limit queue1 queue2
By default, the standard queue (queue 1) receives 80 percent of the available
space, whereas the strict-priority queue (queue 2) receives 20 percent of
the space. If QoS is disabled, the standard queue receives 100 percent of the
space.
Estimate the ratio of normal and priority traffic coming into a switch port. Use
the queue1 and queue2 values to set the percentage (1 to 99) for the two receive
queues. These values must total 100 percent.
■ (Optional) Use standard tail-drop receive queues:
(interface) rcv-queue threshold queue-id threshold-percent-1 ...
threshold-percent-n
OR
(interface) wrr-queue threshold queue-id threshold-percent-1 ...
threshold-percent-n
For most switch port receive queues (1q4t, 1p1q4t, 2q2t, and 1p1q0t), stan-
dard tail-drop congestion avoidance can be used. By default, frames with a
CoS 5 are assigned to the strict-priority queue. All other frames are assigned
to the standard queue.
The number of queue thresholds available is the number preceding the t in
the queue type. For each threshold, you can assign the percentage of the
buffer that is available to receive frames. The threshold-percentage-n values
(1 to 100 percent) are given in sequential order. When the buffer rises above
the threshold level, new inbound frames are dropped.