Quality of Service (QoS): Managing Bandwidth More Effectively
Preparation for Configuring QoS
DSCPs in IP packets from the switch, configure them to do so by enabling
ToS Differentiated Service mode and making sure the same DSCP policies
are configured.
5. If you are planning a QoS configuration on a 3400cl or 6400cl switch, refer
to the next section, “Planning QoS for the Series 3400cl/6400cl Switches”.
Note On the 3400cl/6400cl switches, ACLs and Rate-Limiting use the same internal
resources (per-port rules) as QoS. For this reason, plus the limit on per-port
rule resources, it is important to consider rule usage when preparing to
configure QoS on the switch. For more information, refer to the next section,
“Planning QoS for the Series 3400cl/6400cl Switches”.
Planning QoS for the Series 3400cl/6400cl Switches
QoS, ACLs, and Rate Limiting share certain internal, per-port resources on
3400cl/6400cl switches. Thus, QoS (and ACL) configurations can load internal
resources in ways that require more careful attention to resource usage when
planning a configuration using these features. Otherwise, there is an increased
possibility of oversubscribing some switch resources, which means that at
some point the switch would not support further QoS, ACL, and/or Rate-
Limiting configuration. This section describes resource planning for QoS
features on a 3400cl or 6400cl switch. For ACL planning, refer to chapter
10,
“Access Control Lists (ACLs) for the Series 3400cl and Series 6400cl Switches”.
For information on Rate-Limiting, refer to the “Rate-Limiting” section in the
chapter titled “Port Traffic Controls” of the Management and Configuration
Guide for your switch.
Prioritizing and Monitoring QoS, ACL, and Rate Limiting
Feature Usage on the 3400cl/6400cl Switches
If you want to configure QoS and either ACLs or Rate-Limiting (or both) on a
3400cl or 6400xl switch, plan and implement your configuration in descending
order of feature importance. This will help to ensure that the most important
features are configured first. Also, if insufficient resources become a problem,
this approach can help you recognize how to distribute the desired feature
implementations across multiple switches to achieve your objectives. For
example, adding ACLs consumes resources faster than QoS rules and policies.
If QoS is more important on a particular 3400cl or 6400cl switch than ACLs,
then you should plan and configure your QoS resource usage first for that
switch. If insufficient resources remain for all of the ACL implementation you
want, try spreading this implementation across multiple switches.
8-15
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