Buffer And Bandwidth Allocation - Cisco Catalyst 2960 series Configuration Manual

Buffer and Bandwidth Allocation

You define the ratio (allocate the amount of space) with which to divide the ingress buffers between the two
queues (normal and expedite) by using the mls qos srr-queue input buffers percentage1 percentage2 global
configuration command. The buffer allocation together with the bandwidth allocation control how much data
can be buffered and sent before packets are dropped. You allocate bandwidth as a percentage by using the
mls qos srr-queue input bandwidth weight1 weight2 global configuration command. The ratio of the weights
is the ratio of the frequency in which the SRR scheduler sends packets from each queue.
Priority Queueing
You can configure one ingress queue as the priority queue by using the mls qos srr-queue input priority-queue
queue-id bandwidth weight global configuration command. The priority queue should be used for traffic
(such as voice) that requires guaranteed delivery because this queue is guaranteed part of the bandwidth
regardless of the load on the stack or internal ring.
SRR services the priority queue for its configured weight as specified by the bandwidth keyword in the mls
qos srr-queue input priority-queue queue-id bandwidth weight global configuration command. Then, SRR
shares the remaining bandwidth with both ingress queues and services them as specified by the weights
configured with the mls qos srr-queue input bandwidth weight1 weight2 global configuration command.
You can combine the above commands to prioritize traffic by placing packets with particular DSCPs or CoSs
into certain queues, by allocating a large queue size or by servicing the queue more frequently, and by adjusting
queue thresholds so that packets with lower priorities are dropped.
Related Topics
Configuring Ingress Queue Characteristics, on page 612
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
Information About QoS
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