3Com 4007, Руководство по внедрению, Страница: 573 / 684

Key Guidelines for Implementation 573
Key Guidelines for
Implementation
Consider the following guidelines when you configure QoS on your
Layer 3 switching module.
Procedural Guidelines Configure classifiers and controls in the following order:
1 Define a classifier, or choose a predefined classifier. Identify a particular
type of traffic that you want to regulate and define a classifier for this
traffic via the Administration Console. The rules for defining classifiers are
different for flow versus nonflow classifiers.
2 Create controls to apply to your classifiers. A control enables the
Multilayer Switching Module to direct the traffic to one of the available
transmit queues or drop the traffic. When you define a control, you can:
a Assign a rate limit to the incoming classified traffic (optionally, on a
per-port basis).
b If you specify a rate limit, define what should be done with the
nonconforming excess (that is, traffic that exceeds the rate-limit
parameters).
c Apply an IEEE 802.1p priority tag value to forwarded traffic.
General Guidelines
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You must define a classifier before you can assign a control to it.
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A classifier does not affect traffic scheduling until you configure a
control for that classifier.
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Traffic that is not classified and controlled is treated with a transmit
priority of best (best effort) using the default classifier (499) and the
default control (1). All such packets are conforming packets.
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You cannot remove or modify the default classifier (499).
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You cannot remove the default control (1) , but you can modify it.
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When you specify a TCP or UDP source and destination port range for
a flow classifier, limit the range as much as possible (for example, to a
single TCP or UDP port or to a small range of ports). If the classifier
applies to a wide range of TCP or UDP ports, you increase the amount
of classified traffic on the Multilayer Switching Module and consume
valuable QoS resources (cache entries).
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If you have defined a control and you want to remove or modify the
associated classifier, you must remove the control before you can
remove or modify the classifier.