Quality of Service (QoS): Managing Bandwidth More Effectively

Preparation for Configuring QoS

QoS Classifier

Rules Used

 

 

ToS Diff-Services QoS

Up to 64 rules per switch, depending on how the switch is configured

VLAN QoS

1 rule per port membership in a QoS-specified VLAN. If a port belongs

 

to multiple, QoS-specified VLANs, then 1 rule is used for each such

 

VLAN membership.

Source-Port QoS

1 rule for each port configured for source-port QoS.

 

 

Planning and Monitoring Rule Usage

The following two CLI commands are useful for planning and monitoring rule usage in a QoS configuration.

Syntax: qos resources help

Provides a quick reference on how QoS uses rule resources for each configuration option. See table 6-8.

Syntax: show qos resources

Shows the number of rules that have been used out of the total rules available for that feature. This command is useful for verifying rule availability as you proceed with configuring QoS.

Managing QoS Resource Consumption

As shown in table 6-8, QoS classifiers use 1, 2, or 8 rules depending on the classifier selected. Extensive QoS configurations can either fully subscribe the rules available or leave an insufficient number of rules available for configuring another QoS policy on the switch. If there are not enough rules to support another QoS policy, you cannot configure an additional policy.

Problems with an insufficient number of rules available can occur in either of the following QoS scenarios:

Attempting to configure a policy when there are an insufficient number of rules available

Attempting to add a port to a QoS-configured VLAN where the policy already on the VLAN requires more rule resources than are available.

6-16