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Tuning Your Switch Performance (Layer 2 & Layer 3)

Overview

This chapter and its procedures are common to both Layer 2 and Layer 3 configuration. Buffer management features help you to optimize traffic throughput through the switch fabric.

Included in this chapter:

❒How Queues Work

❒Managing Buffers and Queues

How Queues Work

Frames are buffered in the I/O modules, before and after traversing the switch. Each queue can hold 256K bytes. (Architecturally they can support up to 1 MB each).

Each buffer is divided into two queues, one for High-priority Traffic and one for Normal-priority Traffic. The factory default is for the high-priority queue uses 20% (51K) of the buffer. The normal-priority queue uses the remaining 80% (205K). These values can be modified using either the Web Agent or SNMP.

Note: When you change these values, you must reboot the switch before they can take effect.

Less buffer memory gets assigned to the high-priority queue because the high-priority queue gets serviced more frequently than the normal-priority queue. Since a frame spends less time on the high-priority queue, less buffer space is required for the queue.

The Service Ratio can be chosen to match traffic patterns and performance requirements using a weighted round robin scheduling algorithm. The available service ratios of the algorithm are defined in “Managing Buffers and Queues”. The factory default service ratio for fabric ports is 999/1. The factory default service ratio for physical ports is 1023 to 1. If there is traffic to be serviced from both the high- and normal-priority queues, 999 packets of high-priority traffic will be processed for each normal-priority packet.

Cajun P550/P220 Switch Operation Guide

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