Cabletron Systems 9032578-05 manual Traffic Prioritization for Layer-2 Flows, SSR Queuing Policies

Chapter 21: QoS Configuration Guide

Precedence for Layer-3 Flows

A precedence from 1 - 7 is associated with each field in a flow. The SSR uses the precedence value associated with the fields to break ties if packets match more than one flow. The highest precedence is 1 and the lowest is 7. Here is the default precedence of the fields:

•IP: destination port (1), destination IP address (2), source port (3), source IP address (4), TOS (5), interface (6), protocol (7)

•IPX: destination network (1), source network (2), destination node (3), source node (4), destination port (5), source port (6), interface (7)

Use the qos precedence ip and qos precedence ipx commands to change the default precedence.

SSR Queuing Policies

You can use one of two queuing policies on the SSR:

•Strict priority: Assures the higher priorities of throughput but at the expense of lower priorities. For example, during heavy loads, low-priority traffic can be dropped to preserve throughput of control-priority traffic, and so on.

•Weighted fair queuing: Distributes priority throughput among the four priorities (control, high, medium, and low) based on percentages.

You can set the queuing policy on a per-port basis. The default queuing policy is strict priority.

Traffic Prioritization for Layer-2 Flows

QoS policies applied to layer-2 flows allow you to assign priorities based on source and destination MAC addresses. A QoS policy set for a layer-2 flow allows you to classify the priority of traffic from:

•A specific source MAC address to a specific destination MAC address (use only when the port is in flow bridging mode)

•Any source MAC address to a specific destination MAC address

Before applying a QoS policy to a layer-2 flow, you must first determine whether a port is in address-bridging mode or flow-bridging mode. If a port operates in address-bridging mode (default), you can specify the priority based on the destination MAC address and a VLAN ID. You can also specify a list of ports to apply the policy.

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